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Supplement to the National Building Code of Canada: 1990
National Research Council of Canada. Associate Committee on the National
Building Code
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The Secretary
Canadian Commission on Building and Fire Codes
National Research Council
Ottawa, Ontario
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stamp I
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Droits ré
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The Supplement to the National Building Code of Canada 1990 is subject to periodic review, which may result in
amendments being published from time to time. Also, the NBCINFC News contains explanatory articles and comments on
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Supplement to the
National Building Code
of Canada
1990
Issued by the
Associate Committee on the National Building Code
National Research Council of Canada
pays
First Edition 1980
Second Edition 1985
Third Edition 1990
ISSN 0700-1207
©National Research Council of Canada 1990
Ottawa
World Rights Reserved
NRCC No. 30629
Printed in Canada
Second Printing
Includes revisions and errata of January 1991 and 1992
pays
Table of Contents
.•...••••••••.•....•••••••..•.•.•••••.•..•...••••..•.•.. v
Preface
Committee Members •••••••••••••••••••••••••••••••••••••••• vii
Chapter 1 Climatic Information for
Building Design in Canada ••••••••••••• 1
Chapter 2 Fire-Performance Ratings •••••••••••• 31
Chapter 3 Measures for Fire Safety in
High Buildings .............................. 67
Chapter 4 Commentaries on Part 4 of the
National Building Code of
Canada 1990 ............................... 131
iii
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iv
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F
Preface
The Supplement to the National Building Code
1990 is published by the Associate Committee on the
National Building Code and contains material
intended to assist the Code user in applying the
Code. However, the user is not precluded from
using other approaches provided that they are
acceptable to the authority having jurisdiction.
The Supplement is made up of the following four
chapters:
Chapter 1 Climatic Information for
Building Design in Canada
This Chapter contains information on the climatic
loads to be expected in all parts of Canada. It is
through the use of these climatic factors, with
appropriate adjustments for climate variation in
different localities, that the Code can be used
nationally.
Chapter 2 Fire-Performance Ratings
This Chapter provides a guide to the
determination of the combustibility, flame spread
rating and smoke developed classification of
construction materials and fire-resistance ratings of
construction assemblies in relation to the provisions
of the Code. It gives a procedure for calculating the
fire-resistance rating of construction assemblies
based on generic descriptions of materials used in
the assemblies.
Chapter 3 Measures for Fire Safety in High
Buildings
This Chapter contains material in support of the
high-rise requirements in Part 3.
Chapter 4 Commentaries on Part 4
Chapter 4 consists of explanatory material and
related technical information useful to the designer in
the application of the design requirements in Part 4 of
the Code.
Comments and inquiries on aspects of this
supplement pertaining to the interpretation and use
of the National Building Code should be addressed
to the Secretary, Associate Committee on the National
Building Code, National Research Council of Canada,
Ottawa, Ontario KIA OR6. Requests for technical
information of a non-Code nature are also welcome
and should be directed to the Technical Information
Group, Institute for Research in Construction,
National Research Council of Canada, Ottawa,
Ontario Kl A OR6.
Related Documents The National Research
Council of Canada publishes other code-related
documents that are of interest to code users.
National Building Code of Canada 1990 A model
set of technical requirements designed to establish a
standard of safety for the construction of buildings,
including extensions or alterations, the evaluation of
v
pays
buildings undergoing a change of occupancy and
upgrading of buildings to remove an unacceptable
hazard.
National Fire Code of Canada 1990 A model set
of technical requirements designed to provide an
acceptable level of fire protection and fire prevention
within a community.
Canadian Plumbing Code 1990 Contains detailed
requirements for the design and installation of
plumbing systems in buildings.
Canadian Farm Building Code 1990 A model set
of minimum requirements affecting human health,
fire safety and structural sufficiency for farm
buildings.
Canadian Housing Code 1990 (NEW) A compilation of all requirements from the National
Building Code 1990 that apply to houses, including
detached, semi-detached and row houses without
shared egress.
Measures for Energy Conservation in New
Buildings 1983 A set of minimum requirements that
provide the basis for improving the energy use
characteristics of new buildings.
Commentary on Part 3 (Use and Occupancy) of
the National Building Code 1990 Discusses the
overall arrangement and the basic concepts and
terminology of Part 3, and provides examples to
illustrate and explain the more complicated
requirements in that Part.
Commentary on Part 9 (Housing and Small
Buildings) of the National Building Code 1990
(NEW) Describes the principles behind many of the
requirements of Part 9 and some of the historical
background where this will assist users in
understanding the objectives of certain provisions.
ACNBC Policies and Procedures 1990 Contains
the terms of reference and operating procedures of
the ACNBC and its standing committees, a statement
on the supporting role of the Institute for Research in
Construction of NRC and the membership matrices
for the various standing committees.
vi
Copyright. Copyright in the National Building
Code is owned by the National Research Council of
Canada. All rights are reserved. Reproduction of the
Council's copyright material by any means is prohibited without the written consent of the NRC.
Requests for permission to reproduce the National
Building Code must be sent to: Head, Codes Section,
Institute for Research in Construction, National
Research Council Canada, Ottawa, Ontario K1A OR6.
Ce document est egalement publie en ｦｲ｡ｮｾｩｳＮ＠
pays
Associate Committee on the
National Building Code and
Standing Committees
Associate Committee on the
National Building Code
J. Longworth (Chairman)
J.E Berndt (2) (Deputy Chairman)
R.W. Anderson
O.D. Beck
DJ Boehmer
R Booth (1)
K.W. Butler
J.N. Cardoulis (l)
H.E. Carr
S. Cumming
G.s. Dunlop
V.C. Fenton
S.G. Frost
B. Garceau
E Henderson(1}
D. Hodgson
R.M. Horrocks
J.C. Hurlburt
G. Levasseur
E.1. Lexier
L. Lithgow
(l)
(2)
(3)
E.J. Mackie
P. Masson (1)
W.M. Maudsley (1)
D.O. Monsen
J.R Myles
EL. Nicholson
E-X. Perreault
J. Perrow
L. Pringle 0)
R. Sider 0)
M. Stein
A.D. Thompson
A.M. Thorimbert
J.E. Turnbull
E. Y. Uzumeri
H. Vokey
RJ. Desserud (2)
RH. Dunn 0)
R.A. Hewett (2)
R.A. Kearney (3)
Term completed during preparation of the 1990 Code
IRC staff who provided assistance to the Committee
IRC staff whose involvement with the Committee
ended during the preparation of the 1990 Code.
Standing Committee on Occupancy
DJ Boehmer (Chairman)
D.E.R Anderson
C. Czarnecki
w.s. Drummond
C. T. Fillingham
J.-C. Labelle
A.E. Larden
RL. Maki (1)
L.S. Morrison
J.-P. Perreault
G. Sereda
C. Simard
C.A. Skakun
W. T. Sproule
G.C. Waddell (I)
RT. Wayment
E.K. Zorn (l)
A.J .M. Aikman (2)
J.E Berndt (3)
RB. Chauhan (2)
M. Galbreath (3)
G.C. Gosselin (3)
A.K. Kim (2)
H.W. Nichol (2)
Standing Committee on Structural Design
V.C. Fenton (Chairman)
L.D. Baikie
R.L. Booth (1)
W.G. Campbell (1)
A.G. Davenport
B. deV. Batchelor
G.A. Dring
T.A. Eldridge
M.J. Frye
R. Gagne
M.1. Gilmor (1)
R. Halsall
D.J.L. Kennedy
L.C. King
E. Lerner
J.G. MacGregor
B. Manasc (I)
C. Marsh
A.M. McCrea
M.J. Newark
W. Noseworthy
RE Riffell
J.K. Ritchie
R Schuster
R. V. Switzer
S.M. Uzumeri
G.L. Walt (1)
D.E. Allen (2)
D. A. Lutes (2)
vii
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Standing Committee on
Fire Performance Ratings
E.Y. Uzumeri (Chairman)
J.R. Bateman
H.J. Campbell
D.B. Grant (4)
H.A. Grisack
F.P. Higginson
H. Jabbour
H.A. Locke
W.M. Maudsley (l)
R.J. McGrath
P. Mercier-Gouin (1)
J. Rocheleau (1)
G.D. Shortreed
D.C. Stringer
J.U. Tessier
C.R. Thomson
L.W. Vaughan
R.B. Chauhan (2)
G.C. Gosselin (3)
T.T. Lie (2)
R. A. Kearney (2)
J-J. Shaver (3)
NBC/NFC French Technical Verification
Committee
F.-x. Perreault (Chairman)
R. Ashley (1)
G. Bessens
G. Harvey
S. Lariviere
H.C. Nguyen (1)
G. Pare
(1)
(2)
(3)
(4)
J.-P. Perreault
1. Wagner
D. Chaput (3)
L. Pellerin (3)
L.P. Saint-Martin (2)
J. Wathier (2)
Term completed during preparation of the 1990 Code
IRC staff who provided assistance to the Committee
IRC staff whose involvement with the Committee
ended during the preparation of the 1990 Code.
Deceased
viii
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Chapter 1
Climatic Information
for Building Design in Canada
Introduction ••••••••••••••••••••••••••••••••••••••••••••••••••••• 3
General
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 3
January Design Temperatures ........................ 4
July Design Temperatures
Heating Degree-Days
.............................. 5
...................................... 6
Rainfall Intensity ••••••••••••••••••••••••••••••••••••••••••••• 6
One-Day Rainfall •••••••••••••••••••••••••••••••••••••••••••••• 6
Annual Total Precipitation
.............................. 7
Snow Loads
••••••••••••••••••••••••••••••••••••••••••••••••••••• 7
Wind Effects
•••••••••••••••••••••••••••••••••••••••••••••••••••• 8
Seismic Zones ............................................... 10
References
•••••••••••••••••••••••••••••••••••••••••••••••••••• 1 0
Design Data for Selected Locations
in Canada ••••••••••••••••••••••••••••••••••••••••••••••••••••••• 13
1
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2
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Chapter 1
Climatic Information
for Building Design in Canada
Introduction
The great diversity of climate in Canada has a
considerable effect on the performance of buildings,
consequently, their design must reflect this diversity.
This Chapter explains briefly how the design weather
values are computed and to present recommended
design data for a number of cities, towns and smaller
populated places. Through the use of such data
appropriate allowances can be made for climate
variations in different localities of Canada and the
National Building Code can be applied nationally.
The design data in this Chapter are based on
weather reports supplied by the Atmospheric Environment Service, Environment Canada. They have
been collected and analysed, where necessary, for the
Associate Committee on the National Building Code
by Environment Canada, and appear at the end of
this Chapter under the heading Design Data for
Selected Locations in Canada. Environment Canada
has also devised appropriate methods and estimated
the design values for all the locations in this table
where weather observations were lacking or inadequate.
As it is not practical to list values for all municipalities in Canada, recommended design weather
data for locations not listed can be obtained by
writing to the Energy and Industrial Applications
Section, Canadian Climate Centre, Atmospheric Environment Service, Environment Canada, 4905 Dufferin
Street, Downsview, Ontario M3H 5T4. It should be
noted, however, that these recommended values may
differ from the legal requirements set by provincial or
municipal building authorities.
The information on seismic zones has been provided by the Earth Physics Branch of the Department
of Energy, Mines and Resources. Information for
municipalities not listed may be obtained by writing
to the Division of Seismology and Geomagnetism,
Earth Physics Branch, Energy, Mines and Resources
Canada, Ottawa, Ontario KIA OY3, or to the Pacific
Geoscience Centre, Earth Physics Branch, P.O. Box
6000, Sidney, B.C. V8L 4B2.
General
The choice of climatic elements tabulated in this
Chapter and the form in which they are expressed
have been dictated largely by the requirements for
specific values in several sections of the National
Building Code of Canada. Heating degree-days and
annual total precipitation are also included. The
following notes explain briefly the significance of
these particular elements in building design, and
indicate what observations were used and how they
were analysed to yield the required design values. To
estimate design values for locations where weather
observations were lacking or inadequate, the observed or computed values for the weather stations
were plotted on large-scale maps. Isolines were
drawn on these working charts to show the general
distribution of the design values.
In the table, design weather data are listed for over
600 locations, which have been chosen for a variety of
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reasons. Incorporated cities and towns with populations of over 5000 have been included unless they are
close to other larger cities. For sparsely populated
areas, many smaller towns and villages have been
listed. The design weather data for weather stations
themselves are the most reliable and hence these
stations have often been listed in preference to
locations with somewhat larger populations. A
number of requests for recommended design weather
data for other locations have been received, and
where most of the elements could be estimated, they
were also added to the list. In some cases the values
obtained from the large-scale charts have not been
rounded off.
As previously noted in the Introduction to this
Chapter, Environment Canada will estimate data for
locations not listed in the table using the list of
observed or computed values for weather stations,
the large-scale manuscript charts and any other
relevant information that is available. In the absence
of weather observations at any particular location, a
knowledge of the local topography may be important. For example, cold air has a tendency to collect in
depressions, precipitation frequently increases with
elevation and winds are generally stronger near large
bodies of water. These and other relationships affect
the corresponding design values and will be taken
into consideration where possible in answering
inquiries.
know the most severe weather conditions under
which the system will be expected to function satisfactorily. Failure to maintain the inside temperature
at the pre-determined level will not usually be
serious if the temperature drop is not great and if the
duration is not long. The outside conditions used for
design should, therefore, not be the most severe in
many years, but should be the somewhat less severe
conditions that are occasionally but not greatly
exceeded.
Winter design temperature is based on an analysis
of winter air temperatures only. Wind and solar
radiation also affect the inside temperature of most
buildings, but there is no convenient way of
combining their effects with that of outside air
temperature. Some quite complex methods of taking
account of several weather elements have been
devised and used in recent years, but the use of
average wind and radiation conditions is usually
satisfactory for design purposes.
January Design Temperatures
The winter design temperature is defined as the
lowest temperature at or below which only a certain
small percentage of the hourly outside air
temperatures in January occur. In previous issues of
these climatic data the January design temperatures
were obtained from a tabulation of hourly
temperature distributions for the 10 year period 1951
to 1960 for 118 stations. Hourly data summaries (1)
(which include temperature frequency distributions)
based on the 10 year period 1957 to 1966 have been
published for several stations each year since 1967
and are now available for 109 stations. They provide
a second set of January design temperatures. For the
69 stations that appeared in both lists, the current
design temperature is the average of these two, and
is, therefore, based on the 16 year period 1951 to 1966
with a 4 year overlap. For the 89 stations that
appeared in only one of the lists, the design
temperatures were adjusted to make them more
consistent.
A building and its heating system should be
designed to maintain the inside temperature at some
pre-determined leveL To do this, it is necessary to
The January design temperatures for all the other
locations in the table are estimates, and, where
necessary, have been adjusted to make them more
All the weather records that were used in preparing the table were, of necessity, observed at
inhabited locations, and hence interpolations from
the charts or the tabulated values will apply only to
locations at similar elevations and with similar
topography. This is particularly significant in
mountainous areas where the values apply only to
the populated valleys and not to the mountain slopes
and high passes, where, in some cases, very different
conditions are known to exist.
4
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representative of the 16 year period. Most of the
adjustments were less than one Celsius degree and
only about 16 exceeded 1.5°.
The adjustments mentioned above indicate the
variation in the design temperature from one decade
to another. The design temperatures for the next 20
to 30 years may differ from the tabulated values by
one or two Celsius degrees and, of course, the year to
year variation will be much greater. Most of the
temperatures were observed at airports. Design
values for the core areas of some large cities could be
1 or 2° milder, but values for the fringe areas are
probably about the same as for the airports. No
adjustments have been made, therefore, for the city
effect.
The 2.5 per cent January design temperature is the
value ordinarily used in the design of heating systems. In special cases, when the control of inside
temperature is more critical, the 1 per cent value may
be used.
July Design Temperatures
A building and its cooling and dehumidifying
system should be designed to maintain the inside
temperature and humidity at certain pre-determined
levels. To do this, it is necessary to know the most
severe weather conditions under which the system
will be expected to function satisfactorily. Failure to
maintain the inside temperature and humidity at the
pre-determined levels will usually not be serious if
the increases in the temperature and humidity are not
great and if the duration is not long. The outside
conditions used for design should, therefore, not be
the most severe in many years, but should be the
somewhat less severe conditions that are occasionally
but not greatly exceeded.
The summer design temperatures in this Chapter
are based on an analysis of July air temperatures and
humidities only. Wind and solar radiation also affect
the inside temperature of most buildings and may in
some cases be more important than the outside air
temperature. However, no method of allowing for
variations in radiation has yet become generally
accepted. When requirements have been standardized, it may be possible to provide more complete
weather information for summer conditions, but in
the meantime only dry-bulb and wet-bulb design
temperatures can be provided.
The frequency distribution of combinations of drybulb and wet-bulb temperatures for each month from
June to September have been tabulated for 33 Canadian weather stations by Boughner. (2) If the summer
dry-bulb and wet-bulb design temperatures are
defined as the temperatures that are exceeded 2.5 per
cent of the hours in July, then design values can be
obtained directly for these 33 stations.
The dry-bulb design temperatures in previous
editions of this Chapter were based on the values for
these 33 stations and a relationship between the
design temperatures and the mean annual maximum
temperatures. Hourly data summaries (1) (which
include temperature frequency distributions) based
on the 10 year period 1957 to 1966 are now available
for 109 stations. They provide a second set of July
dry-bulb design temperatures. For the 109 stations
the current dry-bulb temperatures are the averages of
the values in these two sets. For all the other locations in the table the previous values have been
adjusted to make them consistent with the calculated
values. The adjustments exceeded one Celsius
degree in only about 20 cases. All values were
converted to degrees Celsius and rounded off to the
nearest degree.
The July wet-bulb design temperatures have been
obtained in the same way, with one exception. The
previous values were obtained directly for the 33
stations in Boughner's publication, (2) and all the rest
were estimated from these 33 without using any
intermediate statistic. The current values for the 109
stations with hourly data summaries are averages
between the previous values and the values from the
hourly data summaries. For all the other locations
the previous values have been adjusted to make them
consistent. The adjustments exceed one Celsius
degree in only 6 cases. All wet-bulb values were
converted to degrees Celsius and rounded off to the
nearest degree.
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Heating Degree-Days
The rate of consumption of fuel or energy required to keep the interior of a small building at
21°C when the outside air temperature is below
18°C is roughly proportional to the difference
between 18°C and the outside temperature. Wind
speed, solar radiation, the extent to which the
building is exposed to these elements and the
internal heat sources also affect the heat required,
but there is no convenient way of combining these
effects. For average conditions of wind, radiation,
exposure and internal sources, however, the proportionality with the temperature difference still holds.
Heating degree-days based on temperature alone
are, therefore, still useful when more complex
methods of calculating fuel requirements are not
feasible.
Since the fuel required is also proportional to the
duration of cold weather, a convenient method of
combining these elements of temperature and time
is to add the differences between 18°C and the mean
temperature for every day in the year when the
mean temperature is below 18°C. It is assumed that
no heat is required when the mean outside air
temperature for the day is 18°C or higher.
The degree days below 18°C have been computed
day by day for the length of record available over
the period 1951 to 1980, and an average annual total
determined and published by the Atmospheric
Environment Service. (3) These values are given in
the table to the nearest degree-day.
A difference of only one Celsius degree in the
annual mean temperature will cause a difference of
250 to 350 in the Celsius degree-days. Since differences of O.5°C in the annual mean temperature are
quite likely to occur between two stations in the
same city or town, heating degree-days cannot be
relied on to an accuracy of less than about 100
degree-days.
Rainfall Intensity
Roof drainage systems are designed to carry off
the rainwater from the most intense rainfall that is
6
likely to occur. A certain amount of time is required
for the rainwater to flow across or down the roof
before it enters the gutter or drainage system. This
results in the smoothing out of the most rapid
changes in rainfall intensity. The drainage system,
therefore, need cope only with the flow of rainwater
produced by the average rainfall intensity over a
period of a few minutes, which can be called the
concentration time.
In Canada it has been customary to use the 15 min
rainfall that will probably be exceeded on an average
of once in 10 years. The concentration time for small
roofs is much less than 15 min and hence the design
intensity will be exceeded more frequently than once
in 10 years. The safety factors included in the tables
in the Canadian Plumbing Code will probably reduce
the frequency to a reasonable value and, in addition,
the occasional failure of a roof drainage system will
not be particularly serious in most cases.
The rainfall intensity values tabulated in the
previous edition of this Chapter were based on
measurements of the annual maximum 15 min
rainfalls at 139 stations with 7 or more years of
record. They were the 15 min rainfalls that would be
exceeded once in 10 years on the average, or the
values that had one chance in 10 of being exceeded in
anyone year.
It is very difficult to estimate the pattern of rainfall
intensity in mountainous areas, where precipitation
is extremely variable. The values in the table for
British Columbia and some adjacent areas are mostly
for locations in valley bottoms or in extensive, fairly
level areas. Much greater intensities may occur on
mountainsides.
One Day Rainfall
If for any reason a roof drainage system becomes
ineffective, the accumulation of rainwater may be
great enough in some cases to cause a significant
increase in the load on the roof. Although the period
during which rainwater may accumulate is unknown, it is common practice to use the maximum
one day rainfall for estimating the additional load.
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•
For most weather stations in Canada the total
rainfall for each day is published. The maximum
1/1 day" rainfall (as it is usually called) for several
hundred stations has been determined and published
by the Atmospheric Environment Service. (4) Since
these values are all for predetermined 24-h periods,
beginning and ending at the same time each morning, most of them have probably been exceeded in
periods of 24 h including parts of two consecutive
days. The maximum "24 h" rainfall (i.e. any 24-h
period) according to Hershfield and Wilson is, on the
average, about 113 per cent of the maximum 1/1 day"
rainfall. (5)
Most of the one day rainfall amounts in the table
have been copied directly from the latest edition of
Climatic Normals.(4) Values for the other locations
have been estimated. These maximum values differ
greatly within relatively small areas where little
difference would be expected. The variable length of
record no doubt accounts for part of this variability,
which would probably be reduced by an analysis of
annual maxima instead of merely selecting the
maximum in the period of record.
Annual Total Precipitation
The total amount of precipitation that normally
falls in one year is frequently used as a general
indication of the wetness of a climate, and is therefore
included in this Chapter. Total precipitation is the
sum in millimetres of the measured depth of rainwater and 0.1 of the measured depth of snow (since
the average density of fresh snow is about 0.1 that of
water).
Most of the average annual total precipitation
amounts in the table have been copied directly from
the latest edition of Climatic Normals, (4) where
averages for the 30 year period 1951 to 1980 have
been tabulated. For all other locations the values
have been estimated.
Snow Loads
The roof of a building should be able to support
the greatest weight of snow that is likely to accumu-
late on it. Some observations of snow on roofs have
been made in Canada, but not enough to form the
basis for estimating roof snow loads throughout the
country. Similarly, observations of the weight, or
water equivalent, of the snow on the ground are
inadequate. The observations of roof loads and
water equivalents are very usefuL as noted below,
but the measured depth of snow on the ground is
required to provide the basic information for a
consistent set of snow loads.
The estimation of the design snow load on a roof
from snow depth observations involves the following
steps:
(1) The depth of snow on the ground which has
an annual probability of exceedence of l-in30 is computed.
(2) The appropriate unit weight is selected and
used to convert snow depth to loads, Ss'
(3) The load, Sr' due to rain falling on the snow
is computed.
(4) Because the accumulation of snow on roofs is
often different from that on the ground,
certain adjustments should be made to the
ground snow load to provide a design snow
load on a roof.
The annual maximum depth of snow on the
ground has been assembled for 1618 stations for
which such data has been recorded by the Atmospheric Environment Service (AES). The period of
record used varies from station to station, ranging
from 7 to 38 years. These data were analysed using a
Fisher-Tippett Type 1(6) extreme value distribution as
reported by Newark et al. (7) The resulting values are
the snow depths which have a probability of l-in-30
of being exceeded in anyone year.
The unit weight of old snow generally ranges from
2 to 5 kN / m 3, and it is usually assumed in Canada
that 1 kN/m3 is the average for new snow. Average
unit weights of the seasonal snow pack have been
derived for different regions across the country(8) and
an appropriate value has been assigned to each
climatological station. Typically the values average
2.01 kN / m 3 east of the continental divide (except for
2.94 kN/m 3 north of the treeline), and range from
7
pays
2.55 to 4.21 kN/m3 to the west of the divide. The
product of the 1-in-30 snow depth and the average
unit weight of the seasonal snow pack at a station is
converted to the snow load (SL) in units of kilopascals (kPa).
The values of ground snow load at AES stations
were normalized assuming a simple linear variation
of the load with elevation above sea level in order to
account for the effects of topography. They were then
smoothed using a weighted moving-area average in
order to minimize the uncertainty due to snow depth
sampling errors and site-specific variations. Interpolation from analysed maps of the smooth normalized
values yielded a value for each location in the Table,
which could then be converted to the listed code
values (S) by means of an equation in the form:
Ss = smooth normalized SL + bZ
where b is the rate of change of SL with elevation at
the location and Z is the location's elevation above
mean sea level (MSL). Although they are listed in the
Table of Design Data to the nearest tenth of a kilopascal, values of Ss typically have an uncertainty of
about 20 per cent. Areas of sparse data in northern
Canada were an exception to this procedure. In these
regions, an analysis was made of the basic SL values.
The effects of topography, variations due to local
climates, and smoothing were all subjectively assessed, and values derived in this fashion were used
to modify those derived objectively.
Tabulated values cannot be expected to indicate all
the local differences in S5' For this reason, values
should not be interpolated from the Table for unlisted
locations. The values of Ss in the Table apply only to
the named point at a specific latitude and longitude
as defined by the Gazetteer of Canada (Energy, Mines
and Resources Canada) available from Mail Order
Services, Canadian Government Publishing Centre,
DSS, Ottawa, Ontario, KIA OS9. Values at intermediate locations can be easily obtained from Environment Canada maps of smooth normalized SL (available for selected locations in Canada from the National Climatalogical Information Services, Environment Canada, 4905 Dufferin Street, Downsview,
B
Ontario, M3H 5T4), and the value of the location's
elevation above MSL (which can be obtained from
1:50000 or 1:250000 maps in the National Topographic Series available from the Canada Map Office,
Energy, Mines and Resources Canada, Ottawa,
KIA OE9). Instructions for this purpose are provided
with the Environment Canada maps.
The heaviest loads frequently occur when the
snow is wetted by rain, thus the rain load (Sr) was
estimated to the nearest 0.1 kPa and is provided in
the Table. Values of Sr' when added to
provide a
1-in-30 year estimate of the combined ground snow
and rain load. The values of Sr are based on an
analysis of about 2100 climate station values of the 1in-30 year one-day maximum rain amount. This return period is appropriate because the rain amounts
correspond approximately to the joint frequency of
occurrence of the one-day rain on maximum snow
packs. For the purpose of estimating rain on snow,
the individual observed one-day rain amounts were
constrained to be less than or equal to the snowpack
water equivalent which was estimated by a snow
pack accumulation model reported by Bruce and
Clark.(9)
The results from surveys of snow loads on roofs
indicate that average roof loads are generally less
than loads on the ground. The conditions under
which the design snow load on the roof may be taken
as a percentage of the ground snow load are given in
Section 4.1 of the National Building Code 1990. The
Code also permits further decreases in design snow
loads for steeply sloping roofs, but requires substantial increases for roofs where snow accumulation may
be more rapid due to such factors as drifting. Recommended adjustments are given in Chapter 4 of this
Supplement.
Wind Effects
All structures should be built to withstand the
pressures and suctions caused by the strongest gust
of wind that is likely to blow at the site in many
years. For many buildings this is the only wind effect
that needs to be considered, but tall or slender
structures should also be designed to limit their vib-
pays
rations to acceptable levels. Wind induced vibrations
may require several minutes to built up to their
maximum amplitude and hence wind speeds averaged over several minutes or longer should be used
for design. The hourly average wind speed is the
value available in Canada.
The provision of velocity pressures for both
average wind speeds and gust speeds for estimating
pressures, suctions and vibrations involves the
following steps:
(1) The annual maximum hourly wind speeds
were analysed to obtain the hourly wind
speeds that will have one chance in 10,30
and 100 of being exceeded in anyone year.
(2) An average air density was assumed in order
to compute the velocity pressures for the
hourly wind speeds.
(3) A value of 2 was assumed for the gust effect
factor to compute the velocity pressures for
the gust speeds.
The actual wind pressure on a structure increases
with height and varies with the shape of the structure. The factors needed to allow for these effects are
tabulated in Section 4.1 of the National Building
Code of Canada 1990 and Chapter 4. The other three
steps are discussed in more detail in the following
paragraphs.
Until recently the only wind speed record kept at a
large number of wind-measuring stations in Canada
was the number of miles of wind that pass an anemometer head in each hour, or the hourly average
wind speed. Many stations are now recording only
spot readings of the wind speed each hour, and these
may have to be used for design at some future time.
For the present, however, the older hourly mileages
are the best data on which to base a statistical analysis. The annual maximum hourly mileages for over
100 stations for periods from 10 to 22 years were
analysed using Gumbel's extreme value method to
calculate the hourly mileages that would have one
chance in 10,30 and 100 of being exceeded in anyone
year.
Values of the l-in-30 hourly mileages for the
additional 500 locations in the table have been
estimated. To obtain the l-in-l0 and l-in-l00 values
for these locations, the value of the parameter 1/ a,
which is a measure of the dispersion of the annual
maximum hourly mileages, was estimated. The 100
known values were plotted on a map from which
estimates of 1/ a were made for the other locations.
Knowing the l-in-30 hourly mileages and the values
of l/a, the l-in-l0 and l-in-l00 values could be
computed.
Pressure, suctions and vibrations caused by the
wind depend not only on the speed of the wind but
also on the air density and hence on the air temperature and atmospheric pressure. The pressure, in turn,
depends on elevation above sea level and varies with
changes in the weather systems. If V is the design
wind speed in miles per hour, then the velocity
pressure, P, in pounds per square foot is given by the
equation
P
CV 2
where C depends on air temperature and atmospheric pressure as explained in detail by Boyd. (10)
The value 0.0027 is within 10 per cent of the monthly
average value of C for most of Canada in the windy
part of the year. This value (0.0027) has been used to
compute all the velocity pressures corresponding to
the hourly mileages with annual probabilities of
being exceeded of l-in-l0, l-in-30 and l-in-l00. The
pressures were then converted from psf to kPa and
are shown in the table in columns headed only by the
numerical values of the probabilities.
The National Building Code requires the design
gust pressures for structural elements to be twice the
corresponding hourly pressures in the table. Because
wind speeds are squared to get pressures, this
statement is equivalent to saying that the gust factor
is the square root of 2.
In Chapter 1 of this Supplement, the velocity pressure, P,
and the design wind speed, V, are meterological terms,
wind pressure, q, and the
equivalent to the ｲ･ｦｾ｣＠
reference wind speed, V, which are engineering terms used
in Commentary B of Chapter 4.
9
pays
For buildings over 12 m high, the gust velocity
pressures and suctions must be increased according
to a table in Section 4.1 of the National Building Code
of Canada 1990 which is based on the assumption
that the gust speed increases in proportion to the 0.1
power of the height. The average wind speeds used
in computing the vibrations of a building are more
dependent on the roughness of the underlying
surface. A method of estimating their dependence on
roughness and height is given in Chapter 4.
The calculations for building vibrations in Chapter
4 have been drawn up for wind speeds measured in
metres per second. The equation
P=CV2
could be used to convert the tabulated pressures to
wind speeds provided constant C was converted to
e SI units. If P is in Pascals and V in metres per second,
the value of C would be 0.64689. In SI units,
however, the equation can be written in the form
P lpV2
2
where p is the air density in kg/ m 3. The density of
dry air at O°C and the standard atmospheric pressure
of 101.325 kPa is 1.2929 kg/m3. Half this value, or
0.64645, is very close to the converted value of C.
The difference (less than 1 in 1000) is negligible and,
therefore, the density of air at O°C and standard
atmospheric pressure has been adopted for converting wind pressures to wind speeds. The following
table has been arranged to give speeds to the nearest
m/ s for all pressures appearing in the main table.
The value "P" is assumed to be equal to
o.00064645V2.
Seismic Zones
The parameters used in establishing the seismic
zones are the ground acceleration and ground
velocity that have a 10 per cent probability of being
exceeded in 50 years. The zones are based on a
statistical analysis of the earthquakes that have been
experienced in Canada and adjacent regions using a
method that provides for inclusion of geological and
10
Conversion of Wind Pressures to Wind Speeds
P
kPa
0.14 to 0.15
0.16 to 0.17
0.18 to 0.19
0.20 to 0.22
0.23 to 0.24
0.25 to 0.27
0.28 to 0.29
0.30 to 0.32
0.33 to 0.35
0.36 to 0.38
0.39 to 0.42
0.43 to 0.45
V
m/s
15
16
17
18
19
20
21
22
23
24
25
26
P
kPa
0.46 to 0.48
0.49 to 0.52
0.53 to 0.56
0.57 to 0.60
0.61 to 0.64
0.65 to 0.68
0.69 to 0.72
0.73 to 0.76
0.77 to 0.81
0.82 to 0.86
0.87 to 0.90
0.91 to 0.95
V
m/s
27
28
29
30
31
32
33
34
35
36
37
38
P
kPa
0.96 to 1.00
1.01 to 1.06
1.07 to 1.11
1.12 to 1.16
1.17 to 1.22
1.23 to 1.28
1.29 to 1.33
1.34 to 1.39
1.40 to 1.45
1.46 to 1.52
1.53 to 1.58
1.59 to 1.64
V
m/s
39
40
41
42
43
44
45
46
47
48
49
50
tectonic information in support of the seismic
data.(11,12) The assigned zones reflect the opinions of
experts in the fields of seismology, geology and
engineering, from industry, government and universities, comprising members of the Canadian National
Committee on Earthquake Engineering and various
relevant committees responsible to the Associate
Committee on the National Building Code.
The velocity and acceleration zones and assigned
zonal velocity ratio, v, for each zone, as a fraction of a
velocity of 1 m/ s, are shown in the table. The zone
boundaries in terms of peak horizontal velocity and
peak horizontal acceleration, are shown in Table J-1
of the Commentary on Effects of Earthquakes in
Chapter 4 of this Supplement.
References
Hourly Data Summaries. Dept. of Transport,
Meteorological Branch and later Dept. of the
Environment, Atmospheric Environment
Service, various dates from May 1967 to March
1974.
(2) Boughner, C.C., Percentage Frequency of Dryand Wet-bulb Temperatures from June to September at Selected Canadian Cities. Dept. of
(1)
pays
-=
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
Transport, Meteorological Branch, Canadian
Meteorological Memoirs, No.5, Toronto, 1960.
Environment Canada, Canadian Climate
Normals. Vol. 4, Atmospheric Environment
Service, Downsview, Ontario, 1982.
Environment Canada, Canadian Climate
Normals. Vol. 3, Atmospheric Environment
Service, Downsview, Ontario, 1983.
Hershfield, D.M. and Wilson, W.T., Generalizing Rainfall Intensity - Frequency Data. International Association of Scientific Hydrology,
General Assembly, Toronto, Vol. I, 1957, pp.
499-506.
Gumbel, E.J., Statistics of Extremes. Columbia
University Press, New York, 1958.
Newark, M.J., Welsh, L.E., Morris, R.J. and
Ones, W.V. Revised Ground Snow Loads for
the 1990 NBC of Canada. Can. J. Civ. Eng., Vol.
16, No.3, June 1989.
Newark, M.J., A New Look at Ground Snow
Loads in Canada. Proceedings, 41st Eastern
Snow Conference, Washington, D.C., Vol. 29,
pp. 59-63, 1984.
Bruce, J.P. and Clark, R.H., Intro. to Hydrometeorology. Pergammon Press, London, 1966.
Boyd, D.W., Variations in Air Density over
Canada. National Research Council of Canada,
Division of Building Research, Technical Note
No. 486, June 1967.
Basham, P.W. et al., New Probabilistic Strong
Seismic Ground Motion Maps of Canada: a
Compilation of Earthquake Source Zones,
Methods and Results. Earth Physics Branch
Open File Report 82-33, p. 205, 1982.
Heidebrecht A.C. et al., Engineering Applications of New Probabilistic Seismic GroundMotion Maps of Canada. Can. J. Civ. Eng., Vol.
10, No.4, pp. 670-680, 1983.
11
pays
12
pays
Design Data for Selected Locations in Canada
Design Temperature
Province
and
Location
e
e
e
e
January
2.5% 1%
°C
°C
July 2.5 %
Dry
°C
Wet
°C
DegreeDays
Below
18°C
15
Min.
Rain
mm
One
Day
Rain
mm
Ann.
Tot.
Ppn.
mm
Hourly Wind
Pressures
Ground
Snow
Load
kPa
Seismic
Data
Zonal
Velocity
Z! Ratio
v
v
I
Ss
SR
1/10
kPa
1/30
kPa
1/100
kPa
Za
British Columbia
100 Mile House
Abbotsford
Agassiz
Albemi
Ashcroft
- 28
-10
-13
-5
- 25
- 31
-11
15
-7
- 28
30
29
31
31
34
18
20
20
18
20
5154
3146
2984
3312
3666
10
10
8
10
10
51
83
116
125
45
386
1513
1693
2033
222
2.4
1.8
2.2
2.7
1.0
0.3
0.3
0.6
0.4
0.1
0.30
0.42
0.55
0.47
0.28
0.36
0.55
0.75
0.58
0.35
0.43
0.71
1.00
0.70
0.43
1
4
3
5
1
1
4
3
5
2
0.05
0.20
0.15
0.30
0.10
Beatton River
Burns Lake
Cache Creek
Campbell River
Carmi
37
- 30
25
-7
- 24
- 39
- 33
28
-9
- 26
25
25
34
26
33
18
17
20
18
20
6977
5773
3800
3448
5212
13
10
10
10
10
50
48
63
105
98
485
490
250
1656
561
3.0
3.5
1.2
3.0
3.5
0.1
0.2
0.2
0.4
0.2
0.22
0.30
0.29
0.46
0.24
0.27
0.36
0.35
0.58
0.33
0.34
0.43
0.43
0.72
0.44
0
1
1
6
1
1
3
2
6
1
0.05
0.15
0.10
0.40
0.05
Castlegar
Chetwynd
Chilliwack
Comox
Courtenay
19
- 35
12
7
-7
- 22
- 38
-13
9
-9
32
27
30
27
28
20
18
20
18
18
3683
5801
2990
3197
3197
10
15
8
10
10
51
63
122
113
103
642
467
1594
1215
1484
2.5
2.2
2.0
2.4
2.4
0.1
0.2
0.3
0.4
0.4
0.23
0.32
0.48
0.45
0.45
0.30
0.37
0.63
0.58
0.58
0.39
0.44
0.83
0.74
0.74
1
0
4
6
6
1
1
4
6
6
0.05
0.05
0.20
0.40
0.40
Cranbrook
Crescent Valley
Crofton
Dawson Creek
Dog Creek
- 27
- 20
-6
- 36
28
30
- 23
8
- 39
- 30
32
31
28
27
29
19
19
18
18
18
4727
4303
3170
6232
5139
10
10
8
18
10
43
52
76
67
47
411
789
1042
474
388
2.7
3.8
1.1
2.3
1.3
0.2
0.1
0.2
0.2
0.2
0.22
0.22
0.48
0.31
0.31
0.29
0.29
0.58
0.37
0.37
0.37
0.37
0.69
0.44
0.44
1
1
5
0
1
1
1
5
1
2
0.05
0.05
0.30
0.05
0.10
Duncan
Elko
Fernie
Fort Nelson
Fort St. John
6 -8
28 -31
- 29 - 32
-40 - 42
- 36
38
29
29
29
28
26
18
19
19
18
18
3170
4426
4817
7087
6122
8
13
13
13
15
110
54
106
81
80
1042
605
1128
452
493
1.6
4.0
4.1
2.2
2.5
0.4
0.2
0.2
0.1
0.1
0.48
0.27
0.33
0.19
0.31
0.58
0.37
0.43
0.24
0.36
0.69
0.50
0.55
0.29
0.42
5
1
1
0
0
5
1
1
1
1
0.30
0.05
0.05
0.05
0.05
Glacier
Golden
Grand Forks
Greenwood
Hope
- 27
28
20
- 20
16
-30
-31
- 22
- 22
-18
27
29
35
35
32
17
17
20
20
20
6233
4930
4046
4524
3148
10
8
10
10
8
71
59
41
107
106
1833
477
447
511
1636
8.5
3.4
2.5
2.9
2.5
0.2
0.2
0.1
0.1
0.3
0.24
0.27
0.26
0.29
0.41
0.29
0.32
0.36
0.39
0.55
0.35
0.38
0.48
0.52
0.73
1
1
1
1
3
1
1
1
1
3
0.05
0.05
0.05
0.05
0.15
Kamloops
Kaslo
Kelowna
Kimberley
Kitimat Plant
Kitimat Townsite
Ullooet
,
Lytton
Mackenzie
- 25
- 23
-17
26
16
-16
- 23
-19
- 35
28
- 26
20
- 29
-18
-18
25
- 22
38
34
29
33
31
23
23
33
35
26 •
20
19
20
19
16
16
20
20
17
3650
4046
3730
4911
4107
4275
3684
3301
5897
13
10
10
10
13
13
10
10
10
57
51
64
49
185
119
114
77
63
252
828
317
520
2702
2299
356
450
692
1.3
2.5
1.1
4.0
5.0
5.9
1.9
2.5
3.4
0.2
0.1
0.1
0.2
0.7
0.7
0.1
0.3
0.2
0.30
0.22
0.34
0.22
0.27
0.27
0.32
0.31
0.24
0.37
0.28
0.43
0.29
0.33
0.33
0.39
0.39
0.29
0.45 1
0.36 1
0.53 1
0.37 1
0.40 2
0.40 12
0.49 1
0.49 2
0.35 0
1
1
1
1
4
4
2
2
2
0.05
0.05
0.05
0.05
0.20
0.20
0.10
0.10
0.10
2
3
4
5
6
7
8
9
10
11
12
13
Column 1
14
15 16
17
13
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
°C
DegreeDays
Below
Wet
18°C
°C
July 2.5 %
2.5%1 1 % Dry
°C :
15
Min.
Rain
mm
One
Day
Rain.
mm
Ann.
Tot.
Ppn.
mm
i
e
S5
SR
1/10
kPa
1/30
kPa
I 1/100
kPa
Masset
McBride
7
-34
-9
-37
17
30
15
18
3855
5078
13
13
76
50
1403
652
1.6
3.9
0.4
0.2
0.49
0.27
0.58
0.32
0.68
0.38
6
0
6
1
0.40
0.05
McLeod Lake
Merritt
Mission City
Montrose
Nakusp
- 35
- 26
-9
-17
24
37
- 29
-11
20
-27
27
34
30
32
31
17
20
20
20
19
5800
4348
3064
3683
3988
10
8
13
10
10
63
57
98
51
51
802
319
1701
642
811
3.7
2.3
2.2
3.7
2.9
0.2
0.3
0.3
0.1
0.1
0.24
0.32
0.47
0.22
0.24
0.29
0.39
0.60
0.30
0.30
0.35
0.49
0.77
0.41
0.37
0
1
4
1
1
2
2
4
1
1
0.10
0.10
0.20
0.05
0.05
Nanaimo
Nelson
Ocean Falls
Osoyoos
Penticton
-7
- 20
12
-16
-16
-9
24
14
-18
18
26
31
23
33
33
18
19
16
20
20
3065
3734
3627
3289
3502
8
10
13
10
10
92
66
234
35
45
1019
669
4387
320
274
1.6
4.6
3.5
0.5
0.9
0.4
0.1
0.7
0.1
0.1
0.47
0.22
0.47
0.30
0.40
0.58
0.29
0.55
0.43
0.52
0.71
0.37
0.65
0.59
0.68
4
1
2
1
1
4
1
4
1
1
0.20
0.05
0.20
0.05
0.05
Port Alberni
Port Hardy
Port McNeill
Powell River
Prince George
5
5
-5
-9
- 33
-7
-7
-7
11
- 36
31
20
22
26
28
18
16
17
18
18
3152
3674
3459
3056
5376
10
13
13
8
15
140
131
127
80
50
1987
1785
1555
1174
628
2.7
0.8
1.0
1.7
3.1
0.4
0.4
0.4
0.4
0.2
0.47
0.49
0.49
0.42
0.25
0.58
0.58
0.58
0.55
0.30
0.70
0.66
0.68
0.71
0.36
5
6
6
5
0
5
6
6
5
2
0.30
0.40
0.40
0.30
0.10
Prince Rupert
Princeton
Qualicum Beach
Quesnel
Revelstoke
-14
- 27
7
- 33
- 26
-16
30
-9
- 35
-29
19
32
27
30
32
15
20
18
17
19
3987
4531
3236
4938
4201
13
10
10
10
13
141
37
102
72
78
2463
372
1317
558
1006
1.7
1.8
2.0
1.7
5.3
0.4
0.5
0.4
0.1
0.1
0.42
0.24
0.46
0.25
0.24
0.50
0.32
0.58
0.29
0.29
0.59
0.42
0.72
0.34
0.35
3
2
4
0
1
5
2
4
2
1
0.30
0.10
0.20
0.10
0.05
Salmon Arm
Sandspit
Sidney
Smith River
Smithers
23
-6
-6
-46
- 29
- 26
-7
-8
48
-31
33
15
26
26
25
20
15
18
17
17
3945
3668
3083
7616
5431
13
13
8
8
13
43
80
102
68
60
533
1281
874
481
495
2.7
1.6
1.0
2.5
3.4
0.1
0.4
0.2
0.1
0.2
0.29
0.54
0.46
0.19
0.31
0.35
0.63
0.55
0.25
0.37
0.43
0.74
0.66
0.33
0.44
1
6
5
1
1
1
6
5
2
3
0.05
0.40
0.30
0.10
0.15
Squamish
Stewart
Taylor
Terrace
Totino
-11
23
- 36
- 20
-2
-13
25
- 38
- 22
-4
29
23
26
25
19
20
16
18
16
16
3379
4654
6122
4380
3316
10
13
15
13
13
112
178
56
117
174
2285
1870
432
1234
3288
2.9
7.2
2.1
5.5
1.0
0.6
0.7
0.1
0.5
0.4
0.38
0.32
0.32
0.27
0.54
0.50
0.39
0.37
0.33
0.63
0.65
0.48
0.44
0.40
0.74
3
2
0
2
5
3
4
1
4
5
0.15
0.20
0.05
0.20
0.30
17
-2
- 20
-4
33
19
20
16
3574
3120
10
13
51
140
703
3335
2.4
0.9
0.1
0.4
0.17
0.54
0.24
0.63
0.33
0.74
1
5
1
5
0.05
0.30
-9
-10
25
29
17
20
3307
3102
10
8
172
102
1935
1322
4.4
1.5
0.6
0.2
0.49
0.46
0.58
0.58
0.72
0.72
4
4
4
4
0.20
0.20
-9
-11
30
20
3264
10
117
2201
1.8
0.2
0.47 : 0.60
0.20
2
3
4
5
6
7
8
9
10
11
12
0.77 4 4
14
15 16
Trail
Ucluelet
Vancouver & Region
Burnaby (Simon Fraser Univ.)
Cloverdale
Haney
Column 1
14
Seismic
Data
Zonal
Velocity
Za Zv Ratio
v
Hourly Wind
Pressures
Ground
Snow
Load
kPa
-7
8
i
i
!
13
i
17
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
location
e
e
e
e
e
e
e
January
2.5% 1%
°C
°C
July 2.5 %
Dry
°C
Wet
°C
DegreeDays
Below
18°C
15
Min.
Rain
mm
One
Day
Rain
mm
Hourly Wind
Pressures
Ground
Snow
load
kPa
Ann.
Tot.
Ppn.
mm
Ss
SR
Seismic
Data
1/10
kPa
1/30
kPa
1/100
kPa
Za
Zv
Zonal
Velocity
Ratio
v
Ladner
langley
New Westminster
North Vancouver
- 6 -8
8 -10
8 10
-7
9
27
29
29
26
19
20
19
19
3253
3117
2947
2978
10
8
10
10
62
118
132
100
982
1504
1578
1889
1.2
1.6
1.6
2.7
0.2
0.2
0.2
0.3
0.45
0.45
0.44
0.44
0.55
0.58
0.55
0.55
0.67
0.73
0.68
0.68
5
4
4
4
4
4
4
4
0.20
0.20
0.20
0.20
Richmond
Surrey (88 Ave. & 156 St)
Vancouver
Vancouver (Granville & 41 Av)
West Vancouver
-7
9
-8 -10
-7
-9
- 6 -8
8 -10
27
29
26
28
28
19
20
19
20
19
3030
3067
2924
2880
3250
8
10
10
10
9
114
131
94
93
139
1113
1574
1329
1324
1933
1.4
2.2
1.6
2.5
1.9
0.2
0.3
0.2
0.3
0.2
0.45
0.46
0.45
0.45
0.45
0.55
0.58
0.55
0.55
0.55
0.67
0.72
0.67
0.67
0.67
4
4
4
4
4
4
4
4
4
4
0.20
0.20
0.20
0.20
0.20
Vernon
Victoria & Region
Victoria (Gonzales Hts)
Victoria (Mt Tolmie)
Victoria
20
23
33
20
3887
13
40
381
2.0
0.1
0.32
0,39
0.49
1
1
0.05
-5
-6
-5
-7
8
-7
23
24
24
17
16
17
2947
3150
3016
9
9
5
83
74
81
647
790
845
1.4
1.9
1.0
0.3
0.3
0.2
0.49
0.49
0.48
0.58
0.58
0.58
0.69
0.69
0.70
6
6
5
5
5
5
0.30
0.30
0.30
Williams lake
Youbou
31 - 34
5 -7
29
31
17
19
4920
2945
10
10
37
114
400
1874
2.2
3.5
0.2
0.6
0.30
0.46
0.35
0.55
0.41
0.66
1
4
2
4
0.10
0.20
Alberta
Athabasca
Banff
Barrhead
Beaverlodge
Brooks
- 35
- 30
- 34
35
32
38
- 32
- 37
- 38
- 34
28
27
28
28
32
19
17
19
18
19
6256
5657
6088
5983
5307
18
18
20
25
18
88
53
102
101
89
506
471
467
467
351
1.4
3.3
1.6
2.2
1.1
0.1
0.1
0.1
0.1
0.1
0.30
0.39
0.32
0.27
0.39
0.37
0.45
0.39
0.33
0.48
0.45
0.52
0.49
0.40
0.57
0
0
0
0
0
1
1
1
1
0
0.05
0.05
0.05
0.05
0.00
Calgary
Campsie
Cam rose
Cardston
Claresholm
31
- 34
- 33
- 30
- 31
33
37
- 35
33
-34
29
28
29
29
29
17
19
19
18
18
5321
6088
5885
4870
4848
23
20
20
20
15
95
111
92
102
97
437
467
448
550
466
1.0
1.6
1.8
1.4
1.2
0.1
0.1
0.1
0.1
0.1
0.40
0.32
0.21
0.74
0.66
0.46
0.39
0.29
0.93
0.80
0.54
0.49
0.39
1.15
0.96
0
0
0
0
0
1
1
0
0
0
0.05
0.05
0.00
0.00
0.00
Cold lake
Coleman
Coronation
Cowley
Drumheller
36
- 31
31
31
- 31
-38
34
- 33
34
- 33
28
28
30
29
29
20
18
19
18
18
6166
5404
5879
5207
5283
15
15
20
15
20
94
62
99
74
73
460
569
374
501
348
1.6'
2.5
2.0
1.5
1.1
0.1
0.3
0.1
0.1
0.1
0.31
0.54
0.23
0.73
0.32
0.37
0.69
0.32
0.91
0.39
0.44
0.87
0.43
1.13
0.49
0
0
0
0
0
1
0
1
0
0.00
0.05
0.00
0.05
0.00
Edmonton
Edson
Embarras Portage
Fairview
Fort Macleod
- 32
- 34
- 41
38
31
- 34
- 37
-44
-40
- 33
28
28
27
27
31
19
18
19
18
18
5782
6027
6937
6166
4692
23
18
10
15
16
114
79
82
64
98
488
553
409
432
434
1.6
1.9
1.7
2.4
1.1
0.1
0.1
0.1
0.1
0.1
0.32
0.36
0.31
0.26
0.68
0.40
0.43
0.37
0.32
0.83
0.51
0.50
0.45
0.39
1.00
0
0
0
0
0
1
1
0
1
0
0.05
0.05
0.00
0.05
0.00
• - 39
41
28
19
6661 • 13
61
472
1.3
0.1
0.27
0.32
0.38 , 0
0
0.00
10
11
Fort McMurray
Column 1
2
3
4
5
6
7
8
9
12
13
14
1
15 16
17
15
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
e
e
e
e
2.5% 1%
°C
DegreeDays
Below
Wet
18°C
°C
July 2.5 %
Dry
°C
15
Min.
Rain
mm
One
Day
Rain.
mm
Ann.
Tot.
Ppn.
mm
Hourly Wind
Pressures
Ground
Snow
Load
kPa
Ss
SR
1/10
kPa
1/30
kPa
1/100
kPa
Seismic
Data
Zonal
Velocity
Za Zv Ratio
v
Fort Saskatchewan
Fort Vermilion
Grande Prairie
Habay
- 32 - 35
-41 - 43
- 36 - 39
41
43
28
28
27
28
19
18
18
18
5783
6999
6136
7300
20
13
23
13
78
60
78
63
423
383
453
387
1.5
1.9
2.0
2.2
0.1
0.1
0.1
0.1
0.31
0.22
0.37
0.20
0.39
0.26
0.44
0.24
0.49
0.32
0.52
0.28
0
0
0
0
1
1
1
1
0.05
0.05
0.05
0.05
Hardisty
High River
Hinton
Jasper
Keg River
-33
-31
- 34
- 32
- 40
- 35
- 33
-38
- 35
- 42
30
28
27
28
28
19
17
17
18
18
5965
5455
5679
5570
6832
20
18
13
10
13
56
111
70
108
60
412
455
502
475
444
1.6
1.2
2.7
3.0
2.2
0.1
0.1
0.1
0.1
0.1
0.24
0.51
0.36
0.37
0.19
0.32
0.60
0.43
0.43
0.24
0.42
0.72
0.50
0.50
0.29
0
0
0
1
0
0
1
1
1
1
0.00
0.05
0.05
0.05
0.05
Lac la Biche
Lacombe
Lethbridge
Manning
Medicine Hat
-35
- 33
·30
- 39
31
38
- 35
- 33
-41
- 34
28
29
31
27
33
19
18
18
18
19
6196
5823
4787
6850
4868
15
23
20
13
23
82
71
93
51
122
517
443
418
404
348
1.5
1.9
1.1
2.1
1.0
0.1
0.1
0.1
0.1
0.1
0.31
0.24
0.64
0.21
0.39
0.37
0.31
0.76
0.26
0.49
0.44
0.40
0.91
0.32
0.60
0
0
0
0
0
0
1
0
1
0
0.00
0.05
0.00
0.05
0.00
Peace River
Pincher Creek
Ranfurly
Red Deer
Rocky Mountain House
- 37 - 40
- 32 - 34
-34 37
-32 35
31 - 33
27
29
29
29
28
18
18
19
18
18
6469
5028
6015
5933
5613
15
18
18
23
20
48
128
89
154
77
375
551
439
498
556
1.7
1.4
1.7
1.8
1.7
0.1
0.1
0.1
0.1
0.1
0.24
0.70
0.23
0.31
0.26
0.29
0.88
0.29
0.37
0.32
0.36
1.08
0.36
0.44
0.39
0
0
0
0
0
1
0
0
1
1
0.05
0.00
0.00
0.05
0.05
Slave Lake
Stettler
Stony Plain
Suffield
Taber
- 36
32
- 32
- 32
-31
- 39
-34
- 35
34
·33
27
30
28
33
31
19
19
19
19
19
6302
5669
5713
5095
4772
15
20
23
20
20
76
165
102
69
93
482
431
529
338
382
1.7
2.0
1.6
1.2
1.1
0.1
0.1
0.1
0.1
0.1
0.28
0.24
0.32
0.43
0.57
0.34
0.32
0.40
0.52
0.69
0.41
0.42
0.51
0.64
0.82
0
0
0
0
0
1
0
1
0
0
0.05
0.00
0.05
0.00
0.00
Turner Valley
Valleyview
Vegreville
Vermilion
Wagner
- 31
37
34
-35
36
- 33
- 40
- 36
-38
·39
28
27
29
29
27
17
18
19
20
19
5786
5770
6208
6168
6264
20
18
18
18
15
82
51
69
75
72
574
519
404
438
476
1.3
2.1
1.7
1.6
1.7
0.1
0.1
0.1
0.1
0.1
0.51
0.35
0.25
0.23
0.28
0.60
0.43
0.32
0.28
0.34
0.71
0.51
0.40
0.34
0.41
0
0
0
0
0
1
1
0
0
1
0.05
0.05
0.00
0.00
0.05
Wainwright
Westaskiwin
Whitecourt
Wimborne
- 33 36
- 33 - 35
35 38
31
34
29
29
27
29
19
19
18
18
6000
5741
6151
5783
20
23
20
23
63
78
89
89
380
494
553
458
1.8
1.8
1.7
1.5
0.1
0.1
0.1
0.1
0.24
0.24
0.32
0.30
0.32
0.32
0.39
0.37
0.41
0.42
0.48
0.45
0
0
0
0
0
1
1
0
0.00
0.05
0.05
0.00
- 32 - 34
- 32 -34
- 34 -36
- 34 36
- 36 39
32
32
31
30
29
21
20
20
22
21
5462
5428
6060
6129
6402
33
28
23
25
20
78
63
104
104
67
397
351
352
425
379
1.5
1.1
1.9
1.6
1.6
0.1
0.1
0.1
0.1
0.1
0.44
0.49
0.48
0.28
0.28
0.52
0.60
0.60
0.32
0.34
0.63
0.74
0.76
0.37
0.41
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
4
5
6
7
8
9
10
11
12
13
14
Saskatchewan
Assiniboia
Battrum
Biggar
Broadview
Dafoe
Column 1
16
January
2
3
15 16
17
pays
a
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
2.5% 1%
°C
°C
July 2.5 %
Dry
°C
Wet
°C
DegreeDays
Below
18°C
15
Min.
Rain
mm
One
Day
Rain
mm
Ann.
Tot.
Ppn.
mm
Ground
Snow
Load
kPa
S5
SR
Hourly Wind
Pressures
1/10
kPa
1/30
kPa
1/100
kPa
Seismic
Data
Zonal
Velocity
Ratio
Za Zv
v
Dundurn
Estevan
Hudson Bay
Humboldt
Island Falls
- 35
32
37
- 36
39
-37
- 34
- 39
39
-41
31
32
29
28
26
20
22
21
21
20
5877
5497
6538
6346
7319
10
36
18
20
10
122
68
62
76
69
380
434
468
376
514
1.4
1.5
1.8
1.9
1.9
0.1
0.1
0.1
0.1
0.1
0.39
0.42
0.28
0.29
0.45
0.48
0.51
0.34
0.36
0.56
0.57
0.62
0.41
0.44
0.70
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
Kamsack
Kindersley
Lloydminster
Maple Creek
Meadow Lake
- 35
- 33
35
31
36
-37
- 35
-38
-34
39
29
32
29
31
28
22
20
20
20
20
6318
5814
6056
4951
6199
20
23
18
28
15
116
91
104
77
63
386
316
449
387
456
1.9
1.3
1.8
1.1
1.6
0.2
0.1
0.1
0.1
0.1
0.32
0.45
0.30
0.47
0.36
0.37
0.58
0.37
0.58
0.45
0.44
0.73
0.46
0.71
0.55
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
Meltort
Melville
Moose Jaw
Nipawin
North Battletord
- 37
- 34
- 32
- 38
- 34
40
- 36
- 34
- 41
- 36
28
29
32
28
30
21
21
21
21
20
6460
6176
5435
6407
6071
18
23
28
18
20
101
59
81
60
93
411
400
378
404
359
1.9
1.6
1.3
1.8
1.6
0.1
0.1
0.1
0.1
0.1
0.26
0.32
0.36
0.27
0.45
0.32
0.37
0.43
0.34
0.62
0.40
0.43
0.51
0.43
0.83
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
Prince Albert
Qu'Appelle
Regina
Rosetown
Saskatoon
37
- 34
34
- 33
- 35
-41
36
36
- 35
- 37
29
30
31
32
30
21
21
21
20
20
6559
6109
5901
5982
5997
20
25
28
25
23
74
104
102
85
84
398
437
380
339
354
1.7
1.6
1.3
1.6
1.6
0.1
0.1
0.1
0.1
0.1
0.26
0.34
0.34
0.47
0.36
0.34
0.39
0.39
0.58
0.44
0.44
0.46
0.46
0.71
0.54
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
Scott
Strasbourg
Swift Current
Uranium City
Weyburn
34
- 34
32
44
- 33
-36
-36
- 34
46
35
31
30
32
26
32
20
21
20
19
22
6243
5945
5427
7860
5589
20
25
33
8
33
68
100
66
47
97
355
402
351
345
382
1.7
1.4
1.3
1.8
1.3
0.1
0.1
0.1
0.1
0.1
0.44
0.33
0.46
0.37
0.38
0.58
0.39
0.56
0.45
0.45
0.75
0.46
0.69
0.54
0.53
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
Yorkton
- 34
37
29
21
6243
23
95
430
1.6
0.1
0.32
0.37
0.44
0
0
0.00
iManitoba
Beausejour
Boissevain
Brandon
Churchill
Dauphin
33
- 32
33
39
- 33
- 35
- 34
-35
-41
·35
28
32
31
24
30
23
23
22
18
22
5951
5732
6046
9190
6152
28
33
36
8
25
66
146
141
52
100
540
506
468
402
496
1.7
2.0
1.9
2.6
1.7
0.2
0.2
0.2
0.2
0.2
0.31
0.44
0.37
0.48
0.31
0.37
0.52
0.45
0.59
0.37
0.45
0.63
0.54
0.72
0.44
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
Flin Flon
Gimli
Island Lake
Lac du Bonnet
Lynn Lake
- 38
·34
- 36
34
40
- 40
- 36
- 38
·36
·42
27
29
26
28
27
20
23
20
23
19
6846
6166
7342
6150
8029
13
28
13
28
8
77
125
63
76
77
466
534
567
567
480
2.0
1.7
2.4
1.7
2.2
0.2
0.2
0.2
0.2
0.2
0.42
0.30
0.37
0.28
0.47
0.52
0.37
0.43
0.34
0.58
0.65
0.45
0.50
0.41
0.71
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
Morden
·31
33
31
23
5561
28
143
527
2.0
0.2
0.40
0.48
0.56
0
0
0.00
10
11
12
13
14
15 16
e
•
Column 1
2
3
4
5
6
7
8
9
17
17
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
i
2.5% 1%
°C
DegreeDays
Below
Wet
ac 18°C
July 2.5 %
Dry
DC
15
Min.
Rain
mm
One
Day
Rain.
mm
Ann.
Tot.
Ppn.
mm
Hourly Wind
Pressures
Ground
Snow
Load
kPa
Ss
SR
1/10
kPa
1/30
kPa
Seismic
Data
Zonal
Velocity
1/100
kPa . Za Zv Ratio
v
Neepawa
Pine Falls
Portage la Prairie
Rivers
- 32
- 34
- 31
-34
- 34
-36
- 33
-36
30
28
30
30
22
23
23
22
5985
6176
5821
6075
33
25
36
33
85
67
131
139
474
540
512
472
2.0
1.7
1.9
1.9
0.2
0.2
0.2
0.2
0.33
0.29
0.36
0.36
0.40
0.35
0.43
0.43
0.49
0.43
0.51
0.51
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
Sandi lands
Selkirk
Split Lake
Steinbach
Swan River
-32
33
38
- 33
36
- 34
35
40
- 35
38
29
29
27
30
29
23
23
19
23
22
5920
5893
8250
5892
6308
28
28
10
28
20
89
89
51
83
85
580
507
483
515
496
2.0
1.7
2.3
1.8
1.8
0.2
0.2
0.2
0.2
0.2
0.31
0.33
0.51
0.31
0.30
0.37
0.39
0.60
0.37
0.35
0.44
0.47
0.71
0.44
0.42
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
The Pas
Thompson
Virden
Winnipeg
- 36
42
33
- 33
- 38
- 45
- 35
- 35
28
26
30
30
21
19
22
23
6787
8017
5933
5871
15
10
33
28
78
51
104
84
496
542
486
506
1.9
2.2
1.8
1.7
0.2
0.2
0.2
0.2
0.35
0.49
0.36
0.35
0.43
0.58
0.43
0.42
0.52
0.68
0.51
0.49
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
Ontario
Ailsa Craig
Ajax
Alexandria
Alliston
Almonte
-17
- 20
- 24
23
- 26
19
- 22
26
25
- 28
30
30
30
29
30
23
23
23
23
23
4000
4080
4700
4400
4774
25
23
28
28
25
89
76
76
114
76
920
800
940
740
736
2.0
0.9
2.2
1.8
2.3
0.4
0.4
0.4
0.4
0.4
0.40
0.43
0.30
0.22
0.30
0.50
0.52
0.37
0.29
0.37
0.62
0.64
0.45
0.38
0.46
0
1
4
1
4
0
1
2
0
2
0.00
0.05
0.10
0.05
0.10
Armstrong
Arnprior
Atikokan
Aurora
Bancroft
39
- 27
34
21
-27
42
- 29
37
- 23
- 29
28
30
29
30
29
21
23
22
23
22
6991
4791
6209
4325
4919
23
23
25
28
25
99
76
93
102
83
738
746
724
800
880
2.5
2.3
2.2
1.8
2.8
0.4
0.4
0.3
0.4
0.4
0.21
0.27
0.21
0.30
0.23
0.25
0.34
0.25
0.39
0.29
0.29
0.42
0.29
0.50
0.36
0
4
0
1
2
0
2
0
0
1
0.00
0.10
0.00
0.05
0.05
Barrie
Barriefield
Beaverton
Belleville
Belmont
- 24
- 22
- 24
- 22
17
- 26
24
- 26
24
19
29
27
30
29
30
22
23
22
23
23
4575
4200
4400
4129
4000
28
23
28
23
25
127
114
140
106
89
950
870
860
855
980
2.3
1.9
2.0
1.6
1.6
0.4
0.4
0.4
0.4
0.4
0.21
0.35
0.24
0.32
0.35
0.29
0.43
0.32
0.39
0.45
0.39
0.52
0.42
0.48
0.58
1
2
1
1
0
1
1
1
1
0
0.05
0.05
0.05
0.05
0.00
Big Trout Lake
Borden CFB
Bracebridge
Bradford
Brampton
- 38
23
- 26
- 23
19
- 40
25
- 28
25
- 21
25
29
29
30
30
20
22
22
23
23
7699
4550
4800
4241
4321
13
28
25
28
28
84
114
114
114
178
581
810
1020
716
816
2.9
2.0
2.8
1.9
1.2
0.2
0.4
0.4
0,4
0.4
0.33
0.21
0.19
0.24
0.32
0.39
0.29
0.25
0.32
0.39
0.46
0.39
0.33
0.42
0.49
0
1
1
1
1
0
0
1
0
0
0.00
0.05
0.05
0.05
0.05
17
- 21
. - 23
·26
I -17
-19
- 23
- 25
- 28
-19
30
29
29
29
31
23
23
23
21
23
3922
4200
4230
5293
3818
23
23
25
25
23
103
76
89
102
77
746
830
974
1066
777
1.2
1.5
2.0
2.5
0.8
0.4
0.4
0.4
0.4
0.4
0.31
0.42
0.32
0.20
0.36
0.37
0.50
0.39
0.26
0.43
0.44
0,60
0.49
0,34
0.51
1
1
3
1
1
0
1
1
1
0
0,05
0.05
0.05
0.05
0.05
3
4
5
6
7
8
9
10
11
12
13
14
15 16
e
Brantford
Brighton
Brockville
Burk's Falls
Burlington
Column 1
18
2
I
i
I
17
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
2.5% 1 0/0
°C
°C
July 2.5 %
Dry
°C
Wet
°C
DegreeDays
Below
18 c C
15
Min.
Rain
mm
One
Day
Rain
mm
Ground
Snow
Load
kPa
Ann.
Tot.
Ppn.
mm
S5
S;;
Hourly Wind
Pressures
1/10
kPa
1/30
kPa
1/100
kPa
Seismic
Data
Zonal
Velocity
Ratio
Za Zv
v
Cambridge
Campbellford
Cannington
Carleton Place
Cavan
18
23
-24
- 25
- 22
- 20
26
26
- 27
25
29
30
30
30
30
23
23
23
23
23
4100
4400
4550
4700
4425
25
25
28
25
28
108
111
127
69
76
899
811
890
787
770
1.5
1.6
2.0
2.3
1.8
0.4
0.4
0.4
0.4
0.4
0.26
0.29
0.24
0.30
0.31
0.32
0.37
0.32
0.37
0.39
0.39
0.47
0.42
0.46
0.50
1
1
1
4
1
0
1
1
2
1
0.05
0.05
0.05
0.10
0.05
Centralia
Chapleau
Chatham
Chesley
Clinton
-17
- 35
16
19
-17
-19
- 38
-18
21
19
30
27
31
29
29
23
21
24
22
23
4041
6214
3607
4450
4100
25
23
28
28
23
80
104
107
76
89
1033
834
808
1120
950
2.1
3.7
0.9
2.6
2.4
0.4
0.4
0.4
0.4
0.4
0.37
0.19
0.32
0.33
0.37
0.48
0.25
0.39
0.43
0.48
0.60
0.31
0.48
0.55
0.60
0
0
0
1
0
0
0
0
0
0
0.00
0.00
0.00
0.05
0.00
Coboconk
Cobourg
Cochrane
Colborne
Collingwood
- 25
- 21
- 34
- 21
- 22
27
- 23
- 36
- 23
- 24
29
30
29
29
29
22
23
21
23
22
4750
4241
6398
4050
4242
25
23
20
23
28
127
76
87
76
128
909
822
885
830
858
2.3
1.1
2.6
1.5
2.5
0.4
0.4
0.3
0.4
0.4
0.22
0.46
0.26
0.44
0.25
0.29
0.55
0.32
0.52
0.34
0.37
0.65
0.39
0.62
0.45
1
1
1
1
1
1
1
0
1
0
0.05
0.05
0.05
0.05
0.05
Cornwall
Corunna
Deep River
Deseronto
Dorchester
- 23
-16
- 29
- 22
-18
25
18
32
24
- 20
30
31
30
28
30
23
23
22
23
23
4418
3800
5125
4100
4050
28
23
23
23
28
71
89
89
89
89
928
800
790
870
890
2.0
0.9
2.3
1.7
1.7
0.4
0.4
0.4
0.4
0.4
0.30
0.35
0.20
0.32
0.33
0.37
0.43
0.24
0.39
0.43
0.46
0.52
0.28
0.48
0.55
4
0
4
1
0
2
0
2
1
0
0.10
0.00
0.10
0.05
0.00
Dorion
Dresden
Dryden
Dunnville
Durham
- 33
16
- 34
-15
20
- 35
-18
- 36
17
- 22
28
31
27
30
29
21
24
22
24
22
5900
3738
6087
3851
4671
20
28
25
23
28
76
76
114
102
86
685
765
698
905
1040
2.6
0.9
2.2
1.8
2.6
0.4
0.4
0.3
0.4
0.4
0.25
0.32
0.21
0.33
0.31
0.29
0.39
0.25
0.39
0.39
0.34
0.48
0.29
0.45
0.50
0
0
0
1
1
0
0
0
0
0
0.00
0.00
0.00
0.05
0.05
Dutton
Earlton
Edison
Elmvale
Embro
-16
- 33
- 34
- 24
18
18
- 36
- 36
- 26
- 20
31
30
28
29
29
24
21
22
22
23
3800
5915
6050
4300
4200
28
23
25
28
28
89
99
89
127
89
870
822
680
900
890
1.2
2.4
2.2
2.4
1.8
0.4
0.4
0.3
0.4
0.4
0.34
0.32
0.20
0.24
0.33
0.43
0.40
0.24
0.32
0.43
0.53
0.51
0.28
0.42
0.54
0
1
0
1
0
0
1
0
1
0
0.00
0.05
0.00
0.05
0.00
Englehart
Espanola
Exeter
Fenelon Falls
Fergus
- 33
25
-17
- 25
- 20
36
27
19
27
- 22
30
28
30
30
29
21
21
23
23
23
5900
4950
4101
4650
4615
23
23
25
25
33
87
89
89
133
118
892
840
962
859
880
2.3
2.1
2.2
2.1
2.0
0.4
0.4
0.4
0.4
0.4
0.29
0.28
0.37
0.25
0.26
0.37
0.37
0.48
0.32
0.32
0.47
0.48
0.60
0.41
0.40
1
1
0
1
1
1
0
0
1
0
0.05
0.05
0.00
0.05
0.05
Forest
Fort Erie
Fort Erie (Ridgeway)
Fort Francis
-16
15
15
- 33
-18
-17
-17
35
31
30
30
29
23
24
24
22
3839
3707
3650
5624
23
23
28
25
87
102
102 •
114
834
995
990
696
1.8
2.4
2.3
2.1
0.4
0.4
0.4
0.3
0.39
0.36
0.37
0.21
0.48
0.43
0.43
0.25
0.58
0.50
0.50
0.29
0
2
0
0
0
0
0.00
0.05
0.05
0.00
2
3
4
5
6
7
8
9
11
12
13
14
15 16
Column 1
10
2.
0
i
17
19
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
2.5% 1%
°C
I July 2.5 % DegreeDry
°C
Wet
°C
Days
Below
18°C
15
Min.
Rain
mm
One
Day
Rain.
mm
Ann.
Tot.
Ppn.
mm
Hourly Wind
Pressures
Ground
Snow
Load
kPa
Seismic
Data
Zonal
Velocity
Z, Z, Ratio
v
,
S5
SF
1/10
kPa
1/30
kPa
1/100
kPa
22
- 24
28
23
4150
23
89
870
1.9
0.4
0.35
0.43
0.52
2
1
0.05
35
-16
16
23
37
-38
18
-18
25
-40
28
31
29
29
29
21
24
23
21
22
6753
4000
3900
4930
6626
20
28
23
23
23
65
66
84
92
62
697
850
910
866
817
2.7
1.4
2.2
2.4
2.4
0.4
0.4
0.4
0.4
0.3
0.20
0.31
0.40
0.30
0.21
0.24
0.39
0.50
0.36
0.25
0.28
0.49
0.62
0.43
0.29
0
0
0
0
0
0
0
0
0
0
0.00
0.00
0.00
0.00
0.00
26
Gravenhurst
Gravenhurst (Muskoka Airport) - 26
16
Grimsby
-19
Guelph
24
Guthrie
28
28
18
21
26
29
29
30
29
29
22
22
23
23
22
4800
4911
3618
4304
4520
25
25
23
28
28
114
115
123
103
127
1020
1009
876
833
870
2.5
2.6
0.8
1.7
2.3
0.4
0.4
0.4
0.4
0.4
0.19
0.19
0.36
0.25
0.21
0.25
0.25
0.43
0.30
0.29
0.33
0.33
0.50
0.36
0.39
1
1
1
1
1
1
1
0
0
1
0.05
0.05
0.05
0.05
0.05
Haileybury
Haldimand (Caledonia)
Haldimand (Hagersville)
Haliburton
Halton Hills (Georgetown)
32
-17
16
- 27
19
35
19
-18
29
- 21
30
30
30
29
30
21
23
23
22
23
5427
3850
3987
4993
4355
23
23
25
25
28
65
104
283
103
128
849
913
842
971
837
2.2
1.1
1.2
2.7
1.3
0.4
0.4
0.4
0.4
0.4
0.32
0.31
0.33
0.19
0.27
0.39
0.37
0.39
0.25
0.34
0.49
0.44
0.46
0.31
0.42
2
1
1
1
1
1
0
0
1
0
0.05
0.05
0.05
0.05
0.05
Hamilton
Hanover
Hastings
Hawkesbury
Hearst
-17
-19
- 23
25
- 34
-19
21
- 26
27
- 36
31
30
30
30
28
23
22
23
23
21
3827
4340
4400
4800
6500
23
28
28
23
20
117
76
89
89
63
799
877
790
961
846
0.8
2.4
1.8
2.1
2.6
0.4
0.4
0.4
0.4
0.3
0.36
0.34
0.29
0.31
0.20
0.43
0.43
0.37
0.37
0.25
0.50
0.54
0.47
0.45
0.32
1
1
1
4
0
0
0
1
2
0
0.05
0.05
0.05
0.10
0.00
Honey Harbour
Hornepayne
Huntsville
Ingersoll
Iroquois Falls
- 24
- 37
- 26
-18
- 33
- 26
- 40
- 29
- 20
- 36
29
28
29
30
29
22
21
22
23
21
4400
6545
4780
4000
6200
23
20
25
28
20
127
83
104
89
63
950
734
971
890
780
2.5
3.3
2.7
1.6
2.7
0.4
0.4
0.4
0.4
0.3
0.25
0.19
0.19
0.33
0.30
0.34
0.25
0.25
0.43
0.37
0.45
0.31
0.33
0.54
0.45
1
0
1
0
1
1
0
1
0
0
0.05
0.00
0.05
0.00
0.05
Jellicoe
Kapuskasing
Kemptville
Kenora
Killaloe
- 36
- 33
- 25
- 33
- 28
- 39
- 35
- 27
-36
- 31
28
28
30
28
30
21
21
23
22
22
6600
6438
4622
5938
5082
20
20
25
25
23
76
80
73
128
62
710
858
867
623
674
2.5
2.6
2.1
2.1
2.5
0.4
0.3
0.4
0.3
0.4
0.21
0.23
0.30
0.20
0.24
0.25
0.28
0.37
0.24
0.29
0.29
0.34
0.46
0.28
0.36
0
0
4
0
3
0
0
2
0
1
0.00
0.00
0.10
0.00
0.05
Kincardine
Kingston
Kinmount
Kirkland Lake
Kitchener
-17
- 22
- 26
- 33
-19
-19
- 24
- 28
- 36
- 21
28
27
29
30
29
22
23
22
21
23
4100
4251
4800
6113
4146
23
23
25
20
28
76
119
102
97
175
890
870
950
856
897
2.4
1.9
2.5
2.7
1.8
0.4
0.4
0.4
0.3
0.4
0.40
0.35
0.20
0.29
0.27
0.50
0.43
0.26
0.37
0.34
0.62
0.52
0.34
0.46
0.42
0
2
1
1
1
0
1
1
1
0
0.00
0.05
0.05
0.05
0.05
Lakefield
Lansdowne House
- 24
- 39
- 26
- 41
30
28
23
21
4550
7199
28
18
89
78
770
666
2.0
2.7
0.4
0.2
0.27
0.24
0.34
0.29
0.43
0.35
1
0
1
0
0.05
0.00
2
3
4
5
v
I
8
9
10
11
12
13
14
15
16
17
Gananoque
Geraldton
Glencoe
Goderich
Gore Bay
Graham
Column 1
20
January
I
pays
p
Design Data for Selected Locations in Canada (Cont'd)
I
Design Temperature
Province
and
Location
January
2.5% 1%
°C
°C
July 2.5 %
Dry
°C
Wet
°C
DegreeDays
Below
18°C
15
Min.
Rain
mm
!
One
Day
Rain
mm
Ground
Snow
Load
kPa
Ann.
Tot.
Ppn.
mm
Ss
I
Hourly Wind
Pressures
Seismic
Data
1/10
kPa
1/30
kPa
1/100
kPa
Za
Zv
SR
Zonal
Velocity
Ratio
v
Leamington
Lindsay
Lion's Head
-15
- 24
-19
17
26
- 21
31
30
27
24
23
22
3556
4513
4490
28
25
25
106
97
76
816
856
890
0.7
2.1
2.5
0.4
0.4
0.4
0.35
0.26
0.33
0.43
0.34
0.43
0.52
0.43
0.54
0
1
1
0
1
0
0.00
0.05
0.05
Listowel
London
Lucan
Maitland
Markdale
19
18
-17
23
- 20
- 21
- 20
-19
25
22
29
30
30
29
29
23
23
23
23
22
4811
4133
4150
4200
4700
30
28
25
25
28
144
83
118
76
76
951
909
927
960
1030
2.4
1.7
2.1
2.0
3.1
0.4
0.4
0.4
0.4
0.4
0.34
0.36
0.39
0.32
0.29
0.43
0.48
0.50
0.39
0.37
0.53
0.61
0.63
0.49
0.47
1
0
0
3
1
0
0
0
1
0
0.05
0.00
0.00
0.05
0.05
Markham
Martin
Matheson
Mattawa
Midland
- 20
- 36
- 33
29
23
22
- 39
- 36
- 31
26
31
29
29
30
29
24
22
21
22
22
4245
6248
6250
5300
4257
25
25
20
23
25
79
114
76
89
96
802
751
830
830
1035
1.2
2.4
2.6
1.9
2.5
0.4
0.3
0.3
0.4
0.4
0.39
0.21
0.30
0.24
0.25
0.48
0.25
0.37
0.29
0.34
0.59
0.29
0.46
0.35
0.45
1
0
1
3
1
0
0
1
1
1
0.05
0.00
0.05
0.05
0.05
Milton
Milverton
Minden
Mississauga
Mississauga (Port Credit)
18
-19
-26
-18
-18
20
21
- 29
- 20
- 20
30
29
29
30
30
23
23
22
23
23
4138
4550
4967
4000
3900
25
30
25
25
25
127
76
94
140
140
875
980
971
760
760
1.2
2.2
2.5
1.0
0.8
0.4
0.4
0.4
0.4
0.4
0.32
0.31
0.19
0.37
0.37
0.39
0.39
0.25
0.45
0.45
0.48
0.49
0.31
0.55
0.55
1
1
1
1
1
0
0
1
0
0
0.05
0.05
0.05
0.05
0.05
Mitchell
Moosonee
Morrisburg
Mount Forest
Nakina
-18
36
·23
- 21
·35
-20
-38
- 25
23
37
29
28
30
29
28
23
21
23
22
21
4519
7011
4550
4694
6816
28
18
25
30
20
72
63
114
84
70
840
728
928
964
811
2.2
2.0
2.1
2.5
2.6
0.4
0.3
0.4
0.4
0.4
0.35
0.19
0.30
0.29
0.20
0.45
0.24
0.37
0.37
0.24
0.57
0.29
0.46
0.47
0.28
0
0
4
1
0
0
0
2
0
0
0.00
0.00
0.10
0.05
0.00
Nanticoke (Jarvis)
Nanticoke (Port Dover)
Napanee
New Liskeard
Newcastle
·16
-15
22
32
- 20
18
·17
-24
- 35
22
30
30
28
30
30
23
24
23
21
23
3875
3881
4150
5664
4200
28
25
23
23
23
102
102
89
82
76
850
948
870
749
810
1.3
1.1
1.7
2.1
1.4
0.4
0.4
0.4
0.4
0.4
0.33
0.36
0.32
0.31
0.46
0.39
0.43
0.39
0.39
0.55
0.47
0.51
0.48
0.49
0.65
1
1
2
2
1
0
0
1
1
1
0.05
0.05
0.05
0.05
0.05
Newcastle (Bowmanville)
Newmarket
Niagara Falls
North Bay
Norwood
- 20
- 22
-16
- 28
24
- 22
24
-18
- 30
- 26
30
30
30
28
30
23
23
23
21
23
4220
4395
3662
4990
4531
23
28
23
28
28
76
102
95
96
89
803
797
942
930
785
1.3
1.8
1.8
2.0
1.9
0.4
0.4
0.4
0.46
0.26
0.33
0.26
0.29
0.55
0.34
0.39
0.31
0.37
0.66
0.44
0.47
0.37
0.47
1
1
2
2
1
1
1
0
1
1
0.05
0.05
0.05
0.05
0.05
Oakville
Orangeville
Orillia
Oshawa
Ottawa
18
-21
- 25
·19
·25
- 20
23
- 27
21
27
30
29
29
30
30
23
23
22
23
23
3915
4775
4690
3968
4634
23
30
25
23
23
74
101
147
76
93
799
789
907
864
846
0.8
2.1
2.2
1.3
2.2
0045
0.4
0.37
0.25
0.19
0.43
0.30
0.32
0.26
0.52
0.37
0.54
0.41
0.35
0.64
0.46
1
1
1
1
4
0
0
1
1
2
0.05
0.05
0.05
0.05
0.10
2
3
4
5
6
7
8
9
10
11
12
13
14
15 16
004
0.4
004
004
004
004
•
Column 1
17
21
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
2.5% 1%
DC
DegreeDays
Below
Wet
D
DC 18 C
July 2.5 %
Dry
DC
15
Min.
Rain
mm
One
Day
Rain.
mm
Ann.
Tot.
Ppn.
mm
I
Ss
SR
Seismic
Data
1/10
kPa
1/30
kPa
1/100
kPa
Za
Zonal
Velocity
Zv Ratio
v
30
31
28
22
21
23
23
21
4236
6595
4025
3900
4730
28
20
23
23
23
138
80
89
89
123
1024
902
860
860
1094
2.6
2.2
1.3
1.9
2.6
0.4
0.4
0.4
0.4
0.4
0.33
0.19
0.31
0.40
0.24
0.43
0.25
0.37
0.50
0.34
0.55
0.31
0.45
0.61
0.46
1
0
1
0
1
0
0
0
0
1
0.05
0.00
0.05
0.00
0.05
17
- 31
26
27
31
30
30
29
30
30
23
22
22
23
22
3700
4873
4275
4650
5160
23
23
25
25
23
102
103
127
76
119
870
770
1025
920
800
2.1
2.3
2.6
2.1
2.4
0.4
0.4
0.4
0.4
0.4
0.33
0.22
0.25
0.29
0.19
0.39
0.26
0.34
0.37
0.24
0.46
0.32
0.45
0.46
0.29
1
4
1
3
4
0
2
1
1
2
0.05
0.10
0.05
0.05
0.10
- 23
16
-19
21
-18
25
18
21
23
20
30
31
30
29
29
23
24
23
23
23
4411
3824
4250
3999
4150
28
25
23
23
28
87
76
102
76
89
793
873
780
947
920
1.8
1.2
0.9
1.8
1.7
0.4
0.4
0.4
0.4
0.4
0.29
0.35
0.43
0.37
0.30
0.37
0.43
0.52
0.45
0.37
0.47
0.52
0.64
0.54
OA6
1
0
1
1
1
1
0
1
1
0
0.05
0.00
0.05
0.05
0.05
29
15
15
17
21
32
17
-17
19
- 23
30
30
30
28
30
22
24
24
22
23
5150
4050
3707
4240
4044
23
25
23
23
23
89
102
102
76
76
790
940
985
860
801
2.3
1.1
2.1
2.6
1.1
0.4
0.4
0.4
0.4
0.4
0.20
0.34
0.37
0.40
0.46
0.24
0.43
0.43
0.50
0.55
0.28
0.53
0.50
0.62
0.65
4
0
1
1
1
2
0
0
0
1
0.10
0.00
0.05
0.05
0.05
Port Perry
Port Stanley
Prescott
Princeton
Raith
22
15
23
17
- 35
- 24
17
- 25
-19
-37
30
31
29
29
28
23
24
23
23
22
4250
4075
4200
4000
6490
25
25
25
25
20
89
84
76
89
76
800
902
970
860
750
2.2
1.1
2.0
1.4
2.5
0.4
0.4
0.4
0.4
0.31
0.34
0.32
0.30
0.21
0.39
0.43
0.39
0.37
0.25
0.50
0.53
0.49
0.46
0.29
1
0
3
1
0
1
0
2
0
0
0.05
0.00
0.10
0.05
0.00
Rayside-Balfour (Chelmsford)
Red Lake
Renfrew
Richmond Hill
Rockland
- 28
34
- 27
20
- 26
- 30
36
- 30
- 22
- 28
29
28
30
31
30
21
22
23
24
23
5451
6350
4912
4427
4800
25
18
23
25
23
76
110
76
88
89
860
589
780
805
900
2.3
2.2
2.3
1.4
2.2
0.29
0.22
0.26
0.39
0.30
0.39
0.26
0.32
0.48
0.37
0.53
0.31
0.39
0.59
0.45
1
0
4
1
4
0
0
2
0
2
0.05
0.00
0.10
0.05
0.10
Sarnia
Sault Ste Marie
Schreiber
Seaforth
Simcoe
-16
25
- 35
17
-17
-18
- 28
- 38
-19
-19
31
29
27
30
30
23
21
21
23
23
3953
4943
6129
4300
3926
23
25
20
25
28
98
117
93
89
115
890
973
860
910
934
1.0
2.8
3.0
2.3
1.2
0.35
0.32
0.25
0.37
0.33
0.43
0.37
0.29
0.48
0.39
0.52
0.43
0.34
0.60
0.47
0
0
0
0
1
0
0
0
0
0
0.00
0.00
0.00
0.00
0.05
Sioux Lookout
Smiths Falls
Smithville
Smooth Rock Falls
- 34
-25
-16
- 34
- 36
- 27
-18
- 36
28
30
30
29
22
23
23
21
6278
4448
3750
6400
28
28
23
20
116
76
114
63
713
782
900
850
2.2
2.1
1.4
2.5
0.25
0.37
0.39
0.29
0.29
0.46
0
3
OA6 1
0.36 • 1
0
2
0.4
0.3
0.21
0.29
0.33
0.24
0.00
0.10
0.05
0.05
2
3
4
5
6
7
8
9
10
11
12
13
14
Owen Sound
Pagwa River
Paris
Parkhill
Parry Sound
-19
34
-17
16
- 24
-21
-36
19
18
26
Pelham (FonthiU)
Pembroke
Penetanguishene
Perth
Petawawa
-15
28
- 23
25
- 29
Peterborough
Petrolia
Pickering (Dunbarton)
Picton
Plattsville
Point Alexander
Port Burwell
Port Colborne
Port Elgin
Port Hope
Column 1
22
Hourly Wind
Pressures
Ground
Snow
Load
kPa
OA
OA
0.3
OA
OA
0.4
0.4
OA
0.4
0.4
0.4
0.3
OA
15
a
0
16
17
I
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
1250/011
%
°C ; °C
July 2.5 %
Dry
°C
Wet
°C
oegree-115
One
Day
Rain
mm
Days . Min.
Below Rain
mm
18°C
i
Ground
Snow
Load
kPa
Ann.
Tot.
Ppn.
mm
!
Ss
SA
I
1/10
kPa
1/30
kPa
I
Seismic
Data
1/100
kPa
I
Za
Z"
Zonal
Velocity
Ratio
v
27
29
28
21
5280
28
89
950
2.6
0.4
0.23
0.29
0.36
1
1
0.05
Southampton
St. Catharines
St. Mary's
St. Thomas
Stirling
-17
16
18
-16
23
-19
18
- 20
-18
- 25
28
30
30
31
30
22
23
23
23
23
4236
3664
4200
3985
4464
23
23
28
25
25
88
89
105
86
866
807
970
912
783
2.5
0.9
2.0
1.3
1.6
0.4
0.4
0.4
0.4
0.4
0.38
0.36
0.35
0.33
0.28
0.48
0.43
0.45
0.43
0.36
0.59
0.50
0.58
0.54
0.46
1
1
0
0
1
0
0
0
0
1
0.05
0.05
0.00
0.00
0.05
Stratford
Strathroy
Sturgeon Falls
Sudbury
Sundridge
-18
-17
-27
-28
- 27
- 20
-19
-29
30
- 29
29
31
29
29
28
23
23
21
21
21
4429
3943
5200
5043
5250
28
25
28
25
28
126
76
89
112
102
1046
894
850
794
950
2.1
1.7
2.0
2.3
2.6
0.4
0.4
0.4
0.4
0.4
0.33
0.36
0.25
0.29
0.23
0.43
0.45
0.32
0.40
0.29
0.54
0.57
0.40
0.55
0.37
0
0
1
1
2
0
0
1
1
1
0.00
0.00
0.05
0.05
0.05
Tavistock
Temagami
Thamesford
Thedford
Thunder Bay
18
-30
18
16
-31
20
- 33
20
18
- 33
29
30
30
31
28
23
21
23
23
21
4450
5300
4200
3850
5673
28
25
28
23
20
89
89
89
89
98
950
870
975
840
712
1.9
2.4
1.7
1.9
2.7
0.4
0.4
0.4
0.4
0.4
0.34
0.27
0.33
0.41
0.25
0.43
0.34
0.43
0.50
0.29
0.53
0.42
0.55
0.61
0.34
1
2
0
0
0
0
1
0
0
0
0.05
0.05
0.00
0.00
0.00
Tillsonburg
Timmins
Timmins (Porcupine)
Timmins (South Porcupine)
17
- 34
- 34
-34
-19
- 36
- 36
-36
30
30
30
30
23
21
21
21
4050
6225
6049
6200
25
18
18
18
102
133
76
76
914
862
836
820
1.2
2.8
2.7
2.7
0.4
0.3
0.3
0.3
0.31
0.25
0.27
0.27
0.39
0.32
0.34
0.34
0.50
0.40
0.42
0.42
0
1
1
1
0
0
0
0
0.00
0.05
0.05
0.05
Toronto (Metropolitan)
Etobicoke
North York
Scarborough
Toronto
Trenton
- 20
20
- 20
-18
21
22
22
- 22
- 20
23
31
31
31
31
29
24
24
24
23
23
3781
3999
4110
3646
4102
26
25
25
25
23
84
82
85
121
97
757
782
821
801
855
1.0
1.1
1.1
0.8
1.5
0.4
0.4
0.4
0.4
0.4
0.39
0.39
0.39
0.39
0.35
0.48
0.48
0.48
0.48
0.43
0.59
0.59
0.59
0.58
0.52
1
1
1
1
1
0
0
0
0
1
0.05
0.05
0.05
0.05
0.05
Trout Creek
Uxbridge
Vaughan (Woodbridge)
ViHoria
Walkerton
27
22
-20
15
-18
- 29
- 24
- 22
-17
- 20
28
30
31
30
30
21
23
24
24
22
5300
4483
4200
3800
4310
28
25
26
25
28
89
83
121
114
125
940
800
768
900
962
2.5
2.2
1.0
1.2
2.5
0.4
0.4
0.4
0.4
0.4
0.24
0.29
0.39
0.35
0.35
0.29
0.37
0.48
0.43
0.45
0.36
0.48
0.59
0.52
0.57
2
1
1
1
1
1
1
0
0
0
0.05
0.05
0.05
0.05
0.05
Wallaceburg
Waterloo
Watford
Wawa
Weiland
-16
-19
16
- 35
-15
-18
- 21
18
- 38
-17
31
29
31
26
30
24
23
24
21
23
3658
4146
3850
5756
3733
28
28
25
20
23
100
102
76
100
118
760
895
880
1030
938
0.8
1.8
1.7
3.8
2.0
0.4
0.4
0.4
0.4
0.4
0.32
0.27
0.34
0.24
0.33
0.39
0.34
0.43
0.28
0.39
0.48
0.42
0.53
0.33
0.47
0
1
0
0
1
0
0
0
0
0
0.00
0.05
0.00
0.00
0.05
West Lome
Whitby
-16
20
-18
22
31
30
24
23
3800
4080
28
23
102
76
870
840
1.2
1.1
0.4
0.4
0.34
0.43
0.43
0.52
0.53
0.64
0
1
0
1
0.00
0.05
2
3
4
5
6
7
8
9
10
11
12
13
14
15 16
South River
e
Hourly Wind
Pressures
I
Column 1
77
!
i
i
i
17
23
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
2.5% 1%
°C
DegreeDays
Below
Wet
18°C
°C
July 2.5 %
Dry
°C
15
Min.
Rain
mm
One
Day
Rain.
mm
Ann.
Tot.
Ppn.
mm
Hourly Wind
Pressures
Ground
Snow
Load
kPa
Seismic
Data
Zonal
Velocity
Ratio
v
1/10
kPa
1/30
kPa
1/100
kPa
Za
Zv
0.48
0.24
0.43
0.59
0.28
0.55
1
0
1
1
0
0
0.05
0.00
0.05
0.36
0.45
0.39
0.43
0.44
0.57
0.50
0.52
0
0
1
0
0
0
0
0
0.00
0.05
0.00
0.29
0.29
0.29
0.32
0.37
0.36
0.36
0.35
0.39
0.46
3
3
2
2
4
2
3
1
2
2
0.10
0.10
0.86
0.58
0.45
0.41
0.41
4
4
3
3
3
2
3
2
2
2
0.10
0.15
0.10
0.10
0.10
0.44
0.45
0.36
0.44
0.41
4
4
4
4
4
2
2
2
2
3
0.10
0.10
0.10
0.10
0.15
0.34
0.32
0.37
0.43
0.40
0.43
0.38
0.45
5
4
2
3
3
4
3
1
2
2
0.20
0.15
0.05
0.10
0.10
0.41
0.32
0.35
0.45
0.35
4
3
3
3
4
2
2
2
2
2
0.10
0.10
0.10
0.10
0.10
1
Ss
SR
1.7
4.1
2.5
0.4
0.4
0.38
0.20
0.4
0.33
0.29
0.35
0.31
Whitby (Brooklin)
White River
Wiarton
- 20
- 39
18
- 22
42
- 20
30
28
28
23
21
22
4250
6479
4486
23
20
25
76
102
105
840
823
965
Windsor
Wingham
Woodstock
Wyoming
16
18
-18
16
-18
- 20
- 20
18
31
30
29
31
24
23
23
24
3622
4250
4131
3800
28
28
28
25
78
89
132
76
849
1040
862
880
0.7
2.4
1.7
1.5
0.4
0.4
0.4
0.4
Quebec
Acton-Vale
Alma
Amos
Asbestos
Alymer
- 24
30
- 34
26
25
27
- 32
36
- 28
- 28
30
29
28
29
30
23
21
21
22
23
4900
5830
6289
4794
4700
20
20
20
23
23
89
76
74
69
89
1092
975
865
1114
890
2.1
3.0
2.9
2.6
2.3
0.4
0.4
0.3
0.5
0.4
Baie-Comeau
Beauport
Bedford
Beloeil
Brome
27
- 25
- 23
- 24
24
29
- 28
25
26
- 26
25
28
29
30
29
19
22
23
23
22
5969
5170
73
114
76
76
76
988
1170
1030
1020
1170
3.9
3.1
1.9
2.2
2.3
0.4
0.5
0.4
0.4
0.4
0.55
0.38
0.31
0.28
0.28
0.69
0.48
4700
4600
4700
18
20
23
23
23
Brossard
Buckingham
Campbell's Bay
Chambly
Chicoutimi
24
26
- 28
- 24
- 30
- 26
- 28
- 30
26
32
30
30
30
30
28
23
23
23
23
21
4600
4934
4750
4550
5435
23
23
23
23
18
76
60
89
76
71
1070
985
850
1020
954
2.2
2.4
2.4
2.1
2.3
0.4
0.4
0.4
0.4
0.4
0.31
0.30
0.24
0.31
0.25
0.37
0.37
0.29
0.37
0.32
Chicoutimi (Bagotville)
Chicoutimi (Kenogami)
Coaticook
Contrecoeur
Cowansville
- 31
29
24
- 24
24
33
- 31
- 26
- 27
- 26
28
29
28
30
29
21
21
22
23
22
5805
5587
4863
4710
75
74
113
89
76
922
940
1023
1040
0.4
0.4
0.5
0.4
0.4
0.34
0.32
1050
2.2
2.8
2.1
2.6
2.1
0.27
0.25
0.27
0.27
4750
18
18
23
20
23
Deux-Montagnes
Dolbeau
Drummondville
Farnham
Fort-Coulonge
- 25
- 31
25
- 24
28
27
33
- 28
26
- 30
29
28
30
29
30
23
21
23
23
23
4600
6000
4702
4632
4900
23
28
20
23
23
76
63
161
88
105
970
890
1004
1050
880
2.2
3.2
2.3
2.0
2.3
0.4
0.3
0.4
0.4
0.4
0.24
0.34
0.26
0.29
0.37
0.29
Gagnon
Gaspe
Gatineau
Gracefield
Granby
- 33
- 23
- 25
- 28
- 25
- 35
25
28
31
27
24
25
30
30
29
19
19
23
22
23
7463
5438
4600
63
114
60
89
67
1020
968
902
5100
4604
20
15
23
25
23
1144
4.2
3.9
2.3
2.4
2.1
0.4
'0.5
0.4
0.4
0.4
0.37
0.81
0.30
0.24
0.26
0.43
0.98
0.37
0.29
0.32
0.50
1.17
0.46
0.35
0.39
1
4
4
3
1
1
2
2
2
0.05
0.05
0.10
0.10
0.10
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
Column 1
24
850
0.35
0.24
0.23
0.24
0.26
0.30
0.31
0.28
0.22
0.24
0.31
0.37
0.34
0.34
0.00
0.10
0.15
0.05
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
July 2.5 %
2.5% 1%
cC
°C
Dry
°C
Wet
°C
DegreeDays
Below
18cC
15
Min.
Rain
mm
One
Day
Rain
mm
Ann.
Tot.
Ppn.
mm
Ground
Snow
Load
kPa
I
Harrington-Harbour
Havre-St-Pierre
Hemmingford
Hull
Iberville
- 25
27
- 23
25
24
- 27
- 29
- 25
- 28
26
17
22
29
30
29
16
18
23
23
23
6084
6019
4588
4600
4448
15
15
25
23
23
104
89
76
89
76
1234
1008
911
875
984
Inukjuak
Joliette
Jonquiere
Kuujjuaq
Kuujjuarapik
38
- 25
- 29
- 39
36
40
28
- 31
- 41
- 38
17
29
29
24
29
16
23
21
17
17
8986
4876
5700
8561
8160
8
20
18
8
10
40
94
76
36
73
La-Malbaie
La-Tuque
Lac-Megantic
Lachute
Lennoxville
26
29
27
- 25
- 28
- 28
31
29
- 27
30
28
29
27
29
29
21
22
22
23
22
5343
5364
5292
4955
4820
20
23
23
23
23
Lery
Loretteville
Louiseville
Magog
Malartic
- 23
- 25
25
- 26
33
- 26
- 28
28
- 28
36
29
28
29
29
29
23
22
23
22
21
4550
5200
5203
4724
6200
Maniwaki
Masson
Matane
Mont-Joli
Mont-Laurier
- 29
- 26
- 24
- 24
- 29
32
28
26
- 26
- 32
29
30
24
25
29
22
23
20
20
22
25
28
28
23
- 23
24
- 23
26
26
- 26
- 26
23
23
23
23
23
- 23
- 23
- 23
Montmagny
Montreal & Region
Beaconsfield
Dorval
Laval
Montreal (Stade Olympique)
Montreal-Est
Montreal-Nord
Outremont
Pierrefonds
St-Lambert
St-Laurent
Ste-Anne-de-Bellevue
Verdun
Column 1
2
.
Hourly Wind
Pressures
ｾ＠
1/10
kPa
ｓｾ＠
Seismic
Data
Zonal
Velocity
Ratio
v
kPa
11100
kPa
Za
Zv
0.94
0.93
0.37
0.37
0.37
1.22
1.14
0.45
0.46
0.45
1
1
4
4
4
1
1
2
2
2
0.05
0.05
0.10
0.10
0.10
2.2
2.0
0.5
0.5
0.4
0.4
0.4
0.72
0.75
0.30
0.30
0.31
387
883
925
504
637
4.0
2.8
2.8
4.4
4.1
0.2
0.4
0.4
0.2
0.3
0.63
0.25
0.25
0.53
0.64
0.81
0.30
0.32
0,66
0.76
1.03
0.36
0.40
0.81
0.92
0
3
4
1
0
0
2
3
0
0
0,00
0,10
0.15
0,05
0.00
165
114
72
89
104
845
952
997
1062
1058
2.8
3.1
2.9
2.2
1.8
0.5
0.4
0.5
0.4
0.5
0.39
0.20
0.45
0.31
0.23
0.50
0.24
0.58
0.37
0,29
0.63
0,28
0.73
0.44
0.36
6
3
3
4
2
6
2
2
2
1
0.40
0.10
0.10
0.10
0,05
23
20
20
23
20
76
102
114
71
76
970
1070
925
1108
940
2,1
3.4
2.7
2.1
3.0
0.4
0.5
0.4
0.4
0.3
0.31
0.38
0.22
0.26
0.24
0,37
0.48
0.26
0.32
0.29
0.44
0.58
0.32
0.39
0.35
4
4
3
2
2
2
3
2
1
1
0.10
0.15
0.10
0.05
0.05
5348
4809
5580
5450
5436
28
23
18
18
28
75
102
79
74
154
867
912
994
898
973
2.2
2.2
3.4
3.7
2.4
0.4
0.4
0.4
0.4
0.4
0.24
0.30
0.53
0.54
0.24
0.28
0.37
0,69
0.70
0.28
0.34
0.45
0.88
0.90
0,33
4
4
3
3
4
2
2
2
2
2
0.10
0.10
0,10
0.10
0.10
22
5065
20
89
1097
2.7
0.5
0.39
0.50
0.63
5
4
0.20
30
30
29
30
23
23
23
23
4550
4538
4600
4463
23
23
23
23
76
70
89
87
970
946
1050
1071
2.1
2.2
2.4
2.4
0.4
0.4
0.4
0.4
0.31
0,31
0.32
0.31
0.37
0.37
0.37
0.37
0.44
0.44
0.44
0.44
4
4
4
4
2
2
2
2
0.10
0.10
0.10
0.10
- 26
- 26
26
26
26
30
30
30
30
30
23
23
23
23
23
4468
4600
4600
4600
4550
22
23
23
23
23
23
87
89
89
76
89
1071
1070
1070
970
1070
2.5
2.4
2.6
2.2
2.3
0.4
0.4
0.4
0.4
0.4
0.31
0.31
0.31
0,31
0.31
0.37
0.37
0.37
0.37
0.37
0.44
0.44
0.44
0.44
0.44
4
4
4
4
4
2
2
2
2
2
0.10
0.10
0.10
0,10
0.10
- 26
- 26
- 26
30
29
30
23
22
23
4491
4550
4550
23
23
89
92
89
982
920
1070
2.3
2,1
2.3
0.4
0.4
0.4
0.31
0.31
0.31
0.37
0.37
0.37
0.44
0.44
0.44
4
4
4
2
2
2
0.10
0.10
0.10
7
8
3
4
5
9
10
1----"1
12
!
13
14
i
15 16
17
25
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
2.5 "/" 1%
°C
DegreeJuly 2.5 %
Days
Below
Dry Wet
18°C
°C
°C
I
15 lone
Min. 1 Day
Rain Rain.
mm
mm
Ann.
Tot.
Ppn.
mm
Hourly Wind
Pressures
Ground
Snow
Load
kPa
1i10
kPa
Ss
SR
1/30
kPa
•
1/100
kPa
Seismic
Data
Zonal
Velocity
Za Zv Ratio
- 25
- 38
- 33
28
40
- 36
30
23
29
23
19
21
5000
8033
5900
20
15
20
114
60
89
975
784
900
2.6
3.2
2.9
0.4
0.3
0.3
0.23
0.29
0.26
0.28
0.34
0.32
0.34
0.40
0.39
3
0
2
2
1
1
0.10
0.05
0.05
Perce
Pincourt
Plessisville
Port-Cartier
Povungnituk
22
23
- 26
29
- 36
- 25
- 26
- 28
32
38
25
29
29
25
23
19
23
23
19
18
5400
4600
5250
6150
8986
15
23
20
15
5
102
76
102
76
49
970
970
1090
1090
387
3.5
2.1
2.6
3.8
4.1
0.5
0.4
0.5
0.4
0.2
0.82
0.31
0.26
0.67
0.62
0.98
0.37
0.32
0.83
0.81
1.16
0.44
0.39
1.01
1.03
1
4
3
4
1
1
2
2
1
0
0.05
0.10
0.10
0.05
0.05
Quebec City & Region
Ancienne-Lorette
Levis
Quebec
Sillery
Ste-Foy
- 25
- 25
- 25
25
25
- 28
- 28
- 28
- 28
- 28
28
28
28
28
28
22
22
22
22
22
5165
5400
5165
5400
5400
20
20
20
20
20
77
114
131
114
114
1174
1140
1174
1150
1140
3.1
3.0
3.3
2.8
3.4
0.5
0.5
0.5
0.5
0.5
0.38
0.38
0.38
0.38
0.38
0.48
0.48
0.48
0.48
0.48
0.58
0.58
0.58
0.58
0.58
4
4
4
4
4
3
3
3
3
3
0.15
0.15
0.15
0.15
0.15
Richmond
Rimouski
Riviere-du-Loup
Roberval
Rock-Island
- 25
- 25
- 25
- 30
24
27
- 27
27
- 33
-26
29
25
27
28
28
22
20
21
21
22
4800
5260
5533
5884
4900
23
20
23
25
23
89
89
102
103
76
1040
827
879
914
1100
2.0
3.5
3.0
3.2
1.8
0.5
0.4
0.5
0.3
0.4
0.24
0.48
0.41
0.22
0.30
0.29
0.60
0.52
0.26
0.37
0.36
0.75
0.66
0.32
0.46
2
3
6
3
2
2
2
5
2
1
0.10
0.10
0.30
0.10
0.05
Rosemere
Rouyn
Salaberry-de-Valleyfield
Schefferville
Senneterre
- 24
33
- 23
- 38
- 34
- 26
- 36
25
40
36
29
29
29
24
29
23
21
23
17
21
4650
5900
4435
8294
6373
23
20
25
13
23
89
89
71
51
115
1070
900
903
769
953
2.4
2.8
2.1
4.1
3.0
0.4
0.3
0.4
0.3
0.3
0.32
0.26
0.31
0.33
0.24
0.37
0.32
0.37
0.39
0.29
0.44
0.39
0.44
0.46
0.35
4
2
4
0
2
2
1
2
0
1
0.10
0.05
0.10
0.00
0.05
Sept-lies
Shawinigan
Shawville
Sherbrooke
Sorel
·30
26
27
- 28
24
- 32
- 29
- 30
-30
27
24
29
30
29
30
18
23
23
22
23
6154
5047
5074
4568
4672
15
20
23
23
20
115
104
86
109
100
1125
1061
860
950
957
3.8
2.8
2.6
2.0
2.6
0.4
0.4
0.4
0.5
0.4
0.69
0.19
0.26
0.21
0.24
0.84
0.24
0.32
0.26
0.29
1.03
0.29
0.39
0.33
0.35
3
3
4
2
3
1
2
2
2
2
0.05
0.10
0.10
0.10
0.10
St-Felicien
St-Georges-de-Cacouna
St-Hubert
St-Hubert-de-Temiscouata
St-Hyacinthe
- 31
- 25
24
- 26
24
- 33
27
- 26
-28
-27
28
27
30
26
30
21
21
23
21
23
5950
5450
4568
5400
4533
25
23
23
25
20
55
102
78
89
82
870
900
1018
960
1034
3.2
2.9
2.3
4.0
2.1
0.3
0.5
0.4
0.5
0.4
0.22
0.41
0.31
0.41
0.27
0.26
0.52
0.37
0.52
0.32
0.31
0.66
0.44
0.66
0.38
3
6
4
5
3
2
5
2
4
2
0.10
0.30
0.10
0.20
0.10
St-Jean
St-Jerome
St-Jovite
St-Nicolas
Ste-Agathe-des-Monts
- 24
- 25
-27
- 25
- 27
- 26
29
27
29
30 1 27
-28
28
- 29
27
4
3
23
23
22
22
22
4450
5001
5250
5100
5544
76
77
102
102
66
970
1034
960
1120
1164
2.0
2.5
2.6
3.2
3.1
0.4
0.4
0.4
0.5
0.4
0.31
0.29
0.25
0.37
0.27
0.37
0.34
0.30
0.45
0.32
0.45
0.40
0.36
0.55
0.38
3 2
4 2
4 12
4 3
4 2
0.10
0.10
0.10
0.15
0.10
5
6
23
23
25
20
23 .
7
8
9
10
11
12
13
14
15
17
2
I
I
I
V
Nicolet (Gentilly)
Nitchequon
Noranda
Column 1
26
January
16
i
pays
'pi
Design Data for Selected Locations in Canada (Cont'd)
Design Tom ....or!:ltmo
Province
and
Location
January
2.5% 1%
DC
°C
DegreeDays
Below
18°C
July 2.5 %
Dry
°C
I Wet
DC
15
Min.
Rain
mm
One
Day
Rain
mm
Ann
Tot.
Ppn.
mm
Hourly Wind
Pressures
Ground
Snow
Load
kPa
I
i
!
I
1/10
1/30
kPa
kPa
Ss
SR
004
0.31
111 00
kPa
0045
Sutton
Tadoussac
Temiscaming
Thetford Mines
Thurso
- 24
- 26
- 30
26
26
26
28
- 32
- 28
- 28
29
27
30
28
30
22
21
21
22
23
4775
5351
5118
5341
4802
23
20
23
20
23
51
89
89
100
60
1135
982
914
1154
914
2.2
3.1
2.3
3.0
2,2
0.4
0040
004
0,24
0.36
0.30
0.37
0.51
0.29
0.45
0.37
Trois-Rivieres
Val-d'Or
Varennes
Vercheres
Victoriaville
25
33
- 24
- 24
- 26
- 28
- 36
- 26
26
28
29
29
30
30
29
23
21
23
23
23
4993
6199
4600
4620
4920
20
20
23
23
20
111
68
89
89
79
1025
920
1020
1000
1073
2.6
3.1
0.4
0.3
204
004
004
204
0.5
0.26
0.29
0.34
0.32
0.32
0.32
0.35
2.5
0.22
0.24
0,28
0,27
0,26
Ville-Marie
Waterloo
Windsor
31
- 24
25
34
- 27
- 27
30
29
29
21
22
22
5669
4700
4800
23
23
23
108
76
127
816
1050
1200
2.1
2.3
2.1
004
0.30
0.26
0.23
New Brunswick
Alma
Bathurst
Campbellton
Chatham
Edmundston
- 21
23
26
- 24
- 27
23
26
- 28
- 26
29
26
30
29
30
28
20
21
22
21
22
4593
4986
5205
4934
5271
18
20
20
20
23
179
132
102
73
80
1391
949
1050
1097
1121
2,1
3.2
3.3
3.1
3.1
004
Fredericton
Gagetown
Grand Falls
Moncton
Oromocto
24
23
- 27
- 22
- 23
- 27
- 26
- 30
24
- 26
29
28
28
28
29
21
21
22
21
21
4740
4483
5272
4763
4707
23
20
23
20
23
110
127
159
132
104
1109
1093
1012
1179
1077
Sackville
Saint John
Shippegan
St Stephen
Woodstock
- 21
- 22
22
22
- 26
23
24
- 24
- 25
- 29
27
25
28
27
30
21
20
20
21
22
4527
4768
4900
4600
4866
18
18
18
20
23
94
125
63
127
81
Nova Scotia
Amherst
Antigonish
Bridgewater
Canso
Debert
21
- 20
-15
17
22
- 24
23
-19
- 25
27
27
27
25
27
21
21
20
20
21
4700
4550
4208
4477
4553
18
15
15
15
18
17
19
25
28
20
21
3957
4217
-16
18
26
20
2
3
4
5
Digby
Greenwood
Halifax & Region
Halifax
Column 1
-15
17
17
i
i
0.5
004
0.4
0.4
0,5
0.5
3
6
3
3
4
2
5
1
2
2
0.10
0.30
0.05
0.10
0.10
0,38
0.39
3
3
3
3
3
2
1
2
2
2
0.10
0.05
0.10
0,10
0,10
0.37
0.32
0.29
0.45
0,39
0.36
2
3
2
1
2
2
0.05
0.10
0.10
0.50
0.65
0.54
0.60
0.47
0.51
2
1
2
2
3
1
1
1
1
3
0.05
0.05
0,05
0.05
0.15
0.46
0.62
0.72
0.57
2
2
3
2
2
1
1
2
1
1
0.05
0.05
0.10
0.05
0.05
0.63
0.55
0.34
0.66
0.59
0.77
0.67
0.42
1
2
1
2
2
1
1
1
1
1
0.05
0.05
0.05
0.05
0.05
0.66
0.60
0.67
0.68
0.63
1
1
1
1
1
1
1
1
1
1
0.05
0.05
0.05
0.05
0.05
0.50
0,62 1 11
0,61 11
1
0.05
0.05
0,64
0.35
0.56
0045
0041
0.5
0.5
0.38
0,34
0.37
0,29
0,30
0.48
0.37
0.39
2,8
2.5
3.3
2.7
2.7
0.5
0.5
0.5
0,5
0.5
0,30
0.36
0.29
0.46
0.35
0.37
0.48
0.37
0.58
0.45
1135
1444
1000
1140
945
2.3
2.1
3,1
2.3
2.8
0,5
0,5
0,5
0,5
0.5
0041
0.52
0.38
0.52
0048
102
102
107
114
93
1050
1170
1487
1344
1296
2.2
1.9
1.7
1.5
1.9
0.5
0.5
0.5
0,5
0.5
0.41
0.41
0.49
0.39
0.52
0.50
0.52
0.58
0.50
15
15
123
113
1254
1099
2.0
204
0,5
0,5
0.40
0.36
0048
3880
15
140
1282
1.7
0.5
0040
0.52 , 0.67
6
7
8
9
!
10
Ｑｾ＠
0045
0.27
0041
i
12
i
Seismic
Data
Zonal
Velocity
Ratio
Za Zv
v
0043
13
0048
14
1 11
0.05
15 16
17
27
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
I DegreeDays
Below
Wet
18°C
°C
January: July 2.5
2.5 % 1%
°C
Dry
°C
I
15
Min.
Rain
I mm
Ann.
Tot.
Ppn.
mm
One
Day
Rain.
mm
I
i
I
I
I
ｳ･ｪｭｃｾ＠
Hourly Wind
Pressures
I
Ground
Snow
Load
kPa
I
Data
Zonal
1/10
kPa
Ss
SR
1130 111100
kPa
i
I Velocity
1
Z
kPa
a i
Z.
Ratio
v
V
I
I
-16
18
26
20
4186
18
132
1361
1.4
0,5
0.40
0.52
0.67
1
1
0.05
Kentville
Liverpool
Lockeport
Louisburg
Lunenburg
18
-14
-14
15
-15
- 20
16
-16
-17
-17
28
27
25
26
26
21
20
20
20
20
4194
4029
3950
4546
4200
18
15
15
15
15
145
203
127
102
127
1177
1308
1400
1427
1400
2.2
1.5
1.3
1.9
0.36
0.44
0.44
0.52
0.43
0.48
0.55
0.55
0.60
0.55
0.62
0.69
0.68
0.71
0.70
1
1
1.7
0.5
0.5
0.5
0.6
0.5
1
2
1
1
1
1
2
1
0.05
0.05
0.05
0.10
0.05
New Glasgow
North Sydney
Pictou
Port Hawkesbury
Springhill
- 21
-16
- 21
19
- 20
- 23
18
- 24
- 22
23
27
27
27
27
27
21
21
21
21
21
4350
4500
4300
4300
4300
15
13
15
15
18
102
89
102
76
102
1140
1350
1140
1300
1140
2.0
2.2
2.0
1.9
2.8
0.5
0.5
0.5
0.5
0,5
0.40
0.47
0.40
0.59
0.39
0.50
0.55
0.50
0.69
0.50
0.62
0,65
0.62
0.80
0.64
1
2
1
1
1
1
1
1
1
1
0.05
0,05
0.05
0.05
0.05
Stewiacke
Sydney
Tatamagouche
Truro
Wolfville
Yarmouth
- 21
-16
21
21
-19
13
23
-18
- 24
- 23
21
-15
27
27
27
27
28
22
21
21
21
21
21
19
4400
4541
4423
4661
4150
4065
18
13
18
18
18
13
102
97
89
133
127
173
1070
1400
1058
1139
1075
1282
1.6
2.1
2.0
1.8
2.2
1.6
0.5
0.5
0.5
0.5
0.5
0.5
0,39
0.47
0.40
0.37
0.36
0.41
0.50
0.55
0.50
0.48
0.48
0.51
0.63
0.65
0.62
0.60
0.62
0.63
1
2
1
1
1
1
1
2
1
1
1
1
0.05
0.10
0.05
0.05
0.05
0,05
Prince Edward Island
Charlottetown
Souris
Summerside
Tignish
20
-19
- 20
20
- 22
21
22
- 22
26
27
27
27
21
21
21
20
4689
4655
4578
4704
13
13
13
13
164
89
119
102
1169
1039
1039
1032
2.4
2.4
2.8
2,9
0.5
0.5
0.5
0,5
0.46
0.41
0.52
0.61
0.55
0.50
0.63
0.72
0.66
0.60
0.76
0.85
1
1
1
1
1
1
1
1
0,05
0.05
0.05
0.05
Newfoundland
Argentia
Bonavista
Buchans
Cape Harrison
Cape Race
-13
-17
- 21
29
-14
-15
19
- 24
- 31
16
21
24
26
27
19
18
19
19
16
18
4451
4966
5601
6887
4977
15
18
13
15
18
102
104
84
110
157
1068
985
991
861
1379
2.2
2.5
4.3
5.7
2.1
0.6
0.5
0.5
0.4
0.6
0.57
0.52
0.46
0.46
0.79
0.69
0.63
0.55
0.55
0.96
0.83
0.77
0.66
0.66
1.17
1
1
1
1
1
1
1
1
0
1
0.05
0.05
0.05
0,05
0.05
Channel-Port aux Basques
Corner Brook
Gander
Grand Bank
Grand Falls
-15
-19
-18
14
- 21
-17
- 22
- 21
-16
- 24
19
26
27
20
26
18
19
19
18
19
5040
4750
5683
4513
4948
13
13
18
15
15
110
83
98
107
72
1452
1134
1130
1297
991
2.7
3.4
3.4
2.2
3.1
0.6
0.5
0.5
0.6
0.5
0.55
0.58
0.46
0.59
0.46
0.63
0.69
0.55
0.69
0.55
0.73
0.82
0.66
0.81
0.66
1
1
1
2
1
1
1
1
2
1
0,05
0.05
0.05
0,10
0.05
Happy Valley - Goose Bay
Labrador City
St Anthony
St John'S
Stephenville
- 31
- 35
- 24
14
1-17
- 33
37
- 27
-16
·20
27
23
22
24
24
19
18
18
20
19
6585
7900
5945
4824
4811
20
15
13
18
13
79
63
67
121
84
946
875
1081
1514
1167
4.8
3.9
4.6
2.6
3.2
0.4
0.3
0.5
0.6
0.5
0.29
0.31
0.57
0.60
0.62
0.34
0.37
0.76
0.73
0.72
0.40
0.44
1.01
0.89
0.84
0
1
0
1
1
0
1
1
1
1
0.00
0.05
0.05
0.05
0,05
15
16
Dartmouth
I
I
I
I
I
28
I
3
4
5
6
7
8
9
I
I
11
13
14
1
17
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
Province
and
Location
January
12.5% 1 0/0
°C
°C
July 2.5 %
Dry
°C
Wet
°C
Hourly Wind
Pressures
I
DegreeDays
Below
18°C
i
15
Min.
Rain
mm
One
Day
Rain
mm
Ground
Snow
Load
kPa
Ann.
Tot.
Ppn.
mm
Seismic
Data
•
Zonal
Velocity
Ratio
v
!
1/10
kPa
Ss
SR
I
1/30
kPa
1/100
kPa
Za
Zv
35
-15
35
37
-17
37
23
24
23
18
20
18
7650
4800
7939
15
18
15
70
102
47
950
1400
895
4.2
2.7
3.9
0.4
0.6
0.3
0.31
0.56
0.31
0.37
0.69
0.37
0.44
0.84
0.44
0
1
1
0
1
1
0.00
0.05
0.05
Yukon
Aishihik
Dawson
Destruction Bay
Snag
Teslin
44
- 50
43
51
- 41
46
- 51
- 45
53
- 43
23
26
24
23
25
16
16
15
16
16
8155
8409
8200
8773
7213
8
8
8
8
8
45
53
51
53
38
256
306
300
339
327
1.8
1.9
2.0
2.0
1.7
0.1
0.1
0.1
0.1
0.1
0.29
0.20
0.30
0.20
0.19
0.35
0.24
0.35
0.24
0.25
0.42
0.28
0.42
0.28
0.34
3
2
4
3
1
5
4
6
5
4
0.30
0.20
0.40
0.30
0.20
Watson Lake
Whitehorse
- 46
-41
48
43
26
25
16
15
7766
6988
8
8
46
31
425
261
2.2
1.7
0.1
0.1
0.19
0.28
0.24
0.34
0.30
0.42
1
2
2
4
0.10
0.20
Northwest Territories
Aklavik
Alert
Arctic Bay
Baker Lake
Cambridge Bay
44
43
43
45
- 45
- 46
- 45
45
- 46
46
24
13
14
21
16
16
9
10
15
13
9849
13186
11693
10990
12037
5
3
3
3
3
51
19
38
36
34
208
154
118
235
136
2.1
1.5
1.9
2.7
1.5
0.1
0.1
0.1
0.2
0.1
0.37
0.54
0.40
0.42
0.30
0.52
0.69
0.50
0.50
0.34
0.72
0.87
0.62
0.59
0.39
1
0
1
0
0
2
0
1
0
0
0.10
0.00
0.05
0.00
0.00
Chesterfield Inlet
Clyde River
Coppermine
Coral Harbour
Eskimo Point
- 40
41
- 44
41
40
- 41
- 43
- 45
43
- 41
20
15
20
18
21
14
9
13
13
16
10768
11006
10758
10751
10100
5
5
5
5
5
58
37
64
43
63
259
206
202
270
300
2.8
3.2
2.4
3.5
2.7
0.2
0.2
0.1
0.2
0.2
0.44
0.61
0.33
0.88
0.49
0.52
0.80
0.42
1.20
0.59
0.62
1.02
0.52
1.59
0.71
0
5
0
1
0
0
3
1
0
0
0.00
0.15
0.05
0.05
0.00
Eureka
Fort Good Hope
Fort Providence
Fort Resolution
Fort Simpson
47
- 46
- 44
- 42
45
48
- 48
46
44
- 47
12
27
24
26
27
9
17
18
18
18
13733
9415
8031
8043
8101
3
5
8
8
8
42
70
78
39
86
64
282
280
307
351
1.5
2.7
2.2
2.1
2.1
0.1
0.1
0.1
0.1
0.1
0.47
0.48
0.26
0.29
0.30
0.60
0.67
0.32
0.36
0.37
0.76
0.93
0.39
0.44
0.46
1
1
0
0
0
0
1
1
1
1
0.05
0.05
0.05
0.05
0.05
Fort Smith
Frobisher Bay
Hay River
Holman
Inuvik
43
40
41
- 43
-46
- 45
- 42
- 43
45
48
28
16
26
18
25
19
11
18
12
16
7786
9928
7902
11086
10101
8
5
8
3
5
67
53
51
51
33
349
433
340
178
266
2.1
2.7
2.2
1.9
2.1
0.2
0.2
0.1
0.1
0.1
0.30
0.56
0.26
0.63
0.39
0.37
0.69
0.32
0.78
0.55
0.46
0.84
0.39
0.95
0.76
0
1
0
0
1
1
0
1
1
2
0.05
0.05
0.05
0.05
0.10
Isachsen
Mould Bay
Norman Wells
Nottingham Island
Port Radium
-46
48
- 45 - 47
46 - 47
38 .i -40
- 44 - 46
12
10
27
14
22
9
8
17
13
16
13535
13047
8903
9716
9114
3
3
5
5
5
20
48
49
56
52
93
86
328
279
216
1.5
1.4
2.5
4.2
2.8
0.1
0.1
0.1
0.2
0.1
0.68
0.47
0.41
0.46
0.83
0.60
0.58
0.58
0.48
1.00
0.76
0.79
0.72
0.59
4
1
0
1
0
1
1
1
0
1
0.05
0.05
0.05
0.05
0.05
Rae-Edzo
- 44
46
24
17
8800
2
3
4
5
6
Twin Falls
Wabana
Wabush
Column 1
5
7
51
8
I
275
9
2.1
10
0.38
0.1
11
••
i
0.34
0.43
12
13
i
i
0.53
0
14
15 16
1
I
0.05
17
I
29
pays
Design Data for Selected Locations in Canada (Cont'd)
Design Temperature
I
Province
and
Location
January
1
I
1
2.5 % 1%
cC
I
Rankin Inlet
Resolute
Resolution Island
; Tungsten
Yellowknife
!
Column 1
30
1- 40
i
-
44
I!
- 43
I
2
41
-45
37
51
- 45
3
I
July 2.5 % DegreeDays
I
. Below
Dry Wet
D
DC 18 C
cC
20
11
8
26
25
4
15
9
7
16
17
5
10700
12594
8878
7900
8530
6
1
15
Min.
Rain
mm
One
Day
Rain.
mm
Ann.
Tot.
Ppn.
mm
5
3
5
5
5
51
25
70
51
45
280
131
313
645
267
7
8
I
9
!
Ground
Snow
Load
kPa_
SA
Ss
2.8
1.6
4.8
6.6
2.0
10
i
0.2
0.1
0.2
0.1
0.1
11
Hourly Wind
Pressures
!
1/10
kPa
0.46
0.52
0.85
0.29
0.34
12
!
1/30
!
kPa
i
Seismic
Data
Zonal
I
Velocity
11100
I
kPa; Za ZV Ratio
v
I
;
0.55 0.66
0.63 0.77
1.10 ; 1.41
0.39 052
0.43 0.53
1
13
I
i
14
Il
i
1
1°
/15
0
1
0
2
1
0.00
0.05
0.05
0.10
0.05
16
17
!
pays
Chapter 2
Fire-Performance Ratings
Section 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
1.11
1.12
Section 2
2.1
ＲＮｾ＠
2.3
2.4
2.5
2.6
2.7
General
Introduction ........................ 33
Interpretation of Test
Results ................................ 35
Aggregates Used in
Concrete ............................. 36
Types of Concrete •••••••••••••• 36
Gypsum Wallboard .............. 36
Equivalent Thickness ••••••••• 36
Contribution of Plaster or
Gypsum Wallboard Finish
to Fire Resistance of
Masonry or Concrete •••••••••• 37
Tests on Floors and Roofs .39
Moisture Content ................ 40
Permanence and
Durabi lity •••••••••••••••••••••••••••• 40
Structural Steel Members •• 40
Restraint Effects •••••••••••••••• 40
Fire-Resistance Ratings
Masonry and Concrete
Walls ......•..•........••..•........•••. 40
Reinforced and Prestressed
Concrete Floor and Roof
Slabs ......................•..•........• 42
Wood and Steel Framed
Walls, Floors and Roofs •••••• 44
Solid Wood Walls, Floors
and Roofs ............................ 50
Solid Plaster Partitions •••••• 51
Protected Steel Columns ••• 53
Individually Protected Steel
Beams ••••••••••••••••••••••••••••••••• 56
31
pays
2.8
2.9
2.10
2.11
Section 3
3.1
Section 4
4.1
4.2
4.3
Section 5
5.1
5.2
5.3
Reinforced Concrete
Columns •••••••..•••...•••......••••.• 56
Reinforced Concrete
Beams ................................. 58
Prestressed Concrete
Beams •..................•••........•.• 59
Glued·Laminated Timber
Beams and Columns •••••••••• 60
Flame-Spread Ratings
and Smoke Developed
Classifications
Interior Finish Materials •••• 61
Noncombustibility
Test Method ........................ 64
Materials Classified as
Combustible ....................... 64
Materials Classified as
Noncombustible ................. 64
Protection of Openings in
Fire-Rated Assemblies
Scope ••...........•.••.•.......•••..... 64
Installation of Fire Doors
and Fire Dampers ............... 64
Fire Stop Flaps ••••••••••••••••••• 65
Appendix A
Fire Test Reports ................ 65
Obsolete Materials and
Assemblies ......................... 66
32
pays
Chapter 2
Fire-Performance Ratings
Section 1 General
struction and Materials" and describes methods for
determining these ratings.
The contents of this Chapter have been prepared
on the recommendations of the Standing Committee
on Fire Performance Ratings, which was established
by the Associate Committee on the National Building
Code (ACNBC) for this purpose.
(3) Section 3 assigns flame-spread ratings and
smoke developed classifications for surface materials
related to CAN /ULC-S102-M, "Standard Method of
Test for Surface Burning Characteristics of Building
Materials" and CAN /ULC-SI02.2-M, "Standard
Method of Test for Surface Burning Characteristics of
Flooring, Floor Covering, and Miscellaneous Materials and Assemblies."
The fire-performance ratings contained herein are
presented in a form closely linked to the performance
requirements and the minimum materials specifications of the National Building Code of Canada.
These ratings have been assigned only after careful
consideration of all available literature on assemblies
of common building materials, where they are
adequately identified by description. The assigned
values based on this information will, in most
instances, be conservative when compared to the
ratings determined on the basis of actual tests on
individual assemblies.
1.1
Introduction
1.1.1.
(1) The fire-performance ratings set out in this
document are for use with the National Building
Code of Canada. They apply to materials and assemblies of materials which comply in all essential details
with the minimum structural design standards
described in Part 4 of the National Building Code of
Canada. Additional requirements, where appropriate, are described in other Sections of this Chapter.
(2) Section 2 of this Chapter assigns fireresistance ratings for walls, floors, roofs, columns
r and beams related to CAN/ULC-S101-M, "Standard
Methods of Fire Endurance Tests of Building Con-
(4) Section 4 describes noncombustibility in
building materials when tested in accordance with
the specification CAN4-S114-M, "Standard Method
of Test for Determination of Non-Combustibility in
Building ｍ｡ｴ･ｲｩｬｳＮｾＧ＠
(5) Section 5 contains requirements for the installation of fire doors and fire dampers in fire-rated
stud wall assemblies and the installation of fire stop
flaps in fire-rated membrane ceilings.
1.1.2.
(1) Where reference is made in this Chapter to
the National Building Code of Canada, such reference shall be to the 1990 edition.
(2) Where documents are referenced in
this Chapter, they shall be the editions designated in
Table 1.1.A.
1.1.3.
(1) The standard fire tests to which reference
is made in the National Building Code of Canada are
the basis for compliance with the National Building
Code requirements.
(2) The ratings shown in this document apply
if more specific test values are not available. The
33
r2
r2
pays
Issuing
Agency
,
Table 1.1.A.
Forming Part of Sentence 1.1.2.(2)
Documents Referenced in Chapter 2 of the
Supplement to the National Building Code of Canada 1990
Document
Title of Document
Number
Reference
ASTM
C330-89
Lightweight Aggregates for Structural Concrete
1.4.3.(2)
CGSB
CGSB
CGSB
CGSB
4-GP-36M-1978
4-GP-129-1972
CAN/CGSB-11.3-M87
CAN/CGSB-34.16-M89
Carpet Underlay, Fibre Type
Carpets, Commercial
Hardboard
Sheets, Asbestos-Cement, Flat, Fully Compressed
Table 3.1.B.
Table 3.1.B.
Table 3.1.A.
Table 3.1.A.
CSA
CAN/CSA-A23.1-M90
1.4.3.(1 )
CSA
CAN3-A23.3-M84
Concrete Materials and Methods of Concrete
Construction
Design of Concrete Structures for Buildings
CSA
CSA
CSA
A82.5-M 1978
A82.22-M1977
A82.27-M1977
Structural Clay Non-Load-Bearing Tile
Gypsum Plasters
Gypsum Board Products
CSA
A82.30-M1980
Interior Furring, Lathing and Gypsum
Plastering
CSA
CSA
A82.31-M1980
A101-M83
Gypsum Board Application
Thermal Insulation, Mineral Fibre, for Buildings
CSA
CSA
CSA
A126.1-M1984
CAN/CSA-A247-M86
CAN3-086-M84
Vinyl Asbestos and Vinyl Composition Floor Tile
Insulating Fibreboard
Engineering Design in Wood (Working Stress Design)
'2
CSA
CSA
CSA
0115-M1982
0121-M1978
0141-1991
Hardwood and Decorative Plywood
Douglas Fir Plywood
Softwood Lumber
e
CSA
CSA
CSA
CSA
0151-M1978
0153-M1980
CAN3-0188.1-M78
CAN3-0437 -M85
Canadian Softwood Plywood
Poplar Plywood
Interior Mat-Formed Wood Particleboard
Waferboard and Strandboard
NFPA
NFPA 80-1990
Fire Doors and Windows
,
,
I
Column 1
34
2
2.8.2.(1 )
Table 2.8.A.
Table 2.6.A.
Table 3.1.A.
1.5.1.
1.5.2.
Table 3.1 .A.
1.7.3.(1 )
2.3.12.(1 )
Table 2.5.A.
2.3.12.(1 )
Table 2.3.F.
Table 2.6.E.
Table 3.1.B.
Table 3.1.A.
2.11.2.(1 )
2.11.2.(3)
Table 3.1.A.
Table 3.1.A.
2.3.10.(2)
Table 2.4.A.
Table 3.1.A.
Table 3.1.A.
Table 3.1.A.
Table 3.1.A.
5.2.1.
5.2.2.
3
4
I
pays
Table 1.1.A. (Cont'd)
Forming Part of Sentence 1.1.2.(2)
Issuing
Agency
r
Document
Number
Title of Document
ULC
CAN/ULC-S101-M89
Standard Methods of Fire Endurance Tests of
Building Construction and Materials
ULC
CAN/ULC-S102-M88
ULC
CAN/ULC-S102.2-M88
ULC
CAN4-S114-M80
Standard Method of Test for Surface Burning
Characteristics of Building Materials and Assemblies
Standard Method of Test for Surface Burning
Characteristics o'f Flooring, Foor Covering,
and Miscellaneous Materials and Assemblies
Standard Method of Test for Determination
of Non-Combustibility in Building Materials
ULC
S505-1974
Standard for Fusible Links for Fire Protection Service
Reference
1.1.1.(2)
1.12.2.
1.12.3.(1)
2.3.2.
1.1.1.(3)
1.1.1.(3)
Table 3.1.B.
1.1.1.(4)
4.1.1.
4.2.1.
5.3.2.
I
2
3
construction of an assembly that is the subject of an
individual test report must be followed in all essential details if the fire resistance reported is to be
applied as a fire-resistance rating for use in the
National Building Code.
1.2
Column 1
1.1.4. The authority having jurisdiction may allow
higher fire-resistance ratings than those covered in
this Chapter, where supporting evidence justifies a
higher rating. Additional information is provided in
summaries of published test information and the
reports of fire tests carried out by the Institute for
Research in Construction, National Research Council
of Canada, included in the bibliography listed in
Appendix A to this Chapter.
1.1.5. Assemblies containing materials for which
there is no nationally recognized standard are not
included in this Chapter. Many such assemblies
have been rated by Underwriters' Laboratories of
Canada. This information is published in their "List
of Equipment and Materials," Volume II, Building
Construction. Copies of this document may be
obtained from Underwriters' Laboratories of Canada,
7 Crouse Road, Scarborough, Ontario MIR 3A9.
4
Interpretation of Test Results
1.2.1. The fire-performance ratings set out in this
Chapter are based on those that would be obtained
from the standard methods of test described in the
National Building Code. The test methods are
essentially a means of comparing the performance of
one building component or assembly with another in
relation to its performance in fire.
1.2.2. Since it is not practicable to measure the fire
resistance of constructions in situ, they must be
evaluated under some agreed test conditions. A
specified fire-resistance rating is not necessarily the
actual time that the assembly would endure in situ in
a building fire, but is that which the particular
construction must meet under the specified methods
of test.
1.2.3. Considerations arising from departures in
use from the conditions established in the standard
test methods may, in some circumstances, have to be
taken into account by the designer and the authority
having jurisdiction. Some of these conditions are
covered at present by the provisions of the National
Building Code.
35
pays
1.3
Aggregates Used in Concrete
1 .3.1. Low density aggregate concretes generally
exhibit better fire performance than natural stone
aggregate concretes. A series of tests on concrete
masonry walls, combined with mathematical analysis
of the test results, has allowed further distinctions
between certain low density aggregates to be made.
1.4
Types of Concrete
1.4.1.
(1) For purposes of this Chapter, concretes are
described as Types S, N, L, L1, L2, L40S, L120S or
L220S as described in Sentences (2) to (B).
(2) Type S concrete is the type in which the
coarse aggregate is granite, quartzite, siliceous gravel
or other dense materials containing at least 30 per
cent quartz, chert or flint.
(3) Type N concrete is the type in which the
coarse aggregate is cinders, broken brick, blast
furnace slag, limestone, calcareous gravel, trap rock,
sandstone or similar dense material containing not
more than 30 per cent of quartz, chert or flint.
(4) Type L concrete is the type in which all the
aggregate is expanded slag, expanded clay, expanded shale or pumice.
(5) Type L1 concrete is the type in which all
the aggregate is expanded shale.
(6) Type L2 concrete is the type in which all
the aggregate is expanded slag, expanded clay or
pumice.
(7) Type L40S concrete is the type in which
the fine portion of the aggregate is sand and low
density aggregate in which the sand does not exceed
40 per cent of the total volume of all aggregates in the
concrete.
(8) Type L120S and Type L220S concretes are
the types in which the fine portion of the aggregate is
sand and low density aggregate in which the sand
does not exceed 20 per cent of the total volume of all
aggregates in the concrete.
1.4.2. Where concretes are described as being of
Type S, N, L, L1 or L2, the rating applies to the
concrete containing the aggregate in the group that
provides the least fire resistance. If the nature of an
aggregate cannot be determined accurately enough to
36
place it in one of the groups, the aggregates shall be
considered as being in the group that requires a
greater thickness of concrete for the required fire
resistance.
1.4.3.
(1) The descriptions of the aggregates in Type
S and Type N concretes apply to the coarse aggregates only. Coarse aggregate for this purpose means
that retained on a 5 mm sieve using the method of
grading aggregates described in CAN/CSA-A23.1-M, r
"Concrete Materials and Methods of Concrete
Construction."
(2) Increasing the proportions of sand as fine
aggregate in low density concretes requires increased
thicknesses of material to produce equivalent fireresistance ratings. Low density aggregates for Type
L and Types L-S concretes used in load bearing
components shall conform to ASTM C330, "Lightweight Aggregates for Structural Concrete."
1.4.4. Non-Ioadbearing low density components of
vermiculite and perlite concrete, in the absence of
other test evidence, shall be rated on the basis of the
values shown for Type L concrete.
1.5
Gypsum Wallboard
1.5.1. Where the term gypsum wallboard is used
in this Chapter, it is intended to include, in addition
to gypsum wallboard, gypsum backing board and
gypsum base for veneer plaster as described in CSA
AB2.27-M, "Gypsum Board Products."
1.5.2. Where the term Type X gypsum wallboard
is used in this Chapter, it applies to special fireresistant board as described in CSA AB2.27-M, "Gypsum Board Products."
1.6
Equivalent Thickness
1.6.1. The thickness of solid-unit masonry and
concrete described in this Chapter shall be the
thickness of solid material in the unit or component
thickness. For units that contain cores or voids, the
Tables refer to the equivalent thickness determined in
conformance with Articles 1.6.2. to 1.6.6.
1.6.2. Where a plaster finish is used, the equivalent
thickness of a wall, floor, column or beam protection
shall be equal to the sum of the equivalent thick-
pays
nesses of the concrete or masonry units and the
plaster finish measured at the point that will give the
least value of equivalent thickness.
1.6.3.
(1) Except as provided in Sentence (3), the
equivalent thickness of a hollow masonry unit shall
be calculated as equal to the actual overall thickness
of a unit in millimetres multiplied by a factor equal to
the net volume of the unit and divided by its gross
volume.
(2) Net volume shall be determined using a
volume displacement method that is not influenced
by the porous nature of the units.
(3) Gross volume of a masonry unit shall be
equal to the actual length of the unit multiplied by
the actual height of the unit multiplied by the actual
thickness of the unit.
(4) Where all the core spaces in a wall of
hollow concrete masonry or hollow-core precast
concrete units are filled with loose fill materials such
as expanded slag, burned clay or shale (rotary kiln
process), vermiculite or perlite, the equivalent
thickness rating of the wall shall be considered to be
the same as that of a wall of solid units, or a solid
wall of the same concrete type and the same overall
thickness.
1.6.4. The equivalent thickness of hollow-core concrete slabs and panels having a uniform thickness
and cores of constant cross section throughout their
length shall be obtained by dividing the net crosssectional area of the slab or panel by its width.
1.6.5. The equivalent thickness of concrete panels
with tapered cross sections shall be the cross section
determined at a distance of 2 t or 150 mm, whichever
is less, from the point of minimum thickness, where t
is the minimum thickness.
1.6.6.
(1) The equivalent thickness of concrete
panels with ribbed or undulating surfaces shall be
(a) ta for s less than or equal to 2 t,
(b) t + (4 tis 1)(ta t) for s less than 4 t and
greater than 2 t, and
(c) t for s greater than or equal to 4 t
where
t = minimum thickness of panel,
average thickness of the panel (unit
cross-sectional area divided by the
unit width), and
s = centre to centre spacing of ribs or
undulations.
(2) Where the total thickness of a panel in
Sentence 0) exceeds 2 t, only that portion of the
panel which is less than 2 t from the nonribbed
surface shall be considered for the purpose of the
calculations in Sentence 0).
ta
1.7
Contribution of Plaster or
Gypsum Wallboard Finish to
Fire Resistance of Masonry or
Concrete
1.7.1.
(1) Except as provided in Sentences (2), (3)
and (4) and Article 1.7.2., the contribution of a plaster
or gypsum wallboard finish to the fire resistance of
masonry or concrete wall, floor or roof assembly shall
be determined by multiplying the actual thickness of
the finish by the factor shown in Table 1.7.A., depending on the type of masonry or concrete to which
it is applied. This corrected thickness shall then be
included in the equivalent thickness as described in
Subsection 1.6.
(2) Where a plaster or gypsum wallboard
finish is applied to a concrete or masonry wall, the
calculated fire-resistance rating of the assembly shall
not exceed twice the fire-resistance rating provided
by the masonry or concrete because structural
collapse may occur before the limiting temperature is
reached on the surface of the non-fire-exposed side of
the assembly.
(3) Where a plaster or gypsum wallboard
finish is applied only on the non-fire-exposed side of
a hollow clay tile wall, no increase in fire resistance is
permitted because structural collapse may occur
before the limiting temperature is reached on the
surface of the non-fire-exposed side of the assembly.
(4) The contribution to fire resistance of a
plaster or gypsum wallboard finish applied to the
non-fire-exposed side of a monolithic concrete or unit
masonry wall shall be determined in conformance
with Sentence 0), but shall not exceed 0.5 times the
contribution of the concrete or masonry wall.
37
pays
Table 1.7.A.
Forming Part of Sentence 1.7.1.(1)
Multiplying Factors for Various Masonry or Concrete Construction
Type of Masonry or Concrete
Solid Clay Brick,
Cored Clay Brick,
Concrete Unit
Unit
Masonry
and
Clay
Tile,
Monolithic
Masonry,
Type Ll
Type of
Concrete,
Type
L40S
Monolithic
Concrete,
or
L
20S
and
2
Surface Protection
Type N or S
and Unit Masonry,
Monolithic Concrete,
Type L120S
Type L
Portland cement-sand plaster,
lime sand plaster or portland
cement-sand plaster with asbestos fibres
!
.
Concrete
Unit Masonry,
Type L2
1
0.75
0.75
0.50
Gypsum-sand plaster, wood fibred
gypsum plaster or gypsum wallboard
1.25
1
1
1
Vermiculite or perlite aggregate plaster
Column 1
1.75
2
1.5
1.25
4
1.25
5
3
I
•
1.7.2. When applied to the fire-exposed side, the
contribution of a gypsum lath and plaster or gypsum
wallboard finish to the fire resistance of masonry or
concrete walt floor or roof assemblies shall be
determined from Table 2.3.A. or 2.3.B.
1.7.3.
(1) Gypsum plastering shall conform to CSA
A82.30-M, "Interior Furring, Lathing and Gypsum
Plas tering./I
(2) Portland cement-sand plaster shall be
applied in 2 coats; the first coat containing 1 part
portland cement to 2 parts sand by volume, and the
second coat containing 1 part portland cement to 3
parts sand by volume.
(3) Plaster finish shall be securely bonded to
the wall or ceiling.
(4) The thickness of plaster finish applied
directly to monolithic concrete without metal lath
shall not exceed 10 mm on ceilings and 16 mm on
walls.
(5) Where the thickness of plaster finish on
masonry or concrete exceeds 38 mm, wire mesh with
1.57 mm diam wire and openings not exceeding
50 mm by 50 mm shall be embedded midway in the
plaster.
38
1.7.4. Gypsum wallboard and gypsum lath
finishes applied to masonry or concrete walls shall be
secured to wood or steel furring members in conformance with Article 2.3.11.
1.7.5. The following examples are included as a
guide to the method of calculating the fire resistance
of concrete or hollow masonry walls with plaster or
gypsum wallboard protection:
Example (1)
A 3 h fire-resistance rating is required for a
monolithic concrete wall of Type S aggregate with a
20 mm gypsum-sand plaster finish on metal lath on
each face.
(a) The minimum equivalent thickness of
Type S monolithic concrete needed to give
a 3 h fire-resistance rating 158 mm
(Table 2.1.A.).
(b) Since the gypsum-sand plaster finish is
applied on metal lath, Article 1.7.2. does
not apply. Therefore, the contribution to
the equivalent thickness of the wall of
20 mm gypsum-sand plaster on each face
of the concrete is 20 x 1.25 25 mm (see
Article 1.7.1.).
(c) The total contribution of the plaster
finishes is 2 x 25 = 50 mm.
pays
(d) The minimum equivalent thickness of
concrete required is 158 mm - 50 mm =
108mm.
(e) From Table 2.1.A., the 108 mm equivalent
thickness of monolithic concrete gives a
contribution of less than 1.5 h. This is less
than half the rating of the assembly so that
the conditions in Sentence 1.7.1.(2) are not
met. Thus the equivalent thickness of
monolithic concrete must be increased to
112 mm to give 1.5 h contribution.
(f) The total equivalent thickness of the
plaster finishes can then be reduced to
158 mm - 112 mm 46 mm.
(g) The total actual thickness of the plaster
finishes required is therefore 46 mm + 1.25
= 37 mm (Article 1.7.1.) or 18.5 mm on
each face.
(h) Since the thickness of the plaster finish on
each face exceeds 16 mm, metal lath is still
required (Sentence 1.7.3.(4».
(0 Since this wall is symmetrical with plaster
on both faces, the contribution to fire
resistance of the plaster finish on either
face is limited to one-quarter of the wall
rating by virtue of Sentence 1.7.1.(2).
Under these circumstances, the conditions
in Sentence 1.7.1.(4) are automatically met.
Example (2)
A 2 h fire-resistance rating is required for a hollow
masonry wall of Type N concrete with a 12.7 mm
gypsum wallboard finish on each face.
(a) Since gypsum wallboard is used, Article
1.7.2. applies. The 12.7 mm gypsum
wallboard finish on the fire-exposed side
is, therefore, assigned 15 min by using
Table 2.3.A.
(b) The fire resistance required of the balance
of the assembly is 120 min -15 min =
105 min.
(c) Interpolating between 1.5 hand 2 h in
Table 2.1.A. for 105 min fire resistance, the
equivalent thickness for hollow masonry
units required is 95 mm + (18 mm x 15/
30) = 104 mm.
(d) The contribution to the equivalent thickness of the wall of the 12.7 mm gypsum
wallboard finish on the non-fire-exposed
side using Table 1.7.A = 12.7 x 1.25 =
16mm.
(e) Equivalent thickness required of concrete
masonry unit = 104 - 16 = 88 mm.
(f) The fire-resistance rating of a concrete
masonry wall having an equivalent
thickness of 88 mm = 1 h 20 min. As this
is more than 1 h, the conditions of Sentence 1.7.1.(2) are met and the rating of 2 h
is justified.
Example (3)
A 2 h fire-resistance rating is required for a hollow
masonry exterior wall of Type L 220S concrete with a
15.9 mm Type X gypsum wallboard finish on the
non-fire-exposed side only.
(a) According to Table 2.1.A., the minimum
equivalent thickness for Type L 220S
concrete masonry units needed to achieve
a 2 h rating is 94 mm.
(b) Since gypsum wallboard is not used on
the fire-exposed side, Article 1.7.2. does
not apply. The contribution to the equivalent thickness of the wall by the 15.9 mm
Type X gypsum wallboard finish applied
on the non-fire-exposed side is 15.9 xl
16 mm (see Sentence 1.7.1.(1) and Table
1.7.A.).
(c) Therefore, the equivalent thickness
required of the concrete masonry unit is
94 - 16 = 78 mm.
(d) The contribution to fire resistance of a
78 mm L 220S concrete hollow masonry
unit is 85 min. The contribution of the
Type X gypsum wallboard finish is 120
85 = 35 min, which does not exceed half
the 85 min contribution of the masonry
unit or 42.5 min, so that the conditions in
Sentence 1.7.1.(4) are met.
(e) The rating of the wall (120 min) is less
than twice the contribution of the masonry
unit (170 min) so that the conditions in
Sentence 1.7.1.(2) are also met.
1 .8
Tests on Floors and Roofs
1.8.1. All tests relate to the performance of a floor
assembly or floor-ceiling or roof-ceiling assembly
above a fire. It has been assumed on the basis of
39
pays
experience that fire on top will take a longer time to
penetrate the floor than one below, and that the fire
resistance in such a situation will be at least equal to
that obtained from below in the standard test.
1.9
Moisture Content
1.9.1. The moisture content of building materials
at the time of fire test may have a significant influence on the measured fire resistance. In general, an
increase in the moisture content should result in an
increase in the fire resistance, though in some materials the presence of moisture may produce disruptive
effects and early collapse of the assembly.
1.9.2. Moisture content is now controlled in standard fire test methods and is generally recorded in
the test reports. In earlier tests, moisture content was
not always properly determined.
1.10 Permanence and Durability
1.10.1. The ratings in this Chapter relate to tested
assemblies and do not take into account possible
changes or deterioration in use of the materials. The
standard fire test measures the fire resistance of a
sample building assembly erected for the test. No
judgment as to the permanence or durability of the
assembly is made in the test.
1.11
Steel Structural Members
1.11.1. Since the ability of a steel structural member to sustain the loading for which it was designed
may be impaired because of elevated temperatures,
measures shall be taken to provide thermal protection. The fire-resistance ratings, as established by the
provisions of this Chapter, indicate the time periods
during which the effects of heat on protected steel
structural members are considered to be within
acceptable limits.
1.12 Restraint Effects
1.12.1. In fire tests of floors, roofs and beams, it is
necessary to state whether the rating applies to a
thermally restrained or thermally unrestrained
assembly. Edge restraint of a floor or roof, structural
continuity, or end restraint of a beam can significantly extend the time before collapse in a standard
test. A restrained condition is one in which expan40
sion or rotation at the supports of a load-carrying
element resulting from the effects of fire is resisted by
forces or moments external to the element. An
unrestrained condition is one in which the loadcarrying element is free to thermally expand and
rotate at its supports.
1.12.2. Whether an assembly or structural member
can be considered thermally restrained or thermally
unrestrained depends on the type of construction
and location in a building. Guidance on this subject
can be found in Appendix A1 ofCAN/ULC-S101-M,
"Standard Methods of Fire Endurance Tests of
Building Construction and Materials." Different
acceptance criteria also apply to thermally unrestrained and thermally restrained assemblies. These
are described in CAN4-S101-M.
r
1.12.3. The ratings for floors, roofs, and beams in
this Chapter meet the conditions of CAN/ULC-S101- r
M, "Standard Methods of Fire Endurance Tests of
Building Construction and Materials" for thermally
unrestrained specimens. In a thermally restrained
condition, the structural element or assembly would
probably have greater fire resistance, but the extent
of this increase can be determined only by reference
to behavior in a standard test.
Section 2 FireResistance Ratings
2.1
Masonry and Concrete Walls
2.1.1. The minimum thicknesses of unit masonry
and monolithic concrete walls are shown in Table
2.1.A. Hollow masonry units and hollow-core
concrete panels shall be rated on the basis of equivalent thickness as described in Subsection 1.6.
2.1.2.
(1 ) Ratings obtained as described in Article
2.1.1. apply to either loadbearing or non-Ioadbearing
walls, except for walls described in Sentences (2) to
(6).
(2) Ratings for walls with a thickness less
than the minimum thickness prescribed for load bearing walls in the National Building Code of Canada
1990 apply to non-Ioadbearing walls only.
pays
Table 2.1.A.
rormlng PrtfAt'1211
a 0 nce ...
Minimum Equivalent Thicknesses(l) of Unit Masonry and Monolithic Concrete Walls
Loadbearing and Non-Loadbearing, mm
Type of Wall
Fire-Resistance Rating
1.5 h
2h
30 min
45 min
1h
Solid brick units (80 per cent solid
76
128
63
108
and over), actual overall thickness
90
I
!
Cored brick units and hollow tile
72
102
50
60
units (less than 80 per cent solid),
86
equivalent thickness
Solid and hollow concrete masonry
units, equivalent thickness
Type S or N concrete (2)
73
44
95
113
59
42
54
102
Type L120S concrete
66
87
42
54
64
82
97
Type L1 concrete
42
54
64
81
94
Type L220S concrete
79
42
54
63
91
Type L2 concrete
Monolithic concrete and concrete
I
panels, equivalent thickness
77
112
130
60
90
Type S concrete
i 74
108
124
87
Type N concrete
59
72
49
62
103
Type L40S or Type L concrete
89
4
5
6
2
3
Column 1
3h
4h
152
178
i
!
122
I
142
I
I
i
i
!
i
!
I
Notes to Table 2.1.A.:
See definition of equivalent thickness in Subsection 1.6.
(1)
(3) Masonry cavity walls (consisting of 2
wythes of masonry with an air space between) that
are loaded to a maximum allowable compressive
stress of 380 kPa have a fire resistance at least as great
as that of a solid wall of a thickness equal to the sum
of the equivalent thicknesses of the 2 wythes.
(4) Masonry cavity walls that are loaded to a
compressive stress exceeding 380 kPa are not considered to be within the scope of this Chapter.
(5) A masonry wall consisting of 2 types of
masonry units, either bonded together or in the form
of a cavity wall, shall be considered to have a fireresistance rating equal to that which would apply if
the whole of the wall were of the material that gives
the lesser rating.
(2)
i
142
129
122
116
111
158
150
124
7
167
152
143
134
127
!
i
180
171
140
8
Hollow concrete masonry units made with Type S or N
concrete must have a 28-day compressive strength of at
least 7.5 MPa.
(6) A non-Ioadbearing cavity wall made up of
2 precast concrete panels with an air space or insulation in the cavity between them shall be considered
to have a fire-resistance rating as great as that of a
solid wall of a thickness equal to the sum of the
thicknesses of the 2 panels.
2.1.3. If wood joists are built into a masonry walt
the thickness of masonry material between the end of
the joist and the fire-exposed side of the wall shall be
not less than the equivalent thickness shown in the
Tables for the fire resistance required.
2.1.4. On monolithic walls and walls of unit masonry, the full plaster finish on one or both faces
multiplied by the factor shown in Table l.7.A. shall
41
pays
be included in the wall thickness shown in Table
2.1.A., under the conditions and using the methods
described in Subsection 1.7.
(f)
2.1.5.
(1) Except as permitted in Sentence (2),
portions of loadbearing reinforced concrete walls,
which do not form a complete fire separation and
thus may be exposed to fire on both sides simultaneously, shall have minimum dimensions and minimum cover to steel reinforcement in conformance
with Articles 2.8.2. to 2.8.5.
(2) A concrete wall exposed to fire from both
sides as described in Sentence 2.1.5.(1) has a fireresistance rating of 2 h if the following conditions are
met:
(a) its equivalent thickness is not less than
200mm,
(b) its aspect ratio (width/thickness) is not
less than 4.0,
(c) the minimum thickness of concrete cover
over the steel reinforcement specified in
Clause (d) is not less than 50 mm,
(d) each face of the wall is reinforced with
both vertical and horizontal steel reinforcement in conformance with either
Clause 10 or Clause 14 of CAN3-A23.3-M,
"Design of Concrete Structures for Buildings,"
(e) the structural design of the wall is governed by the minimum eccentricity
requirements of Clause 10.11.6.3. of
CAN3-A23.3-M, "Design of Concrete
Structures for Buildings," and
2.2
the effective length of the wall, klu' is not
more than 3.7 m
where
k = effective length factor obtained from
CAN3-A23.3-M, "Design of Concrete
Structures for Buildings,"
lu = unsupported length of the wall in
metres.
Reinforced and Prestressed
Concrete Floor and Roof Slabs
2.2.1.
(1 ) Floors and roofs in a fire test are assigned
a fire-resistance rating which relates to the time that
an average temperature rise of 140°C or a maximum
temperature rise of 180°C at any location is recorded
on the unexposed side, or the time required for
collapse to occur, whichever is the lesser. The
thickness of concrete shown in Table 2.2.A. shall be
required to resist the transfer of heat during the fire
resistance period shown.
(2) The concrete cover over the reinforcement
and steel tendons shown in Table 2.2.B. shall be
required to maintain the integrity of the structure
and prevent collapse during the same period.
2.2.2. The fire resistance of floors containing
hollow units may be determined on the basis of
equivalent thickness as described in Subsection 1.6.
2.2.3.
(1) For composite concrete floor and roof
slabs consisting of one layer of Type S or N concrete
and another layer of Type L40S or L concrete in
Table 2.2.A.
Forming Part of Sentence 2.2.1.(1)
Minimum Thickness of Reinforced Concrete Floor or Roof Slabs, mm
Fire-Resistance Rating
Type of Concrete
30 min 45 min
1 h 1.5 h
2h
77
112
Type S Concrete
60
90
130
74
87
108
124
Type N concrete
59
72
103
Type L40S or Type L concrete
49
62
89
Column 1
2
4
3
5
6
42
3h
158
150
124
7
4h
180
171
140
8
pays
Table 2.2.B.
19 Part of Sentence 2.2.1.(2)
Minimum Concrete Cover over Reinforcement in Concrete Slabs, mm
Fire-Resistance Rating
Type of Concrete
1h
1.5 h
2h
30 min 45 min
20
20
20
Type S, N, L40S or L concrete
25
I
20
Prestressed concrete slabs Type S,
20
25
25
32
39
N, L40S or L concrete
4
2
6
Column 1
3
5
which the minimum thickness of both the top and
bottom layers is not less than 25 mm, the combined
fire-resistance rating may be determined using the
following expressions:
(a) when the base layer consists of Type S or
N concrete,
R
0.0002 t
2
-
0.0001 d· t + 10, and
t
(b) when the base layer consists of Type L40S
or L concrete,
R
2
0.00009 t 2 + 0.00018 d· t - 0.00009 d +
where
R = fire resistance of slab, h,
t = total thickness of slab, mm, and
d
thickness of base layer, mm.
50
64
7
8
,
2.2.4.
(1) The contribution of plaster finish securely
fastened to the underside of concrete may be taken
into account in floor or roof slabs under the conditions and using the methods described in Subsection
1.7.
(2) Plaster finish on the underside of concrete
floors or roofs may be used in lieu of concrete cover
Table 2.2.C.
Forming Part of Sentence 2.2.3.(2)
:
;
(3) The minimum concrete cover over the
main reinforcement for composite concrete floor and
roof slabs with base slabs of less than 100 mm thick
shall conform to Table 2.2.D. For base slabs of
100 mm or more thick, the minimum cover thickness
requirements of Table 2.2.B. shall apply.
4h
39
(4) Where the top layer of a 2-layer slab is less
than 25 mm thick, the fire-resistance rating for the
slab shall be calculated as though the entire slab were
made up of the type of concrete with the lesser fire
resistance.
!
(2) If the base course described in Sentence 0)
is covered by a top layer of material other than Type
S, N, L40S or L concrete, the top course thickness
may be converted to an equivalent concrete thickness
by multiplying the actual thickness by the appropriate factor listed in Table 2.2.C. This equivalent
concrete thickness may be added to the thickness of
the base course and the fire-resistance rating calculated using Table 2.2.A.
3h
32
Multiplying Factors for Equivalent Thickness
Base Slab
I Base Slab
Top Course Material
Normal Density Low Density
Concrete
Concrete
(Type S or N) (Type L40S or L)
Gypsum wallboard
2.25
3
Cellular concrete
(mass density 400
2
560 kg/m 3 )
1.50
Vermiculite and perlite
concrete (mass density
1.75
1.50
560 kg/m 3 or less)
Portland cement with sand
aggregate
1
0.75
1
Terrazzo
0.75
Column 1
2
3
43
pays
Table 2.2.D.
Forming Part of Sentence 2.2.3.(3)
Minimum Concrete Cover under Bottom Reinforcement in Composite Concrete Slabs, mm
I
FIre- R't
eSls ance R'
atmg
Base Slab Concrete Type
2h
1h
1.5 h
3h
30 min 45 min
Reinforced concrete
15
20
25
40
Type S, N, L40S or L
15
30
Prestressed concrete
25
40 I 50
20
30
65
Type S
20
25
45
Type N
20
35
60
40
20
20
25
30
50 I
Type L40S or L
4
7
5
6
Column 1
2
3
ｾ＠
1-----
I
I
I
I
4h
I
I
55
75
70
60
8
Wood and Steel Framed Walls,
Floors and Roofs
referred to in Sentence 2.2.1.(2) under the conditions
and using the methods described in Subsection 1.7.
2.3
2.2.5.
2.3.1. The fire-resistance rating of walls, floors and
roofs, incorporating wood, steel, light-gauge steel
members and open-web steel joists for ratings up to
and including 1.5 h shall be determined by this Subsection.
(1) In prestressed concrete slab construction,
the concrete cover over an individual tendon shall be
the minimum thickness of concrete between the
surface of the tendon and the fire-exposed surface of
the slab, except that for ungrouted ducts the assumed
cover thickness shall be the minimum thickness of
concrete between the surface of the duct and the
bottom of the slab. For slabs in which several tendons are used, the cover is assumed to be the average
of those of individual tendons, except that the cover
for any individual tendon shall be not less than half
of the value given in Table 2.2.B. nor less than 20 mm.
Except as provided in Sentence (3), in
post-tensioned prestressed concrete slabs, the concrete cover to the tendon at the anchor shall be at
least 15 mm greater than the minimum cover required by Sentence 0). The minimum concrete cover
to the anchorage bearing plate and to the end of the
tendon, if it projects beyond the bearing plate, shall
be 20 mm.
(2)
(3) The requirements of Sentence (2) do not
apply to those portions of slabs not likely to be
exposed to fire, such as the ends and tops.
2.2.6. Minimum dimensions and cover to steel
tendons of prestressed concrete beams shall conform
to Subsection 2.10.
44
2.3.2. The ratings in this Subsection apply to both
loadbearing and non-Ioadbearing wood framed
walls, to non-load bearing steel framed walls and to
load bearing floors and roofs. Loadbearing conditions shall be as defined in CAN/ULC-SI0I-M,
"Standard Methods of Fire Endurance Tests of
Building Construction and Materials."
2.3.3. The fire-resistance rating of a framed assembly shall be calculated by adding the time assigned in
Article 2.3.4. for the membrane on the fire-exposed
side plus the time assigned in Article 2.3.5. for the
framing members plus the time assigned in Article
2.3.10. for additional protective measures such as the
inclusion of insulation or the reinforcement of a
membrane. The assigned times in Articles 2.3.4.,
2.3.5. and 2.3.10. are not intended to be construed as
the fire-resistance ratings of the individual components of an assembly. These assigned times are the
individual contributions to the overall fire-resistance
rating of the complete assembly.
2.3.4. The fire-resistance rating of a framed
assembly depends on the time during which the
membrane on the fire-exposed side remains in place.
r
pays
!
Table 2.3.A.
Forming Part of Article 2.3.4.
Time Assigned to Wallboard Membranes
on Fire Exposed Side
between failure of the membrane and collapse of the
assembly.
Time!
min
12.5 mm fibreboard
5
8.0 mm Douglas Fir plywood phenolic bonded
5
10
11.0 mm Douglas Fir plywood phenolic bonded
14.0 mm Douglas Fir plywood phenolic bonded
15
9.5 mm gypsum wallboard
10
15
12.7 mm gypsum wallboard
12.7 mm Type X gypsum wallboard
25
15.9 mm gypsum wallboard
20
15.9 mm Type X gypsum wallboard
40
25
Double 9.5 mm gypsum wallboard
12.7 mm and 9.5 mm gypsum wallboard
35
Double 12.7 mm gypsum wallboard
40
50(1)
Double 12.7 mm gypsum wallboard
80(2)
Double 12.7 mm Type X gypsum wallboard
40(3)
4.5 mm asbestos cement and 9.5 mm gypsum wallboard
4.5 mm asbestos cement and 12.7 mm gypsum wallboard 50(3)
ICorllf,Ju::>llt,; 3 mm asbestos cement on 11 mm fibreboard
20
Column 1
2
Notes to Table 2.3.A.:
(1)
Wire mesh with 1.57 mm diam wire and 25 mm by 25 mm
openings must be fastened between the two sheets of
wallboard.
(2)
Applies to non-Ioadbearing steel framed walls only.
(3)
Values shown apply to walls only.
Description of Finish
i
Tables 2.3.A. and 2.3.B.list the times which have
been assigned to membranes on the fire-exposed side
of the assembly based on their ability to remain in
place during fire tests. This is not to be confused
with the fire-resistance rating of the membrane,
which shall also take into account the rise in temperature on the unexposed side of the membrane.
2.3.5. When the membrane on the fire-exposed side
of a framed assembly falls off, there is a brief period
of time before structural failure occurs during which
the studs or joists are exposed directly to flame.
Table 2.3.C. lists the times which have been assigned
to the framing members based on the time involved
2.3.6. Interior vertical fire separations shall be rated
for exposure to fire on each side, and it is assumed,
therefore, that membrane protection will be provided
on both sides of the assembly. In the calculation of
the fire-resistance rating of such an asserrlbly, however, no contribution to fire resistance should be
assigned for a membrane on the non-fire-exposed
side, since this membrane may fail when the structural members fail.
2.3.7. When an exterior wall assembly is required
to be rated from the interior side only, such wall
assemblies may have an outer membrane consisting
of sheathing and exterior cladding combinations
listed in Table 2.3.D. or may be any membrane that is
assigned a time for contribution to fire resistance of
at least 15 min in Table 2.3.A. or 2.3.B.
2.3.8. In the case of a floor or roof, the standard
test provides only for testing for fire exposure from
below. Floor or roof assemblies of wood, light-gauge
steel members or open-web steel joist framing shall
have an upper membrane consisting of a subfloor
and finish floor conforming to Table 2.3.E. or any
other membrane that has a contribution to fire
resistance of at least 15 min in Table 2.3.A.
2.3.9.
(1) Insulation used in the cavities of a wood
floor assembly will not reduce the assigned fireresistance rating of the assembly provided:
(a) the insulation is preformed of rock, slag or
glass fibre conforming to CSA A101-M,
"Thermal Insulation, Mineral Fibre, for
Buildings" ha ving a mass of not more than
1.1 kg/m 2 and is installed adjacent to the
bottom edge of the framing member,
directly above steel furring channels,
(b) the gypsum wallboard ceiling membrane
is attached to
(i) wood trusses in conformance with
Sentence 2.3.11.(2) by way of steel
drywall furring channels spaced not
more than 400 mm o.c., and the
channels are secured to each bottom
truss member with a double strand
of 1.2 mm galvanized steel wire, or
45
pays
Table 2.3.B.
Forming Part of Article 2.3.4.
Type of Lath
Time Assigned to Lath and Plaster Protection on Fire Exposed Side, min (1)
Type of Plaster Finish
Portland Cement, ,
Gypsum and
Plaster
Portland Cement
and Sand (2) or
Sand or
Sand and Asbestos
Thickness
Fibre (1.4 kg/bag Gypsum Wood Fibred
mm
Lime and Sand
I
of cement)
10
20
13
5
20
13
35
13
40
16
50
19
35
50
19
20
40
65
25
23
80
30
50
26
4
5
2
3
i
I
Wood lath
12.5 mm fibreboard
9.5 mm gypsum lath
9.5 mm gypsum lath
9.5 mm gypsum lath
Metal lath
Metal lath
Metal lath
Column 1
Notes to Table 2.3.B.:
Values shown for these membranes have been limited to 80
min because the fire resistance ratings of framed assemblies
derived from these Tables shall not exceed 1.5 h.
(1)
(2)
i
46
55
65
80(1)
80(1)
80(1)
80(1)
6
For mixture of portland cement-sand plaster, see Sentence
1.7.3.(2}.
Table 2.3.0.
Forming Part of Article 2.3.7.
Table 2.3.C.
Forming Part of Article 2.3.5.
Time Assigned for Contribution
of Wood or Light Steel Frame
Time assigned
Description of Frame
to Frame
min
Wood studs 400 mm o.c.
20
Steel studs 400 mm o.C.
10
Wood floor and wood roof joists 400 mm o.c.
10
Open web steel joist floors and roofs with
ceiling supports 400 mm o.c.
10
Wood roof and wood floor truss assemblies
600 mm o.c.
5
Column 1
2
Gypsum and
Perlite or Gypsum
and Vermiculite
I
Membrane on Exterior Face
of Wood or Steel Stud Walls
Exterior Cladding
Sheathing
16 mm T &G lumber
Lumber siding
7.5 mm exterior grade plywood Wood shingles and shakes
12.7 mm gypsum board
6 mm plywood exterior grade
6 mm hardboard
Metal siding
Stucco on metal lath
I
Masonry veneer
9.5
mm exterior grade
\ None
plywood
i
2
Column 1
I
pays
Table 2.3.E.
Ing Part 0 fA'
rtlc Ie 2.3.8.
Flooring or Roofing over Wood, Cold Formed Steel Members or Open-Web Steel Joists
Subfloor or Roor Deck
Finish Flooring or Roofing
Structural Members
Type of
Assembly
i
I
12.5 mm plywood or
17 mm T & G softwood
Wood or steel joists
and wood trusses
Floor
50 mm reinforced concrete
or 50 mm concrete on metal
lath or formed steel sheet,
or 40 mm reinforced gypsum-fibre
concrete on 12.7 mm gypsum
wallboard
Steel joists
I
I
Steel joists
Column 1
Finish flooring
12.5 mm plywood or
17 mm T & G softwood
Wood or steel joists
and wood trusses
Roof
Hardwood or softwood
flooring on building paper
Resilient flooring, parquet
floor felted synthetic fibre
floor coverings, carpeting,
or ceramic tile on 8 mm thick
panel-type underlay
Ceramic tile on 30 mm mortar bed
50 mm reinforced concrete
or 50 mm concrete on metal
lath or formed steel sheet
or 40 mm reinforced gypsum-fibre
concrete on 12.7 mm gypsum
wallboard
2
(ii) wood joists by way of drywall or
resilient steel furring channels
spaced not more than 400 mm o.c. in
conformance with Sentences
2.3.11.(2) and (3), and
(c) a steel furring channel is installed midway
between each furring channel mentioned
in Clause (b) to provide additional support for the insulation.
2.3.10. Preformed rock or slag fibre insulation
provides additional protection to wood studs by
shielding the studs from exposure to the furnace and
thus delaying the time of collapse. The use of
Finish roofing material
with or without insulation
3
reinforcement in the membrane exposed to fire also
adds to the fire resistance by extending the time to
failure. Table 2.3.F. shows the time increments that
may be added to the fire resistance if these features
are incorporated in the assembly.
2.3.11.
(1) The values shown in Tables 2.3.A., 2.3.B.
and 2.3.H. apply to membranes supported on framing members spaced in conformance with Table
2.3.C.
(2) Wood studs and wood roof and floor
framing members are assumed to be not less than
38 mm by 89 mm. Wood trusses are assumed to
47
p
pays
Table 2.3.F.
Forming Part of Article 2.3.10.
Time Assigned for Additional Protec'tion
Description of Additional Protection
Add to the fire-resistance rating of wood stud walls if the spaces between the studs are filled with preformed
insulation of rock or slag fibres conforming to CSA A101, ''Thermal Insulation, Mineral Fibre, for Buildings"
and with a mass of not less than 1.22 kg/m2 of wall surface (1)
Add to the fire-resistance rating of non-Ioadbearing wood stud walls if the spaces between the studs are filled
with preformed insulation of glass fibres conforming to CSA A101, "Thermal Insulation, Mineral Fibre, for
Buildings" and having a mass of not less than 0.6 kg/m 2 of wall surface
Add to the fire-resistance rating of plaster on gypsum lath ceilings if 0.76 mm diam wire mesh with
25 mm by 25 mm openings or 1.57 mm diam diagonal wire reinforcing at 250 mm o.c. is placed between
lath and plaster
Add to the fire-resistance rating of plaster on gypsum lath ceilings if 76 mm wide metal lath strips are placed
over joints between lath and plaster
Add to the fire-resistance rating of plaster on 9.5 mm thick gypsum lath ceilings (Table 2.3.B.) if supports
for lath are 300 mm o.c.
Column 1
Note to Table 2.3.F.:
(1)
There is no test data to justify the 15 min additional protection for preformed glass fibre insulation.
consist of wood chord and web framing members
and connector plates fabricated from at least 1 mm
thick galvanized steel with projecting teeth at least
8 mm long. Dimensions for dressed lumber are
given in CSA 0141, "Softwood Lumber."
(3) The allowable spans for wood joists listed
in Part 9 of the National Building Code of Canada
1990 are provided for floors supporting specific
occupancies.
(4) Except as otherwise required in this
Chapter, metal studs shall be of galvanized steel not
less than 0.5 mm thick.
(5) The thickness of plaster finish shall be
measured from the face of gypsum or metal lath.
(6) Gypsum wallboard installed over framing
or furring shall be installed so that all edges are supported, except that 15.9 mm thick Type X gypsum
wallboard may be installed horizontally with the
horizontal joints unsupported.
48
Fire
Resistance
min
15
5
30
10
10
2
(7) Except as required in Article 2.3.9., resilient or drywall furring channels may be used to
attach a gypsum wallboard ceiling membrane to a
floor or roof assembly provided the channels are of
galvanized steel not less than 0.5 mm thick and are
placed at a spacing of not more than 600 mm o.c.
perpendicular to the framing members with an
overlap of not less than 100 mm at splices and a
minimum end clearance between the channels and
walls of 15 mm.
2.3.12.
(1) Except as provided in Sentences (2) to (6),
the fastening of lath and plaster or gypsum wallboard finish shall conform to CSA A82.30-M, "Interior Furring, Lathing and Gypsum Plastering" or
CSA A82.31-M, "Gypsum Board Application."
(2) Where membrane protection referred to in
Tables 2.3.A., 2.3.B. and 2.3.H. is applied to steel
framing or furring, fasteners shall penetrate at least
10 mm through the metal.
I
pays
(3) Except as provided in Sentences (4) and
(5), where membrane protection referred to in Tables
2.3.A., 2.3.B. and 2.3.H. is applied to wood framing or
furring, minimum fastener penetrations into wood
members shall conform to Table 2.3.G. for the time
assigned to the membrane.
(4) Where membrane protection is applied in
2 layers, the fastener penetrations described in Table
2.3.G. shall apply to the base layer. Fasteners for the
face layer shall penetrate at least 20 mm into wood
supports.
Table 2.3.G.
Forming Part of the Article 2.3.12.
Minimum Fastener Penetrations for Membrane
Protection on Wood Frame, mm
Type
1 Assigned Contribution of Membrane
of
to Fire Resistance, (1) min
Membrane
5-25 30-35 40
50 55-70 80
Single layer
20
32
29
Double layer
20
20
29
20
35 44
Gypsum or
fibreboard lath
20
20
23
23
29 ,29
2
7
[Column 1
3
4
5
6
Note to Table 2.3.G.:
(1)
Assigned contributions of membranes to fire resistance
are determined in Tables 2.3.A., 2.3.B. and 2.3.H.
(5) Where adhesives are used to attach the
face layer of gypsum wallboard in a double layer
application for walls, the top and bottom of the face
la yer shall be secured to the supports by mechanical
fasteners having lengths as required in Sentences (2)
and (4) and spaced not more than 150 mm o.c. for
wood supports and not more than 200 mm o.c. for
steel supports.
(6) In a double layer application of gypsum
wallboard on wood supports, fastener spacing shall
conform to Section 9.29 of the National Building
Code of Canada 1990.
2.3.13.
(1) Where a beam is included with an openweb steel joist or similar construction and is protected by the same continuous ceiling, the beam is
assumed to have a fire-resistance rating equal to that
assigned to the rest of the assembly.
(2) The ratings in this Supplement assume
that the construction to which the beam is related is a
normal one and does not carry unusual loads from
the floor or slab above.
2.3.14. Metal studs in walls required to have a
fire-resistance rating shall be installed with not less
than 12 mm clearance between the top of the stud
and the top of the runner to allow for expansion in
the event of fire. Where attachment of the studs is
necessary for alignment purposes during erection,
such attachment shall be made to the bottom runners
only.
2.3.15. Where the fire-resistance rating of a ceiling
assembly is to be determined on the basis of the
membrane only and not of the complete assembly,
the ratings may be determined from Table 2.3.H.,
provided no openings are located within the ceiling
membrane.
Table 2.3.H.
Forming Part of Article 2.3.15.
Fire-Resistance Rating for Ceiling Membranes
FireDescription of Membrane
Resistance
Rating, min
19.5 mm gypsum wallboard and 12.7 mm gypsum
30
wallboard
IDouble 12.7 mm gypsum wallboard
30
115.9 mm Type X gypsum wallboard with at least
30
75 mm mineral wool batt insulation above wallboard
19 rnm gypsum-sand plaster on metal lath
30
Double 14.0 mm Douglas Fir plywood phenolic
30
bonded
Double 12.7 mm Type X gypsum wallboard
45
25 mm gypsum-sand plaster on metal lath
45
Double 15.9 mm Type X gypsum wallboard
60
32 mm gypsum-sand plaster on metal lath
60
Column 1
2
!
!
I
Ｍｾ＠
49
.
pays
2.3.16.
Except as provided in Article 2.3.15.,
where a floor or roof assembly of combustible
construction is assigned a fire-resistance rating on the
basis of this Subsection and incorporates a ceiling
membrane described in Table 2.3.A. or 2.3.B., the
ceiling membrane may be penetrated by openings
leading to ducts within concealed spaces above the
membrane provided:
(a) the assembly is not required to have a fireresistance rating in excess of 1 h,
(b) the area of any openings does not exceed
930 cm2 (see Sentence (2»,
(c) the aggregate area of openings does not
exceed 1 per cent of the ceiling area of the
fire compartment,
(d) the depth of the concealed space above the
ceiling is not less than 230 mm,
(e) the dimension of any opening does not
exceed 310 mm,
(0 supports are provided for openings with
any dimension exceeding 150 mm where
framing members are spaced greater than
400 mm o.c.,
(g) individual openings are spaced not less
than 2 m a part,
(h) the ducts above the membrane are sheet
steel and are supported by steel strapping
firmly attached to the framing members,
and
(0 the clearance between the top surface of
the membrane and the bottom surface of
the ducts is not less than 100 mm.
(2) Where an individual opening permitted in
Sentence (1) exceeds 130 cm2 in area, it shall be
protected by
(a) a fire stop flap conforming to Subsection
5.3, or
(b) thermal protection above the duct consisting of the same materials as used for the
ceiling membrane, mechanically fastened
to the ductwork and extending 200 mm
beyond the opening on all sides (see
Figure 2.3.(a».
2.3.17.
(1) Except as permitted in Article 2.3.15.,
where a floor or roof assembly of noncombustible
construction is assigned a fire-resistance rating on the
(1)
50
basis of this Subsection, and incorporates a ceiling
membrane described in Table 2.3.A. or 2.3.B., the
ceiling membrane may be penetrated by openings
leading to ducts located within concealed spaces
above the membrane provided:
(a) the area of any opening does not exceed
930 cm2 (see Sentence (2»,
(b) the aggregate area of openings does not
exceed 2 per cent of the ceiling area of the
fire compartment,
(c) the dimension of any opening does not
exceed 400 mm,
(d) individual openings are spaced at least
2 m apart,
(e) openings are located at least 200 mm from
major structural members such as beams,
columns or joists,
(f) the ducts above the membrane are sheet
steel and are supported by steel strapping
firmly attached to the framing members,
and
(g) the clearance between the top surface of
the membrane and the bottom surface of
the duct is at least 100 mm.
(2) Where an individual opening permitted in
Sentence (1) exceeds 130 cm2 in area, it shall be
protected by
(a) a fire stop flap conforming to Subsection
5.3, or
(b) thermal protection above the duct consisting of the same materials as used for the
ceiling membrane, mechanically fastened
to the ductwork and extending 200 mm
beyond the opening on all sides (see
Figure 2.3.(a».
2.4
Solid Wood Walls, Floors and
Roofs
2.4.1. The minimum thickness of solid wood walls,
floors and roofs for fire-resistance ratings from
30 min to 1.5 h is shown in Table 2A.A.
2.4.2.
(1) The fire-resistance rating of the assemblies
described in Table 2.4.A. may be increased by 15 min
if one of the finishes described in Clauses (a) to (c) is
applied on the fire-exposed side:
(a) 12.7 mm thick gypsum wallboard,
pays
(b) 20 mm thick gypsum-sand plaster on
metal lath, or
(c) 13 mm thick gypsum-sand plaster on
9.5 mm gypsum lath.
(2) Fastening of the plaster to the wood
structure shall conform to Subsection 2.3.
2.4.3. Supplementary ratings based on tests are
included in Table 2.4.B. The ratings given shall apply
to constructions that conform in all details with the
descriptions given.
Table 2.4.B.
Forming Part of Article 2.4.3.
Fire-Resistance Rating of Non-Loadbearing
Built-up Solid Wood Partitions (1)
Construction Details
Figure 2.3.{a) Thermal protection above a duct
Table 2.4.A.
Forming Part of Article 2.4.1.
!
Minimum Thickness of Solid Wood Walls,
Roofs and Floors, mm(1)
Fire-Resistance Rating
1 h 1.5 h
Type of Construction
30 min 45 min
Solid wood floor with
building paper and finish
flooring on top (2)
Solid wood, splined or
I
tongued and grooved floor
with building paper and
finish flooring on top (3)
Solid wood walls of
load bearing vertical plank (2)
Solid wood walls of nonI loadbearing horizontal plank (2)
Column 1
i
I
89
114
165
235
64
76
-
-
114
140
184
89
3
89
4
140
5
I
89
I
Solid panels of wood boards
64 mm to 140 mm wide grooved
and joined with wood splines, nailed
together, boards placed vertically
with staggered jOints, 3 boards thick
Solid panels with 4 mm plywood
facings(2) glued to 46 mm solid
wood core of glued, tongued and
grooved construction for both
sides and ends of core pieces with
tongued and grooved rails in the
core about 760 mm apart
,
Column 1
Notes to Table 2.4.A.:
(1)
(2)
(3)
See CSA 0141, "Softwood Lumber" for sizes.
The assembly shall consist of 38 mm thick members on edge
fastened together with 101 mm common wire nails spaced not
more than 400 mm o.c. and staggered in the direction of the grain.
The floor shall consist of nominal 64 mm by 184 mm wide planks
either tongued and grooved or with 19 mm by 38 mm splines set in
grooves and fastened together with 88 mm common nails spaced
not more than 400 mm o.c.
58
0.5 h
54
1h
2
3
Notes to Table 2.4.B.:
(1)
I
89
2
Actual
Overall Fire-Resistance
Thickness
Rating
mm
h
(2)
The ratings and notes are taken from "Fire Resistance
Classifications of Building Constructions," Building Materials and
Structures Report BMS 92, National Bureau of Standards,
Washington, 1942.
Ratings for plywood faced panel are based on phenolic resin glue
being used for gluing facings to wood frames. If other types of glue
are used for this purpose, the ratings apply if the facings are nailed
to the frames in addition to being glued.
2.5 Solid Plaster Partitions
2.5.1. The minimum thickness of solid plaster
partitions for fire-resistance ratings from 30 min to
4 h is shown in Table 2.5.A.
51
pays
Table 2.S.A.
Forming Part of Article 2.5.1.
Minimum Thickness of Non-Loadbearing Solid Plaster Partitions, mm
Fire-Resistance Rating
Type of Plaster on Metal Lath (1)
45
min
1h
1.5 h
30 min
2h
50(3)
Portland cement-sand (2) or Portland cel11ent-lime-sand
50 (3)
50(3)
Gypsum-sand
64
Gypsum-vermiculite, Gypsum-perlite,
50(3)
50(3)
50 (3)
Portland cement-vermiculite or Portland cement-perlite
58
64
,J
4
Column 1
5
6
Notes to Table 2.S.A.:
Metal lath shall be expanded metal lath or welded woven wire fabric
supported on 19 mm vertical light steel studs spaced not more than
600 mm o.c. Plaster shall be applied to both sides of the lath.
(ll
(3)
Notes to Table 2.6.A.:
Applies to cast-in-place concrete reinforced with S.21 mm diam wire
wrapped around column spirally 200 mm o.c., or 1.S7 mm diam wire
mesh with 100 mm by 100 mm openings.
(21
The space between the protective covering and the web or flange of
the column shall be filled with concrete, cement mortar or a mixture
of cement mortar and broken bricks.
(3)
Concrete masonry reinforced with S.21 mm diam wire or wire mesh
with 1.19 mm diam wire and 10 mm by 10 mm openings, laid in
every second course.
(4)
Brick cover 77 mm thick or less shall be reinforced with 2.34 mm
diam wire or 1.19 mm diam wire mesh with 10 mm by 10 mm
25
25
25
25
25
25
25
25
39
32
50
50
50
50
50(6)
50(6)
50
50
50
50
50(6)
50(6)
50
50
50
50
64
50
50
50
2
3
(1)
52
(5)
161
(7)
4h
-
-
83
7
102
8
For mixture for portland cement-sand plaster, see Sentence
1.7.3.(2).
CSAA82.30-M, "Interior Furring, Lathing and Gypsum Plastering"
does not permit solid plaster partitions less than SO mm thick.
Table 2.6.A.
Forming Part of Article 2.6.1.
Minimum Thickness of Concrete or Masonry Protection to Steel Columns, mm
Fire-Resistance Rating
Description of Cover
1h
1.5 h
2h
iMonolithic concrete
. Type S concrete (1) (column spaces filled) (2)
Type N or L concrete (1) (column spaces filled) (2)
Concrete masonry units (3) or precast reinforced concrete units
Type S concrete (column spaces not filled)
Type Nor L concrete (column spaces not filled)
Clay or shale brick (4) (column spaces filled) (2)
Clay or shale brick (4) (column spaces not filled)
Hollow clay tile (5) (column spaces filled) (2)
Hollow clay tile (5) (column spaces not filled)
Column 1
3h
(7)
6
3h
4h
64
50
77
89
89
77
115
102
64
77
77
102
(7)
(7)
7
8
openings, laid in every second course.
Hollow clay tiles and masonry mortar reinforced with 1.19 mm diam
wire mesh with 10 mm by 10 mm openings, laid in every horizontal
joint and lapped at corners.
Hollow clay tiles shall conform to CSAA82.S.-M "Structural Clay
Non-Load-Bearing Tile."
SO rnm nominal hollow clay tile, reinforced with 1.19 mm diam wire
mesh with 10 mm by 10 mm openings laid in every horizontal joint
and covered with 19 mm gypsum-sand plaster and with limestone
concrete fill in column spaces, has a 4 h fire-resistance rating.
I
pays
{..
Table 2.6.B.
Forming Part of Article 2.6.1 .
.
Minimum Thickness of Plaster Protection to Steel Columns, mm
Fire-Resistance Rating (1, 2)
Description
1h
1.5 h
2h
ｾＴＵｭｩｮ＠
Gypsum-sand plaster on
I
9.5 mm gypsum lath (3)
13
13
20
13
Gypsum-perlite or vermiculite plaster on
9.5 mm gypsum lath (3)
13
13
13
20
25
---I Gypsum perlite or vermiculite plaster on
12.7 mm gypsum lath (3)
13
13
13
20
25
Gypsum perlite or vermiculite plaster on double
12.7 mm gypsum latll (3)
13
13
13
20
25
25
Portland cement-sand plaster on metal lath (4,5)
25
25
4
Column 1
2
5
3
6
3h
4h
-
-
32
50
25
32
-
-
7
8
i
!
I
!
I
Notes to Table 2.6.B.:
Fire-resistance ratings of 30 min and 45 min apply to columns
whose MID ratio is 30 or greater. Fire-resistance ratings greater
than 45 min apply to columns whose MID ratio is greater than 60.
Where the MID ratio is between 30 and 60 and the required fireresistance rating is greater than 45 min, the total thickness of
protection specified in the Table shall be increased by 50 per cent.
(To determine MID, refer to Article 2.6.4.)
(2)
Where the thickness of plaster over gypsum lath is 25 mm or more,
wire mesh with 1.57 mm diam wire and openings not exceeding
50 mm by 50 mm shall be placed midway in the plaster.
(3)
Lath held in place by 1.19 mm diam wire wrapped around lath
450 mm o.c.
( 4)
il)
Table 2.6.C.
Forming Part of Article 2.6.1.
Minimum Thickness of Gypsum-Sand Plaster on
I
Metal Lath Protection to Steel Columns, mm
Fire-Resistance Rating
MID (1)
30 min 45 min 1 h 1.5 h 2h 3h
- 30 to 60
16
16
32
16
16
16
32 lover 60 to 90
-!
over 90 to 120
25 39
16
16
over 120 to 180
16
16 25
16
over 180
16
16
16
16 25
39
7
Column 1
2
4
5
3
6
!
ｾ＠
Note to Table 2.6.C.:
To determine the MID ratio, refer to Article 2.6.4.
(1)
(5)
Expanded metal lath 1.36 kg/m 2 fastened to 9.5 mm by 19 mm
steel channels held in vertical position around column by 1.19 mm
diam wire ties.
For mixture for portland cement-sand plaster, see Sentence
1.7.3.(2).
2.6 Protected Steel Columns
2.6.1. The minimum thickness of protective covering to steel columns is shown in Tables 2.6.A. to
2.6.F. for fire-resistance ratings from 30 min to 4 h.
Table 2.6.0.
Forming Part of Article 2.6.1.
Minimum Thickness of Gypsum-Perlite or
Gypsum-Vermiculite Plaster on
Metal Lath Protection to Steel Columns, mm
Fire-Resistance Rating
MID (1)
30 min 45 min 1 h 1.5 h 2h 3h 4h
30 to 60
16
16 20 32 35 over 60 to 90
16
16
16 20 26 35 45
over 90 to 120
16
16 I 16 16 26 35 45
over 120 to 180 16
16 16 20 32 35
16
16
16
over 180
16 16 16 26 35
4
Column 1
7
2
5
3
6
8
i
Note to Table 2.6.0.:
(1)
To determine the MID ratio, refer to Article 2.6.4.
53
pays
I
Table 2.6.E.
Forming Part of Article 2.6.1.
Steel Columns with Sheet-Steel Membrane and Insulation as Shown in Figures 2.6(a) and 2.6(b)
Type
of
Protection
I
Steel
Thickness
mm
Fastening (2)
(1)
Insulation
I
FireResistance
Rating
45 min
See Figure 2.6.(a)
0.51
NO.8 sheet-metal screws
9.5 mm long, 200 mm o.c.
50 mm mineral,
wool batts (3)
See Figure 2.6.{b)
0.64
Self-threading screws or NO.8
sheet-metal screws, 600 mm o.c.
2 layers 12.7 mm
gypsum wallboard
1.5 h
Figure 2.6.{a)
0.64
NO.8 sheet-metal screws,
9.5mm 19 200 mm o.c.
75 mm mineral wool batts (3)
12.7 mm gypsum wallboard
2h
i
•
See Figure 2.6.(b)
Column 1
0.76
Crimped joint or NO.8
sheet-metal screws, 300 mm o.c.
2
4
(3)
!
Notes to Table 2.6.F.:
(1)
To determine the MID ratio, refer to Article 2.6.4.
(21
See Article 2.6.5.
54
2h
allboard
3
Notes to Table 2.6.E.:
(1)
Minimum thickness, galvanized or wiped-zinc-coated sheet-steel.
(2)
Sheet-steel shall be securely fastened to the floor and superstructure, or where sheet-steel cover does not extend floor to floor,
Table 2.6.F.
Forming Part of Article 2.6.1.
Minimum MID Ratio for Steel Columns Covered
withType X Gypsum Wallboard Protection (1)
Minimum Thickness of
Fire-Resistance Rating
Type X Gypsum Wallboard I
Protection, (2) mm
1 h 1.5 h 2h 3h
12.7
75
15.9
55
25.4
35
60
28.6
35
50
40
75
31.8
35
38.1
35
35
55
41.3
45
35
35
44.5
35
35
35
47.6
35
35
35
50.8
75
35
35
35
63.5
35
35 I 35
45
2
4
[
Column 1
3
5
rayers 15.9 mm gypsum
i
5
fire stopping shall be provided at the level where sheet-steel
protection ends. In the latter case, an alternate type of fire protection shall be applied between the fire stopping and the superstructure.
Conforming to CSA A101-M, "Thermal Insulation, Mineral Fibre, for
Buildings" Type 1A, minimum density 30 kg/m 3 : column section and
batts wrapped with 25 mm mesh chicken wire.
2.6.2. For hollow-unit masonry column protection,
the thickness shown in Tables 2.6.A. to 2.6.0. is the
equivalent thickness as described in Subsection 1.6.
2.6.3. The effect on fire-resistance ratings of the
addition of plaster to masonry and monolithic
concrete column protection is described in Subsection
1.7.
2.6.4.
(1) The ratio MID to which reference is made
in Tables 2.6.B., 2.6.C., 2.6.0. and 2.6.F. shall be found
by dividing "M" the mass of the column in kilograms per metre by "0", the heated perimeter of the
steel column section in metres.
(2) The heated perimeter "0" of steel columns, shown as the dashed line in Figure 2.6.(c),
shall be equal to 2 (B + H) in Examples (1) and (2),
and 3.14B in Example (3). In Figure 2.6.(d), the
heated perimeter "0" shall be equal to 2 (B + H).
I
i
pays
sheet metal screws
example (1)
rOil
L
_ _
.J
example (2)
Figure 2.6.(a) Column protected by sheet-steel membrane and
mineral-wool insulation
example (3)
screw or crimp joint
Figure 2.6.(c) Example (1), standard or wide-flange beam,
Example (2) hollow structural section (rectangular or square),
Example (3), hollow structural section (round)
2.6.5.
Figure 2.6.(b) Column protected by sheet-steel membrane and
gypsum wallboard
(1) Where Type X gypsum wallboard is used
to protect a steel column without an outside sheetsteel membrane, the method of wallboard attachment
to the column shall be as shown in Figure 2.6.(d) and
shall meet the construction details described in
Sentences (2) to (7).
(2) The Type X gypsum wallboard shall be
applied vertically without horizontal joints.
(3) The first layer of wallboard shall be
attached to steel studs with screws spaced not more
than 600 mm o.C. and other layers of wallboard shall
be attached to steel studs and steel corner beads with
screws spaced at a maximum of 300 mm o.c. Where
55
pays
1
01
ｻ｢ｬｾ＠
B
wallboard with 25.4 mm screws spaced not more
than 300 mm o.c.
(7) In a 4-layer system, metal angles shall be
fabricated of galvanized steel and shall be at least
0.46 mm thick with legs at least 51 mm long.
"I
2.7
Individually Protected Steel
Beams
2.7.1. The minimum thickness of protective covering on steel beams exposed to fire on 3 sides for fireresistance ratings from 30 min to 4 h is shown in
Table 2.7.A.
1 layer
2 layers
2.7.3. The effect on fire-resistance ratings of the
addition of plaster finish to concrete or masonry
beam protection is described in Subsection 1.7.
6
5
3 layers
4 layers
1. structural member
2. steel studs
3. gypsum wallboard
(type X)
4. steel corner bead
5. tie wire
6. sheet metal angle
Figure 2.6.(d) Columns protected by Type X gypsum wallboard
without sheet-steel membrane
a single layer of wallboard is used, attachment
screws shall be spaced not more than 300 mm o.c.
(4) Steel tie wires spaced at a maximum of
600 mm o.c. shall be used to secure the second last
layer of wallboard in 3- and 4-1ayer systems.
(5) Studs shall be fabricated of galvanized
steel, be at least 0.53 mm thick, and at least 41.3 mm
wide with legs at least 33.3 mm long and shall be
12.7 mm less than the assembly height.
(6) Corner beads shall be fabricated of
galvanized steel, shall be at least 0.41 mm thick and
shall have legs at least 38.1 mm long attached to the
56
2.7.2. Concrete is referred to as Type S, N or L,
depending on the nature of the aggregate used. This
is described in Subsection 1.4.
2.7.4. The fire resistance of protected steel beams
depends on the means used to hold the protection in
place. Because of the importance of this factor, no
rating has been assigned in Table 2.7.A. to masonry
units used as protective cover to steel beams. These
ratings, however, may be determined on the basis of
comparison with column protection at the discretion
of the authority having jurisdiction, if satisfactory
means of fastening are provided.
2.7.5. A steel beam or steel joist assembly that is
entirely above a horizontal ceiling membrane will be
protected from fire below the membrane and will
resist structural collapse for a period equal to the fireresistance rating determined in conformance with
Subsection 2.3. The support for this membrane shall
be equivalent to that described in Subsection 2.3. The
rating on this basis shall not exceed 1.5 h.
2.8
Reinforced Concrete Columns
2.8.1. Minimum dimensions for reinforced
concrete columns and minimum concrete cover for
vertical steel reinforcement are obtained from
Articles 2.8.2. to 2.8.5., taking into account the type of
concrete, the effective length of the column and the
area of the vertical reinforcement.
pays
Table 2.7.A.
Forming Part of Article 2.7.1.
Minimum Thickness of Cover to Individually Protected Steel Beams, mm (1)
Fire-Resistance Rating
Description of Cover
30 min 45 min 1 h
.5 h 2h
Type S concrete (2) (beam spaces filled solid)
25
25
25
25
32
Type N or L concrete (2) (beam spaces filled solid)
25
25
25
25
25
Gypsum-sand plaster on 9.5 mm gypsum lath (3)
13
13
13
20
Gypsum-perlite or vermiculite plaster on 9.5 mm gypsum lath (3)
13
13
13
13
25
Gypsum-perlite or gypsum-vermiculite on 12.7 mm gypsum lath (3)
13
13
20
25
13
Gypsum-perlite or vermiculite plaster on double 12.7 mm gypsum lath (3)
13
13
25
13
20
Portland cement-sand on metal lath (4)
23
23
23
Gypsum-sand on metal lath (4) (plaster in contact with lower flange)
16
20
25
39
Gypsum-sand on metal lath with air gap between plaster and lower flange (4) 16
16
16
25
25
Gypsum-perlite or gypsum-vermiculite on metal lath (4)
16
16
16
23
23
Column 1
2
4
3
5
6
Notes to Table 2.7 .A:
Where the thickness of plaster finish applied over gypsum
lath is 26 mm or more, the plaster shall be reinforced with
wire mesh with 1.57 mm diam wire and 50 mm by 50 mm
openings placed midway in the plaster.
(2) Applies to cast-in-place concrete reinforced by 5.21 mm diam
wire spaced 200 mm o.c. or 1.57 mm diam wire mesh with
100 mm by 100 mm openings.
(1)
2.8.2.
(1) The minimum dimension, t, in millimetres
of a rectangular reinforced concrete column shall be
equal to
(a) 75 f (R + 1) for all Types Land L40S
concrete,
(b) BO f (R + 1) for Type S concrete when the
design condition of the concrete column is
defined in columns (2) and (4) of Table
2.B.A,
BO f (R + 0.75) for Type N concrete when
the design condition of the concrete
column is defined in columns (2) and (4)
of Table 2.B.A., and
(d) 100 f (R + 1) for Types Sand N concrete
when the design condition of the concrete
column is defined in column (3) of Table
(c)
3h
50
39
4h
64
-
-
-
50 I
39
25
-
50
39
-
-
-
48(5)
35
7
-
8
Lath held in place by 1.18 mm diam wire wrapped around the
gypsum lath 450 mm o.c.
(4)
Expanded metal lath 1.63 kg/m2 fastened to 9.5 mm by
19 mm steel channels held in position by 1.19 mm diam wire.
(5) Plaster finish shall be reinforced with wire mesh with
1.57 mm diam wire and 50 mm by 50 mm openings placed
midway in the plaster.
(3)
where
f = the value shown in Table 2.B.A.,
R = the required fire-resistance rating in
hours,
k = the effective length factor obtained
from CAN3-A23.3-M, "Design of
Concrete Structures for Buildings,"
h
the unsupported length of the
column in metres, and
p
the area of vertical reinforcement in
the column as a percentage of the
column area.
(2) The diameter of a round column shall be
not less than 1.2 times the value "t" determined in
Sentence 2.B.2.(1) for a rectangular column.
2.B.A.
57
I
pays
Table 2.B.A. (1)
Forming Part of Article 2.8.2.
Values of Factor" f "
Values of Factor f to be Used in
Applying Article 2.8.2. (3,4)
Overdesign
Factor (2)
Where
kh is not
more than
3.7 m
i
I
I
1.00
1.25
1.50
Column 1
1.0
0.9
0.83
2
I
I
Where kh is more than 3.7 m
but not more than 7.3 m
t is not more
All other
than 300 mm
cases
p is not more
than 3 per cent
1.2
1.1
1.0
3
1.0
0.9
0.83
4
Notes to Table 2.B.A.:
For conditions that do not fall within the limits described in
Table 2.8.A., further information may be obtained from Reference (7) in Appendix A.
(2) Overdesign factor is the ratio of the calculated load carrying
capacity of the column to the column strength required to
carry the specified loads determined in conformance with
CAN3-A23.3-M, "Design of Concrete Structures for BUildings."
(3)
Where the factor "f" selected from Column 3 results in a "t"
greater than 300 mm, the appropriate factor "f" in Column 4
shall be applicable.
(4) Where up" is equal to or less than 3 per cent and the factor
"f" selected from Column 4 results in a "t" less than 300 mm,
the minimum thickness shall be 300 mm.
(1)
2.8.3
(1) Where the required fire-resistance rating
of a concrete column is 3 h or less, the minimum
thickness in millimetres of concrete cover over
vertical steel reinforcement shall be equal to 25 times
the number of hours of fire resistance required or
50 mm, whichever is less.
(2) Where the required fire-resistance rating
of a concrete column is greater than 3 h, the minimum thickness in millimetres of concrete cover over
vertical steel reinforcement shall be equal to 50 plus
12.5 times the required number· of hours of fire
resistance in excess of 3 h.
58
(3) Where the concrete cover over vertical
steel in Sentence (2) exceeds 62.5 mm, wire mesh reinforcement with 1.57 mm diameter wire and
100 mm openings shall be incorporated midway in
the concrete cover to retain the concrete in position.
2.8.4. The structural design standards may require
minimum column dimensions or concrete cover over
vertical steel reinforcement differing from those
obtained in Sentences 2.8.2.0) and (2). Where a
difference occurs, the greater dimension shall govern.
2.8.5. The addition of plaster finish to the concrete
column may be taken into account in determining the
cover over vertical steel reinforcement by applying
the multiplying factors described in Subsection 1.7.
The addition of plaster shall not however, justify any
decrease in the minimum column sizes shown.
2.8.6. The fire-resistance rating of a reinforced
concrete column that is built into a masonry or
concrete wall so that not more than one face may be
exposed to the possibility of fire at one time may be
determined on the basis of cover to vertical reinforcing steel alone. In order to meet this condition, the
wall shall conform to Subsection 2.1 for the fireresistance rating required.
2.9
Reinforced Concrete Beams
2.9.1. The minimum thickness of cover over
principal steel reinforcement in reinforced concrete
beams is shown in Table 2.9.A. for fire-resistance
ratings from 30 min to 4 h where the width of the
beam or joist is at least 100 mm.
2.9.2. No rating over 2 h may be assigned on the
basis of Table 2.9.A. to a beam or joist where the
average width of the part that projects below the slab
is less than 140 mm, and no rating over 3 h may be
Table 2.9.A.
mg Part of Article 2.9.1.
Minimum Cover to Principal Steel Reinforcement in
Reinforced Concrete Beams, mm
Type of
Fire-Resistance Rating
Concrete
30 min 45 min 1 h 1.5 h 2 h 3h 4h
Type S, Nor L 20
20
20 25
25
39
50
7
Column 1
2
3
4
5
6
8
pays
2.9.3. For the purposes of these ratings, a beam
may be either independent of or integral with a floor
or roof slab assembly.
the surface of the beam. For beams in which several
tendons are used, the cover is assumed to be the
average of the minimum cover of the individual
tendons. The cover for any individual tendon shall
be not less than half the value given in Table 2.l0.A.
nor less than 25 mm.
2.9.4. Where the upper extension or top flange of a
joist or T-beam in a floor assembly contributes
wholly or partly to the thickness of the slab above,
the total thickness at any point shall be not less than
the minimum thickness described in Table 2.2.A. for
the fire-resistance rating required.
2.10.3. The ratings in Table 2.10.A. apply to a beam
that is either independent of or integral with a floor
or roof slab assembly. Minimum thickness of slab
and minimum cover to steel tendons in prestressed
concrete slabs are contained in Subsection 2.2.
2.9.5. The addition of plaster finish to a reinforced
concrete beam may be taken into account in determining the cover over principal reinforcing steel by
applying the multiplying factors described in Subsection 1.7.
2.10.4. The addition of plaster finish to a
prestressed concrete beam may be taken into account
in determining the cover over steel tendons by
applying the multiplying factors described in Subsection 1.7.
2.10 Prestressed Concrete Beams
2.10.5.
(1) Except as provided in Sentence (2), in
unbonded post-tensioned prestressed concrete
beams, the concrete cover to the tendon at the anchor
shall be at least 15 mm greater than the minimum
required away from the anchor. The concrete cover
to the anchorage bearing plate and to the end of the
tendon, if it projects beyond the bearing plate, shall
be at least 25 mm.
(2) The requirements in Sentence (1) do not
apply to those portions of beams not likely to be
exposed to fire (such as the ends and the tops of
flanges of beams immediately below slabs).
assigned where the average width of the part that
projects below the slab is less than 165 mm.
2.10.1. The minimum cross-sectional area and
thickness of concrete cover over steel tendons in
prestressed concrete beams for fire-resistance ratings
from 30 min to 4 h are shown in Table 2.10.A.
2.10.2. The cover for an individual tendon shall be
the minimum thickness of concrete between the
surface of the tendon and the fire-exposed surface of
the beam, except that for ungrouted ducts the assumed cover thickness shall be the minimum thickness of concrete between the surface of the duct and
Table 2.10.A.
rtlc e .1 ..
t-ormmg Part 0fA'I201
!
Minimum Thickness of Concrete Cover over Steel Tendons in Prestressed Concrete Beams, mm (1)
Fire-Resistance Rating
Area of Beam
Type of
cm 2
Concrete
45 min
1h
1.5 h
2h
30 min
3h
Type S or N
260 to 970
25
50
64
39
45
64
Over 970 to 1940
25
26
39
77
26
Over 1940
50
25
39
39
77
Type L
25
Over 970
25
25
50
39
7
Column 1
4
2
5
6
8
3
Note to Table 2.10.A.:
Where the thickness of concrete cover over the tendons
exceeds 64 mm, a wire mesh reinforcement with 1,57 mm
diam wire and 100 mm by 100 mm openings shall be
(1)
4h
!
-
102
102
9
incorporated in the beams to retain the concrete in position
around the tendons. The mesh reinforcement shall be
located midway in the cover.
59
pays
2.11
Glued·Laminated Timber
Beams and Columns
This Subsection applies to glued-laminated timber beams and columns required to have
fire-resistance ratings greater than those afforded
under the provisions of Article 3.1.4.5. of the National
Building Code of Canada 1990.
1.6 ｲＭｾ＠
2.11.1.
2.11.2.
The fire-resistance rating of glued-laminated timber beams and columns in minutes shall be
equal to
(a) 0.1 fB [4 - 2(B/0)] for beams which may
be exposed to fire on 4 sides,
(b) 0.1 fB [4 - (B/O)] for beams which may be
exposed to fire on 3 sides,
(c) 0.1 fB [3 - (B/O)] for columns which may
be exposed to fire on 4 sides, and
(d) 0.1 fB [3 (B/20)] for columns which may
be exposed to fire on 3 sides,
where
f = the load factor shown in Figure
2.11.(a),
B
the full dimension of the smaller side
of a beam or column in millimetres
before exposure to fire (see Figure
2.11.(b»,
o = the full dimension of the larger side
of a beam or column in millimetres
before exposure to fire (see Figure
2.11.(b»,
k = the effective length factor obtained
from CAN3-086-M, "Engineering
Design in Wood," and
L = the unsupported length of a column
in millimetres.
(2) The allowable load on a beam or column
shall be determined by using the allowable stresses
specified in CAN3-086-M, "Engineering Design in
Wood."
(1)
60
1. 5
1.4
'+-
ｾ＠
1--------------"
i
1. 3
-g
.3
1. 2
1.1
1--------------""10.
columns KL ｾ＠ 12
B
and all beams
ＱＮﾰｏｾＭＲＵＷ＠
Applied load/allowable load l1 ), %
Figure 2.11.(a) Factors to compensate for partially loaded
columns and beams
Note to Figure 2.11.(a):
(1) See Sentence 2.11.2.(2)
pays
Section 3 Flame-Spread
Ratings and Smoke
Developed Classifications
3.1
Interior Finish Materials
3.1.1. Tables 3.1.A. and 3.1.B. show flame-spread
ratings and smoke developed classifications for
combinations of some common interior finish materials. The values are based on all the evidence available at present. Many materials have not been
included because of lack of test evidence or because
of inability to classify or describe the material in
generic terms for the purpose of assigning ratings.
beam
"-"-B-
3.1.2. The ratings shown in Tables 3.1.A. and 3.1.B.
are arranged in groups corresponding to the provisions of the National Building Code of Canada 1990.
The ratings apply to materials falling within the
general categories indicated.
3.1.3. In Tables 3.1.A. and 3.1.B., the upper nurnber
of each entry relates to flame spread and the lower
number to smoke developed limit. For example:
25/50
represents a flame-spread rating of 0 to
25 and a smoke developed classification of 0 to 50.
150/300 -
represents a flame-spread rating of 75
to 150 and a smoke developed classification of 100 to 300.
x/x
applied to floors means a flamespread rating over 300 and a smoke
developed classification over 300, and
J.-.-..----1-- beam
Figure 2.11.(b) Full dimensions of glued-laminated beams
and columns
X/X
-
applied to walls and ceilings means a
flame-spread rating over 150 and a
smoke developed classification over
500.
3.1.4. Thin surface coatings can modify flamespread characteristics either upward or downward.
Table 3.1.A. includes a number of thin coatings that
increase the flame-spread rating of the base materiat
so that these may be considered where more precise
control over flame spread hazard is desired.
61
pays
Table 3.1.A.
Forming Part of Article 3.1.1.
Assigned Flame-Spread Ratings and Smoke Developed Classifications
for Combinations of Wall and Ceiling Finish Materials and Surface Coatings
I
Paint or Varnish not
more than 1.3 mm Thick,
Minimum
Thickness
Unfinished
Cellulosic Wallpaper not
Applicable
mm
more than One Layer
Standard
i
Materials
I
i
I
I
e
Asbestos
cement
board
Brick
concrete
tile
Steel,
copper
aluminum
Gypsum
plaster
Gypsum
wallboard
Lumber
Douglas Fir
plywood (1)
Poplar
plywood (1)
Plywood with
Spruce face
veneer (1)
Douglas Fir
plywood (1)
Fiberboard
low density
Hardboard
Type 1
Standard
Particleboard
Waferboard
Column 1
CAN/CGSB-34.16
None
None
None
62
25150
25/50
150/300
None
0.33
CSA A82.22
None
CSA A82.27
None
9.5
16
25/50
150/300
11
150/100
CSA 0121
CSA 0153
150/300
i
CSA 0151
CSA 0121
6
150/100
150/100
CSAA247
11
X/100
150/100
CGSB-11.3
9
6
12.7
150lX
150/300
150/300
150/300
(2)
(2)
4
5
CAN3-0188.1
CAN3-0437
2
Notes to Table 3.1.A.:
The 'flame-spread ratings and smoke developed
classifications shown are for those plywoods without a
cellulose resin overlay.
(1)
010
3
(2)
(2)
Insufficient test information available.
(2)
p
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Table 3.1.B.
Forming Part of Article 3.1.1.
Flame-Spread Ratings and Smoke Developed Classifications
for Combinations of Common Floor Finish Materials and Surface Coatings (1)
IYIOlt,;IIOI;:)
Applicable
Standard
Hardwood or softwood flooring either unfinished or finished with
None
a spar or urethane varnish coating
Vinyl-asbestos flooring not more than 4.B mm thick applied over
CSA A126.1
plywood or lumber subfloor or direct to concrete
CGSB 4-GP-129
Wool carpet (woven), pile weight not less than 1120 g/m 2,
applied with or without felt underlay (2)
Nylon carpet, pile weight not less than 610 g/m 2and not more
CGSB 4-GP-129
than BOO g/m 2, applied with or without felt underlay (2)
Nylon carpet, pile weight not less than 610 g/m 2and not more
CGSB 4-GP-129
than 1355 g/m2, glued down to concrete
CGSB 4-GP-129
Wool/nylon blend carpet (woven) with not more than 20 per cent
nylon and pile weight not less than 1120 g/m 2
CGSB 4-GP-129
Nylon/wool blend carpet (woven) with not more than 50 per cent
wool, pile leig not less than 610 g/m 2and not more than BOO g/m 2
CGSB 4-GP-129
Polypropylene carpet, pile weight not less than 500 g/m 2and not
more than 1200 g/m2, glued down to concrete
1
2
Coil
..
i
i
I
!
'---"
Notes to Table 3.1.B.:
Tested on the floor of the tunnel in conformance with
provisions of CAN4-S1 02.2-M, "Standard Metl10d of Test for
Surface Burning Characteristics of Flooring, Floor Covering,
and Miscellaneous Materials and Assemblies."
(1)
3.1.5.
(1) Information on flame-spread rating of
proprietary materials and fire-retardant treatments
that cannot be described in sufficient detail to ensure
reproducibility is available through the listing and
labelling service of Underwriters' Laboratories of
Canada or other recognized testing laboratory.
(2) A summary of flame spread test results
published prior to 1965 has been prepared by the
Institute for Research in Construction of the National
Research Council of Canada (see Item (1) in Appendix A).
3.1.6.
(1) The propagation of flame along a surface
in the standard test involves some finite depth of the
(2)
Finished or
Unfinished
300
300
300
300
300
300
300
500
300
500
300
500
300
500
300
500
3
Type 1 or 2 underlay as described in CGSB 4-GP-36M,
"Carpet Underlay, Fiber Type."
material or materials behind the surface, and this
involvement extends to the depth to which temperature variations are to be found during the course of
the test; for many commonly used lining materials,
such as wood, the depth involved is about 25 mm.
(2) For all the combustible materials described in Table 3.1.A., a minimum dimension is
shown, and this represents the thickness of the test
samples on which the rating has been based; when
used in greater thicknesses than that shown, these
materials may have a slightly lower flame-spread
rating, and thinner specimens may have higher
flame-spread ratings.
(3) No rating has been included for foamed
plastic materials because it is not possible at this time
to identify these products with sufficient accuracy on
63
pays
a generic basis. Materials of this type which melt
when exposed to the test flame generally show an
increase in flame-spread rating as the thickness of the
test specimen increases.
3.1.7. In Tables 3.1.A. and 3.1.B., the standards
applicable to the materials described are noted
because the ratings are dependent on conformance
with these specifications.
Section 4
Noncombustibility
4.1
Test Method
4.1.1. Noncombustibility is required of certain
components of buildings by the provisions of the
National Building Code of Canada 1990, which
specifies noncombustibility by reference to CAN4Sl14-M, "Standard Method of Test for Determination
of Non-Combustibility in Building Materials."
4.1.2. The test to which reference is made in Article
4.1.1. is severe, and it may be assumed that any
building material containing even a small proportion
of combustibles will itself be classified as combustible. The specimen, 38 mm by 51 mm, is exposed to
a temperature of 750°C in a small furnace. The
essential criteria for noncombustibility are that the
specimen does not flame or contribute to temperature
rise.
4.2
Materials Classified as
Combustible
fibred gypsum plaster would also be classed as
combustible.
4.2.3. The addition of a fire-retardant chemical is
not sufficient to change a cOITtbustible product to a
noncombustible product.
4.3
Materials Classified as
Noncombustible
4.3.1. Noncombustible materials include brick,
ceramic tile, concrete made from portland cement
with noncombustible aggregate, asbestos cement,
plaster made from gypsum with noncombustible
aggregate, metals commonly used in buildings, glass,
granite, sandstone, slate, limestone and marble.
Section 5 Protection of
Openings in Fire-Rated
Assemblies
5.1
Scope
5.1.1.
(1) This Section specifies requirements for
(a) the installation of fire doors and fire
dampers in gypsum wallboard-protected
stud wall assemblies, and
(b) fire stop flaps for installation in fire-rated
membrane ceilings.
5.2
Installation of Fire Doors and
Fire Dampers
4.2.1. Most materials from animal or vegetable
sources will be classed as combustible by CAN4S114-M, "Standard Method of Test for Determination
of Non-CoITtbustibility in Building Materials," and
wood, wood fibreboard, paper, felt made from
animal or vegetable fibres, cork, plasticS, asphalt and
pitch would therefore be classed as combustible.
5.2.1. Fire doors and fire dampers in gypsum wallboard-protected steel stud non-loadbearing walls
required to have a fire-resistance rating shall be
installed in conformance with Section 9.24 of the
National Building Code of Canada 1990 and the
applicable requirements of NFPA 80, "Fire Doors and
Windows."
4.2.2. Materials that consist of combustible and
noncoITtbustible elements in combination will in
many cases also be classed as combustible, unless the
proportion of combustibles is very small. Some
mineral wool insulations with combustible binder,
cinder concrete, cement and wood chips and wood-
5.2.2. Fire doors and fire dampers in gypsum wallboard-protected wood stud walls required to have a
fire-resistance rating shall be installed in conformance with Section 9.23 of the National Building
Code of Canada 1990 and the applicable requirements of NFPA 80, "Fire Doors and Windows."
64
I
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...
Appendix A to Chapter 2
5.3 Fire Stop Flaps
5.3.1. Fire stop flaps shall be constructed of steel at
least 1.5 mm thick, covered on both sides with
painted asbestos paper at least 1.6 mm thick and
equipped with pins and hinges of corrosion-resistant
material (see Figure 5.3.(a».
5.3.2. Fire stop flaps shall be held open with fusible
links conforming to ULC-S505, "Standard for Fusible
Links for Fire Protection Service" or other heatactivated devices having a temperature rating
approximately 30°C above the maximum temperature that would exist in the system either with the
system in operation or shut down.
fusible link
spring catch
diffuser opening
blade
membrane ceiling
hinge
:::---"---- diffuser
(a) Hinged type
Sliding
closure
Ｚ［ｰＭＬｾ］
spring mechanism
held by fusible link
membrane ceiling
diffuser
(b) Sliding type
Figure 5.3.(a) Typical fire stop flaps
Fire Test Reports
Summaries of available fire-test information have
been published by the Institute for Research in
Construction (formerly the Division of Building
Research) as follows:
M. Galbreath, Flame Spread Performance of
(1)
Common Building Materials. Technical Paper
No. 170, Division of Building Research, National Research Council Canada, Ottawa, April
1964. NRCC 7820.
(2)
M. Galbreath and W.W. Stanzak, Fire Endurance of Protected Steel Columns and Beams.
Technical Paper No. 194, Division of Building
Research, National Research Council Canada,
Ottawa, April 1965. NRCC 8379.
(3)
T.Z. Harmathy and W.W. Stanzak, ElevatedTemperature Tensile and Creep Properties of
Some Structural and Prestressing Steels.
American Society for Testing and Materials,
Special Technical Publication 464, 1970, p. 186
(DBR Research Paper No. 424). NRCC 11163.
(4)
T.Z. Harmathy, Thermal Performance of
Concrete Masonry Walls in Fire. American
Society for Testing and Materials, Special
Technical Publication 464, 1970, p. 209 (DBR
Research Paper No. 423). NRCC 1116l.
(5)
L.W. Allen, Fire Endurance of Selected NonLoadbearing Concrete Masonry Walls. DBR
Fire Study No. 25, Division of Building Research, National Research Council Canada,
Ottawa, March 1970. NRCC 11275.
(6)
A. Rose, Comparison of Flame Spread Ratings
by Radiant Panel, Tunnel Furnace, and Pittsburgh-Corning Apparatus. DBR Fire Study No.
22, Division of Building Research, National
Research Council Canada, Ottawa, June 1969.
NRCC 10788.
(7)
T.T. Lie and D.E. Allen, Calculation of the Fire
Resistance of Reinforced Concrete Columns.
DBR Technical Paper No. 378, Division of
Building Research, National Research Council
Canada, Ottawa, August 1972. NRCC 12797.
(8)
W.W. Stanzak, Column Covers: A Practical
Application of Sheet Steel as a Protective
Membrane. DBR Fire Study No. 27, Division of
65
(9)
(10)
(11 )
(12)
(13)
(14)
(15)
(16)
(17)
66
Building Research, National Research Council
Canada, Ottawa, February 1972. NRCC 12483.
W.W. Stanzak, Sheet Steel as a Protective Membrane for Steel Beams and Columns. DBR Fire
Study No. 23, Division of Building Research,
National Research Council Canada, Ottawa,
November 1969. NRCC 10865.
W.W. Stanzak and T.T. Lie, Fire Tests on Protected Steel Columns with Different CrossSections. DBR Fire Study No. 30, Division of
Building Research, National Research Council
Canada, Ottawa, February 1973. NRCC 13072.
G. Williams-Leir and L.W. Allen, Prediction of
Fire Endurance of Concrete Masonry Walls.
DBR Technical Paper No. 399, Division of
Building Research, National Research Council
Canada, Ottawa, November 1973. NRCC
13560.
G. Williams-Leir, Prediction of Fire Endurance
of Concrete Slabs. DBR Technical Paper No.
398, Division of Building Research, National
Research Council Canada, Ottawa, November
1973. NRCC 13559.
A. Rose, Flammability of Fibreboard Interior
Finish Materials. Building Research Note No.
68, Division of Building Research, National
Research Council Canada, Ottawa, October
1969.
L.W. Allen, Effect of Sand Replacement on the
Fire Endurance of Lightweight Aggregate
Masonry Units. DBR Fire Study No. 26,
Division of Building Research, National
Research Council Canada, Ottawa, September
1971. NRCC 12112.
L.W. Allen, W.W. Stanzak and M. Galbreath,
Fire Endurance Tests on Unit Masonry Walls
with Gypsum Wallboard. DBR Fire Study No.
32, Division of Building Research, National
Research Council Canada, Ottawa, February
1974. NRCC 13901.
W.W. Stanzak and T.T. Lie, Fire Resistance of
Unprotected Steel Columns. Journal of Structural Division, Proc., Am. Soc. Civ. Eng.,
Vol. 99, No. ST5 Proc. Paper 9719, May 1973
(DBR Research Paper No. 577) NRCC 13589.
T.T. Lie and T.Z. Harmathy, Fire Endurance of
Concrete-Protected Steel Columns. A.C.1.
Journal, January 1974, Title No. 71-4 (DBR
Technical Paper No. 597) NRCC 13876.
(18)
T.T. Lie, A Method for Assessing the Fire Resistance of Laminated Timber Beams and Columns. Can. J. Civ. Eng., Vol. 4, No.2, June
1977 (DBR Technical Paper No. 718) NRCC
15946.
(19) T.T. Lie, Calculation of the Fire Resistance of
Composite Concrete Floor and Roof Slabs.
Fire Technology, Vol. 14, No. I, February 1978
(DBR Technical Paper No. 772) NRCC 16658.
Obsolete Materials and Assemblies
Building materials, components and structural
members and assemblies in buildings constructed
ｾ｡Ｇｹ＠
before the present edition of the ｓｵｰｬ･ｾｮｴ＠
have been assigned ratings based on earlIer edItIons
of this document or older reports of fire tests. To
assist users in determining the ratings of these
obsolete assemblies and structural members, the
following list of reference documents has been
prepared. Although some of these publications are
out of print, reference copies are available at the
Institute for Research in Construction, National
Research Council of Canada, Ottawa, Ont., KIA OR6.
(1)
M. Galbreath, Fire Endurance of Unit Masonry
Walls. Technical Paper No. 207, Division of
Building Research, National Research Council
Canada, Ottawa, October 1965. NRCC 8740.
(2)
M. Galbreath, Fire Endurance of Light Framed
and Miscellaneous Assemblies. Technical
Paper No. 222, Division of Building Research,
National Research Council Canada, Ottawa,
June 1966. NRCC 9085.
(3)
M. Galbreath, Fire Endurance of Concrete Assemblies. Technical Paper No. 235, Division of
Building Research, National Research Council
Canada, Ottawa, November 1966. NRCC 9279.
(4)
Guideline on Fire Ratings of Archaic Materials
and Assemblies. Rehabilitation Guideline #8,
U.s. Department of Housing and Urban Development, Germantown, Maryland 20767,
October 1980.
(5)
T .Z. Harmathy, Fire Test of a Plank Wall Construction. Fire Study No.2, Division of Building Research, National Research Council
Canada, Ottawa, July 1960. NRCC 5760.
(6)
T.Z. Harmathy, Fire Test of a Wood Partition.
Fire Study No.3, Division of Building Research, National Research Council Canada,
Ottawa, October 1960. NRCC 5769.
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Chapter 3
Measures for Fire Safety
in High Buildings
Introduction •••••••••••••••••••••••••••••••••••••••••••• 69
Section 1
Scope of Measures for Fire
Safety in High Buildings •••••• 70
Section 2
Measures for Life Safety in
High Buildings
Measure A Fully Sprinklered
Buildings ••••••••••••••••••••••••••••••••••• 88
Measures Band COpen
Corridor Access to Stairs and
Elevators •••••••••••••••••••••••••••••••••• 89
Measures D and E Protected
Vestibule Access to Stairs and
Elevator Shafts ......................... 91
Measures F and G Pressurized
Stair and Elevator Shafts ••••••••• 95
Measure H Fully Pressurized
Buildings ••••••••••••••••••••••••••••••••••• 99
Measures I and J Partially
Pressurized Buildings ••••••••••••• 101
Measure K Vertically Divided
Buildings ................................. 103
Measure L Areas of Refuge •• 105
Measure M Residential
Buildings with Balconies ••••••• 107
Measure N Connected
Buildings ................................. 108
Section 3
Venting of Floor Areas ....... 108
Appendix A
Graphs for Applying Smoke
Control Measures •••••••••••••• 112
Appendix B
Assumptions Used in
Developing Fire Safety
Measures ••••••••••••••••••••••••••• 118
67
Appendix C
Check of a Smoke Control
Systell1 ••••••••••••••••••••••••••• 1 27
References
•••••••••••••••••••••••••••••••••••••••••• 1 28
6B
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...
Chapter 3
Measures for Fire Safety
in High Buildings
Introduction
Experience has shown that the time required for
the complete evacuation of a high building can
exceed that which is considered necessary for the safe
egress of all occupants. Studies of the "chimney
effect" and observations of smoke movement in fires
have shown that present measures for containing a
fire on a lower storey will not usually prevent the
movement of smoke through the elevator, stair or
other vertical shafts to the upper storeys of a high
building. Occupants of high buildings, and particularly those on upper storeys, may be faced with
severe smoke conditions from fires occurring in
storeys below them before their own evacuation is
possible.
The measures described in this Chapter are
designed to implement the requirements of NBC
Subsection 3.2.6. by providing safe conditions for the
occupants of a high building who may have to
remain in the building during a fire, by protecting
exit routes and by assisting fire fighters with the
provision of efficient access to the fire floor.
The knowledge requirements of these measures
are well within the capabilities of the competent
designer. The designer should appreciate, however,
that the successful application of the measures
requires a clear understanding of the principles that
govern smoke movement, as well as an awareness of
the assumptions on which the measures are based.
The assumptions regarding building characteristics
associated with each measure are included in the text.
If the building under consideration has characteristics
that are significantly different from these, appropriate
adjustments must be made to the design.
This is particularly true of methods employing airhandling systems where, for example, a realistic
assessment of the leakage characteristics of the
enclosures of spaces into which air is introduced may
be critical. In this context, special attention is drawn
to the building pressurization approach used in
conjunction with a smoke shaft. The recommendations contained in this Chapter for this approach
were developed assuming a building with fairly
uniform leakage characteristics. Where a building
departs substantially from this model, the design
must be adjusted to compensate. An example of the
latter condition would be a building which contains
at the lower levels a large shopping complex of much
greater floor area than at the higher levels.
The designer is cautioned that the tabular and
graphical information presented herein have been
developed for buildings having the characteristics
listed in this document. It will be for the designer to
judge the extent to which the building under
consideration has characteristics that will allow the
application of this information. This is particularly
important where a designer intends to develop an
original smoke control approach.
The National Building Code requires that a check
be made of the smoke control system when requested
by the authority having jurisdiction in accordance
with the procedures described in Appendix C of this
Chapter. This check will indicate deficiencies caused
by inexact estimates of the leakage characteristics or
of air supply requirements and, in all but the most
extreme cases, will provide an opportunity for
appropriate adjustments before the system is put into
service.
69
Section 1 Scope of
Measures for Fire Safety
in High Buildings
Where Measures C, E, G and J in Section 2 are
applied, it is assumed that occupants of all floors will
move immediately into the stairshafts and will then
proceed slowly to the outdoors following the
sounding of a general fire alarm.
This Chapter includes a number of detailed
measures that may be incorporated in a building in
order to comply with the requirements relating to
control of smoke that are included in Subsection
3.2.6. of the National Building Code. It is not the
intention to exclude other means of attaining the
same objectives. Where smoke control methods other
than those described in this Chapter are developed,
they may be based on the information in Appendix B
of this Chapter.
Where Measure K in Section 2 is applied (i.e. the
building is divided vertically into two zones), it is
assumed that occupants of the floor on which the fire
originates will leave by exit stairs, and that the
occupants of all other floors in the zone in which the
fire is discovered will move through vestibules or
bridges to floor areas on the same level in the fire-free
smoke control region immediately following the
sounding of a fire alarm. Occupants may remain in
these areas of refuge until further directed by the fire
department officer.
Smoke control measures required by NBC Subsection 3.2.6. vary depending on the height and occupancy of a building. In a sprinklered building, the
requirements for control of smoke movement are
minimal (see Measure A, Section 2). In very tall
buildings, limits are placed on the penetration of
smoke into exit stairs, elevators for fire fighters and
all floor areas other than the one on which fire occurs.
Such limits are achieved by Measures B, 0, F, H and I
in Section 2. In certain buildings of lesser height and
limited popUlation, exit stairs and elevators for fire
fighters are protected and smoke may be expected to
enter upper floor areas. This situation applies where
Measures C, E, G and J, described in Section 2, are
employed. In other buildings, the spread of smoke
into shafts and floor areas is accepted, but areas of
refuge are provided that are maintained smoke free,
that can be reached by all people in the building
within a few minutes and that are linked to outdoors
by safe means of egress. They are described in
Measures K and L in Section 2.
Where Measures A, B, 0, F, H and I in Section 2 are
applied, it is assumed that in the event of fire
occupants of the floor on which the fire occurs will
leave by exit stairs immediately following the
sounding of a fire alarm, and that occupants of the
floor immediately above the floor on which the fire
occurs will be advised to leave by the first fire
department officer on the scene or other person
assigned this responsibility. Occupants of all other
floors may remain on their floors unless otherwise
directed.
70
Where Measure L in Section 2 is applied, it is
assumed that occupants of the floor on which the fire
originates will leave by the exit stairs, and that
occupants of all other floors will move by corridors
or stairs to areas of refuge that are distributed
throughout the building immediately following the
sounding of the fire alarm. Occupants may remain in
these areas of refuge until otherwise directed.
In a residential building where reliance is placed
on balconies as places of refuge from smoke, as
described in Measure M in Section 2, occupants may
remain in their suites when a general fire alarm is
given, but should be prepared to move on to their
balconies if conditions in the suite should become
untenable.
It is assumed that the cumulative population of
storeys below grade divided by 1.8 times the width of
all exit stairs at the storey under consideration will
not exceed the 300 limit referred to in NBC Article
3.2.6.1., and that occupants of storeys below grade
will evacuate the building by the stairshafts
immediately after the discovery of a fire in a storey
below grade.
It is also important that fire fighters are provided
with a smoke-free access to fire floors below grade.
Measures A, B, C, 0, E, F, G, Land M include
provisions designed to separate the exit stairs serving
storeys above grade from those serving storeys below
grade, and to limit entry of smoke into these shafts.
Elevator shafts and service shafts are required to be
pays
pi
provided with a separation near grade, or be
designed to limit their functioning as paths of smoke
movement into upper floor areas. In Measures H, I
and J, no special precautions are necessary to protect
shafts in storeys below grade, because the system of
pressurization plus venting of the fire floor protects
all shafts, whether or not these penetrate storeys
below grade. In Measure K, the separation into two
zones is maintained in storeys below grade. Smokefree access will thus be available to any floor on
which the fire occurs.
Synopsis of Measures for Fire
Safety in High Buildings
(7) Voice communication system required if
building is more than 36 m high (NBC Article
3.2.6.13.).
(8) Fire protection required for electrical
feeders to emergency equipment (NBC Article
3.2.6.14.).
(9) Power to operate emergency lighting, fire
alarm and voice communication systems (NBC
Article 3.2.7.8.).
(10) Emergency power to operate elevators
required if building is more than 36 m high (NBC
Article 3.2.7.9.).
Each of the measures is illustrated by a sketch with
notes describing the applicable conditions (Figures 1
to 18). These sketches are intended as a guide to the
detailed requirements and as an aid to finding the
relative clauses, but they are not intended to limit in
any way the scope of the detailed provisions which
in general provide a wider range of choice than can
be shown in the sketches and notes. A summary of
requirements applicable to all buildings, regardless of
the measure being used, is given in the following
paragraph.
Requirements Common to all
Measures for Fire Safety in High
Buildings
(1) Elevators controlled by keyed switch
(NBC Article 3.2.6.8.).
(2) Elevator for fire fighters required (NBC
Article 3.2.6.9.).
(3) Means of venting each floor area to
outdoors by smokeshaft, windows or building
exhaust system (NBC Article 3.2.6.10.).
(4) Certain floor areas in the building to be
sprinklered (NBC Articles 3.2.1.5.,
3.2.2.11. and 3.2.6.11.).
(5) Limits on flame-spread rating and smoke
developed classification for interior finish materials
in certain locations (NBC Article 3.1.13.7.).
(6) Central alarm and control facility required
(NBC Article 3.2.6.12.).
71
Measure A
Fully Sprinklered Building
1.
2.
3.
Door to outdoors in each stairshaft held open
during a fire emergency (2A(2».*
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that storey (2A(3».
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2A(3».
Elevator shaft terminates not lower than the
first floor below the lowest exit storey or has
elevator vestibules in every storey below the
lowest exit storey (2A(5».
Vertical service spaces, other than elevator
shafts, provided with firestops at the first floor
below the lowest exit storey or vented to outdoors at top during a fire emergency (2A(6».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (NBC Sentence 3.2.6.4.(1».
Figure 1 Typical floor plan, Measure A
Measure A satisfies NBC Sentence 3.2.6.4.(1) for any
major occupancy classification.
No limit on height.
All floor areas sprinklered (NBC Sentence 3.2.6.4.(1».
Limits on flame-spread ratings and smoke developed
classifications described in NBC Sentence 3.1.13.7.(1)
are relaxed (NBC Sentence 3.1.13.7.(2».
72
*
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
pays
Measure B
Open Corridor Access to Stairs and Elevators (including
restrictions on movement of smoke from floor to floor)
1.
ttttm
1
LIT
-
2.
3.
3
4.
4
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that storey (2B(3».*
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2B(3».
Elevator shaft terminates not lower than the
first floor below the lowest exit storey or has
elevator vestibules in every storey below the
lowest exit storey (2B(4».
Vertical service spaces, other than elevator
shafts, provided with fires tops at the first floor
below the lowest exit storey and at intervals of
not more than five storeys or vented to outdoors at top during a fire emergency (2B(5».
Open corridor or balcony providing access to
stairs and elevator for fire fighters (2B(2).
Elevator shaft and stairshaft heating restrictions.
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2B(6».
Certain dampers close in air handling ducts
during a fire emergency (2B(8».
--J
1
1
+H ｾ＠
*
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
Figure 2 Typical floor plan, Measure B
Measure B satisfies NBC Sentences 3.2.6.2.(2), (3) and
(4) for any major occupancy classification.
No limit on height.
73
Measure C
Open Corridor Access to Stairs and Elevators (no additional
restrictions on movement of smoke from floor to floor)
1.
2.
3.
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that storey (2C(3».*
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2C(3».
Elevator shaft terminates not lower than the
first floor below the lowest exit storey or has
elevator vestibules in every storey below the
lowest exit storey (2C(4».
Open corridor or balcony providing access to
stairs and elevator for fire fighters (2C(2».
Elevator shaft and stairshaft heating restrictions.
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2C(5».
3
*
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
Figure 3 Typical floor plan, Measure C
Measure C satisfies NBC Sentence 3.2.6.5.(1) for
Group A, C, D, E or F major occupancy classification.
Limit on population (NBC Sentence 3.2.6.5.(1».
Limited to buildings not more than 75 m high (NBC
Sentence 3.2.6.5.(1».
74
I
jDP
pays
....
Measure D
Protected Vestibule Access to Stairs and Elevators (including
restrictions on movement of smoke from floor to floor)
1.
#H+H I
5
1
,
J
L
r
2.
5
-,J
00
3.
4.
L4
J
r
1
5.
1
5
#H+H I
Figure 4 Typical floor plan, Measure 0
Measure 0 satisfies NBC Sentences 3.2.6.2.(2), (3) and
(4) for any major occupancy classification.
Door to outdoors in each stairshaft held open
during a fire emergency (20(7».*
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that level (20(8».
Stairs haft serving floors below the lowest exit
level is pressurized during a fire emergency
(20(8».
Elevator shaft terminates not lower than the
first floor below the lowest exit storey or has
elevator vestibules in every storey below the
lowest exit storey (20(13».
Shaft containing an elevator for fire fighters is
provided with vent to outdoors at bottom
during a fire emergency if the vestibule protection is by pressurization (20(9».
Vertical service spaces, other than elevator
shafts, provided with fires tops at the first floor
below the lowest exit storey and at intervals of
not more than five storeys or vented to outdoors at top during a fire emergency (20(11».
Vestibule vented to outdoors during a fire
emergency or pressurized (20(5».
Vents to vestibules openable from central
control facility if building is more than 36 m
high (20(6».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (20(14».
Certain dampers close in air handling ducts
during a fire emergency (20(15».
No limit on height.
*
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
75
Measure E
Protected Vestibule Access to Stairs and Elevators (no additional restrictions on movement of smoke from floor to floor)
1.
2.
3.
4.
Figure 5 Typical floor plan, Measure E
Measure E satisfies NBC Sentence 3.2.6.5.0) for
Group A, C, D, E or F major occupancy classification.
Limit on population (NBC Sentence 3.2.6.5.0».
Limited to buildings not more than 75 m high (NBC
Sentence 3.2.6.5.0».
76
*
Door to outdoors in each stairshaft held open
during a fire emergency (2E(6».*
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that level (2E(7».
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2E(7».
Elevator shaft terminates not lower than the
first floor below the lowest exit storey or has
elevator vestibules in every storey below the
lowest exit storey (2EOO».
No special protection against smoke for
elevator shafts or vertical service spaces other
than a shaft containing an elevator for fire
fighters.
Shaft containing an elevator for fire fighters is
provided with vent to outdoors at bottom
during a fire emergency (2E(8».
Vestibule vented to outdoors during a fire
emergency or pressurized (2E(4».
Vents to vestibules openable from central
control facility if building is more than 36 m
high (2E(5».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2E01».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
pays
....
Measure F
Pressurized Stairshafts and Elevator Shafts (including
restrictions on movement of smoke from floor to floor)
1.
2.
3.
Figure 6 Typical floor plan, Measure F
Measure F satisfies NBC Sentences 3.2.6.2.(2), (3) and
(4) for any major occupancy classification.
No limit on height.
*
Door to outdoors in each stairshaft held open
during a fire emergency (2F(2». *
Stairs haft pressurized during a fire emergency
(2F(2».
Stairs haft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that level (2F(3».
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2F(3».
Shaft containing an elevator for fire fighters is
pressurized during a fire emergency (2F(4».
Vertical service spaces, other than elevator
shafts, provided with firestops at the first floor
below the lowest exit storey and at intervals of
not more than five storeys or vented to outdoors at top during a fire emergency (2F(7».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2F(11).
Certain dampers in air-handling ducts close
during a fire emergency (2F(12».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
77
Measure G
Pressurized Stairshafts and Elevator Shafts (no additional
restrictions on movement of smoke from floor to floor)
1.
2.
3.
Door to outdoors in each stairshaft held open
during a fire emergency (2G(2». *
Stairshaft pressurized during a fire emergency
(2G(2».
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that level (2G(3».
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2G(3».
Shaft containing an elevator for fire fighters is
pressurized during a fire emergency (2G(4».
No special protection against smoke for
elevator shafts or vertical service spaces other
than a shaft containing an elevator for fire
fighters.
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2G(7».
Figure 7 Typical floor plan, Measure G
Measure G satisfies NBC Sentence 3.2.6.5.(1) for
Group A, C, 0, E or F major occupancy classification.
Limit on population (NBC Sentence 3.2.6.5.(1».
Limited to buildings not more than 75 m high (NBC
Sentence 3.2.6.5.(1».
78
*
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
ｾ＠
pays
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .t
Measure H
Building Fully Pressurized
1.
ｾＳ＠
Ｓｾ＠
2.
3.
4.
4
Figure 8 Typical floor plan, Measure H
Measure H satisfies NBC Sentences 3.2.6.2.(2), (3) and
(4) for any major occupancy classification.
No limit on height
*
All floor areas pressurized during a fire
emergency (2H(2».*
Provision for modulating air supply for
building pressurization during warm weather
(2H(4»).
Fire floor provided with means of venting to
outdoors by smokeshaft or windows (2H(7».
A proportion of air for building pressurization
directed into stairshafts (2H(2».
Doors to outdoors in stairshafts not held open
during a fire emergency (2H(5».
Except as required for venting, all openings in
perimeter walls and roof are kept closed
during a fire emergency (2H(5».
Except as required for pressurization, air
moving fans are stopped during a fire emergency in a system that serves more than two
storeys (2H(4».
Certain dampers in air handling ducts are
closed during a fire emergency (2H(6».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
79
Partially Pressurized Building (including restrictions on movement of smoke from floor to floor outside core)
Measure I
1.
1
ｉｾ＠
2.
2
3.
4
3
4.
Figure 9 Typical floor plan, Measure I
Enclosing wall of core is a fire separation with
self closing doors.
Central core is pressurized during a fire
emergency (21(2».*
All openings in perimeter walls and roof of
core kept closed during a fire emergency
(21(3».
Fire compartment is vented to outdoors during
a fire emergency by smokeshaft or windows
(21(4».
Vertical service spaces, other than elevator
shafts, outside core provided with fires tops at
the level of the first floor below the lowest exit
storey and at intervals of not more than five
storeys or vented to outdoors at the top during
a fire emergency (21(6».
Doors to outdoors in stairshafts not held open
during a fire emergency except as required for
pressurizing the core (21(3».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (21(7».
Certain dampers in air handling ducts are
closed during a fire emergency (21(8».
Measure 1 satisfies NBC Sentences 3.2.6.2.(2), (3) and
(4) for any major occupancy classification.
No limit on height.
80
*
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
I
pays
.....
Measure J
Partially Pressurized Building (no additional restrictions on
movement of smoke from floor to floor outside core)
1.
2.
*
Enclosing wall of core is a fire separation with
self closing doors.
Central core is pressurized during a fire
emergency (2} (2». *
All openings in perimeter walls and roof of
core are kept closed during a fire emergency
(2}(3».
Doors to outdoors in stairshafts not held open
during a fire emergency (2}(3».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2}(4».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
Figure 10 Typical floor plan, Measure J
Measure} satisfies NBC Sentence 3.2.6.5.(1) for
Group A, C, 0, E or F major occupancy classification.
Limit on population (NBC Sentence 3.2.6.5.(1».
Limited to buildings not more than 75 m high (NBC
Sentence 3.2.6.5.(1».
81
Measure K
Vertically Divided Building (with spatial separation)
1.
2.
3.
4.
Door to outdoors in each stairshaft held open
during a fire emergency (2K(13».*
One elevator for fire fighters and one stairshaft
in each smoke control region (2K(4».
If bridges do not occur at each storey, two stairshafts are required in each smoke control
region (NBC 3.4.2.1.).
Building designed as two smoke control
regions with spatial separation between
(2K(2».
5.
5
4
6
6.
*
Figure 11
Typical floor plan, Measure K
Measure K satisfies NBC Sentence 3.2.6.3.(1) for
buildings of Group A, C, 0, E or F major occupancy
classifica tion.
No limit on height.
82
Bridges at intervals of not more than five
storeys, except that in buildings of Group C
major occupancy more than 75 m high, the
bridge is at each storey (2K(3».
Bridges vented to outdoors or pressurized
during a fire emergency (2K(11».
Fire separation in storeys below grade to
maintain separation between smoke control
regions (2K(15».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2K(14».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
pays
...
Measure K
Vertically Divided Buildings (with fire separation)
1.
2.
1
I
5
1tH11t1
3.
2
J
-'IIDCI°1'--
3
4.
ｾ＠
5
2
1tH11t1
I
1
5.
Door to outdoors in each stairshaft held open
during a fire emergency (2K(13».*
One elevator for fire fighters and one stairshaft
in each smoke control region (2K(4».
If vestibules do not occur at each storey, two
stairshafts are required in each smoke control
region (NBC 3.4.2.1.).
Building designed as two smoke control
regions with fire separation between (2K(2».
Fire separation in storeys below grade to
maintain separation between smoke control
regions (2K(15».
Vestibule at intervals of not more than five
storeys, except that in the case of buildings of
Group C major occupancy more than 75 m
high, the vestibule is at each storey (2K(3».
Vestibules vented to outdoors or pressurized
during a fire emergency (2K(11».
Vent to outdoors in each smoke control region
on floors below mid height of building
(2K(12».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2K(14».
Figure 12 Typical floor plan, Measure K
Measure K satisfies NBC Sentence 3.2.6.3.(1) for
buildings of Group AI C I D, E or F major occupancy
classification.
*
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
No limit on height.
83
pays
Measure L
Areas of Refuge (duplicate groups of areas of refuge at every
fifth storey except as required in item 5)
1.
2
2.
3.
4.
Figure 13 Typical floor plan, Measure L
5.
Measure L satisfies NBC Sentence 3.2.6.3.(1) for
buildings of Group A, C, D, E or F major occupancy
classification.
No limit on height.
*
84
Stairshaft and shaft containing an elevator for
fire fighters protected by area of refuge or
vestibule (2L(II».*
Door to outdoors in each stairshaft held open
during a fire emergency (2L(14».
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that storey (2L(15».
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2L(15».
Stairshaft and shaft containing an elevator for
fire fighters is protected at intermediate floors
by pressurized vestibules (2L(11».
Shaft containing an elevator for fire fighters
termina tes not lower than the first floor below
the lowest exit storey or has elevator vestibules
in every storey below the lowest exit storey
(2L(13».
Shaft containing an elevator for fire fighters
provided with vent to outdoors at bottom
during a fire emergency (2L(16».
No special protection against smoke for
elevator shafts or vertical service spaces other
than a shaft containing an elevator for fire
fighters.
Two areas of refuge on each fifth floor pressurized during a fire emergency (2L(10», or areas
of refuge staggered on intermediate storeys
(see Figure 15), except that in buildings of
Group C major occupancy more than 75 m
high the areas of refuge shall be located on
each storey.
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2L(18».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
pays
•....
Measure L
Areas of Refuge (areas of refuge located in pairs)
1.
i
I
I
I
I
area of refuge
5
I
ＭｾＧ＠
,-
80
2.
area of refuge
5
3.
Figure 14 Typical floor plan, Measure L
4.
A
A
v
v
§
§
§'
area of refuge
:E
§
E
area of refuge
ｾ＠
.. §
........
ｾ＠
§
E
..
1§ ｾ＠
••• ,>.
ｾ＠
§ ｾ＠
v
•
area of refuge
E
area of refuge
stairshaft
§
.l
v
Figure 15 Typical cross section showing areas of refuge on
intermediate floors
*
Stairshaft and shaft containing an elevator for
fire fighters protected by area of refuge or
vestibule (2L(ll».*
Door to outdoors in each stairshaft held open
during a fire emergency (2L(14».
Stairs haft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that storey (2L(15».
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2L(l5».
Two areas of refuge are pressurized during a
fire emergency (see Figure 14 for area of refuge
every fifth storey), except that in buildings of
Group C major occupancy more than 75 m
high, the areas of refuge are located on each
storey (2L(10».
No special protection against smoke for
elevator shafts or vertical service spaces other
than a shaft containing an elevator for fire
fighters.
Shaft containing an elevator for fire fighters
terminates not lower than the first floor below
the lowest exit storey or has elevator vestibules
in every storey below the lowest exit storey
(2L(13».
Shaft containing an elevator for fire fighters is
provided with vent to outdoors at bottom
during a fire emergency (2L(16»
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2L(18».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
Measure L satisfies NBC Sentence 3.2.6.3.(1) for
buildings of Group A, C, Df E or F major occupancy
classifica tion.
No limit on height.
85
pays
Measure M
Building with Balconies
1.
2.
3.
*
Figure 16 Typical floor plan, Measure M
Measure M satisfies NBC Sentence 3.2.6.6.(1) for
buildings of Group C major occupancy classification.
86
Door to outdoors in each stairshaft held open
during a fire emergency (2M (2». *
Stairshaft serving floors below the lowest exit
level is separate from stairshaft serving floors
above that level (2M(3».
Stairshaft serving floors below the lowest exit
level is pressurized during a fire emergency
(2M(3».
Each suite is provided with a balcony (NBC
3.2.6.6.(1».
Elevator shaft terminates not lower than the
first floor below the lowest exit storey or has
elevator vestibules in every storey below the
lowest exit storey (2M(4».
Air moving fans are stopped during a fire
emergency in a system that serves more than
two storeys (2M(5».
First number indicates Section number. Letter
indicates Measure. Last number indicates
number of Sentence in that Measure.
p
pays
...
Measure N
Connected Buildings
building A
1, Vestibule vented to outdoors or
pressurized
building B
grade
,.,..,
.
Ｌｾ＠
ＮＬＢｾ＠
1
I
tunnel
ｾ＠
Figure 17 Section through building linked by underground tunnel
building A
2, Vestibules vented to outdoors or pressurized
building B
2
ＢｾＬＮ＠
2
I
grade
ｾＧｉ｜＠
ｉｾＢ＠
1
Figure 18 Section through buildings joined at firewall
Measure N satisfies NBC Article 3.2.6.7. for
connected buildings.
87
pays
Section 2 Measures for
Life Safety in High
Buildings
Measure A
Buildings
Fully
ｓｰｲｩｮｫｬ･ｾ､＠
General
The steps described in this Measure amount to an
adequate smoke control measure, satisfying the
requirements of NBC Sentence 3.2.6.4.0). Reliance is
placed on the full sprinkler installation to limit fire
spread and hence the generation of smoke.
Some additional protection of exit stairs is afforded by the provision of an opening to the outdoors at the foot of the stairshaft. In cold weather,
when stack action is likely to be most significant, this
measure may give a general increase in air pressure
in the stairshaft, thus restricting entry of smoke.
In this Measure is included the requirement that
elevator shafts and service shafts should not be
continuous from above to below grade, except when
vestibules are provided at elevator doors in below
grade storeys.
Where Measure A is adopted and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that the occupants of
the fire floor will walk downstairs to the street floor
or to a safe intermediate floor area. Occupants of
other floors may remain where they are until advised
to evacuate by the person operating the central alarm
and control facility.
Measure A
(1 ) The requirements of NBC Sentence
3.2.6.4.0) may be met by incorporating the requirements in Sentences (2) to (8).
(2) A stairway serving storeys above the
lowest exit level has a vent or door to the outdoors at
or near the bottom of the stairshaft, as described in
Sentence (4).
(3) A stairway serving floors below the lowest
exit level
88
(a)
has a vent or door to the outdoors at or
near the top of the stairshaft that has an
openable area of not less than 0.1 m 2 for
each storey served by the stairway, less
0.01 m 2 for each weathers tripped door and
0.02 m 2 for each non-weatherstripped door
opening into the stairs haft,
(b) is enclosed in a shaft that does not pass
through the floor above the lowest exit
level and is separate from a shaft that
contains a stairway serving upper storeys,
or is enclosed in a shaft that contains a
stairway serving upper storeys, but is
separated from that stairway at the lowest
exit level by a fire separation having a fireresistance rating not less than that required for the shaft enclosure, and
(c) is provided with equipment capable of
maintaining a flow of air introduced at or
near the bottom of the stairshaft, at a rate
equal to 0.47 m 3 / s for each storey served
by the stairway.
(4) A stairshaft required to be vented to the
outdoors by Sentence (2) or by other provisions in
this Chapter is provided with a vent or door that
(a) has an openable area of 0.05 m 2 for every
door between the stairshaft and a floor
area, but not less than 1.8 m 2,
(b) opens directly to the outdoors or into a
vestibule or exit corridor that has a
similar opening to the outdoors, and
(c) has a door or closure that is openable
manually and can remain in this open
position during a fire emergency.
(5) Any elevator shaft that passes through the
floor above the lowest exit storey does not penetrate
the floor of the storey immediately below the lowest
exit storey, except where there is a vestibule between
the shaft and each floor area below grade as described in Sentence (3) of Measure D.
(6) A vertical service space, other than an
elevator shaft, that passes through the floor above the
lowest exit storey, is provided with a tight-fitting
noncombustible seal or fire stop at the floor level of
the storey immediately below that storey, except
where the vertical service space is vented to the
outdoors at the top as described in Sentence (0) of
Measure F.
pays
(7) A supply of air required by Sentence (3) is
carried in ducts as described in Sentence (13) of
Measure F.
(8) The central control facility required by
NBC Article 3.2.6.12. is provided with additional
controls capable of
(a) opening closures to vents in shafts that
may be required by Sentence (6),
(b) stopping air handling systems as required
by NBC Sentence 3.2.6.4.(1), and
(c) initiating the mechanical air supply to
stairshafts as may be required in Sentence
permanentopening
corridor
or balcony
(3).
Measures Band C Open Corridor
Access to Stairs and Elevators
General
Measures Band C can be applied to a building
where habitable floor areas are approached along
access ways open to the outdoors.
Each corridor that provides access to stairs or
elevators is permanently open to the outside as
shown in Figures 2 and 19. The situation is illustrated by the pressure characteristic diagram shown
in Figure 20. Air flow through openings that may
exist in floors is likely to be more pronounced than
with other smoke control methods because of the
reduction in the influence of vertical shafts, so it is
desirable that openings through the floor-ceiling
assembly be minimized. This should not, however,
present an immediate smoke problem except on the
floor directly above the floor where a fire occurs.
Measure C is the same as Measure Bt except that
no steps are taken to limit smoke movement into
upper storeys through vertical service spaces or
shafts in Measure C.
Where shafts enclosing plumbing and electrical
services penetrate floor spaces and a decision has
been made to use Measure B for control of smoke
movement, these shafts should be sealed at least at
every fifth storey at a horizontal fire separation and
at the floor immediately below the lowest exit storey
or have vents to the outside at the top. In the latter
case there is still some possibility that smoke may
pass into the uppermost floor because the air pressures in these floor areas are in the same range as the
Section through
corridors or balconies
Figure 19
Illustration of Measures Band C designs
floor
eas
r
I
t
1
Section through building
showing air flow
Figure 20
outSide air pressure
PreSSure characteristics
Lower
Higher
Pressure characteristics in a Measure B design
outside pressures. It is therefore important that any
leakage areas in the enclosing walls between floor
areas and shaft be kept to a minimum.
In order to avoid creation of pressures that may
interfere with the opening of doors to stairshafts and
elevator shafts t it is recommended that the building
heating system be so designed that temperatures in
89
heated stairshafts and elevator shafts be not more
than 12°C above outside air temperature.
Where Measure B is adopted and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that the occupants of
the fire floor will walk down stairs to a safe floor
area. In buildings more than 36 m high, occupants of
other floors may remain until advised to evacuate by
the person operating the central alarm and control
facility.
Where Measure C is adopted, and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that occupants of all
floors will walk down stairs to the street floor or to a
safe intermediate floor area.
Measure B (including restriction on the
movement of smoke from floor to floor)
(1) The requirements of Sentences 0), (2) and
(3) of NBC Article 3.2.6.2. may be met by incorporating the requirements in Sentences (2) to (9).
(2) All public corridors leading to the required exit stairs and elevators for fire fighters from
every floor area on a floor above the lowest exit
storey are provided with permanent openings to the
outdoors that
(a) are distributed along the length of the
corridor,
(b) have the top of the opening not more than
250 mm below the ceiling of the corridor,
and
(c) have an aggregate open area that is not
less than 10 per cent of the floor area of the
corridor or 1 m 2, whichever is greater.
(3) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(4) Any elevator shaft that passes through the
floor above the lowest exit storey does not penetrate
the floor of the storey immediately below the lowest
exit storey except where there is a vestibule between
the elevator door or doors and each floor area below
grade as described in Sentence (3) of Measure D.
90
(5) A vertical service space, other than an
elevator shaft, within a heated floor area is provided
with
(a)
tight-fitting noncombustible fire stops
located at the level of the floor immediately below the lowest exit storey and at
the level of certain other floors that are fire
separations provided the space between
fire stops is not more than five storeys, or
(b)
a vent to the outdoors as described in
Sentence (0) of Measure F.
(6) Except for exhaust from kitchens, washrooms and bathrooms in dwelling units, air moving
fans are stopped during a fire emergency in an air
handling system that serves more than two storeys.
(7) Supply, return and exhaust ducts more
than 130 cm 2 in cross-sectional area at the point of
entry to a vertical service space in an air handling
system that is required to shut down by the provisions of Sentence (6) are provided with dampers that
will close when the air moving fans are stopped.
(8) Where a supply of air is required by the
provisions of Sentence (3), it is carried in ducts as
described in Sentence (3) of Measure F.
(9) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) stopping the air handling systems and
closing dampers as required by Sentences
(6) and (7),
(b) opening closures to vents in vertical
service spaces where required by Sentence
(5), and
(c) initiating the air supply to stairshafts as
may be required by Sentence (3).
Measure C (no restriction on the movement of smoke from floor to floor)
(1) The requirements of Sentences (2) and (3)
of NBC Article 3.2.6.2. may be met by incorporating
the requirements of Sentences (2) to (7).
(2) The public corridors leading to the required exit stairs and elevators for fire fighters from
every floor area on a floor above the storey on which
egress directly to the outdoors occurs are provided
with permanent openings to the outdoors that
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(a)
are distributed along the length of the
corridor,
(b) have the top of the opening not more than
250 mm below the ceiling of the corridor,
and
(c) have an aggregate open area that is not
less than 10 per cent of the floor area of the
corridor or 1 m 2, whichever is greater.
(3) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(4) Any elevator shaft that contains an
elevator for fire fighters and passes through the floor
above the lowest exit storey does not penetrate the
floor of the storey immediately below the lowest exit
storey except where there is a vestibule between the
elevator door or doors and each floor area below
grade as described in Sentence (3) of Measure D.
(5) Except for exhaust from kitchens, washrooms and bathrooms in dwelling units, air moving
fans are stopped during a fire emergency in an air
handling system that serves more than two storeys.
(6) Where a supply of air is required by
Sentence (3), it is carried in ducts described in
Sentence (13) of Measure F.
(7) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) stopping the air handling systems as
required by Sentence (5), and
(b) initiating the air supply to stairshafts as
may be required by Sentence (3).
Measures D and E Protected
Vestibule Access to Stairshafts and
Elevator Shafts
General
In Measures D and E movement of smoke through
stairshafts and elevator shafts is limited by the
provision of vestibules that are either open to the
outdoors during a fire emergency or have outdoor air
injected into them. Stairshafts are further protected
by opening a door to the outdoors at the bottom of
the shaft. Where vestibules are protected by the
injection of outdoor air, the elevator shaft is provided
with a large opening to the outdoors at the bottom.
Where NBC Article 3.2.6.2. requires the movement
of smoke into floor areas to be limited, service shafts
are either sealed at intervals or provided with an
opening to the outdoors at the top of the shaft as
described in Measure B. A typical plan of a building
in which this method of smoke control is appropriate
is shown in Figure 4.
Measure E is the same as Measure D, except that
no measures are taken to limit movement of smoke
into upper storeys in Measure E.
Where a vestibule has a vent or opening to the
outdoors that is much larger than the leakage area
around doors between the vestibule and other parts
of the building, the air pressure in the vestibule will
be approximately equal to the outdoor pressure at the
same level. This is illustrated in Figure 7. In cold
weather in storeys below the neutral pressure plane,
air pressure in the vestibule will be substantially
higher than that in the floor area. Air will tend to
flow from the vestibule into the floor area. In upper
storeys the air pressure in the vestibules will be less
than that in the floor area, and air will flow from the
floor area to the vestibule. The vent or opening at the
foot of the stairshaft referred to above has the effect
of increasing pressure in the shaft, so that it approaches outdoor air pressure at ground level (see
Figure 21). On upper storeys the pressure in the
stairshaft will be higher than that in the vestibules,
and smoke that may enter the vestibules will not pass
into the stairshaft.
In warm weather when outdoor air may be as
warm or warmer than that inside a building, the
stack effect is likely to be minimal. In these circumstances, the major problem is expansion of the hot
gases on the fire floor. This will tend to force air
around doors into the vestibule. The large vent
opening, however, will create a situation where the
greater proportion of the air entering the vestibule
will pass to the outdoors and a much smaller quantity may enter the shafts. The effect of wind is
variable and difficult to predict. In warm weather
the effect may be to protect vestibules on one side of
the building and to allow smoke to enter those on the
other side.
Where air is injected into vestibules, the pressure
characteristics in cold weather are likely to be as
shown in Figure 22. The rates of air injection should
91
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floor
outside air pressure &
pressure in vestibules
pressure
in top
vented
service
shaft
Section through building showing
airflow
Elevator and stair shafts are shown
separate because access from floor
area to shaft is by a vestibule open
to exterior
Pressure characteristics
Lower
Higher
Figure 21 Pressure characteristics in a Measure 0 building
with vented vestibules
(f)
ro
ｾ＠
ro
(5
0
;;:::
(f)
<ll
ｾ＠ u;
<ll
>
ro
<ll
<ll
ro ＠ｾ
(5 u;
0
;;:::
<ll
>
pressure In
vestibules
Section through building showing
airflow
Pressure characteristics
Lower
Higher
Figure 22 Pressure characteristics in a Measure 0 building
having air injected into vestibules
be sufficient to keep the pressures in the vestibules a
little higher than the pressure in the shaft. This limits
the possibility of movement of smoke into the
vestibules from the floor areas. In cold weather vents
at the bottom of the stairshafts and elevator shafts
provide additional protection.
doors where Measure 0 (but not Measure E) requires
that movement of smoke into upper floors be limited.
However, some smoke may pass from top vented
service shafts into the top floor or floors, because air
pressures at the top of the shafts and in the floor area
of the top storey are approximately equal.
Service shafts that will not be used in a fire emergency are provided with vents at the top to the out-
Stack action and the operation of smoke control
measures may provide pressures that will interfere
92
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p
with the normal operation of certain doors. Where a
vestibule is vented to the outdoors, this may apply to
any door between a vestibule and an elevator shaft
that is farther above or below the mid-height of a
building than the height given by Graph 8 in Appendix A of this Chapter and to any door between a
vestibule and a stairshaft that is farther above grade
than the height given by Graph 8.
Where a vestibule is pressurized, this may apply
to any door between a vestibule and a floor space
that is farther above grade than the height shown in
Graph 8.
As an alternative to the provision of a mechanical
air supply for a vestibule to an elevator shaft, as
described in Sentence (5) of Measure 0, the mechanical air supply can be introduced directly into the
shaft as described in Sentence (4) of Measure F
provided there are no open vents to the elevator shaft
as described in Sentence (9) of Measure O.
Where a mechanical air supply is required by
Sentence (5) of Measure 0 and Sentence (4) of
Measure E, it may be desirable to heat the air supply
and to provide two air intakes in separate locations
on the building face as discussed in the general
provisions to Measures F and G.
Where Measure 0 is adopted, and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that the occupants of
the fire floor will walk down stairs to the street floor
or to a safe intermediate floor area. Occupants of
other floors may remain until advised to evacuate by
the person operating the central alarm and control
facility.
Where Measure E is adopted, and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that occupants of all
floors will walk down stairs to the street floor or to a
safe intermediate floor area.
Measure D (including restriction on the
movement of smoke from floor to floor)
(1) The requirements of Sentences (1), (2) and
(3) of NBC Article 3.2.6.2. may be met by incorporating the requirements of Sentences (2) to (17).
(2) Between each floor area and each stair
shaft or elevator shaft that contains an elevator for
fire fighters, a vestibule is provided as described in
Sentence (3).
(3) Where a vestibule is required by Sentence
(2) or by other provisions of this document
(a) a fire separation is provided between a
public corridor and the vestibule that has
a fire-resistance rating of not less than
45 min,
(b) a fire separation is provided between a
floor area, other than the corridor described in Clause (a), and the vestibule
that has a fire-resistance rating not less
than that required for an exit in NBC
Article 3.4.4.1.,
(c) a fire separation is provided between a
stair or elevator enclosure and the vestibule that has a fire-resistance rating not
less than that required for an exit in NBC
Article 3.4.4.1., and
(d) a door in the fire separation described in
Clauses (a), (b) or (c) (except for an elevator door) is provided with a self-closing
device as required by NBC Subsection
3.1.8., and opens in the direction of travel
from the floor area to the exit stairway.
(4) On each floor any vestibule that has a
door to an exit stair may also have a door to an
elevator for fire fighters, but two exit stairs may not
open onto the same vestibule.
(5) Each vestibule described in Sentence (2)
that provides access to a stairshaft or an elevator
shaft
(a) has a vent opening to the outdoors that
has an opening area not less than 0.1 m 2
for each door that opens onto the vestibule, but not less than 0.4 m 2, or
(b) has equipment capable of providing for a
vestibule to a stairshaft or an elevator
shaft a mechanical air supply not less than
that obtained from Graph 3 in Appendix
A of this Chapter.
(6) The vent to each vestibule referred to in
Clause (5)(a) may be provided with a closure that is
openable manually, and in a building that is more
than 36 m high, it can be opened from the central
control facility as provided in Sentence (17).
93
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(7) A stairway serving storeys above the
lowest exit level is vented to the outdoors at the
bottom of the stairshaft as described in Sentence (4)
of Measure A.
(8) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(9) Each elevator shaft protected by a vestibule having a mechanical air supply as described in
Clause (5)(b) has a vent at or near the bottom of the
shaft, opening directly to the outdoors or into a
vestibule or corridor that has a similar opening to the
outdoors, having an openable area not less than
0.02 m 2 for every door into the shaft, other than doors
at street floor level.
(10) The vent at the bottom of an elevator shaft
referred to in Sentence (9) may be provided with a
closure which is openable manually and is designed
to remain open during a fire emergency.
(11 ) A vertical service space other than an
elevator shaft is provided with
(a) a tight-fitting noncombustible fire stop at
the level of the floor immediately below
the lowest exit storey, and at the level of
certain other floors that are fire separations, provided the space between fire
stops is not more than five storeys, or
(b) a vent to the outdoors as described in
Sentence (10) of Measure F.
(12) Except as provided in Sentence (13), an
elevator shaft other than a shaft that contains an
elevator for fire fighters is protected against entry of
smoke by a vestibule as described in Sentence (5).
(13) The provisions in Sentence (12) are waived
for an elevator shaft that serves floor areas below the
lowest exit storey and does not penetrate the floor
immediately above that storey.
(14) Except for air moving fans supplying
vestibules as provided in Clause (S)(b), and except
for exhaust from kitchens, washrooms and bathrooms in dwelling units, air moving fans are stopped
during a fire emergency in an air handling system
that serves more than two storeys.
(15) In an air handling system that is required
to shut down by the provisions of Sentence (14),
supply, return and exhaust ducts more than 130
in cross-sectional area at the point of entry to a verti94
cal service space are provided at that point with
dampers that will close when air moving fans are
stopped.
(16) Where a supply of air is required by the
provisions of Sentences (5) and (8), it is carried in
ducts described in Sentence (13) of Measure F.
(17) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) opening closures to vents to the outdoors
in vestibules on all floors as required by
Sentence (6), and in elevator shafts as
required by Sentence (9),
(b) stopping air handling systems and closing
dampers in ducts as required by Sentences
(14) and (15),
(c) initiating the mechanical air supply to vestibules required by Clause (5)(b), and
(d) opening closures to vents in vertical
service spaces where required by Sentence
(11).
Measure E (no restriction on the movement of smoke from floor to floor)
(1) The requirements of Sentences (2) and (3)
of NBC Article 3.2.6.2. may be met by incorporating
the requirements in Sentences (2) to (13).
(2) Between each floor area and each stairshaft or each elevator shaft that contains an elevator
for fire fighters, a vestibule is provided as described
in Sentence (3) of Measure D.
(3) On each floor any vestibule that has a
door to an exit stairshaft may also have a door to an
elevator for fire fighters, but two exit stairs may not
open onto the same vestibule.
(4) Each vestibule described in Sentence (2)
that provides access to a stairshaft or an elevator
shaft
(a)
has a vent opening to the outdoors that
has an openable area of not less than
0.1 m 2 for each door that opens onto the
vestibule but not less than 0.4 m 2, or
(b)
has equipment capable of providing for a
vestibule to a stairshaft or an elevator
shaft a mechanical air supply not less than
that obtained from Graph 3 in Appendix
A of this Chapter.
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(5) The vent to each vestibule referred to in
Clause (4)(a) is provided with a closure that is
openable manually, and in a building that is more
than 36 m high can be opened from the central
control facility as provided in Sentence (13).
(6) A stairway serving storeys above the
lowest exit level is vented to the outdoors at the
bottom of the stairshaft as described in Sentence (4)
of Measure A.
(7) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(8) Each elevator shaft protected by a vestibule having a mechanical air supply as described in
Clause (4)(b) has a vent at or near the bottom of the
shaft opening directly to the outdoors, or into a
vestibule or corridor that has a similar opening to the
outdoors, having an openable area not less than
0.02 m 2 for every door into the shaft other than doors
at street floor level.
(9) The vent at the bottom of an elevator shaft
referred to in Sentence (8) may be provided with a
closure that is open able manually and is designed to
remain open during a fire emergency.
(10) Any elevator shaft that contains an
elevator for fire fighters and passes through the floor
above the lowest exit storey does not penetrate the
floor of the storey immediately below the lowest exit
storey except where there is a vestibule between the
elevator door or doors and each floor area below
grade as described in Sentence (3) of Measure O.
(11) Except for air moving fans supplying
vestibules as provided in Clause (4)(b), and except
for exhaust from kitchens, washrooms and bathrooms in dwelling units, air moving fans are stopped
during a fire emergency in an air handling system
that serves more than two storeys.
(12) Where a supply of air is required by the
provisions of Sentences (4) and (7), it is carried in
ducts described in Sentence (13) of Measure F.
(13) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) opening closures to vents to the outdoors
in vestibules on all floors as required in
Sentence (5),
(b)
(d
stopping air handling systems as required
by Sentence (11), and
initiating the mechanical air supply to vestibules as required by Clause (4)(b).
Measures F and G Pressurized
Stairshafts and Elevator Shafts
General
Measures F and G are suitable for use in buildings
that have central cores containing elevator shafts and
stairshafts and in buildings that have a spine corridor. The objective is to inject sufficient air from
outdoors to provide air pressures in stairshafts and in
one or more protected elevator shafts that will be at
least equal to the outdoor air pressure at ground
level. Protected elevator shafts may, in addition, be
provided with vestibules on each floor in order to
reduce the effect of the large leakage areas around
elevator doors, which may otherwise require injection of excessive quantities of air in order to achieve
the desired pressurization. An opening to the
outdoors at the bottom of each stairshaft is required
in conjunction with air injection in order to maintain
the desired pressure conditions, though some doors
on upper floors may be held open for a time, and to
provide for dilution of smoke that may enter the
stairshaft. A typical plan of a building where this
method of smoke control is appropriate is shown in
Figure 6.
Measure G is the same as Measure F, except that
no provisions are made in Measure G to limit movement of smoke into upper floors by way of service
shafts and unprotected elevator shafts.
Where NBC Article 3.2.6.2. requires that movement of smoke into floor areas be limited, service
shafts, other than elevator shafts, are either sealed at
intervals or vented to the outdoors at the top, as
described in the general provisions of Measures B
and C. This system is, however, likely to be more
efficient than that achieved by Measure 0, because
injection of air into some shafts has the effect of
increasing the air pressure in all floor areas. This is
illustrated in Figure 23, where the pressure in the
floor area of the top storey is greater than that at the
top of the vented shaft.
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floor
floor
ｾＡ｡ｲ･ｳ＠
Table 1
Maximum Height of Building
Not Requiring Airflow Modulation
floor
__ｾ｡ｲ･ｳ＠
l-+-1-
-ｾｉＭＱ＠
-""
-
_Ql
ｬＭＫｌｾ＠
Minimum January Design
Temperature, °C
Maximum Height of
Building, m
1------1
-7
1------1
-18
E 1-------1
-29
-40
94
70
55
46
2
1------1
..t-+-i ｾ＠
ｾ＠
r---+--I
ｾ＠
Section through building
showing air flow
Figure 23
Pressure characteristics
Lower
Higher
Pressure characteristics in a Measure F building
Treads and landings in a stairshaft present an
obstacle to free flow of air. Where air is injected only
at the top of a stairshaft, there is likely to be a pressure gradient between the top and the bottom of the
stairshaft. This may produce pressure differences of
sufficient magnitude to interfere with the opening of
doors into the stairshaft in the upper part of the
building. This is discussed more fully in Appendix B
of this Chapter.
Stack action and the operation of smoke control
measures may produce pressures across certain doors
that will interfere with their normal operation. These
pressures may affect any door between a floor space
and a stairshaft or an elevator vestibule that is farther
above grade than the height shown in Graph 8 in
A ppendix A of this Chapter.
In order to avoid excessive pressures across doors
when outdoor temperatures are appreciably above
the January design temperatures, it is recommended
that the air flow into elevator shafts in buildings
employing Measures F or G be reduced, but not to
less than that obtained by the factor Fs = 5.59
according to the proportion of the air flow referred to
in Sentence (4) of Measure F and Sentence (4) of
Measure G. The flow reduction factors are shown in
Graph 6 in Appendix A of this Chapter.
The limits are such that no modulation is required
for a building whose maximum height is not more
than the value in Column 2 of Table 1, provided the
January design temperature is not less than the
corresponding value in Column 1.
96
Column 1
Heating of the air supply referred to in Sentences
(2) and (4) of Measure F or Sentences (2) and (4) of
Measure G may be necessary, since to maintain the
efficiency of the smoke control measures the
temperature of the incoming air should be not less
than the mean of indoor and outdoor temperatures at
the time. To avoid damage to water systems, the
temperature of air entering critical locations should
be not less than O°C. To maintain tolerable conditions
for occupants, the temperature of air entering
occupied spaces should be not less than 10°C.
Where a mechanical air supply is specified in
Sentences (2) and (4) of Measure F or Sentences (2)
and (4) of Measure G, the air should be drawn from
at least two remote locations, each on a different face
of the building. Each air intake should be provided
with a damper that will close on a signal from a
smoke detector in the duct following 30 s exposure to
smoke or other products of combustion. The damper
should have a manual override to reopen it when the
smoke condition that caused it to close has cleared.
Where Measure F is adopted, and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that the occupants of
the fire floor will walk down stairs to the street floor
or to a safe intermediate floor area. Occupants of
other floors may remain until advised to evacuate by
the person operating the central alarm and control
facility.
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...
Where Measure G is adopted, and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that occupants of all
floors will walk down stairs to the street floor.
Measure F (including restriction on the
movement of smoke from floor to floor)
(1) The requirements of Sentences (1), (2) and
(3) of NBC Article 3.2.6.2. may be met by incorporating the requirements in Sentences (2) to (14).
(2) A stairshaft serving storeys above the
lowest exit level has
(a) a vent or door to the outdoors at or near
the lowest exit level of the stairshaft, as
described in Sentence (4) of Measure A,
except that the vent or door will open
when the air supply referred to in Clause
(b) is initiated, and
(b) equipment capable of providing to the
shaft a mechanical air supply of not less
than 4.72 m 3 /s plus 0.094 m 3 /s for every
door opening into the stairshaft.
(3) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(4) An elevator shaft that contains an elevator
for fire fighters is provided with equipment capable
of maintaining a flow of air to the shaft that is not
less than that obtained from Graph 4 in Appendix A
of this Chapter.
(5) Where an elevator shaft referred to in
Sentence (4) is provided with a vestibule on every
floor, the vestibule enclosure conforms to Sentence
(3) of Measure D.
(6) Any elevator shaft that contains an
elevator for fire fighters and passes through the floor
above the lowest exit storey does not penetrate the
floor of the storey immediately below the lowest exit
storey, except where each floor area below the lowest
exit storey is provided with a vent to the outdoors
that
(a) has a net area of not less than 0.2 m 2 for
every 1 000 m 2 of floor area,
(b) will remain open during a fire emergency,
and
(c)
may be incorporated in the conventional
exhaust duct system serving storeys below
grade.
(7) A vertical service space, other than an
elevator shaft, is provided with
(a) a tight-fitting fire stop at the level of the
floor immediately below the lowest exit
storey and at the level of certain other
floors that are fire separations provided
the space between fire stops is not more
than five storeys, or
(b) a vent to the outdoors as described in
Sentence (10).
(8) Except as provided in Sentence (9), an
elevator shaft, other than a shaft that contains an
elevator for fire fighters, is pressurized as described
in Sentence (4).
(9) The provisions of Sentence (8) are waived
for an elevator shaft that serves floor areas below the
lowest exit storey and does not penetrate the floor
immediately above that storey.
(10) Where a vent to the outdoors is required
by Sentence (7) or other provisions of this document,
the vent
(a) if it is a vertical service space in a building
in which other shafts are not mechanically
pressurized, has an openable area that is
not less than that obtained from Graph 1
in Appendix A of this Chapter, or if it is in
a building in which other shafts are
mechanically pressurized, has an openable
area that is not less than that obtained
from Graph 2 in Appendix A of this
Chapter,
(b) if it is in a shaft serving floor areas above
the lowest exit storey, is located at or near
the top of the shaft where the top of the
shaft is above the mid-height of the
building, or at or near the foot of the shaft
at or near the exit level where the top of
the shaft is below the mid-height of the
building,
(c) if it is in a shaft serving floor areas below
the lowest exit storey, is located at or near
the top of the shaft, and
(d) if it is provided with a closure, is openable
both manually and on a signal from a
smoke detector located at or near the top
97
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of the shaft and by a control device located
at the central alarm and control facility
referred to in NBC Article 3.2.6.12.
(11) Except for air moving fans supplying
stairs and elevators as provided in Sentences (2), (3)
and (4) and, except for exhaust from kitchens,
washrooms and bathrooms in dwelling units, air
moving fans in an air handling system that serves
more than two storeys are capable of being stopped
as provided in Sentence (14).
(12) In an air handling system that is required
to shut down by the provisions of Sentence (11),
supply, return and exhaust ducts more than 130 cm2
in cross-sectional area at the point of entry into a
vertical service space are provided with dampers that
will close when air moving fans are stopped.
(13) Where a supply of air is required by the
provisions of Sentences (2), (3) or (4) or by other
provisions of this document, the duct system is
installed in a service space conforming to NBC
Section 3.5 or is otherwise protected against the effect
of fire from the point of fresh air intake to the shaft or
to the storey that contains the protected floor area,
vestibule or area of refuge that is required to be so
protected.
(14) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) stopping air handling systems and closing
dampers in ducts required in Sentences
(11), (12) and (13),
(b) initiating the mechanical air supply to
stairshafts and elevator shafts required in
Sentences (2), (3) and (4), and
(c) opening closures to vents in vertical
spaces where required in Sentence (7).
Measure G (no restriction on the movement of smoke from floor to floor)
(1) The requirements of Sentences (2) and (3)
of NBC Article 3.2.6.2. may be met by incorporating
the requirements in Sentences (2) to (9).
(2) A stairs haft serving storeys above the
lowest exit level has
(a) a vent or door to the outdoors at or near
the lowest exit level of the stairshaft
described in Sentence (4) of Measure A,
except that the vent or door will open
98
when the air supply referred to in Clause
(b) is initiated, and
(b) equipment capable of providing to the
stairshaft a mechanical air supply of not
less than 4.72 m 3 /s, plus 0.094 m 3 /s for
every door opening into the stairshaft.
(3) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(4) An elevator shaft that contains an elevator
for fire fighters is provided with equipment capable
of maintaining a flow of air to the shaft that is not
less than that obtained from Graph 4 in Appendix A
of this Cha pter.
(5) Where an elevator shaft referred to in
Sentence (4) is provided with a vestibule on every
floor, the vestibule enclosure is as described in
Sentence (3) of Measure D.
(6) Any elevator shaft that contains an
elevator for fire fighters and passes through the floor
above the lowest exit storey does not penetrate the
floor of the storey immediately below the lowest exit
storey, except where each floor area below the lowest
exit storey is provided with a vent to the outdoors
that
(a) has a net area of at least 0.2 m 2 for every
1 000 m 2 of floor area,
(b) will remain open during a fire emergency,
and
(c) may be incorporated in the conventional
exhaust duct system serving storeys below
grade.
(7) Except for air moving fans supplying
stairshafts and elevator shafts as provided in Sentences (2), (3) and (4) and, except for exhaust from
kitchens, washrooms and bathrooms in dwelling
units, air moving fans in an air handling system that
serves more than two storeys are capable of being
stopped as provided in Sentence (9).
(8) Where a supply of air is required by
Sentences (2), (3) and (4)1 it is carried in ducts as
described in Sentence (13) of Measure F.
(9) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) stopping air handling systems as required
by Sentence (7), and
pays
(b)
initiating the mechanical air supply to
stairshafts and elevator shafts as required
by Sentences (2), (3) and (4).
Measure H
Buildings
Fully Pressurized
General
Measure H is appropriate for buildings having
central cores that contain stairshafts and elevator
shafts and windows that are not normally opened, as
shown in Figure 8. The air pressure in the whole
building is increased so that at grade level it is at
least equal to outdoor air pressure. When a vent to
the outdoors is provided on the fire floor by a window in an exterior wall, by an opening into a smoke
shaft as described in Section 3 or by the building
mechanical exhaust system if the building is sprinklered, the pressure in the floor area is reduced
substantially, as is shown in Figure 24. Air will then
flow from the shafts and other floor areas into the fire
floor. The combination of building pressurization
and venting of the fire floor provides that smoke will
not pass into other floor areas or shafts other than the
smoke shaft.
It is important that air be uniformly distributed
throughout the building. This may be achieved by
supplying the air through the conventional duct
system or through vertical shafts. A minimum
proportion of the air is required to be injected directly
floor
areas
air
pressure
effect of
Section through
building showing
airflow
Figure 24
Pressure characteristics
Lower
Higher
Pressure characteristics in a Measure H building
into stairshafts. This is designed to reduce the
possibility, particularly in warm weather, that a
substantial drop in pressure will occur in these shafts
when a door to the outdoors at grade is opened, with
the consequent danger that smoke will enter the
shafts.
Where venting is by smoke shafts, the air supply
to the floor on which fire occurs should be cut off by
closing the dampers on that floor in order not to
overload the smoke shaft.
The total air flow for building pressurization is
modulated relative to outdoor air temperature. This
is intended, in part, to limit the potential pressure
drop in stairshafts and elevator shafts referred to
above and, in part, to avoid excessive pressures
across doors to stairshafts and elevator shafts that
would interfere with their normal use.
This requirement for modulation of air flows
applies generally to higher buildings. The conditions
described in Sentence (3) of Measure H are such that
no modulation is required where the January design
temperature and the building height are as shown in
Table 1.
In Toronto, for example, where the January design
temperature is -18°C, no modulation of air flow
would be required for a building not more than 70 m
high.
This measure is not appropriate for a building
where windows may normally be held open. The air
flow requirements in Graph 5 in Appendix A of this
Chapter are based on an assumed air leakage
through the external walls that is appropriate to
modern air-conditioned buildings having reasonably
tight-fitting non-openable windows. If the leakage
area is other than that noted above, the air flow
requirement must be adjusted proportionately, as
described in the notes to Graph 5.
Stack action and the operation of smoke control
measures may produce pressures across certain doors
that will interfere with their normal operation. This
may apply to any door between a floor space and
stairshaft or an elevator shaft that is farther above
grade than the height shown in Graph 8 in Appendix
A of this Chapter.
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pays
Where a mechanical air supply is required by
Sentence (2) of Measure H, it may be desirable to heat
the air supply and to provide two air intakes in
separate locations on the building face, as discussed
in the general provisions to Measures F and G.
Where a floor area is subdivided by walls, provision should be made for a free air passage from any
part of the floor area to the vent or vents required by
Sentence (6) of Measure H. Such provisions for venting need not apply to public corridors or washrooms
that normally have a minimum of combustibles.
There should be no problem where vents are on
outside walls, and each room or space can be vented
directly to the outdoors. Where a smoke shaft is
used, however, a fire may occur in a space adjacent to
a stairshaft or elevator shaft which is separated by
partitions from the smoke shaft vent. The solution
may be to vent each space to the smoke shaft through
the ceiling plenum or to provide suitable openings in
the partitions. Where each room or space opens on to
a corridor leading to stairshafts and elevator shafts,
location of the smoke shaft vent in the corridor will
be effective in limiting movement of smoke to other
floors, but may also present problems to the fire
fighter, who may have to approach the fire through a
smoke-filled corridor.
Where Measure H is adopted, and a fire is detected by an au tomatic device or a manual pull
station is actuated, it is intended that a fire alarm will
sound on all floors simultaneously, and that the
occupants of tj,(> fire floor will walk down stairs to
the street floor or to a safe intermediate floor area.
Occupants of other floors may remain until advised
to evacuate by the person operating the central alarm
and control facility.
Measure H
(1) The requirements of Sentences (1), (2) and
(3) of NBC Article 3.2.6.2. may be met by incorporating the requirements in Sentences (2) to (9).
(2) The building air handling system is
designed and installed so that
(a) supply fans are capable of maintaining an
air flow into the building not less than that
obtained from Graph 5 in Appendix A of
this Chapter when the outdoor air temperature is equal to the January design
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temperature on a 2.5 per cent basis, and
a portion of the air flow referred to in
Clause (a) is directed into each stairshaft
in a quantity equal to 0.094 m 3 / s for every
weatherstripped door into the stairshaft
and 0.142 m 3 /s for every non-weatherstripped door into the stairshaft.
(3) Exit stairs shall discharge to the outdoors
through a vestibule described in Sentence (3) of
Measure 0 and be provided with a mechanical air
supply of not less than 0.094 m 3 / s per weatherstripped door and 0.189 m 3 /s per non-weatherstripped
door in the vestibule, except that the vestibule may
be a corridor, lobby or other space.
(4) When smoke control measures are initiated by the controls referred to in Sentence (9)
(a) all main return and exhaust fans are
stopped,
(b) supply fans provide the air flow into the
stairshafts described in Clause (2)(b), and
(c) supply fans maintain an air flow into the
building controlled in relation to outdoor
air temperature, so that the total air flow
into the building is substantially equal to
the proportion of the air flow referred to
in Clause (2)(a) shown in Graph 6 in Appendix A of this Chapter, but not less
than the air flow obtained when the factor
Fb equals 0.0025.
(5) All openings in external walls and roofs,
including vents to vertical service spaces other than
those referred to in Sentence (7), have closures that
will close as provided in Sentence (9).
(6) All return and exhaust ducts more than
130 cm2 in cross-sectional area at the point of entry to
a vertical service space are provided with dampers
that will close on the floor on which fire occurs as
required by Sentence (9), other than those covered by
Sentence (7).
(7) In order to achieve a reduction in air
pressure on the floor on which fire occurs relative to
that on other floors, means of venting each floor
space to the outdoors are provided as described in
Section 3.
(8) Where a supply of air is required by
Sentence (2), it is carried in ducts as described in
Sentence (13) of Measure F.
(b)
pays
pta
(9) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls capable of
(a) stopping main return and exhaust fans
and maintaining the air flow in the supply
systems as provided in Sentence (2),
(b) closing the closures and dampers required
in Sentences (5) and (6), and
(c) opening closures to the vent openings on
the fire floor as provided in Sentence (7).
Measures I and J Partially
Pressurized Buildings
General
Measures I and J are very similar to Measure H,
except that they may be applied to buildings where
windows may be open during normal use. They are
thus particularly suitable for controlling smoke
movement in residential buildings. Plans of typical
buildings where Measures I and J are appropriate are
shown in Figures 9 and 10. The central core, which
includes exit stairshafts, elevator shafts and public
corridors, is separated from the remainder of the
floor areas. It is important that the leakage area of
walls around the core be less than that of the exterior
walls of the building.
Measure Jis the same as Measure I, except that no
provision is made in Measure J to limit smoke movement into upper floors by way of vertical shafts and
ducts that are outside the core.
leakage areas exceed those given in the notes to
Graph 5, the air flow should be increased in direct
proportion.
Stack action and the operation of smoke control
measures may produce pressures across certain doors
that will interfere with their normal operation. This
may apply to any door between a suite and a corridor that swings into the corridor and is farther above
grade than the height shown in Graph 8 in Appendix
A of this Chapter.
Within a suite that is subdivided by partitions, the
space that includes the vent to the outdoors described in Sentence (4) of Measure I should be in the
same space as the door to the public corridor or
linked to it by a leakage area of not less than 0.05 m 2 •
Where a mechanical air supply is required by
Sentence (2) of Measure I and Sentence (2) of Measure J, it may be desirable to heat the air supply and to
provide two air intakes in separate locations on the
building face as discussed in the general provisions
to Measures F and G.
Where Measure I is adopted and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that the occupants of
the fire floor will walk down stairs to the street floor
or to a safe intermediate floor area. Occupants of
other floors may remain until advised to evacuate by
the person operating the central alarm and control
facility.
Air is injected into the core so that the air pressure
in the core at the ground floor is equal to exterior air
pressure at the same leveL Provision of a vent to the
outdoors in the fire suite will cause air to flow from
ad jacent parts of the building into the fire suite. This
is the only method, apart from Measure B, that
enables smoke to be confined to the fire suite.
Where Measure J is adopted and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that a fire alarm will sound on
all floors simultaneously, and that occupants of all
floors will walk down stairs to the street floor or to a
safe intermediate floor area.
Where movement of smoke from floor to floor
outside the central core is to be limited as in Measure
I (but not J), all vertical service shafts, other than
elevator shafts, penetrating floor areas must be sealed
at intervals or vented to the outdoors at the top, as
discussed in the general requirements of Measure D.
Measure I (including restriction on the
movement of smoke from floor to floor)
(1) The requirements of Sentences (1), (2) and
(3) of NBC Article 3.2.6.2. may be met by incorporating the requirements in Sentences (2) to (10).
(2) The building air handling system is
designed and installed so that supply fans are
capable of maintaining an air flow into the space that
includes all required exit stairshafts, all shafts
The air flow requirements in Graph 5 in Appendix
A of this Chapter are based on the air leakage characteristics of typical corridor walls and doors. If the
101
pays
containing elevators for fire fighters and public
corridors, not less than that obtained from Graph 5
in Appendix A of this Chapter, when the outdoor air
temperature is equal to the January design temperature on a 2.5 per cent basis.
(3) Any vent at the top of a vertical service
shaft within the central core and all other openings
penetrating the space that includes the stairshafts,
elevator shafts and public corridors are provided at
the point of penetration with closures that will close
in the event of a fire, as provided in Sentence (10).
(4) Means of venting each fire compartment
to the outdoors are provided by
(a) an opening in an exterior walt such as an
openable window or panel, having an
openable area of not less than 0.4 m 2,
(b) an opening into a smoke shaft, as described in Section 3, operated by a smoke
detector, or
(c) an exhaust system, such as a kitchen or
washroom exhaust, that has an air flow to
the outdoors of not less than 0.189 m 3 / s
per fire compartment served, provided the
exhaust system is designed to function as
a smoke shaft and meets the relevant
requirements of Section 3.
(5) Where a closure is provided in an opening
referred to in Clauses (4)(a) or (b) it will open
(a) by operation of a fusible link, or
(b) on a signal from a smoke detector in the
room or suite.
(6) A vertical service space that is outside the
pressurized space referred to in Sentence (2) is
provided with
(a) a tight-fitting noncombustible seal or fire
stop
(D at the level of the floor immediately
below the storey in which egress
directly to the outdoors occurs, and
(ii) at the level of certain other floors
that are fire separations, provided
the space between fire stops is not
more than five storeys, or
(b) a vent to the outdoors as described in
Sentence (10) of Measure F.
(7) Except as otherwise provided in Sentences
(2) and (4), and except for exhaust from kitchens,
102
washrooms and bathrooms in dwelling units, air
moving fans are stopped during a fire emergency in
an air handling system that serves more than two
storeys.
(8) In an air handling system that is required
to shut down by Sentence (7), supply, return and
exhaust ducts more than 130 cm 2 in cross-sectional
area at the point of entry to a vertical service space
are provided with dampers that close when the air
moving fans are stopped.
(9) Where a supply of air is required by
Sentence (4), it is carried in ducts as described in
Sentence (13) of Measure F.
(10) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) stopping return and exhaust fans, closing
dampers in ducts and maintaining the air
flow in the supply system to the space that
includes stairshafts, elevator shafts and
corridors as provided in Sentences (2) and
(7),
(b)
(c)
causing dampers and closures in the
enclosing walls of the space that includes
stairshafts, elevator shafts and corridors to
close as required by Sentence (3),
opening closures to vents in vertical
service spaces where required by Sentence
(6),
(d)
(e)
opening closures in vents referred to in
Sentence (4), individually or in groups
limited to one floor at a time, and
initiating the air flow in the exhaust
system from any floor, where required by
Clause (4)(c).
Measure J (no restriction on the movement of smoke from floor to floor)
(1) The requirements of Sentences (2) and (3)
of NBC Article 3.2.6.2. may be met by incorporating
the requirements in Sentences (2) to (6).
(2) The building air handling system is
designed and installed so that supply fans are
capable of maintaining an air flow into the space that
includes all required exit stairshafts, all shafts
containing elevators for fire fighters and public
corridors, not less than that obtained from Graph 5 in
pays
Appendix A of this Chapter, when the outdoor air
temperature is equal to the January design temperature on a 2.5 per cent basis.
(3) Any vent at the top of a vertical service
shaft within the central core, and all other openings
penetrating the space that includes the stairshafts,
elevator shafts and public corridors, are provided at
the point of penetration with closures that will close
in the event of fire, as provided in Sentence (4).
(4) Except as otherwise provided in Sentence
(2), and except for exhaust fans from kitchens,
washrooms and bathrooms in dwelling units, air
moving fans are stopped during a fire emergency in
an air handling system that serves more than two
storeys.
(5) Where a supply of air is required by
Sentence (2), it is carried in ducts as described in
Sentence (13) in Measure F.
(6) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) stopping return and exhaust fans and
maintaining the air flow in the supply
system to the space that includes stairshafts, elevator shafts and corridors as
provided in Sentence (2), and
(b) causing dampers and closures in the
enclosing walls of the space that includes
stairshafts, elevator shafts and corridors to
close as required by Sentence (3).
Measure K
Buildings
Vertically Divided
General
In Measure K a degree of protection for occupants
is achieved by providing either a spatial separation
or a fire separation between two parts of the building
as shown in Figures 11 and 12. Under these conditions, except as subsequently noted, air pressures on
either side of the division will be symmetrical and
smoke should not pass from one side to the other.
Smoke from fire in one part of the building may be
expected to pass into the stairshafts, elevator shafts
and floor areas on the fire side, while the equivalent
spaces on the other side will remain smoke free.
Vestibules and bridges are provided as means of
access to refuge areas for occupants of floor areas in
the part of the building that is exposed to fire and
smoke.
Vestibules or bridges are either vented to the
outdoors or pressurized mechanically in order to
prevent their acting as paths for the transmission of
smoke. In vented vestibules below the neutral
pressure plane of the building, air will normally flow
from the vestibules to the floor areas and no smoke
should enter the vestibules. In vestibules above the
neutral pressure plane, air will flow from the floor
area to the vestibule and thence to the outdoors.
If a window breaks in the fire area, the pressure in
the fire area will be the same as that in the vestibule
and no smoke transfer should occur. Where vestibules are mechanically pressurized, the air flow will
always be from the vestibule to the floor areas on
either side, thus limiting the possibility of smoke
entering the vestibule.
Provision of an opening to the outdoors at the foot
of a stairshaft will increase the air pressure in the
shaft in winter and thus reduce the probability of
entry of smoke from a floor on which a fire occurs.
Where a dividing wall is used to separate the two
parts of a building (Figure 12), breakage of a window
in a fire compartment below the neutral pressure
plane can be undesirable. The pressure in the fire
compartment will increase to a level approximately
the same as exterior pressure, and this may cause
substantial smoke flow through the dividing wall
from the fire side to the other side of the building.
This consideration does not apply to a spatial separation as shown in Figure 11. Provisions have been
included to allow windows below the mid-height of
a building on the side away from a fire to be opened
manually in order to bring the pressure in that space
to the exterior pressure and to eliminate the pressure
difference across the dividing wall.
While the most efficient solution to the problem of
moving occupants to a place of safety is to have
bridges or connecting vestibules at each floor level,
the requirements in Measure K are that such bridges
or vestibules should be at intervals of not more than
five storeys, and in the case of residential buildings
more than 75 m high, the bridges or vestibules
should be on each storey. The approaches to the
103
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bridges or vestibules are by stairs and corridors
whose width is controlled by Sentences (6) and (7) of
Measure K. These provisions combine to enable all
occupants to reach a place of safety in about three
minutes.
Stack action and the operation of smoke control
measures may produce pressures across certain doors
that will interfere with their normal operation. This
may apply where a building has vestibules vented to
the outdoors
(a) at any door that swings into a vestibule
from a floor space farther below the midheight of the building than the distance
shown in Graph 8 in Appendix A of this
Chapter,
(b) at any door that swings out of a vestibule
from a floor space that is farther above the
mid-height of the building than the
distance shown in Graph 8 in Appendix A
of this Chapter,
(c) at any door between a floor space and an
elevator shaft that is farther above or
below the mid-height of the building than
the distance shown in Graph 8 in Appendix A of this Chapter,
(d) at any door between a floor space and a
stairshaft that is farther above grade than
the height shown in Graph 8 in Appendix
A of this Chapter.
In a building that has vestibules that are pressurized, pressures that may interfere with the normal
operation of doors may occur with any door between
a vestibule and a floor space where the rate of air
injection exceeds 0.165 m 3 / s for each weatherstripped door, or 0.33 m 3 / s for each door that is not
weathers tripped, and any door between a floor space
and an elevator shaft that is farther above or below
the mid-height of the building than the height shown
in Graph 8 in Appendix A of this Chapter.
Where a mechanical air supply is required by
Sentence (11) of Measure K, it may be desirable to
heat the air supply and to provide two air intakes in
separate locations on the building face as discussed
in the general provisions to Measures F and G.
Where Measure K is adopted and a fire is detected
by an automatic device or a manual pull station is
actuated in a smoke control region of the building, it
104
is intended that a fire alarm will sound on all floors
in that smoke control region, and that the occupants
on all floors will move through the dividing vestibules or bridges to the other smoke control region.
Measure K
(1) The requirements of Sentences (1), (2) and
(3) of NBC Article 3.2.6.2. may be met by incorporating the requirements of Sentences (2) to (17).
(2) The building is designed as
(a)
(b)
a structure divided into two smoke control
regions by a continuous vertical fire
separation that has a fire-resistance rating
not less than that required for a floor in
NBC Subsection 3.2.2., or
two or more smoke control regions separated by spatial separations that conform
to the provisions of NBC Subsection 3.2.3.
(3) Bridges or vestibules are provided at
intervals of not more than five storeys to permit
movement of occupants from one smoke control
region to the other, except that in the case of residential buildings more than 75 m high, the bridges or
vestibules are located on each storey.
(4) In each smoke control region referred to in
Sentence (2), there is not less than one exit stairshaft
and one elevator in a shaft that meets the requirements of NBC Article 3.2.6.9. and that is not common
to both smoke control regions.
(5) The floor area on either side of a bridge or
vestibule is of sufficient size to accommodate its own
normal population, plus the occupants of the one to
five storeys of the adjacent smoke control region
who may have to enter the floor area during a fire
emergency, assuming 0.5 m 2 per ambulatory person
and 1.5 m 2 per non-ambulatory person.
(6) The width of each bridge or vestibule and
each connecting corridor and door on the same
storey is sufficient to provide not less than 3.67 mm
of width for each person who may have to use these
passages to reach the floor area referred to in Sentence (5) from the adjacent smoke control region.
(7) The width of each stair or ramp that
provides access to a floor having a bridge or vestibule from intervening floors is sufficient to provide
not less than 5.5 mm of width for each person who
pays
may have to use the stair to reach the bridge or
vestibule referred to in Sentence (6).
(8) Between each bridge or vestibule and
public corridor is a fire separation that has a 45 min
fire-resistance rating.
(9) Between each bridge or vestibule and a
floor area other than the public corridor referred to in
Sentence (8), is a fire separation that has a fireresistance rating as required for exits in NBC Subsection 3.4.4.
(10) Each door opening into a bridge or
vestibule conforms to NBC Articles 3.4.6.9. and
3.4.6.10. and is suitably identified as an access to an
area of refuge.
(11 ) Each bridge or vestibule is provided with
(a) a vent opening to the outdoors that has an
open area not less than 1 m 2 and that may
be provided with a closure that is
openable manually, or
(b) a mechanical air supply not less than that
obtained from Graph 7 in Appendix A of
this Chapter that will be initiated as
provided in Sentence (17).
(12) Where the building is divided into two
smoke control regions by a fire separation as described in Clause (2)(a), each floor area below the
mid-height of each smoke control region is provided
with a vent opening to the outdoors that has an open
area of not less than 1.5 m 2 and that is normally
closed but can be opened manually.
(13) Each stairshaft is vented to the outdoors as
described in Sentence (4) of Measure A.
(14) Except as provided in Sentence (11), and
except for exhaust from kitchens, washrooms and
bathrooms in dwelling units, air moving fans are
stopped during a fire emergency in an air handling
system that serves more than two storeys.
(15) Floor areas below the lowest exit storey
are divided by a fire separation that has a fireresistance rating not less than that required in Clause
(2)(a) and is in a location corresponding to the fire or
spatial separations required for upper storeys.
Doorways protected by pressurized vestibules are
provided in the separations as described in Clause
(11)(b).
(16) Where a supply of air is required by
Sentences (11) and (15), it is carried in ducts as described in Sentence (13) of Measure F.
(17) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) closing doors in fire separations required
by Sentences (8), (9) and (15) between
floor areas and vestibules,
(b) initiating the mechanical air supply to the
vestibules where required by Clause
(11)(b) and Sentence (15), and
(c) stopping air handling systems where
required by Sentence (14).
Measure L Areas of Refuge
(smoke free areas)
General
Measure L is intended to provide refuge areas
which occupants may enter during a fire. It may be
used for buildings that have many openings between
floors so that it is impracticable to confine smoke to
one floor level.
This measure is basically the same as described in
Measure D, except that larger quantities of air must
be injected into each area of refuge than into a
comparable vestibule in order to maintain tolerable
conditions for the occupants. A typical floor plan is
shown in Figure 13. The area of refuge may include
normally occupied space in the building, and because
fire may occur in one of these spaces, provision is
made for alternative groups of areas of refuge.
Except in the case of Group C buildings more than
75 m high, areas of refuge may be provided on every
fifth floor if the access routes are made wide enough
to allow all occupants to reach the area of refuge
within three minutes (see Figure 14). Stairshafts and
elevators for fire fighters must be protected on
intermediate floors by vestibules or by pressurization
of the shafts.
Stack action and the operation of smoke control
measures may produce pressures across certain doors
that will interfere with their normal operation. This
may apply to any door between an area of refuge and
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pays
a floor space that is farther above grade than the
height shown in Graph 8 in Appendix A of this
Chapter.
Between every area of refuge and the floor space
the building should have a vent fitted with a selfclosing damper that will permit air to move from the
area of refuge to the floor space but not vice-versa. It
should have an openable area not less than 6 cm 2 for
every 0.005 m 3 / s of air injected into the area of
refuge in excess of that specified in Measure D for a
pressurized vestibule.
Where Measure L is adopted and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that an alarm will sound on
all floors simultaneously, and that occupants of all
floors will move to areas of refuge distributed
throughout the building and await instructions over
the voice communication system.
Where a mechanical air supply is required by
Sentence (9) of Measure L, it may be desirable to heat
the air supply and to provide two air intakes in
separate locations on the building face, as discussed
in the general provisions to Measures F and G.
Measure L
(1) The requirements of Sentences (1), (2) and
(3) of NBC Article 3.2.6.2. may be met by incorporate ing the requirements of Sentences (2) to (20).
(2) Two independent groups of areas of
refuge are distributed through the building so that
there is an area of refuge in each group at least at
every fifth storey, and each group is linked by a
common exit stair to the exterior at grade.
(3) On any floor area any area of refuge that
has a door to an exit stair may also have a door to a
elevator for fire fighters, but two exit stairs may not
open on to the same area of refuge if no other vertical
shaft is common to the two independent systems
described in Sentence (2).
(4) Each group of areas of refuge referred to
in Sentence (2) can accommodate all the occupants of
above grade storeys at the rate of 0.5 m 2 of floor area
per ambulatory person or 1.5 m 2 per non-ambulatory
person.
(5) The width of corridors and doors leading
to an area of refuge on the same storey is sufficient to
106
provide 3.67 mm of width for each person who Il1ay
have to use these passages to reach the area of refuge.
(6) The width of stairs or ramps leading to an
area of refuge from intervening floors is sufficient to
provide 5.5 mm of width for each person who may
have to use the stairs or ramps to reach the area of
refuge.
(7) Between each area of refuge and a public
corridor is a fire separation that has a 45 min fireresistance rating.
(8) Between each area of refuge and a floor
area other than the public corridor referred to in
Sentence (7), is a fire separation that has a fireresistance rating as required for exits in NBC Subsection 3.4.4.
(9) Each door opening into an area of refuge
conforms to the provisions for doors in NBC Article
3.4.6.10. and is suitably identified as an access to an
area of refuge.
(10) Each area of refuge is provided with a
mechanical air supply not less than that required for
a vestibule providing access to a stairshaft or an
elevator shaft in Clause (5)(b) of Measure D, and
obtained from Graph 3 in Appendix A of this Chapter, or not less than 0.002 m 3 / s for each occupant of
the area of refuge during a fire emergency, whichever is greater.
(11) Any door in an exit stairshaft or in a shaft
that contains an elevator for fire fighters that does not
open directly into an area of refuge is provided with
a pressurized vestibule as described in Sentence (5) of
Measure D, except where the stairshaft or elevator
shaft is pressurized as described in Sentences (2) and
(4) of Measure F.
(12) Except as provided in Sentence (11), an
elevator shaft that contains an elevator for fire
fighters is provided with a pressurized vestibule as
described in Sentences (2), (3) and (5) of Measure D
or is pressurized as described in Sentence (4) of
Measure F.
(13) Any elevator shaft that contains an
elevator for fire fighters or opens into an area of
refuge and passes through the floor above the lowest
exit storey does not penetrate the floor of the storey
immediately below the lowest exit storey, except
where there is a vestibule between the elevator door
pays
or doors and each floor area below grade as described in Sentence (3) of Measure D.
(14) A stairshaft serving storeys above the
lowest exit level is vented to the outdoors at or near
the bottom of the stairshaft as described in Sentence
(4) of Measure A.
(15) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(16) Each elevator shaft protected by a vestibule or area of refuge having a mechanical air supply
as described in Sentences (9) and (10) has a vent at or
near the bottom of the shaft opening directly to the
outdoors or into a vestibule or corridor that has a
similar opening to the outdoors having an openable
area not less than 0.023 m 2 for every door into the
shaft, other than doors at street floor level.
(17) The vent at the bottom of an elevator shaft
referred to in Sentence (16) may be provided with a
closure which is openable manually and is designed
to remain open during a fire emergency.
(18) Except for air moving fans serving areas of
refuge and vestibules as provided in Sentences (10),
(11) and (12), and except for exhaust from kitchens,
washrooms and bathrooms in dwelling units, air
moving fans are stopped during a fire emergency in
an air handling system that serves more than two
storeys.
(19) Where a supply of air is required by
Sentences (10), (11), (12) and (15), it is carried in ducts
as described in Sentence (14) of Measure F.
(20) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) closing doors in fire separations required
by Sentences (7) and (8) between floor
areas and areas of refuge or vestibules,
(b) stopping air handling systems as required
by Sentence (18),
(c) opening closures in vents to the outdoors
in elevator shafts that may be required by
Sentence (12), and
(d) initiating the mechanical air supply to the
areas of refuge, vestibules and shafts as
may be required by Sentences (10), (11),
(12) and (15).
Measure M Residential Buildings
with Balconies
General
In residential buildings the greater part of the
requirements for control of smoke movement are
waived where each suite has direct access to a
balcony. The protective features are limited to
stopping air handling systems, providing an opening
to the outdoors at the foot of stairshafts serving
upper floors and protection of stairshafts in storeys
below grade. A typical arrangement is shown in
Figure 16.
Where Measure M is adopted and a fire is detected
by an automatic device or a manual pull station is
actuated, it is intended that occupants on the fire
floor will evacuate if possible, and that occupants of
other floors may remain in their suites to await
instructions.
Measure M
(1) The requirements of NBC Sentence
3.2.6.6.(1) may be met by incorporating the requirements of Sentences (2) to (7).
(2) A stairshaft serving storeys above the
lowest exit level has a vent or door to the outdoors at
or near the bottom of the stairshaft, as described in
Sentence (4) of Measure A.
(3) A stairway serving storeys below the
lowest exit level is protected as described in Sentence
(3) of Measure A.
(4) Any elevator shaft that passes through the
floor above the lowest exit storey does not penetrate
the floor of the storey immediately below the lowest
exit storey, except where there is a vestibule between
the elevator door or doors and each floor area below
grade as described in Sentence (3) of Measure D.
(5) Except for exhaust from kitchens, washrooms and bathrooms in dwelling units, air moving
fans are stopped during a fire emergency in an air
handling system that serves more than two storeys.
(6) Where a supply of air is required by
Sentence (3), it is carried in ducts as described in
Sentence (13) of Measure F.
107
pays
(7) The central alarm and control facility
required by NBC Article 3.2.6.12. is provided with
additional controls that are capable of
(a) stopping air handling systems as required
by NBC Sentence 3.2.6.6.(1), and
(b) initiating the mechanical air supply to
stairshafts as may be required by Clause
(3)(c).
Measure N
Connected Buildings
General
The measures described here are intended to
prevent movement of smoke from one building to
another. They are of particular significance where
two buildings of unequal height are joined together.
The techniques suggested are the provision of a large
opening to the outdoors in a connecting vestibule so
that smoke entering through leakage areas around
doors will be vented to the outdoors, or pressurization to maintain a higher pressure in the vestibule
than in adjacent spaces as illustrated in Figures 17
and 18.
The requirements for protection of openings are
described in terms appropriate to a doorway. Any
other openings should be avoided if possible. Where
they occur, they should be protected by the provision
of an air lock that gives the same standard of protection as the vestibule described in Sentence (3).
Measure N
(1) The requirement of NBC Sentence 3.2.6.7.
that limits movement of smoke from one building to
another may be met by incorporating in the link
between the buildings the requirements in Sentences
(2) and (3).
(2) Between one building and the other is a
firewall as described in NBC Subsection 3.1.10.
(3) Any opening in the firewall is protected
against passage of smoke by a vestibule described in
Sentence (3) of Measure D and has
(a) a vent to the outdoors that has a net area
of 10(O.023d + 0.00045a) m 2, where d is the
number of doors having a perimeter not
more than 6 m that open into the vestibule, or if the perimeter of doors exceeds
6 m, the value of d is increased in direct
108
(b)
proportion to the increase in the perimeter, and a is the area in square metres of
enclosing walls, floors and ceilings whose
outer face is in contact with the outside
air, except that where the outer face of a
wall is in contact with the ground or fill, it
is assumed that there is no leakage
through that portion, and the value of a is
assumed to be zero, or
equipment capable of maintaining a
supply of air into the vestibule sufficient
to ensure that the air pressure in the
vestibule when the doors are closed is
higher by at least 12 Pa than that in
adjacent floor areas when the outdoor
temperature is equal to the January design
temperature on a 2.5 per cent basis.
Section 3 Venting of
Floor Areas
(1) The requirements of NBC Sentence
3.2.6.10.(1) and of Measures H or I are met by incorporating in a floor area windows or wall panels as
described in Sentence (2), by smoke shafts as described in Sentences (3) to (7) or by the use of building exhaust systems as described in Sentence (8).
(2) Where windows or wall panels are used
for venting as required in Sentence (1), they must
(a) be uniformly distributed along the exterior wall of each storey,
(b) have a total area of not less than one per
cent of the exterior wall area of each
storey,
(c) be readily openable from the interior
without the use of wrenches or keys,
(d) be readily identified from the interior, and
from the exterior where they are accessible
to fire fighters, and
(e) be designed so that when opened they will
not endanger persons outside the building
during a fire.
(3) Where one or more smoke shafts or
vertical service spaces are used for venting to meet
the requirements of Sentence (1), they must
(a) have an opening or openings into each
storey with an aggregate area not less than
I
pays
that obtained from Table 2 for the height
of the shaft, the area of the largest floor
area served by the smoke shaft and the
leakage characteristics of the shaft wall
and dampers obtained from Tables 3
and 4,
(b) have an aggregate unobstructed crosssectional area equal to that provided in
Clause (a), and
(c) be designed to comply with the requirements of Sentence (4).
(4) Each smoke shaft or vertical service space
described in Sentence (3) must
(a) be separated from the remainder of the
building by a fire separation that has a
fire-resistance rating at least equal to that
required for the floor assembly through
which it passes, or be designed as a
chimney conforming to Part 6 of the
National Building Code of Canada 1990,
except that flue liners need not be provided,
(b) have an opening to the outdoors at the top
that has an area not less than the crosssectional area of the shaft which may be
protected from the weather,
(c) terminate not less than 900 mm above the
roof surface where it penetrates the roof,
and
(d) contain no combustible material, fuel lines
or services that are required for use in an
emergency.
(5) Each opening required by Clause (3)(a)
must be located so that the top of the opening is not
more than 250 mm below the ceiling, except that the
opening may be above the ceiling if the ceiling freely
allows passage of air and the opening into the
smokeshaft is provided with a closure that
(a) has a fire-protection rating conforming to
NBC Sentence 3.1.8.4.(2), except that the
temperature on the unexposed face of the
closure is not more than 250°C after 30
min during the fire test and there is no
combustible material within the distances
described in Table 5, and except that paint
or tightly-adhering paper covering not
more than 1 mm thick shall be exempted
from these requirements when applied to
a noncombustible backing,
(b) can be opened from a remote location such
as a stairshaft, the storey immediately
below or the central alarm and control
facility, and
(c) must not open automatically on any floor,
other than the fire floor, when smoke or
hot gases pass through the shaft.
(6) Closures for openings described in Clause
4(b) are to be openable from the outside and will
open automatically on a signal from a smoke detector
in the shaft, by operation of the fire alarm system and
when a closure required in Sentence (5) opens.
(7) A smoke shaft opening referred to in
Sentence (2) or (3) that is less than 1070 mm above
the floor must conform to NBC Article 3.3.1.17.
(8) In a sprinklered building the air handling
system may be used for smoke venting provided
(a) the system can maintain an exhaust to the
outdoors at the rate of six air changes per
hour from any floor area, and
(b) emergency power to the fans required by
(a) is provided as described in NBC
Article 3.2.7.9.
(9) Where a damper is required by Sentence
(5), the leakage area between damper components
and between damper and frame must be not more
than 3 per cent of the openable area of the damper.
109
pays
110
Table 2
Minimum Size of Vent Openings into Smoke Shafts from Each Floor Area, m2 (1,3)
Building Height, m
Floor
Leakage
146
110
183
220
37
73
Area, m2 Area,%(2)
18
0.16
0.18
0.19
0.10
0.11
0.13
0.15
200
0.32
0.36
0.37
0.39
0.25
0.29
0.22
500
0.53
0.67
0.71
0.59
0.63
0.43
0.48
1 000
1.22
1.29
1.16
1.01
1.08
0.83
0.91
2 000
1.67
1.75
1.82
1.21
1.46
1.55
1.33
3 000
a
2.02
2.15
2.35
2.25
1.62
1.75
1.90
4 000
2.74
2.86
2.17
2.34
2.46
2.63
2.01
5 000
2.91
3.10
3.23
3.37
2.57
2.76
2.39
6 000
0.12
0.19
0.22
0.27
0.35
0.10
0.15
200
0.40
0.49
0.69
0.57
0.27
0.35
0.23
500
1.01
1.19
0.71
0.72
0.86
0.44
0.50
1 000
1.81
2.10
1.15
1.56
1.33
0.97
2 000
0.85
1
1.26
1.42
1.67
1.91
2.23
2.56
2.97
3 000
2.18
2.49
2.37
3.79
1.88
3.28
4 000
1.66
4.60
2.32
2.69
3.05
3.51
3.99
2.07
5 000
4.14
4.68
5.37
2.47
2.76
3.18
3.59
6 000
1.28
0.24
0.13
0.18
0.37
0.61
200
0.10
1.13
2.10
0.52
0.24
0.29
0.39
0.75
500
3.27
0.72
0.94
1.30
1.90
0.46
0.55
1 000
5.36
1.73
1.34
2.32
3.28
0.88
1.05
2 000
1.31
2.47
3.29
4.58
7.28
1.95
2
1.53
3 000
2.01
3.20
4.23
9.12
1.73
2.55
5.83
4 000
2.15
5.15
7.05 10.90
3.92
2.49
3.13
5 000
4.63
2.57
3.73
6.07
8.26 12.65
2.96
6 000
0.11
0.14
0.21
0.37
0.88
2.06
200
1.58
9.00
0.76
0.31
0.47
0.25
500
11.99
1.33
2.60
0.47
0.59
0.86
1 000
1.12
1.60
2.41
4.47
17.46
0.91
2 000
2.31
5.21
22.48
1.64
1.35
3.43
3 000
3
2.17
4.43
7.91
27.29
1.79
3.02
4 000
3.71
2.22
2.68
5.42
9.55
31.95
5 000
4.40
11.18
36.47
2.65
3.20
6.39
6 000
24.83
0.11
0.15
0.28
0.70
200
29.18
0.25
0.34
0.58
1.33
500
1.06
2.27
36.07
1 000
0.49
0.63
1.21
1.97
3.99
48.56
0.95
2 000
1.41
2.84
60.15
4
1.78
6.63
3 000
71.15
2.34
3.70
7.22
1.86
4 000
81.81
2.21
2.90
4.55
8.79
5 000
3.46
5.40
10.33
90.05
2.75
6 000
0.11
0.16
0.36
3.33
200
0.28
0.36
0.76
5.09
500
1.37
7.67
0.50
0.69
1 000
1.31
2.54
12.35
0.99
2 000
16.75
1.46
1.94
3.65
3 000
5
4.75
20.99
1.92
2.55
4 000
25.11
2.40
3.16
5.84
5 000
29.11
3.74
6.92
2.87
6 000
4
7
8
Column 1
5
6
9
2
3
256
0.20
0.41
0.75
1.34
1.90
2.44
2.88
3.47
0.43
0.83
1.43
2.48
3.47
4.40
5.32
6.20
4.60
6.11
8.29
12.14
15.63
19.97
22.15
25.39
293
0.22
0.43
0.77
1.39
1.97
2.53
3.07
3.58
0.55
1.04
1.73
2.95
4.08
5.16
6.21
7.23
89.57
94.50
102.11
116.80
130.83
144.03
157.05
169.29
10
11
pays
...
Notes to Table 2:
(1) The minimum size of a vent opening into a smoke shaft is
obtained from Table 2 and is dependant on the floor area and
total leakage area of the smoke shaft walls and dampers.
This total leakage area may be estimated by adding the
leakage areas for the shaft wall obtained from Table 3 and for
the dampered openings obtained from Table 4 provided the
cross-sectional area of the smoke shaft, the opening into the
Table 3
Leakage Area of Smoke Shaft Wall
Leakage Area as a Per Cent
Wall Construction
of Wall Area
0.5
Monolithic concrete
1.5
Masonry wall unplastered
Masonry wall plastered
0.5
1.0
Gypsum board on steel studs
r---2
Column 1
Table 4
Leakage Area of Dampered Openings in Smoke Shaft
Leakage Area as a Per Cent
Type of Damper (1)
of Damper Area (2,3)
2.5
Curtain fire damper
Single-blade fire damper
3.5
4.5
Multi-blade fire damper
Column 1
2
(2)
(3)
shaft and the opening to the outdoors at the top of the shaft
are equal.
Leakage area is the total of the leakage area of smoke shaft
wall obtained from Table 3 and the leakage area of dampered opening in smoke shafts obtained from Table 4.
The size of the vent opening refers to the free or unobstructed area of the opening.
Table 5
Minimum Distance from Damper to Combustible Material
Area of Damper (1) Minimum Distance Minimum Distance
m2
in Front of or
to the Sides or
Above Damper, m Below Damper, m
0.20
0.5
0.35
1.0
0.50
0.25
1.5
0.60
0.30
2.0
0.70
0.35
2.5 (2)
0.80
0.40
I
2
Column 1
3
Notes to Table 5:
(1) For damper areas between those given in Table 5, interpolation may be used to determine the appropriate distances,
For damper areas greater than 2.5 m2, the minimum distance
in front of or above the damper shall be one half of the
square root of the damper area, and the minimum distance to
the sides or below the damper shall be one quarter of the
square root of the damper area.
Notes to Table 4:
For descriptions of dampers refer to NBC Article 3.1.8.9.
(2) Values include allowance for 0.5 per cent leakage between
frame and wall construction.
(3) These leakage data contemplate clearances applicable to
'fire dampers which have been tested in accordance with
CAN4-S112-M82, "Standard Method of Fire Test of FireDamper Assemblies."
(1)
111
pays
Appendix A to Chapter 3
Graphs for Applying Smoke Control Measures
100
100
90
a
c
u
ｑＩｾ＠
Q..c
III
'<-0)
a
ｾ＠
III III
0)ｾ＠
III
III C
70
ｾｃｊＩ＠
III 0)
C CJ)
a
,
a
E U
ｾ＠
C
0)
Cii
0)ｾ＠
III
50
ｾＲ＠
III C
60
50
.ou
III 0)
C CJ)
0)
,
Q.CJ)
40
a
::J
Ｎｾ＠
20
ｾ＠
C
40
ｾ＠
E U
30
10
30
20
10
0
0
50
100
150
0
200
250
300
0
Height of shaft, m
Graph 1 Vent to a vertical service space where no other shaft
in the building is pressurized
Notes to Graphs 1 and 2:
(1) Curve A applies to a vertical service space that is
enclosed by unplastered unit masonry or by
plaster and steel stud construction with all
openings in the shaft sealed to the degree
required by Articles 3.1.9.2. to 3.1.9.4. of the NBC
1990.
(2) Curve B applies to a vertical service space that is
enclosed by monolithic concrete or by plastered
unit masonry with all openings in the shaft
sealed tightly to minimize air leakage.
112
III
aIII
60
70
a
>
::J
Ｎｾ＠
C,<0)
.ou
ｑＮｾ＠
80
Q..c
c'<0) a
0)
u
0)
ｑＩｾ＠
ｾｃｊＩ＠
ｾＲ＠
90
80
0)
>
a
c
50
100
150
200
250
300
Height of shaft, m
Graph 2 Vent to a vertical service space where other shafts in
the building are pressurized
A shaft having a vent that is 100 per cent of the
cross-sectional area of the shaft is acceptable for
buildings up to 1.5 times the height shown by
the appropriate curve in Graphs 1 and 2.
(4) The total leakage area, based on measurements
arrived at in typical high buildings, is assumed
to be 0.025 m 2 for every 10m2 of shaft wall area
in the case of Curve A and 0.015 m 2 for every
10m2 of shaft wall area in the case of Curve B.
(3)
I
pays
....
ｾＭ
0.25
__Ｍｾ
__
0.20
LL""
c5
13
rn
LL
0.15
0.10 ｾＭ＠
o
50
100
150
200
250
300
350
Height of building, m
Graph 3 Factor for mechanical air supply to a vestibule
Notes to Graph 3:
(1)
The air supply to each vestibule in cubic metres
per second equals
F3d + 0.071e + 0.094s
where
F3 is a factor obtained from Graph 3,
d
the number of doors having a perimeter
not more than 6 m between each vestibule
and a floor area,
e = the number of doors having a perimeter
not more than 6 m between each vestibule
and an elevator shaft, and
the number of doors having a perimeter
s
not more than 6 m between each vestibule
and a stairshaft.
The quantity uF3d + 0.071e + 0.094s" represents
the total leakage from the vestibule.
(2)
(3)
(4)
(5)
If the perimeter of a door exceeds 6 m, the
value of d, e or s must be increased in direct
proportion to the increase in the perimeter.
A double leaf door is counted as two doors in
this formula.
A door provided with tight-fitting
weatherstripping is counted as one half of a
door.
The height of the building is the number of
metres between the roof and the floor level of
the lowest basement floor.
113
pays
16
14
January design temperature
12
10
v
LL
c5
t5
til
LL
ｯｾＭ＠
o
350
Height of shaft, m
Graph 4 Factor for air supply to an elevator shaft
Notes to Graph 4:
(1)
The air supply to each elevator shaft in cubic
metres per second equals
F/O.023d4 + 0.0014a 4)
where
F4 is the factor obtained from Graph 4
d 4 total number of doors having a perimeter
not more than 6 m that open into the
elevator shaft, and
a 4 = area of enclosing walls of the shaft in
square metres.
The expression "O.023d 4+ O.0014a/, represents
the total leakage area in the walls of the shaft.
(2) If the perimeter of a door exceeds 6 m, the
value of d 4 must be increased in direct proportion to the increase in the perimeter.
114
(3)
(4)
(5)
(6)
A double leaf door is counted as two doors in
this formula.
A door provided with tight-fitting weatherstripping is counted as one half of a door.
If the enclosing walls of the shaft are of monolithic concrete or of unit masonry plastered on
one side, the value of a 4 may be halved.
If an elevator shaft is provided with vestibules
on each floor, the enclosing walls considered in
this formula may be taken as including those of
the vestibules if it leads to an economy in air
supply requirements. In this case d 4 above
refers to doors between the vestibules and the
floor areas and doors between the elevator
shaft and the vestibules do not enter into the
calculation.
p ll..................................................................................................
ｾ｣＠
..
pays
ｾ＠
0.007
January design temperature
0.006
0.005
ｵＮｾ＠
<5
0.004
t)
(\l
u..
0.003
0.002
0.001
0
0
50
100
150
200
250
300
Height of building. m
Graph 5
(4)
Factor for air supply for building pressurization
(5)
Notes to Graph 5:
(1)
If Measure H is used, the air supply delivered
to the whole building in cubic metres per
second equals
(2)
(3)
where
is a factor obtained from Graph 5, and
as
area of all exterior wall surfaces of the
building in square metres measured
between ground level and underside of
the roof.
(Where the outer face of a wall is in direct
contact with the ground or fill, it is assumed
that there is no leakage through that portion,
and the value of as is assumed to be zero.)
Graph 5 is based on an air leakage rate of
0.003 m 31s per square metre of exterior wall at
a pressure difference of 75 Pa, based on the
measured leakage rate in high buildings
having fixed windows and curtain wall panels.
This is equivalent to a leakage area in exterior
walls of 0.045 m 2 per 100 m 2 of wall area. If the
leakage area in a building differs significantly
from this, the air supply should be adjusted in
direct proportion,
(6)
(7)
(8)
(9)
The height of building is measured
between the underside of the roof
and the floor level of the lowest
basement floor,
If Measure I or J is used, the air supply delivered to the space that includes stairshafts,
elevator shafts and corridors in cubic metres
per second equals
FS(a 6 + 51d6 )
where
is a factor obtained from Graph 5 that is not
less than 0.0025,
a 6 = area in square metres of the walls enclosing the space that includes stairshafts,
elevator shafts and associated corridors
on all floors, and
d 6 total number of doors having a perimeter
not more than 6 m in the wall area
described in a 6 ,
If the enclosing walls described above are of
monolithic concrete or of unit masonry plastered on one side, the value of a6 may be
halved.
If the perimeter of a door exceeds 6 m, the
value of d 6 must be increased in direct proportion to the increase in the perimeter,
A double leaf door is counted as two doors in
this formula.
A door provided with tight-fitting weatherstripping is counted as a one half of a door.
115
pays
1.0
0.8
January design
temperature
0
ｾ＠
t3
0.6
c
0
t5:::J
"0
ｾ＠
ｾ＠
0
0.4
u:
0.2
-40
-30
-20
-10
10
20
30
Outdoor temperature, °C
Notes to Graph 7:
Graph 6 Flow reduction factors
(1)
2.0 ｾＭｲＧ＠
J!2
E
1 .5
ｾ＠
:::J
..0
ｾ＠
(2)
Q)
>
..c
u
m
1.0
.8
(3)
0.5
(4)
ｯｾＭ＠
o
50
100
150
200
250
Height of building, m
Graph 7 Air supply to vestibule in a vertically divided building
116
300
350
(5)
Curve A shows the air supply to
each vestibule in cubic metres per
second for a vestibule that has four
doors (or two double doors), each
door having a perimeter of not
more than 6 m, between the
vestibule and the floor areas on
either side of the building.
Curve B shows the air supply to
each vestibule in cubic metres per
second for a vestibule that has two
single doors, each door having a
perimeter of not more than 6 m,
between the vestibule and the floor
areas on either side of the building.
If the perimeter of a door exceeds
6 m, the air supply must be increased in direct proportion to the
increase in the perimeter.
If the doors are provided with tightfitting weatherstripping, the air
supply may be halved.
The height of building is the distance between the roof and the floor
level of the lowest basement floor.
L
pays
75 ｾＭｲ＠
60
E
.E 45
OJ
'0:;
I
30
15 ｾＭ
-50
-45
-40
-35
-30
- 25
-20
- 15
10
-5
January design temperature, °C
Graph 8 Height of the shaft relative to grade, or the neutral
pressure plane at which pressure across a door may exceed
95 Pa
117
pays
Appendix B to Chapter 3
Assumptions Used in Developing
Fire Safety Measures
The objectives of the measures for fire safety in
high buildings are
(a) to provide for the safety of the occupants of a
building, either by maintaining the tenability of
the occupied floor spaces during the period of
a fire emergency or by making it possible for
occupants to move to a place of safety,
(b) to maintain tenable conditions in which
occupants may remain in exit stairs leading
from floor spaces to the outdoors, and
(c) to maintain tenable conditions in elevators that
can be used to transport fire fighters and their
equipment from the street floor to the floor
immediately below the fire floor.
It is assumed that the fire fighters will use one of
the protected stairshafts referred to in (b) to walk up
to the fire floor from the floor below.
The first of these objectives may be met by the
evacuation of all occupants to the outdoors in from
seven to ten minutes, by the movement of occupants
to safe areas within the building in from three to five
minutes (as in Measures C, E, G,], K, Land M) or by
maintaining the tenability of all floor areas except
those on the fire floor and the floor above the fire
floor (as in Measures A, B, 0, F, H and I).
The requirements in the National Building Code
covering wid ths of exits and travel distances to exits
make it possible for occupants of a floor on which a
fire occurs to leave that floor within one or two
minutes provided their escape route is not cut off by
the fire.
The objectives of the measures are to maintain
certain spaces substantially smoke free for a significant period of time during a fire emergency, and
hence some criterion of tenability is called for. The
criterion for long term tenability is that a space shall
not include more than one per cent by volume of the
contaminated atmosphere from the fire region. The
criterion of tenability is based on visibility and
carbon monoxide concentration.
118
Mechanisms of Smoke Movement in
Buildings
Movement of a smoky atmosphere within a
building is not significantly different from that of a
normal atmosphere at the same temperature. The
principal constituent of both atmospheres is nitrogen.
The fact that the concentrations of other component
gases will differ and that a smoky atmosphere will
contain particulate matter will not influence its
overall density to an extent that will significantly
affect its movement. The mechanisms to be discussed do, therefore, relate to the movement of a
smoky atmosphere as well as a normal atmosphere.
Air Circulating Systems
An obvious mechanism for the dispersal of smoke
within a building is the recirculating air handling
system. Assuming that the system has been competently designed, the approximate extent of the
recirculation under any particular circumstances is
known, and hence the build-up in any area of contamination can be predicted.
Effect of Wind
Exterior winds create pressure differentials within
buildings, which lead to internal air movement,
principally horizontal. Some upward movement also
results, however, from the non-uniformity of the
wind profile up the side of a building. In addition, if
one side of the building is facing the wind, only that
face will be subjected to a positive pressure, the
remainder being subjected to negative pressure.
Expansion
Another smoke movement mechanism, which is of
considerable significance during the early stages of
any fire that is not well vented to the outdoors, is the
expansion process associated with heating. The
leakage characteristics of virtually any building are
such that the rate of temperature rise occurring in the
fire region cannot create pressure differentials greater
pays
....
than about 250 Pa (gauge). Instead, the volume of
the atmosphere increases linearly with absolute
temperature. During the development of a fire in a
compartment, absolute temperature may be expected
to triple, and the volume of gas will increase by
approximately the same factor. At least two-thirds of
the original atmosphere in the fire region will,
therefore, be displaced by this mechanism.
warm
air
cold
air
neutral
Generation of gases as a result of combustion has
also been considered. The volume created by this
phenomenon cannot, however, exceed 20 per cent of
the original volume, and is not likely to be significant
compared to expansion due to temperature rise.
Stack Effect
Whenever a temperature differential exists between the interior and exterior of an enclosure, a
phenomenon known as stack or chimney effect
prevails. Figure B-1 illustrates the case where the
interior temperature is higher than the exterior, and
there is an inflow of cold air at low levels and a
corresponding outflow at high levels.
This effect can result from building heating and
from temperature differentials created by the fire
itself and is particularly important in Canadian
buildings because of the cold winter conditions. The
pressure differentials generated by stack effect can be
calculated by considering the densities of the internal
and external atmospheres.
Figure B-1 represents a simplified model in which
air flows in at a low level and out at a high level,
while there is an intermediate level where there is no
pressure differential between interior and exterior.
This level is referred to as lithe neutral pressure
plane." Taking the pressure at the neutral plane as
Po, the pressures at the lower or upper openings can
be derived, for they are associated with the weights
of the columns of gas above them.
The resulting expression for the pressure
difference across the lower opening is
where
op = pressure difference,
hl is defIned in Figure B-1,
To = absolute outdoor temperature,
h,
I
L==J>
Figure B·1
e
Pe
g
Stack action
difference between indoor and
outdoor temperature,
= density of indoor air, and
acceleration due to gravity.
Substituting H (h 1 + h) will give the total of the
pressure head (the sum of the pressure differentials
across the upper and lower openings) generated by
stack effect.
Importance of Mechanisms Responsible
for Smoke Movement
Expansion due to heating of the atmosphere in a
fire compartment is largely a transient phenomenon
occurring at the development stage of a fire. Twothirds of the atmosphere of the fire region is likely to
be displaced and, if the region were not vented to the
exterior, there could be a significant movement of
smoke laden atmosphere to other parts of the building. Dispersed evenly throughout the building, and
taking into account leakage to outdoors, this displaced atmosphere could render untenable a space
equal to about 50 times that of the fire region.
Pressures Due to Stack Effect
In discussing the steady state conditions responsible for smoke movement, total pressure heads
generated may be compared. These pressure heads
are tabulated in Table B-1 together with the flow rates
that they will create beneath a typical door having a
119
pays
Table 8·1
Magnitudes of Pressures
Developed by Thermal and Wind Effects
Height of
Flow
Heated Compartment, m
Wind
Beneath
BOO°C
Pressure
Speed Door with Gap
50°C
above
Head,Pa
km/h 900 x 12.5 mm
above
ambient
m3/s
ambient
I (i.e,. on fire)
2.9
10.3
23
0.045
25
0.064
5.B
20.6
50
33
0.100
125
14.5
51.6
52
29.1
0.142
103.3
73
250
104 I
0.201
5B.2
206.4
500
4
Column 1
2
5
3
free space of 900 mm x 12.5 mm beneath it. In
Columns 2 and 3, the total head given by stack action
resulting from a fire in a single storey is also given by
stack action associated with building heating during
cold weather in a building three to four storeys high.
Assuming that a building is compartmented, fire
other than one in a shaft should be confined to a
single storey. The total pressure head generated by
the fire is thus not likely to exceed about 25 Pa. As
buildings are generally heated in their entirety, stack
effect associated with building heating can give a
total head significantly more than 25 Pa if the building is more than about four storeys high. Thus
combating stack action associated with building
heating in high buildings is likely to pose more of a
problem than combating stack action directly associated with a fire. In high buildings emphasis should
be placed on the building heating rather than the fire
stack action problem.
Effect of Wind
Column 4 of Table B-1 indicates that pressures
resulting from winds can be substantial. As mentioned earlier, the greater part of the resulting airflow
is horizontal. This does not create as great a hazard
as vertical movement via the shafts in a building. An
upward flow does exist, however, and its effect is
virtually identical to that of stack action associated
with building heating. Combating the latter will,
therefore, take account of the more hazardous
influence of winds.
120
Contribution of Air Handling Systems
The effect of recirculating air handling systems is
not shown in Table B-1, but it is substantial and hence
it must be considered when smoke control techniques
are being devised for buildings including such
systems.
Significance of Smoke Movement
Mechanisms
Given the considerations just discussed, the most
significant smoke movement mechanisms to be
combated are
(1)
operating recirculating air-handling
systems,
(2)
the expansion process occurring during
the initial stages of a fire, and
(3)
stack action associated with building
heating.
Techniques for Avoiding Widespread
Smoke Contamination
Techniques for avoiding widespread smoke
contamination in a high building can be divided into
the following categories:
(1) Avoidance of any significant fire. The
first approach in this category is to exclude or limit
combustible materials from a building. Calculations
of air movement due to stack effect have indicated
that the destruction by fire of very small quantities of
combustible material can produce enough smoke to
produce untenable conditions in upper floors and
vertical shafts of a high building. Limits on the use
of smoke producing materials are thus unlikely to be
adequate as a sole means of smoke control. Automatic extinguishment of a fire can also be considered
as an approach to limiting smoke generation provided the quantity of combustibles destroyed is held
within strict limits.
(2) Compartmentation. Where a floor area is
divided into a number of fire compartments, the
potential size of a fire will be limited to the contents
of one compartment. In addition there will be, in
some circumstances, dilution of smoke moving from
the fire compartment to other floors.
Where the fire occurs below the neutral plane, in
cold weather the path of smoke travel may be along a
corridor to stairshafts and elevator shafts. In this
pays
case the smoke in the corridor will be diluted by
clean air coming from other compartments. In an
ideal situation (uniform compartments, no expansion
and no wind), dilution of the smoke laden air will be
in proportion to the number of compartments.
Breaking of a window in the fire compartment will,
however, increase the pressure in that space and will
reduce the effect of dilution.
Where smoke travel occurs through a vertical shaft
from a compartment involved in fire to higher
compartments, the level of contamination will not be
related to the number of units on one floor, but will
likely be restricted to units on other floors that are
ad jacent to the vertical shaft.
The result of compartmentation is, therefore, likely
to be beneficial, but does not eliminate the need for
smoke control measures.
(3) Location of shafts outside the building
envelope. The vertical transfer of smoke to the
upper storeys of a building from fire on a lower
storey occurs largely by the vertical shafts in the
building rather than through the floors, about 95 per
cent or more in the case of a typical20-storey building. Separation of the shafts from the building would
thus largely solve the problem. This approach
constitutes one of the suggested methods of smoke
control.
(4) Dilution. Dilution by a factor of about 100
of the smoke gases issuing from a fire region will
provide a tenable atmosphere. This feature could
form the basis of a smoke control method, air being
injected into the building at appropriate rates at those
locations where smoke is being discharged from the
fire region into adjacent parts of the building. When
cold weather conditions are considered, however,
dilution alone is not likely to be very practical. In
general, it would be better if the injection of air were
directed to modifying the pressure pattern within a
building in order to limit any undesirable movement
of smoke.
Dilution as a means of reducing smoke contamination should, nevertheless, be considered as an
important secondary factor governing a designer's
choice of smoke control method. Its importance is in
dispersing contamination that might develop as a
result of delay in implementing smoke control
measures, or of other occurrences such as the opening of a number of doors that might interfere with the
operation of a smoke control measure. The amount
of air required to dilute a contaminated atmosphere
to a tenable level can be calculated approximately. If
no mixing were to occur between the contaminated
and the clean air, and the contaminated air were to
move out ahead of the clean air, one volume of the
clean air injected into a compartment would prod uce
a smoke free atmosphere. In practice, however, some
mixing does occur. If perfect mixing is assumed in a
compartment that has reached a level of contamination equivalent to that of the fire compartment, and
no more smoke is entering, the amount of clean air
needed to create the one per cent tenable atmosphere
discussed would be five times the volume of the
compartment. If, however, we are considering a
compartment isolated from the fire compartment by
a fire separation and self closing doors, it is more reasonable to assume that the level of contamination
likely to occur is about one-fifth of that in the fire
compartment. In these circumstances, injection of
three volumes of clean air would be sufficient to
produce a tenable atmosphere. If clean air is injected
at the rate of one volume every two minutes, the atmosphere in the compartment would be satisfactory
in about six minutes.
These figures are based on the expression
c coe at
where
Co = initial concentration of contaminant,
c
final concentration of contaminant,
a
rate of diluent air flow in number of
air changes per minute,
time in minutes between occurrence
of initial and final concentration, and
e
2.718.
Based on this calculation, assuming perfect mixing
of the contaminated air and the diluent air,
c/ Co = 0.368 after injection of one volume of
clean air,
0.135 after injection of two volumes
of clean air,
0.050 after injection of three volumes
of clean air,
0.018 after injection of four volumes
of clean air, and
121
pays
0.007 after injection of five volumes
of clean air.
(5) Adjustment of pressure differential
distribution. This category of smoke control technique involves modification of the pressure pattern
within the building. The pressure distribution within
a building is illustrated by the pressure characteristic
diagrams in Figure B-2. The graphs represent in an
exaggerated manner, the pressure differences between floor areas, shafts and exterior at the same
height above ground. The pressure difference shown
amounts to little more than 500 Pa, whereas the total
pressures involved are about 100 kPa. The graphs do
relate pressure to heights, and thus cannot be used to
determine pressure difference between one floor and
another at a different height. Given any set of
characteristics as in Figure B-2, the important feature
is that, during cold weather, air flow from one region
to another at the same level will be towards the
region that is at a lower pressure. In the typical
building whose characteristics are illustrated, smoke
generated at a low level will flow into shafts, up
through the shafts and out into floor spaces at the
higher levels.
Shafts provide the major paths for the spread of
smoke within a building, so one should note the
effect of venting on their characteristics. Figure B-3
shows the characteristics of a simple heated shaft
under three different venting arrangements, the
second and third (Figures B-3(b) and B-3(c» having
obvious advantages in controlling smoke movement
in buildings.
In Figure B-3(b) the shaft is vented to the outdoors
at the top, and smoke entering the shaft at any level
would not leave it until it reached the top opening. If
a corresponding condition were established within a
building, the shaft would, therefore, not constitute a
path for the transmission of smoke from low level to
high level floor spaces. In Figure B-3(c) the shaft is
vented to the outdoors at the bottom, fresh air enters
the shaft at the lowest level and leaves it through any
leakage area at any other level in the shaft. Such a
condition for a shaft in a building would be most
valuable, for as well as being eliminated as a path for
smoke dispersal, the shaft also has a clear atmosphere. These conditions, however, may not be
sustained long as the atmosphere in the shaft will
122
floor
areas
pressure difference
between floor
and outside air
Seclion through
building showing
airflow
Figure B·2
Pressure characteristics
lower
Higher
Pressure characteristics of a typical building
1::
OJ
iii
:r:
(a) Vented top and bottom
(b) Top vented
(c) Bottom vented
Figure B·3 Shaft characteristics
pays
F
cool as a result of the influx of cold air, and the
characteristic will approach that of the exterior
atmosphere. Injection of warm air into the shaft is
necessary to maintain these conditions over a prolonged period.
Where a smoke control method is concerned with
changing the pressure pattern within a building,
many of the measures involved are based on the
preceding concept of changing the pressure characteristic of a shaft. Since shafts are the principal paths
by which smoke disperses throughout a building, the
aim will be either to decrease or to increase shaft
pressures substantially. 80th measures will eliminate
vertical smoke transfer by the shaft between floor
spaces. Top venting the shaft as in Figure 8-3(b) or
use of mechanical exhaust to approach these pressure
characteristics will, however, also result in the entry
of smoke into the shaft, while pressurizing the shaft,
such as by mechanical injection, will maintain a
tenable atmosphere in the shaft.
(6) Smoke shafts. A smoke shaft differs from
a vented service shaft in that an opening is provided
into the shaft from the fire floor in addition to the
opening to the outside at the top of the shaft.
Until windows in outer walls are broken, a smoke
shaft alone can be an effective means of limiting
movement of smoke into other floors and shafts. In
cold weather, the shaft air is warmer than the outdoor air and the shaft will begin to function as a vent
as soon as the dampers are opened. During warm
weather there will be some delay, as the smoke shaft
cannot function as a vent until hot air has entered the
shaft as a result of initial expansion in the fire region.
The pressure conditions that prevail during cold
weather are shown in Figure 8-4. The air pressure on
the fire floor, having an opening into the smoke shaft,
is below that in adjacent unvented shafts and adjacent floor areas. Air flow will be from the adjacent
floor areas and shafts into the fire floor, and from the
fire floor into the smoke shaft. If, however, a window
is broken on a fire floor at a lower level, the air
pressure in the fire region will be increased to approximately that of outdoor air at the same level.
Smoke may then flow into stairshafts and elevator
shafts and adjacent floor areas. During warm
weather, breaking of a window will allow venting of
smoke to the outdoors for a fire on any floor, except
when wind is blowing towards the open window. In
Floor
ｾｴ＠
Ｍｾ＠
,,
,,
\
Ｍｾ＠
Ｍｾ＠
\
\
\
ideal'
F=-=-=i ｾ＠
_
Fire
floor
__0
J:-+-:
ｾ＠
J--+---j
-
--
Section through
building showing
airflow
Figure 8-4
ｾ＠
pressure
in smoke
shaft wl!hc,P T
opening;-to fire \
ｦｬｾｯｲ＠
Pressure characteristics
Lower
Higher
Pressure differences produced by a smoke shaft
this event, breaking of the window will cause the
action of the smoke shaft to be overwhelmed. The
smoke shaft, therefore, is not fully effective as a sole
method of smoke control in a floor area with windows, but can be used in conjunction with building
pressurization as part of a smoke control method.
The size of a smoke shaft is related to conditions to be
established in the event of a fire at a lower level of the
building and is dependent on the leakage characteristics of the building. Any increase in the air leakage
through the walls of the building and the shafts
requires a corresponding increase in the size of the
smoke shaft. In Figure 8-4 the idealized smoke shaft
pressure characteristic is indicated by a dotted line
and assumes no pressure losses inside the shaft. As
the smoke shaft is open to the outside at the top,
pressure at the top level of the smoke shaft is equal to
that of outside air.
Assuming an air temperature inside a smoke shaft
equal to that of the building, as may occur in the case
of a small fire, the slope of the smoke shaft pressure
characteristic is the same as those of the vented
shafts. In Figure 8-4 the total pressure (APT) acting
across the vent opening at the bottom is represented
by the horizontal distance between floor space and
smoke shaft pressure characteristics. The value of
APT is about one half of the total pressure head generated by stack action over the height of the building.
The values of APT are plotted against building height
123
pays
for various outside temperatures in Figure B-5. The
movement of air through the smoke shaft causes a
decrease in building pressures, which results in the
shifting of the floor space pressure characteristic to
the left in the pressure diagram. This results in ｾ＠
lower effective value of ｾｰ＠ T' The values of ｾｰ＠ T In
Figure B-5 have been adjusted to take this factor into
account. So far it has been assumed that no pressure
losses occur inside the smoke shaft. Friction, momentum and dynamic pressure losses can, ｾｯｷ･ｶｲＬ＠
occur inside the smoke shaft, as a result of aIr flow
through the open vent of the fire floor, as well as
through leakage openings in the walls of the smoke
shaft. The smoke shaft pressure characteristic
including pressure losses is also ｳｨｯｾｮ＠
in Figure B-4
as a solid line. The actual pressure dIfference across
the open smoke vent ｾｰ＠
is less than ｾｰ＠ T' the differrepresenting the presence between the two ｶｾｩｵ･ｳ＠
sure losses inside the smoke shaft. The flow requirement to achieve the desired venting action depends
on the pressure differences across the fire floor
enclosure caused by stack action, and on the air
tightness of the various interior and exterior. ｳ･ｰｾｲ｡ﾭ
tions of the building. The flow rates shown In FIgure
B-6 were calculated initially for a 20-storey building
having a floor plan measuring 36 m by 36 m, with
assumed leakage through walls and floors consistent
with the results of air movement measurement
obtained in several multi-storey buildings. Extrapolation was made for buildings of various heights,
floor areas and outside temperatures using the
following relationships:
(1) QV is proportional to FA,
(2) QV is proportional to (H)l/2, and
(3)
QV is proportional to
(Ti - To)I/2
To
where
QV is the required flow rate through the floor
vent of the smoke shaft,
FA is the flow area of a typical floor,
H is the height of building,
T is the indoor absolute temperature, and
TIo is the outdoor absolute temperature.
A number of other considerations may have to be
taken into account in applying measures for control
of smoke movement.
124
500 Ｍｾｲ｟＠
Outside temperature
400
300
a:l
Il..
0:
<J
200
100
ｯｾＭ＠
o
50
100
150
200
250
300
Height of building, m
Figure B·5
Available total pressure versus building height
(7) Make-up air. In the case of smoke control
systems that depend on a supply of.make-u.p ｡ｾｲ＠ from
outside the building for pressurIzatIon or dIlutIon,
the air intakes should be located so that there is little
possibility of smoke or other products of combustion
being drawn into the air handling system. The
source of the smoke could be a fire in the building.
The smoke could reach the air intakes as a result of
siting the intakes close to the discharge from a smoke
shaft or as a result of wind patterns directing smoke
that has been vented out through the building
envelope towards the intakes. Other sources of
smoke are vents from fuel fired equipment, including
furnaces and emergency electricity generators, and
fire in an adjacent part of a building separated from
the building under consideration by fire separations
and vestibules, as would occur in the use of Measure
K. Air intakes located near ground level should be
sited so that exhausts from emergency and other
vehicles are not likely to be drawn into the air
handling system.
L
pays
12.0
...--.....,..--...,...--..,.--.......,r---....,..----,
outside temperature
10.0
8.0
ｾ＠
E
ｾ＠
a)
6.0
ｾ＠
o
u::
when the pressure across a door exceeds 100 Pa.
Pressure differences of this magnitude may occur in
cold weather where a door communicates with a
space that is substantially at outdoor air pressure.
This commonly occurs at the entrance doors to high
buildings during normal use. The problem is resolved in this case by use of revolving doors or by
special hinges which permit the door to rotate about
the centre until a sufficient opening is formed to
relieve the pressure on the door. It may also occur
when windows on a fire floor are broken or where
vestibules vented to the outdoors are employed, as in
Measure D in Section 2. Situations where such
problems may arise are indicated in the explanatory
notes to each smoke control measure.
Explosions in Smoke Shafts
4.0
Note:
Values are for floor area of
2000 m2, for other areas
adjust values in proportion
2.0
ｯｾＭ＠
An explosion may occur in a smoke shaft during a
fire. The maximum over-pressure predicted on the
basis of a British report would probably not exceed
about 16.5 kPa. This has been considered, and
because it is a somewhat remote possibility, no
special precautions are recommended.
a
50
100
150
200
250
300
Height of building, m
Figure 8·6
Required venting capacity of smoke shaft
Breaking of Windows on the Fire Floor
Where the room in which a fire occurs has windows, they will probably be broken at a fairly early
stage. This will result in a change of pressure in the
fire region to substantially that of outdoor air pressure at that level. In Figure B-2, for a fire at a low
level in the building during cold weather, breaking of
windows will greatly increase the pressure in the
region involved. As a result more smoke may be
expected to pass into adjacent floors and vertical
shafts. This has been taken into consideration in the
measures described in Section 2.
Pressures Across Doors
Problems may occur where air pressures across
typical hinged doors and sliding elevator doors
interfere with their normal use. This may occur
Pressure Drop in Stairs
Recent studies have shown that air supply requirements for stairwells with an open door at grade level
can cause a substantial pressure drop due to friction.
If the air is injected only at the top of particular
designs of stairwell in a high building, a non-uniform
pressure distribution over the height of the stairshaft
may occur. This may produce an undesirably high
pressure differential across stairwell doors at high
levels. This problem may be avoided by injection of
the air at several levels rather than only at the top.
Warm Weather Conditions
The smoke control techniques have been developed to function under cold weather conditions; their
performance under warm weather conditions has,
however, been carefully considered. Undesirable
pressures may be created across certain doors, and
certain spaces such as a stairshaft may be contaminated when the door to the outdoors is open. Where
air injection is used, modulation of the supply with
exterior temperature can be a solution to the problem, although such action reduces the effect of the air
supply in diluting transient smoke contamination.
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Where no interior-exterior temperature differential
exists, building heating does not cause stack action
and its influence as a smoke movement mechanism
disappears. Assuming air handling systems to be
shut down, expansion becomes a major factor in
spreading smoke throughout a building. Under
these conditions the influence of a simple vent
opening in an external wall can be readily assessed.
Flow through all openings in the walls around the
fire region will be roughly in proportion to their area.
If the area of the vent to the exterior is ten times the
area of the openings communicating to the remainder
of the building, only about ten per cent of the displaced smoke laden atmosphere will pass into other
parts of the building.
During cold weather, expansion may be responsible for a slight overall increase in pressure of about
25 Pa in the fire region for about 20 minutes.
126
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f
Appendix C to Chapter 3
Check of a Smoke Control System
The efficiency of a smoke control system may be
checked by measuring pressure differences and the
directions of air flow around doors and through
separating walls of compartments. A pressure roeter
can be used to measure pressure differences on either
side of a door or partition. Where this is impracticable, a punk stick held near a crack will give an
indication of the direction of air flow. Measurements
of air flow may be taken on the intake side of supply
fans or in supply ducts to determine whether the
specified air flow is being provided.
In general, air flow should be from the spaces
which may be occupied during a fire emergency (e.g.,
stairshafts) toward the space in which the fire is
assumed to have occurred. For each method of
smoke control measurements may be taken at certain
critical locations to check the overall efficiency of the
system.
In buildings designed by Measure H, C, D or E,
where protection is obtained by venting corridors or
vestibules to the outdoors, inspection of the building
to determine whether the requirements have been
met should be sufficient. In buildings incorporating
Measure H, C, D, E, F or G, service shafts may be
vented to the outdoors at the top. In this case a check
may be made of the wall between the shaft and the
uppermost occupied floor areas, to ensure that the
direction of flow is from each floor area into the shaft,
when the vent to the outside is open and the outdoor
air temperature is significantly less than that indoors.
In a building incorporating Measure D or E, where
mechanically pressurized vestibules are used, and in
a building incorporating Measure L, a check may be
made to ensure that the pressure in each vestibule or
area of refuge is greater than that in the adjacent floor
areas at each floor level.
In a building incorporating Measure F or G, the
efficiency of a protected elevator shaft can be checked
by using a meter to measure pressure differences
between the shaft and the outdoors at grade, before
and after actuation of the air injection system. The
difference between the two readings gives the
mechanical pressurization of the shaft, which should
be at least equal to one half of the calculated pressure
difference caused by stack action over the height of a
building for the January design temperature and the
design flow rate specified in Sentence (4) of Measure
F or Sentence (4) of Measure G. Where the air flow is
modulated, the mechanical pressurization should
vary between 50 Pa when the outdoor temperature is
equal to that indoors, and one half of the pressure
difference noted above when the outdoor temperature is equal to the January design temperature.
Flow rates into the elevator shaft may be checked
against that specified in Sentence (4) of Measure F
and Sentence (4) of Measure G. Stairshafts may be
checked with the air injection system operating and
the door or vent to the outdoors open. Flow rate
through the shaft should be equal to that required by
Sentence (2) of Measure F and Sentence (2) of Measure G. Top vented service shafts may be checked as
described for a building incorporating Measure H, C,
DorE.
In a building incorporating Measure H, the
efficiency of the system may be checked by measuring pressure differences between floor areas at grade
and outdoors before and after actuation of the air
injection system. The magnitude of the mechanical
pressurization is obtained as described above in the
case of elevator shafts in a building incorporating
Measure F or G and should be equal to half the
pressure difference caused by stack action over the
height of the building for the January design temperature and the design flow rate specified in Sentence (2) of Measure H. The effect of modulating air
flow for different temperature conditions is also as
described for elevator shafts. Flow rates into the
building may be checked against those required in
Sentence (2) of Measure H. A check may be made on
each floor individually, with the air injection system
operating and the damper to the smoke shaft or
panel to the outdoors open. Under these circumstances, air flow should be from the stairshafts,
127
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elevator shafts and service shafts into the floor area
that has a damper or panel open.
References
In a building incorporating Measure I or J, pressure differences should be measured between the
central core at grade and a suite that has a number of
windows open to the outdoors before and after
actuation of the air injection system. The magnitude
of mechanical pressurization is obtained as described
above in the case of elevator shafts in a building
incorporating Measure For G and should be equal to
one half of the pressure difference caused by stack
action over the height of the building for the January
design temperature and design flow rate specified in
Sentence (2) of Measure I. The effect of modulating
air flow for different temperature conditions is also as
described for elevator shafts. Flow rates into the
central core may be checked against those required in
Sentence (2) of Measure I.
General
In a building incorporating Measure K, inspection
should indicate whether or not there is a continuous
separation between two parts of the building, extending from the roof through storeys below grade.
Where pressurized vestibules are used, a check may
be made to ensure that the direction of air flow is
from each vestibule into adjacent floor areas at each
level. The check should also be made on a low level
floor with the floor space vents referred to in Sentence (12) of Measure K, or other windows in the two
halves of the building open on that floor. This
represents the condition when the fire has broken
windows in one half of the building and the compensating vent in the other half of the building has been
opened manually.
In a building incorporating Measure L, the method
of checking is the same as in a building incorporating
Measure 0 or E, except that flow rates into areas of
refuge should be measured to ensure that they meet
the requirements of Sentence (9) of Measure 1.
Doors to stairshafts, elevator shafts and vestibules
that are indicated in the notes relating to each measure as being in locations subject to pressure differences that may interfere with normal opening should
be checked when the outdoor temperature is near the
January design temperature, with the air injection
system operating and a number of windows open to
the outdoors on each floor in turn.
12B
(1) High-Rise Building Fires and Fire Safety. Fire
Journal and Fire Technology, NFPA No. SPP18, 1972, 164 pp.
(2) N.B. Hutcheon, Safety in Buildings. CBD 114,
Division of Building Research, National
Research Council Canada, Otta wa, June 1969.
(3) M. Galbreath, Fire in High Buildings. DBR Fire
Study No. 21, Division of Building Research,
National Research Council Canada, Ottawa,
April 1968. NRCC 10081.
(4) G.W. Shorter, Fire in Tall Buildings. Fire
Fighting in Canada, October 1967.
Evacuation
(5) M. Galbreath, Time of Evacuation by Stairs in
High Buildings. Fire Fighting in Canada,
February 1969.
(6) J.1. Pauls, Evacuation and Other Fire Safety
Measures in High-Rise Buildings. ASHRAE
Trans., Vol. 81, Part 1, 1975, pp. 528-533.
Smoke Movement and Control (General)
(7) A.G. Wilson and G.W. Shorter, Fire and High
Buildings. Fire Technology, Vol. 6, No.4,
November 1970, pp. 292-304. NRCC 11789.
(8) J.H. McGuire, G.T. Tamura and A.G. Wilson,
Factors in Controlling Smoke in High Buildings. ASHRAE Symposium Bulletin, January
1970, pp. 8-13. NRCC 12016.
(9) N.B. Hutcheon and G.W. Shorter, Smoke
Problems in High-Rise Buildings. ASHRAE
Journal, Vol. 10, No.9, September 1968, pp. 5761. NRCC 10427.
(10) J.H. McGuire and G.T. Tamura, Smoke Control
in High-Rise Buildings. CBD 134, Division of
Building Research, National Research Council
Canada, Ottawa, February 1971.
(11) G.T. Tamura and J.H. McGuire, Smoke Movement in High-Rise Buildings. CBD 133,
Division of Building Research, National
Research Council Canada, Ottawa, January
1971.
(12) J.H. McGuire and G.T. Tamura, The National
Building Code Smoke Control Measures - An
pays
(13)
(14)
(15)
(16)
Overview, Engineering Digest, Vol. 25, No.9,
October 1979, pp. 35-38. NRCC 17920.
G.T. Tamura, Review of the DBR/NRC Studies
on Control of Smoke from a Fire in High
Buildings. ASHRAE Trans. Vol. 89, Part IB,
1983, pp. 341-361. NRCC 23054.
G.T. Tamura, Smoke-Control Systems in HighRise Buildings, 1976-1980 Survey. Engineering
Digest, Vol. 30, No.7, August 1984, pp. 32-34.
NRCC23874.
G.T. Tamura and P.J. Manley, Smoke Movement Studies in a 15-Storey Hotel. ASHRAE
Trans., Vol. 91, Part 2B, 1985, pp. 1237-1253.
NRCC 26359.
J.H. McGuire and G.T. Tamura, Simple Analysis of Smoke-Flow Problems in High Buildings.
Fire Technology, VoL II, No. I, February 1975,
pp. 15-22. NRCC 14773.
Specialized Aspects of Smoke Control
(17) G.T. Tamura and C.Y. Shaw, Basis for the
Design of Smoke Shafts. Fire Technology, Vol.
9, No.3, August 1973, pp. 209-222. NRCC
13851.
(18) G.T. Tamura and A.G. Wilson, Natural Venting
to Control Smoke Movement in Buildings via
Vertical Shafts. ASHRAE Trans., Vol. 76, Part
II, 1970, pp. 279-289. NRCC 12357.
(19) G.T. Tamura, Analysis of Smoke Shafts for
Control of Smoke Movement in Buildings.
ASHRAE Trans., VoL 76, Part It 1970, pp. 290297. NRCC 12356.
(20) G.T. Tamura, J.H. McGuire and A.G. Wilson,
Air-Handling Systems for Control of Smoke
Movement. ASHRAE Symposium Bulletin,
January 1970, pp. 14-19. NRCC 12017.
(21) N.B. Hutcheon, Fire Protection in Air System
Installations. Heating, Piping and Air Conditioning, Vol. 40, No. 12, December 1968, p. 102.
NRCC 10545.
(22) G.T. Tamura and C.Y. Shaw, Experimental
Studies of Mechanical Venting for Smoke
Control in Tall Office Buildings. ASHRAE
Trans., Vol. 84, Part I, 1978, pp. 54-71. NRCC
17234.
(23) G.T. Tamura, Experimental Studies on Exterior
Wall Venting for Smoke Control in Tall Office
Buildings. ASHRAE Trans., Vol. 84, Part 2,
1978, pp. 204-215. NRCC 17279.
(24) G.T. Tamura, The Performance of a Vestibule
Pressurization for the Protection of Escape
Routes of a 17-Storey Hotel. ASHRAE Trans.,
Vol. 86, Part I, 1980, pp. 593-603. NRCC 19017.
(25) G.T. Tamura and C.Y. Shaw, Field Check on
the Building Pressurization Method for Smoke
Control in High-Rise Buildings. ASHRAE
Journal, Vol. 23, No.2, February 1981, pp. 2125. NRCC 19199.
(26) G.T. Tamura, A Smoke Control System for
High-Rise Office Buildings. ASHRAE Journal,
Vol. 24, No.5, May 1982, pp. 29-32. NRCC
20317.
(27) G.T. Tamura and K. Tsuji, Simplified Method
for Designing a Mechanical Smoke Exhaust
System for High-Rise Buildings. ASHRAE
Trans., Vol. 91, Part 2 B, 1985, pp. 642-656.
NRCC 26341.
(28) G.T. Tamura, Experimental Studies on Pressurized Escape Routes. ASHRAE Trans., Vol. 80,
Part 2, 1974, pp. 224-237. NRCC 14566.
(29) G.T. Tamura and J.H. Klote, Experimental Fire
Tower Studies of Elevator Pressurization
Systems for Smoke Control. ASHRAE Trans.
Vol. 93, Part 2, 1987. NRCC 29121.
(30) J.H. Klote and G.T. Tamura, Experiments of
Piston Effect on Elevator Smoke Control.
ASHRAE Trans. Vol. 93, Part 2, 1987. NRCC
29120.
Computer Studies
(31) H. Yoshida, C.Y. Shaw and G.T. Tamura, A
Fortran IV Program to Calculate Smoke
Concentrations in a Multi-Storey Building.
Computer Program No. 45, Division of Building Research, National Research Council
Canada, Ottawa, June 1979.
(32) G.T. Tamura, Computer Analysis of Smoke
Control with Building Air Handling Systems.
ASHRAE Journal, Vol. 14, No.8, August 1972,
pp.46-54. NRCC 12809.
(33) C.Y. Shaw and G.T. Tamura, Fortran IV
Programs for Calculating Sizes and Venting
Capacities of Smoke Shafts. Computer Program No. 36, Division of Building Research,
National Research Council Canada, Ottawa,
June 1973.
129
pays
(34) C.T. Tamura, Computer Analysis of Smoke
Movement in Tall Buildings. ASHRAE Trans.,
VoL 75, Part II, 1969, pp. 81-92. NRCC 11542.
Air Leakage Studies
(35) C.Y. Shaw, D.M. Sander and C.T. Tamura, Air
Leakage Measurements of the Exterior Walls of
Tall Buildings. ASHRAE Trans., Vol. 79, Part
II, 1973, pp. 40-48. NRCC 13951.
(36) C.T. Tamura and A.C. Wilson, Pressure Differences Caused by Wind on Two Tall Buildings.
ASHRAE Trans., Vol. 74, Part II, 1968, pp. 170181. NRCC 10628.
(37) C.T. Tamura and A.C. Wilson, Pressure Differences Caused by Chimney Effect in Three High
Buildings and Building Pressures Caused by
Chimney Action and Mechanical Ventilation.
ASHRAE Trans., Vol. 73, Part II, 1967. NRCC
9950.
(38) C.T. Tamura and A.C. Wilson, Pressure Differences for a Nine-Storey Building as a Result of
Chimney Effect and Ventilation System Operation. ASHRAE Trans., Vol. 72, Part I, 1966, pp.
180-189. NRCC 9467.
(39) C.T. Tamura and C.Y. Shaw, Air Leakage Data
for the Design of Eleva tor and Stairshaft
Pressurization Systems. ASHRAE Trans., Vol.
82, Part II, 1976, pp. 179-190. NRCC 15921.
Associated Elementary Theory
(40)
A.C. Wilson and C.T. Tamura, Stack Effect and
Building Design. CBD 107, Division of Building Research, National Research Council
Canada, Ottawa, November 1968.
(41) A.C. Wilson and C.T. Tamura, Stack Effect in
Buildings. CBD 104, Division of Building
Research, National Research Council Canada,
Ottawa, August 1968.
130
pays
Chapter 4
Commentaries on Part 4 of the
National Building Code of Canada 1990
Introduction
..........•..•.................••••..••... 133
Commentary A
Serviceability Criteria for
Deflections and
Vibrations ......................... 134
Commentary B
Wind Loads ....................... 141
Commentary C
Structural Integrity •••••.•••• 172
Commentary D
Effects of Deformations in
Building Components ••••••• 174
Commentary E
Load Combinations .......... 178
Commentary F
Limit States Design .......... 180
Commentary G
Tributary Area .................. 184
Commentary H
Snow Loads ...................... 187
Commentary I
Rain Loads ........................ 200
Commentary J
Effects of Earthquakes .... 202
Commentary K
Glass Design ••••••••••••••••••••• 221
Commentary L
Foundations ...................... 229
Commentary M
Structural Integrity of
Firewalls ........................... 256
Appendix A
List of Referenced
Standards ........................ 259
131
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132
I
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r
Chapter 4
Commentaries on Part 4 of the
National Building Code of Canada 1990
Introduction
The purpose of these Commentaries is to make
available to the designer detailed design information
which will assist in the use of the National Building
Code. The Commentaries are provided as background information and, in some cases, as suggested
approaches to certain design questions, but not as
mandatory requirements.
Because the information provided in these Commentaries cannot cover all conditions or types of
structures that occur in practice, and also because
new information may become available in the future,
the designer should try to obtain the latest and most
appropriate design information available. For
unusual types of structures, specialized information
such as theoretical studies, model tests or wind
tunnel experiments may be required to provide
adequate design values.
Building Code on provisions for earthquake engineering in the Code.
Commentary L (Foundations) was prepared with
the assistance of a task group appointed by the
Standing Committee on Structural DeSign and
consisting of the following members: V. Milligan
(Chairman), L. Brzezinski, D. Klajnerman,
W.E. Lardner and E.Y. Uzumeri.
Commentary M (Structural Integrity of Firewalls)
has been developed to provide guidance to the new
requirement in Sentence 4.1.10.3.(1} of the National
Building Code for the design of firewalls.
These commentaries were prepared with the
assistance of the following:
W.R. Schriever
D.E. Allen
D.A. Lutes
A.G. Davenport
W.G. Plewes
J.H. Rainer
D.A. Taylor
W.A. Dalgliesh
J.G. MacGregor
D.J.L. Kennedy
Commentary J (Effects of Earthquakes) was
prepared with the assistance of the Canadian National Committee on Earthquake Engineering, which
advises the Associate Committee on the National
133
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Commentary A
Serviceability Criteria
for Deflections and
Vibrations
1. The advent of stronger materials, lighter, more
rigid cladding, smaller damping, longer spans and
more accurate strength calculations taking account
of the interaction of components, means that excessive deflections and vibrations now have a greater
influence in structural design than before. Excessive
deflections and vibrations are usually controlled in
codes by limiting the member deflection under
specified load to some ratio of the span (L), for
example, L:360 (for cantilevers, L may be taken as
twice the length of the cantilever). Table A-1 summarizes deflection criteria in this form in various
standards pertinent to the National Building Code of
Canada 1990. These deflection criteria depend on
the types of construction and materials and on the
conditions of use. As an aid to the designer, the
problems associated with excessive deflection and
excessive vibration are briefly discussed and references are given.
Deflections
2. Excessive structural deflections can create a
variety of problems: cracks or crushing in nonstructural components such as partitions, lack of fit
for doors, walls out of plumb or eccentricity of
loading caused by rotation, unsightly droopiness
and ponding. Cracks, besides being unsightly, may
transmit unwanted sound through partitions, or
water and cold air through exterior surfaces, and
thus promote corrosion. Control of cracking in
structural concrete is covered separately in CAN3A23.3-M84, "Design of Concrete Structures for
Buildings."
3. A number of alternative design solutions can
prevent problems caused by excessive deflection.
Partition cracking, for example, can be avoided
either by making the supporting structure stiff
134
enough or by providing flexible joints in the partitions. Similarly, to avoid cracking, plastered ceilings
should be hung from the floor beams, not rigidly
attached to them.
4. The deflection criteria in Table A-1 apply to
conventional forms of construction under conventional conditions of use. The most severe deflection
requirement, 1:480, for members supporting plastered ceilings or partitions, (1) may not be sufficient to
prevent cracking of plaster or rigid partitions. (3) For
new or unusual cases, more detailed deflection
criteria are suggested in Reference (2); case histories
of damage due to excessive deflections (including
also differential settlement and temperature movements) are given in References (4) to (7).
Vibrations
5. Two types of vibration problems arise in
building construction: continuous vibrations and
transient vibrations. Continuous vibrations arise due
to the periodic forces of machinery or certain human
activities such as dancing; these vibrations can be
considerably amplified when the periodic forces are
synchronized with a building frequency - a condition
called resonance. Transient vibrations are caused by
footsteps or other impact and decay at a rate which
depends on the available damping.
6. Transient vibrations in floor systems due to foot
impact may cause discomfort or annoyance to the
occupants as a result of, for instance, china rattling.
In Table A-1 the deflection criteria of L:360 for wood
floors m and L:320 for steel floors which do not
support brittle materials attempt to control such
vibration effects. These criteria apply only to conventional floors with spans less than approximately 6 m
and frequencies greater than about 10 Hz. They do
not apply to long span floors, particularly for those
without partitions, or for floors for special purposes;
Reference (8) contains further information and
criteria on these cases. Reference (9) contains criteria
for footbridges. References (1) and (10) contain
further information for light residential floors with
wood decks.
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Table A·1
Summary of Maximum Deflection/Span Ratios in NBC 1990 and Pertinent CSA Standards(1)
CAN3-086-M84
CAN/CSA-086.1-M89
Wood
I
i
Roof or floor members
supporting plastered
ceilings, partitions, etc.
Floor members not
supporting plastered
ceilings, partitions, etc.
Roof members not
supporting plastered
ceilings, etc.
Wall members
Column 1
CAN3-A23.3-M84
Concrete
CAN/CSA-S 16.1-M89
Structural Steel
1:480 (3)
or
1:240 (3)
1:360
1:360 (4)
1:300 (5)
1:180 (4)
1:180 (6)
or
1:240 (6)
1:360 (2)
or
1:180 (2)
1:360 (2)
or
1:180 (2)
1:180 (2)
-
Notes to Table A·1 :
De'fiection under live load only unless otherwise noted.
(2)
Modulus used for calculations based on short term test.
1:360 applies to deflection under sustained load.
(3)
Deflection which occurs after attachment of non-structural
elements, including creep deflection due to sustained load
plus immediate deflection due to additional live load. The
lower figure applies when non-structural elements are not
likely to be damaged by large deflections.
7. The undesirable effects of continuous vibrations
caused by machines can be minimized by special
design provisions, (11) such as locating machinery
away from sensitive occupancies, vibration isolation
or alteration of the frequency of the structure.
Floor Vibrations in Assembly
Occupancies
8. A new NBC Sentence 4.1.10.5.(1) requires an
investigation by means of a dynamic analysis for
floor structures (including footbridges) supporting
assembly occupancies when the fundamental vibration frequency is less than 6 Hz. This requirement
has been introduced because of recent problems with
long-span floor structures used for rhythmic activities.(12-17) The following provides guidance for the
1:360
1:240 (7)
or
1:360
1:180 (8)
or
1:240
-
2
(1)
NBC 1990Part 9
3
(4)
(5)
(6)
(7)
(8)
4
!
5
Immediate live-load deflection. Includes a warning on
ponding for roof members.
Includes a warning clause on vibrations.
1:180 applies to sheet metal or elastic membrane roof cover
and 1:240 to asphaltic built-up roofs. Includes a warning
clause on ponding.
For bedrooms only.
If there is no ceiling.
designer in carrying out a dynamic analysis for such
cases, and also suggests criteria to limit floor vibrations during rhythmic activities to levels acceptable
for human occupancy.
Overloading and Fatigue
9. Dancing, foot stamping, jumping exercises and
marching are rhythmic activities that create periodic
forces with rhythmic frequency in the range 1 to
4
for rhythmic events involving a group of
people, the most critical range is 1.5 to 3 Hz. Typical
loading cases are shown in Figure A-1. For many
rhythmic activities, such as dancing, the periodic
forces can be approximated by a sinusoidal dynamic
load causing vibration at the rhythmic frequency. In
the case of jumping exercises, however, the periodic
135
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forces shown in Figure A-I can also create significant
sinusoidal load at double the rhythmic frequency,
and some sinusoidal load at triple the rhythmic
frequency. The dynamic load for any sinusoidal
component can be represented by aw p sin 21tft, where
f is the forcing frequency, w p is the weight of participants in kPa and a is a dynamic load factor which
depends on the activity and, for jumping, the harmonic multiple of the rhythmic frequency. Table A-2
gives estimated values of forcing frequencies and
dynamic load based on an estimation of density of
participants and dynamic load factor, a, for typical
rhythmic events.(15,lh) If the fundamental natural
frequency of the floor structure, (" is large compared
to the forcing frequency, f, the dynamic load has the
same effect as a static load of the same magnitude,
but if the structural frequency approaches the forcing
frequency, the dynamic effect increases with each
cycle of vibration to a maximum (Figure A-2) whose
ratio to the static effect is given by (11)
lime
0)
For a floor with many people on it, the damping
ratio, ｾＬ＠ is about 0.04 for a solid concrete floor, 0.06
for a concrete and steel floor and 0.12 for a wood
Time
Figure A·1
Load during rhythmic event
Activity
Table A·2
Estimated Loading During Rhythmic Events
Weight of Participants (1)
Dynamic Load
Forcing
Factor, (2) a
Frequency f, Hz
Wp ' kPa
Dynamic Load,
aw p ' kPa
!
0.6 (2.5 m2/couple)
Dancing
1.5 3
0.5
0.3
Lively concert or
1.5 (0.5 m2/person)
1.5 - 3
0.4
sports event
0.25
Jumping exercises
0.2 (3.5 m2/person)
2 - 2.75
1.5
First harmonic
0.3
0.2 (3.5 m2/person)
4-5.5
0.12
Second harmonic
0.6
0.2 (3.5 m2/person)
6 -8.25
0.1
Third harmonic
0.02
Column 1
2
4
3
5
Notes to Table A·2:
(2) Values of a based on commonly encountered events with a
(1)
Density of participants represents maxima for commonly
minimum of 20 participants. Values of a should be
encountered conditions. For special events the density of
increased for well coordinated events with fewer than 20.
participants can be greater.
136
pays
65
Figure A·2
fa =2.6 Hz)
Resonance during rock and roll (precast stands,
floor, and about half these values with few people.
Damping ratios vary from these suggested values,
depending on the influence of non-structural components such as partitions. The dynamic response
factor, p, is shown in Figure A-3.
simply-supported beams on girders supported by
columns is obtained from:
fo=
.
2n
where
10. The fundamental structural frequency, fo'
should be determined from the dynamic properties
of the floor structure, taking into account the flexibility of supports. An approximate determination for
ｾ＠
ｾｂ＠
Ｈｾｂ＠
+ ｾｇＩ＠
rg
V ｾ＠
+ ｾｳＧ＠
=
0.77
=
the elastic deflection of the beam due to
bending and shear,
(2)
(3)
the elastic deflection of the girder due to
bending and shear, and
5
ｾｳ＠
ｾＭｲ＠
axial strain.
Each deflection is the elastic component resulting
from the total weight supported by the member,
including people, and is relative to its supports. Both
supports are considered and the most flexible one
used. For cantilever and two-way slabs, the factor
0.77 is replaced by 0.65. In the case of beams and
girders continuous over supports, the elastic deflection, ｾｂ＠ or ｾｇＧ＠
should be determined by assuming
that adjacent spans deflect in opposite directions with
no change in slope over the supports and that the
weight supported by each span always acts in the
direction of deflection.
4
3
dynamic effect
2
o ｾＭ＠
o
0.5
1.0
1.5
2.0
2.5
fJf
Figure A·3
= the elastic shortening of the column due to
Dynamic response factor, Equation (1)
3.0
11. The total structural effect of a rhythmic activity
can, therefore, be represented by the static effect of
the load w t + pajw p' where w t is the total weight
supported. In the case of jumping forces, the dynamic loading component paw p is replaced by
137
pays
2:p.a.w where a. and p. are the dynamic load and
response factors for each harmonic multiple, i, of the
rhythmic frequency. Overloading occurs if the total
load, including static and dynamic components, is
greater than the total specified load that the structure
is allowed to carry. Potential for fatigue damage can
be assessed by estimating the stress range corresponding to 2 pjajwp and the total number of cycles
of dynamic load ajw p expected during the life of the
structure for each harmonic.
IIp
I
I
13. The maximum acceleration of a floor structure
during a rhythmic event can be determined from (15)
amax/g
1.3awp/w,
1.3awp /wt
(f;f -1
(4)
where the approximation is valid away from the
resonance frequency f = (" The symbols are defined
in Paragraph 9. In the case of jumping, the maximum
acceleration can be determined from (16)
Human Reaction
12. Floor vibration is much more likely to annoy
people than to cause overloading or fatigue. An
acceptable level of vertical vibration depends very
strongly on the activity of the people who feel the
vibration. People in offices or residences become
annoyed when accelerations from continuous vibration exceed approximately 0.5 per cent gravity,
whereas people participating in rhythmic activities
will accept approximately 5 per cent gravity. When a
floor structure is shared with a more sensitive occupancy, then the limit should be based on that occupancy. People such as diners who share a floor
structure with dancing, or weight lifters who share a
floor structure with aerobics will accept approximately 2 per cent gravity. Other factors besides
occupancy affect the acceptability of vibration, in
particular the remoteness of the source of vibration
from the people affected. For this reason, Table A-3
shows a range of acceleration limits for each occupancy. The lower value is generally recommended
for design.
(5)
where a. is the maximum acceleration for the ith
harmonic loading component, which is determined
from Equation (4) by setting f equal to i times the
jumping frequency.
1
14. If a natural frequency of the floor structure
corresponds to a harmonic forcing frequency, resonance occurs and the accelerations during a rhythmic
event become very large, usually greater than the
recommended criterion. Generally, therefore, the
fundamental natural frequency of the floor structure
should be greater than the highest significant harmonic forcing frequency. The following criterion is
recommended (15)
(6)
where
f
=
a,,/g=
Table A-3
Recommended Acceleration Limits for
Vibrations due to Rhythmic Activities
Occupancies Affected
by the Vibration
Office and residential
Dining and weightlifting
Rhythmic activity only
138
Acceleration Limit,
% gravity
0.4 - 0.7
1.5 - 2.5
4-7
K=
forcing frequency (i times the jumping
frequency for jumping exercises),
acceleration limit,
1.3, except for jumping exercises, where
K = 2.0 is recommended.(16)
15. Table A-4 contains examples of the application
of Equation (6) to typical floor structures using the
acceleration limits recommended above. If the
rhythmic activity is restricted to a portion of the floor
span, then an appropriate reduction can be made to
w p ' the weight of participants effectively acting on
the floor span.(16) Similarly, extra mass (other than the
I
.-..
pays
IF
Table A·4
Application of Structural Criteria for Human Reaction
Activity and Construction
Forcing
Frequency
f, Hz
I
.
I
Effective Weight
of Participants
wP' kPa
Dancing and Dining aig = 0.02
Solid concrete 5 kPa
3
2.5 kPa
3
Steel
I
Wood 0.7 kPa
3
Lively Concert or Sports Events aig = 0.05
Solid concrete 5 kPa
3
Steel joist 2.5 kPa
3
Wood 0.7 kPa
3
Jumping Exercises only aolg = 0.06
8.25(1)
Solid concrete 5
8.25 (1)
Steel joist 2.5 kPa
5.5 (1)
Wood 0.7 kPa
Jumping Exercises Shared with Weight Lifting
8.25(1)
Solid concrete 5 kPa
5.5(1)
Steel joist 2.5 kPa
5.5(1)
Wood 0.7 kPa
Column 1
2
Notes to Table A·4:
Equation (6) is applied to three harmonics (i.e. f == 2.75 Hz,
5.5 Hz and 8.25 Hz) and the governing harmonic is used.
(1)
floor) supported by the vibrating structure, including
the supports, can be taken into account in determining the total weight, w t • (6 )
16. Measures to avoid or correct unacceptable
vibration include:
(a) provision of sufficient stiffness, Equation (6),
(b) relocation of the rhythmic activity or the
sensitive occupancy,
(c) prevention of transmission of floor vibration to
sensitive occupancies, for example, by
placing or altering partitions,
(d) increasing the damping sufficiently to reduce
resonance response, or
Total Weight
Wt' kPa
Minimum Structural
Frequency, fo' Hz
Equation (6)
0.6
0.6
0.6
5.6
3.1
1.3
6.4
8.1
12.0
1.5
1.5
1.5
6.5
4.0
2.2
4.8
5.7
7.2
.
!
5.2
2.7
0.9
8.8(2)
9.2
12.8
0.12
0.12
0.12
5.12
2.62
0.82
9.2
10.6
17.2
3
4
5
0.2
0.2
0.2
aolg = 0.02
(2)
This can be reduced if, according to Equation (4), damping
times mass is sufficient to reduce third harmonic resonance
to an acceptable level.
(e) increasing the span to where the fundamental
natural frequency becomes less than a
significant rhythmic frequency; this
would require a special investigation.
Case histories of problems are described in References (14) and (17), including a case where unacceptable aerobics vibration in a tall office building
occurred due to vertical spring action of the columns.
If an existing floor is intended for a rhythmic activity,
a performance test should be carried out before
alterations are made.
139
pays
References
0) W.A. Russell, Deflection Characteristics of
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
140
Residential Wood-Joist Floor Systems. Housing and Home Finance Agency, Housing
Research Paper 30, Washington, D.C., April
1954.
Allowable Deflections. Subcommittee 1, ACI
Committee 435. Journal Am. Concrete Inst.,
Vol. 65, No.6, June 1968, p. 433.
W.G. Plewes and G.K. Garden, Deflections of
Horizontal Structural Members. Canadian
Building Digest No.
Division of Building
Research, National Research Council of Canada, Ottawa, June 1964.
H. Mayer and H. Rusch, Bauschaden als Folge
der Durchbiegung von Stahlbeton-Bauteilen
(Building Damage Caused by Deflection of
Reinforced Concrete Building Components).
Deutscher Ausschuss fur Stahlbeton, Heft 193,
Berlin 1967. National Research Council of
Canada Technical Translation TT]412, 1970.
O. Pfeffermann, Les Fissures dans les Constructions Consequences de Phenomenes
Physiques Naturels. Annales de l'Institut
Technique du Batiment et des Travaux Publics,
No. 250, October 1968.
A.W. Skempton and D.H. MacDonald, The Allowable Settlements of Buildings. Proc., Institution of Civil Engineers, Vol. 5, Part lIt 1956, p.
727.
F.R. Khan and M. Fintel, Effects of Column Exposure in Tall Structures - DeSign Considerations and Field Observations of Buildings.
Journal Am. Concrete Inst., Vol. 65, No.2,
February 1968, p. 99.
CSA Standard CAN3-S16.l-M89. Steel Structures for Buildings - Limit States Design.
Appendix Guide on Floor Vibrations.
Ontario Highway Bridge Design Code 1984.
Ontario Ministry of Transportation and Communications.
D.M. Onysko, Performance of Wood-Joist Floor
Systems. Forest Products Laboratory Information Report OP-X-24, Canadian Forestry
Service, Department of the Environment,
Ottawa, January 1970.
(1) W-J. Smith, Vibrations of Structures; Applications in Civil Engineering Design. Chapman
and Hall, London, 1988.
(2) Pop Concert Shock for Loading Code. New
Civil Engineer International, May 1981, p. 18.
(3) G. Pernica, Dynamic Live Loads at a Rock
Concert. Can. J. Civ. Eng., June 1983, pp. 185191.
(4) H. Bachmann and W. Ammann, Vibrations in
Structures Induced by Man and Machines.
Structural Engineering Document 3e. International Association for Bridge and Structural
Engineering, Zurich, 1987.
OS) D.E. Allen, J.H. Rainer and G. Pernica, Vibration Criteria for Assembly Occupancies. Can. J.
Civ. Eng., Vol. 12, No.3, September, 1985.
(6) D.E. Allen, Floor Vibrations from Aerobics.
Can. J. Civ. Eng., October 1990.
(7) D.E. Allen, Vibrations from Human Activities.
Concrete International - Design and Construction, American Concrete Institute, June 1990.
pays
...
Commentary B
Wind Loads
1. Three different approaches to the problem of
determining design wind loads on buildings are
mentioned in Subsection 4.1.8., "Effects of Wind" of
the 1990 edition of the National Building Code. (1)
2. The first approach, the "simple procedure," is
appropriate for use with the majority of wind loading
applications, including the structure and cladding of
low and medium rise buildings and the cladding
design of high rise buildings. These are situations
where the structure is relatively rigid. Thus, dynamic
actions of the wind do not require detailed knowledge of the dynamic properties of the buildings and
can be dealt with by equivalent static loads. Numerical values for all the factors involved are provided in
the NBC except for climatic data, which is given in
Chapter 1 of this Supplement and pressure coefficients given in this Commentary.
3. The two other approaches to wind load analysis
are referred to in Article 4.1.8.2. of the 1990 NBC, and
are required whenever the building is likely to be
susceptible to wind-induced vibration. This may be
true, for example, of tall and slender structures or
doubly cantilevered canopies for which wind loading
plays a major role in the structural design. Here the
designer is required to use either (a) special wind
tunnel tests or other experimental methods, or (b) a
dynamic approach to the action of wind gusts to be
called the "detailed procedure."
structures, but not cladding and components.(S) It
consists of a series of calculations involving (a) the
intensity of wind turbulence for the site as a function
of height and of the surface roughness of the surrounding terrain, and (b) properties of the building
such as height, width, natural frequency of vibration
and damping. The end-product of the calculations is
the gust effect factor, C g , which is multiplied by the
reference wind pressure, q , the exposure factor, Ce ,
and the pressure coefficient C p ' to give that static
design pressure which is expected to produce the
same peak load effect as the dynamic resonant
response to the actual turbulent wind. The format of
the simple procedure in the NBC has been arranged
to permit an easy transition to this more detailed
consideration of wind effects.
Reference Wind Speed, V, and
Pressure, q
6. In both the simple and detailed procedures the
reference wind speed, V, is determined by extreme
value analysis of meteorological observations of
hourly mean wind speeds, taken at sites (usually
airports) chosen in most cases to be representative of
a height of 10 m in an open exposure. The reference
wind pressure, q, is determined from V by the following equation:
q (in kPa)
CV 2
(1)
7. The factor C depends on the atmospheric
pressure and the air temperature. The atmospheric
pressure in turn is influenced mainly by elevation
above sea level, but also varies somewhat in accordance with changes in the weather.
4. Wind tunnel testing is appropriate when more
exact definition of dynamic response is needed and
for determining exterior pressure coefficients for
cladding design on buildings whose geometry
deviates markedly from more common shapes for
which information is already available. Information
on modern wind tunnel techniques can be found in
References (2), (3) and (4).
8. The following value of C is chosen to represent
Canadian conditions:
if y is in kilometres per hour, C 50 x 10-6
if V is in metres per second, C = 650 X 10-6 •
5. The "detailed procedure," is intended primarily
for determining the overall wind loading and amplified resonant response of tall buildings and slender
In Chapter 1 of this Supplement, the velocity pressure, P,
and the design wind speed, V, are meterological terms,
equivalent to the ｲ･ｦｾ｣＠
wind pressure, q, and the
reference wind speed, V, which are engineering terms used
in this Commentary.
141
pays
9. Chapter 1 of this Supplement contains a description of the procedures followed in obtaining the
reference wind pressures, q, for three different levels
of probability of being exceeded per year (1 in 10, 1 in
30 and 1 in 100), the values commonly referred to as
having return periods of 10, 30 and 100 years. These
values of q are tabulated in Chapter 1 for many
Canadian locations along with other climatic design
data. A reference giving more detail on the choice of
the conversion factor, C, from wind speed to pressure
and a table for converting from pressure in kilonewtons per square metre to speed in metres per second
are also supplied in Chapter 1.
Exposure Factor, C e
Simple Procedure
10. The exposure factor, Ce , reflects changes in
wind speed and height, and also the effects of
variations in the surrounding terrain and topography.
Hills can significantly amplify the wind speeds near
the ground and this should be reflected in the exposure factor. Representative values for use with either
the simple or detailed procedure are presented in
Paragraph 18.
11. For the simple procedure, Ce is based on the
1/5 power law which is appropriate for wind gust
pressure in open terrain (1 /10 power law for wind
gust speeds). The wind gust referred to lasts about
3 to 5 s and represents a "parcel" of wind which is
assumed effective over the whole of most ordinary
buildings.
12. The reference height which is used in determining the exposure factor is related to the manner in
which the pressure coefficient, C p , is defined. In this
Commentary, the reference heignt applicable to low
rise structures is the mean height of the roof or 6 m,
whichever is greater. The eave height may be substituted for the mean height if the slope of the roof is
less than 10°. For tall buildings, the reference height
for pressures on the windward face corresponds to
the actual height above ground; for suctions anywhere on the leeward face of tall buildings, the
reference height is half the height of the structure.
142
Where required in this Commentary, the definition of
the reference height is given along with that of C . In
instances where the reference height is not specified,
it should be taken as equal to the height above
ground of the element considered.
Detailed Procedure
13. For the detailed procedure, the exposure
factor, Ce , is based on the mean wind speed profile,
which varies considerably depending on the general
roughness of the terrain over which the wind has
been blowing before it reaches the building. This
dependence on terrain is much more significant than
is the case for the gust speed profile ( variation of
gust speed with height) and hence three categories
have been established as follows:
Exposure A (open or standard exposure): open
level terrain with only scattered buildings, trees or
other obstructions, open water or shorelines thereof.
This is the exposure on which the reference wind
speeds are based.
Z )0.28
Ce =(10
' Ce 2 1.0
(2)
Exposure B: suburban and urban areas, wooded
terrain or centres of large towns.
, Ce
ｾ＠
0.5
(3)
Exposure C: centres of large cities with heavy
concentrations of tall buildings. At least 50 per cent
of the buildings should exceed 4 storeys.
C e = 0.4
Ｈｾ＠
t72, C
e
ｾ＠
0.4
(4)
In Equations (2) to (4), Z is the height above
ground in metres.
14. Exposure B or C should not be used unless the
appropriate terrain roughness persists in the upwind
direction for at least 1.5 km, and the exposure factor
should be varied according to the terrain if the
roughness differs from one direction to another.
I
pays
Use of Exposure Factors
15. Exposure factors can be calculated from
Equations (2) to (4) or obtained directly from the
graphs in Figure B-1. The exposure factor is needed
in three different capacities in the detailed procedure.
Firstly, the square root of CeH' the value of Ce at the
top of the building, H, is needed to determine the
hourly mean wind speed at the top of the structure
being designed, V H
(5)
16. Secondly, C eH appears in Equation (8) used for
calculating the gust effect factor, Cgo Here again, C eH
is the value of C e evaluated at the top of the structure.
17. Thirdly, C e is used in the calculation of pressures for the windward and leeward faces of tall,
slender buildings. For the windward face, C e corresponds to that for the height, Z, to the point in question and therefore increases with height in accordance with Equations (2), (3) or (4) as is appropriate.
For the leeward face, C e is evaluated at half the
height, H, of the building.
Speed-Up over Hills and Escarpments
The reference wind speed, V, can be obtained from
the reference wind pressure and the conversion table
in Chapter 1 or by applying Equation (1).
400
/A
!
I
I
300
＠
ｾ
Ａ
II /
/
I
200
I
100
80
60
/
i
E
1:i
c
:l
cl
･ｸｰｾｲｅ＠
40
Q)
>
.c.
OJ
"Qi
I
10
•
I
1
ffi#
I
.
/
I
II
!
!
I
00
I
1
0.1
•
i
I
AI
/
/
I
I
/
I
20
0
.0
tll
I
/
V
0
0,
/
I
B/
/
30
IJ
.
i
0.2
0.30.4
0.60.8 1
3
4
5 6
8 10
Exposure factor, C e
Figure B·1 Exposure factor as a function of terrain roughness
and height above ground
18. Buildings on a hill (with a maximum slope> 1
in 10), particularly near a crest, may be subject to significantly higher wind speeds than buildings on level
ground. The exposure factor at height z above the
local ground elevation is then equal to that over flat
terrain multiplied by a factor (1 + ｾｓＨｚﾻＲ＠
where ｾｓＨｺＩ＠
is the "speed-up factor" for the mean wind speed.
This can be applied in both the simple and detailed
procedures. This effect is illustrated in Figure B-2.
Near the crest, and within a distance I x I < kL, the
exposure factor is modified to
C:(z) Ce(z) (1
Ｋｾｭ｡ｸＨｬ＠
ｾＩ･ＨＭ｡ｚＯｌｲ＠
(6) e
where Ce(z) is the exposure factor over flat terrain
given in equation (2), (3) or (4), C;(z) is the
corresponding modified value for use on the hill,
ｾｓｭ｡ｸ＠
is the relative speed-up factor at the crest near
the surface and a is a decay coefficient for the
decrease in speed-up with height. The values of a
and ｾｓｭ｡ｸ＠
depend on the shape and steepness of the
hill. Representative values for these parameters are
given in Table B-1.
The definitions of the hill height H and length L,
shown in Figure B-2, are as follows: H is the height
of the hill or the difference in elevation between the
crest of the hill and that of the terrain surrounding
the hill upstream; L is the distance upwind of the
crest to where the ground elevation is half the height
of the hill. The maximum slope of the hill is roughly
143
pays
H/2L for rounded hill shapes. In these expressions, it
is assumed that the wind approaches the hill along the
direction of maximum slope the direction giving the
greatest speed-up near the crest.
"speed up"
l
These formulae suggest that hills with slopes less
than 1 in 10 are unlikely to produce significant speedup of the wind. A more extended discussion of this
question and other simplied models for three-dimensional hills are given in Reference (6). Background
material may be found in References (7) and (8). Wind
tunnel tests and computational methods may be used
to obtain design information in other cases.
The speed-up principally affects the mean wind
speed and not the amplitude of the turbulent fluctuations. This leads to a correction in the gust effect
factor referred to below.
Escarpment
Dynamic Response and Gust Effect
Factor, C g
Figure B·2 Definitions for wind speed-up over hills and
escarpments
General
19. In this section, procedures are recommended
for determining the dynamic response and "gust effect
factorff referred to in Sentence 4.1.8.1.(6) of the NBC.
This factor, denoted Ch , is defined as the ratio of the
Table B·1
Parameters for Maximum Speed-Up Over Low Hills
k
Hill Shape
2-dimensional ridges
(or valleys with H negative)
2-dimensional escarpments
3-dimensional axisymmetrical hills
Column 1
ｾｓｭ｡ｸ＠
a
x<O
x>O
2.2 H/L
3
1.5
1.5
1.3 H/L
1.6 H/L
2
2.5
4
3
1.5
1.5
4
4
1.5
5
(1)
Note to Table B·1:
For H/L > 0.5, assume in the formulae that H/L =0.5 and
substitute 2H for L in Equation (6).
(1)
144
I
pays
,-jP.
maximum effect of the loading to the mean effect of
the loading. The dynamic response includes the
action of
(a) random wind gusts acting for short durations
over all or part of the structure,
(b) fluctuating pressures induced by the wake of
the structure, including "vortex shedding
forces", and
(c) fluctuating forces induced by the motion of the
structure itself through the wind.
These forces act on the external surfaces of the
structure as a whole or on cladding components and
may also affect internal surfaces. They may act
longitudinally, laterally or torsionally and further
they may be amplified by resonance of the structure
at one or other of its natural frequencies.
All structures are affected to some degree by these
forces. The total response may be considered as a
superposition of a "background component," which
acts quasi-statically without any structural dynamic
magnification, and a "resonant" component due to
excitation close to a natural frequency. For the
majority of structures, the resonant component is
small and the dynamic factor can be simplified by
considering the background component only and
treated using normal static methods. For structures
that are particularly tall, long, slender, light-weight,
flexible or lightly damped, the resonant component
may be dominant.
The majority of structures can be treated using the
"simple procedure."
loading, can be identified as
The form of the fluctuating wind loading effect, a,
varies with the excitation, whether due to gusts,
wake pressures or motion induced forces. For a large
class of smaller structures, only the added loading
due to gusts must be dealt with and simplified
methods are adequate.
Simple Procedure
20. For small structures or structures and components having a relatively high rigidity, a simplified
set of dynamic gust factors is
C g = 2.5 for cladding elements and small
structural components,
2.0 for structural systems including
anchorages to foundations.
For some structures, peak pressure coefficients
have been determined directly from wind tunnel
tests, and composite values of (C C) are obtained
incorporating the aerodynamic shape factors.
Detailed Procedure
21. In the detailed procedure, the value of ｡Ｏｾ＠
be expressed
｡Ｏｾ＠
p
(7)
K=
Ce,H
=
where
＠ｾ
0'
gp
the mean loading effect,
the "root-mean square" loading effect, and
a statistical peak factor for the loading
effect.
According to this expression a dynamic factor,
equal to the ratio of the peak loading to the mean
can
(9)
where
A general expression for the maximum or peak
loading effect, denoted W p ,is
W p ］ｾＫｧ｡＠
(8)
C g = 1 + g p (0'/11)
r
a factor related to the surface roughness
coefficient of the terrain,
0.08 for Exposure A,
0.10 for Exposure B,
0.14 for Exposure C,
exposure factor at the top of the building,
H, evaluated according to Paragraph 13 or
Figure B-1. Over hills the value
should
be used (see Equation (6).
background turbulence factor obtained
from Figure B-3 as a function of W /H,
height of windward face of the building,
width of windward face of the building,
c;
B
=
H=
W=
145
pays
----------_....._--_....._---------------_
s
size reduction factor obtained from Figure
8-4 as a function of W /H and the reduced
frequency no H/V H
natural frequency of vibration, Hz,
mean wind speed (m/ s) at the top of
structure, H,
gust energy ratio at the natural frequency
of the structure obtained from Figure 8-5
as a function of the wave number,
nO/V H , and
critical damping ratio.
I
F =
ｾ＠
=
400
300
200
100
80
E
_ _ ..
inherent or structural damping. Aerodynamic damping in the along-wind direction becomes significant
at high wind speeds, but plays no useful role in
limiting cross-wind motion due to vortex shedding.
Spread footings on soft or medium stiff soil provide
additional damping in comparison to piled foundations or spread footings on stiff soil and rock. Measured damping values from more than 20 stacks are
tabulated in Reference (9) and results from 5 more
stacks are given in Reference (10). The logarithmic
decrement mentioned therein is 21t times the critical
damping ratio. Sachs (9) concludes by stating a range
of 0.0016 to 0.0080 for ｾ＠ for the total damping of
closed circular, unlined welded steel stacks, and
suggests that the minimum value be used in design.
Corresponding ranges for lined welded steel stacks
and for unlined reinforced concrete stacks are given
as 0.0048 to 0.0095 and 0.0095 to 0.0191, respectively.
23. The peak factor, gp' in Equation (7) gives the
number of standard deviations by which the peak
load effect is expected to exceed the mean load effect,
and is given in Figure 8-6 as a function of the average
fluctuation rate. The average fluctuation rate, v, can
be estimated as follows:
60
as
...
40
:s
u
2
1ii
'0
.E
0>
iD
J:
v=no",\/ ＠ｾ
Vi ｳｆＫｾｂ＠
10
8
. .Ｍｾ＠
(10)
where
no = natural frequency of vibration, Hz,
s, F Ｌｾ＠ 8 as defined for Equation (8).
ＱｾＭ＠
'"'''/ .
Explanatory Notes Regarding crill and gp
dx
o
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Background turbulence factor. B
Figure 8·3 Background turbulence factor as a function of
width and height of structure
22. Suggested values for ｾ＠ must be based mainly on
experiments on real structures. Expressed as a fraction
of critical damping, values commonly used in the
design of buildings with steel frames and concrete
frames are 0.01 and 0.02, respectively. Masts and
stacks, on the other hand, may have much lower
146
24. The response of a tall, slender building to a
randomly fluctuating force can be evaluated rather
simply by treating it as a rigid, spring-mounted
cantilever whose dynamic properties are specified by
a single natural frequency and an appropriate damping value. The variance of the output quantity or
loading effect is the area under the spectrum of the
input quantity (the forcing function) after it has been
multiplied by the transfer function. The transfer
function is the square of the well-known dynamic
load magnification factor for a one-degree-of-freedom oscillating mechanical system.
pays
5. 0 1---.Io;:--I---+--oIci-+--14. 0
ｾＭＫＮ､
ＳＮＰｾＭＫＴ｣ｴｲ＠
2. 0
ｉＭＫｾ＠
I>T
O. 7
ｾＭＫｉｴﾷ＠
0.5 I---+--+--+--t-++--I-+-+++-+---I--I-O. 3
t---l--l-
0.2 I---l--l-
__ｾＭｌ＠
ｏＮ｜ｾＭｌ＠
__ｾ＠
0.00\
Size reduction factor, S
Figure 8-4 Size reduction factor as a function of width, height and reduced Irequency of structure
IJ..
II
ｾ＠
0
>0)
m
c
Q)
iii
:::l
(!)
1. 00
0.80
0.60
0.40
0.30
0.20
O. 10
0.08
0.06
0.04
0.03
0.02
0.01
0.0001
•
-
=±=t=--
I
ｾＭＬＮ＠
I
..,.......
.....
1/
II
I I II
mit
x2
F= _ _
o_
ＨｬＫｸｾＩＴＯＳ＠
Xo = (1220 no/V H)
I
ｾｅ＠
"- ....
I
I
0.001
1111
I
ｾＬ＠
II
I
IIII
•
0,01
O. 1
1.0
Wave number, waves/m, noNH
Figure 8-5
Gust energy ratio as a function of wave number
147
pays
25. In the case of wind as the random input, the
spectrum of the wind speed must first be multiplied
by another transfer function called the "aerodynamic
admittance function," which in effect describes how
the turbulence in the wind is modified by its encounter with the building, at least insofar as its ability to
produce a loading effect on the structure is concerned.
to create a new peak or hump centred at the natural
frequency of the structure, usually well to the right of
the broad peak, which represents the maximum
density of input power of the wind.
27. The area under the loading effect spectrum,
the square root of which is the coefficient of variation
a I Il, is taken as the sum of two components: the area
under the broad hump, which must be integrated
numerically for each structure, and the area under
the resonance peak, for which a single analytic
expression is available. These components are
respecrepresented in Equation (9) by B and ｳｆＯｾＬ＠
tively. The factor K/C eH can be thought of as scaling
the result for the appropriate input turbulence level.
If resonance effects are small, then sF I ｾ＠ will be small
compared to the background turbulence B, and vice
versa.
26. For the purposes of calculating alll, the
spectrum of the wind speed is represented by an
algebraic expression based on observations of real
wind. The aerodynamic admittance function is also
an algebraic expression, computed on the basis of
somewhat simplified assumptions but appearing to
be in reasonable agreement with the limited experimental evidence at present available. The spectrum
of wind speed is a function of frequency having the
shape of a rather broad hump (Figure B-5). The effect
of the aerodynamic admittance is to reduce the
ordinates of the curve to the right of the hump more
and more as the frequency increases. This is partly a
reflection of the reduced effectiveness of small gusts
in loading a large area. The effect of the dynamic
load magnification factor or mechanical admittance is
28. The peak factor, gp' depends on the average
number of times the mean value of the loading effect
is crossed during the averaging time of 1 h (3600 s).
The functional relationship in Figure B-6 holds when
the probability distribution of the mean loading effect
is normal (Gaussian). (11)
5.0
4.0
ｾ＠
.E
.:£
til
Q)
c..
.;,<>
3.0
2.0
1. 0 t--I--!-+-+---+-I-
ｏｾＭｌ＠
0.02
O. 04
0.06
II.
Figure 8·6
148
O. 1
0.2
0,4
0.6 0.8 1
Average fluctuation rate, cycles/second
Peak factor as a function of average fluctuation rate
pays
......
Sample Calculation of C g
Vortex Shedding
29. To illustrate the calculation of a gust effect
factor the following sample problem will be worked
in detail:
30. Slender free standing cylindrical structures
such as chimneys, observation towers and in some
cases, high rise buildings, should be designed to
resist the dynamic effect of vortex shedding. When
the wind blows across a slender prismatic or cylindrical body, vortices are shed alternately from one side
and then the other, giving rise to a fluctuating force
acting at right angles to the wind direction along the
length of the body. A structure may be considered
slender in this context if the ratio of height to diameter exceeds 5. The wind speed, VH , at the top of the
structure when the frequency of vortex shedding
equals the natural frequency, n, of the structure is
given by:
Required: To obtain the gust effect factor for a
building with the following properties:
183m
Height
30.5 m
Width
30.5m
Depth
0.2 Hz
Fundamental natural frequency
0.015
Critical damping ratio
Exposure B
Terrain for site
Reference wind speed at
10m open terrain
27.4 m/s
Step 1: Calculate required parameters
C eH 1.90 (from Figure B-1)
Mean wind speed at top of building, Vw from
Equation (5) 27.4 x V1.90 = 37.5 m/s
(Figure B-1)
Aspect ratio W /H 30.5/183 = 0.17
Wave number for calculation of F: n/V H 0.0053
Reduced frequency for calculation of s: nnH/V H
0.975.
Step 2: Calculate (j / Jl, from Equation (9)
(1) K= 0.10 for Exposure B
(2) B = 0.62 (from Figure B-3)
(3) s = 0.11 (from Figure B-4)
(4) F 0.28 (from Figure B-5)
(5) ｾ］＠
0.015 (given)
(6)
1/
--
(0.62 + 0.11 x 0.28) = 0.375.
V 1.90
0.015
Step 3: Calculate v, from Equation (10)
(1) no 0.2 Hz (given)
(j/Jl=
_ __0_.1__1_x .0. . . . . .2_8___
0.11 x 0.28 + 0.015 x 0.62
Step 4: Obtain peak factor gp:
(1) gp = 3.75 (from Figure B-6).
(2) v=0.2
Step 5:
=0.175/ s.
(from Equation (8» = 1 + 3.75 x 0.375 =
2.41.
(11)
where
n
frequency in Hz,
S = Strouhal Number,
VI!
the mean speed at the top of the structure
in m/s, and
D = diameter in metres.
31. For circular and near-circular cylinders, the
Strouhal number is a function of the Reynolds
number, Re. Although the Reynolds number is a
function of Vw a trial-and-error approach to finding
the critical mean speed can be avoided by examining
the product, nD2, and using the appropriate version
of Equation (11) as follows:
if nD2 ::; 0.5 m 2/s, VH = 6 nD
(l1a)
if 0.5 m 2/s < nD2 < 0.75 m 2/s,
VH= 3 nD + (1.5 m 2/s)/D (11b)
2
if n02 ｾ＠ 0.75 m /s, VH= 5 nD.
(11e)
The Reynolds number is given by:
Re = (V HD/15) X 106
Equation (11a) applies when Re < 2 x 105 and S
1/6. Equation (l1b) covers an intermediate region
where, for computational convenience, S is taken to
increase approximately linearly as Re increases to 2.5
x 10 5 • Equation (11c) usually governs, in which Re >
2.5 x 10 5 and S = 1/5.
149
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32. The dynamic effects of vortex shedding from a
cylindrical structure can be approximated by a static
force acting over the top one-third. The equivalent
static force per unit height FL , is given by
Cl
fA
where
ｾ＠
Yｾ＠ -ｃＧｰｾＲ＠
qHD
(12)
the critical damping ratio as defined for
Equation (9),
= aspect ratio (H/D),
H
height of structure,
qH = the velocity pressure corresponding to VHI
where V H is in mis, 0.6VIi inPa,
average mass per unit length over the top
M
one-third of the structure (kg/m), and
p = density of air::::: 1.2 kg/m 3 •
For most situations
C 1 = 3 for A > 16; C 1 = 3'VA for A < 16
If
ｾ＠
0.6.
4
< C2 prj
M
then large amplitude motions up to 1 diam may
result. Amplitude predictions for this case are
discussed in Reference (12), which is suggested as a
general reference on the subject of vortex shedding
on chimneys.
If VH is low, temperature gradients may produce
very low turbulence levels, and in such cases vortex
induced motions are significantly increased, particularly for very slender structures. If VII is less than
10 m/s and Agreater than 12, then
C 1 6, and
= 1.2.
33. For tapered structures some reduction in the
vortex shedding forces can be made. However, if the
variation in the diameter over the top third is less
than 10 per cent of the average diameter of the top
third, then the recommendations of Paragraph 32
apply.
If the diameter variation exceeds 10 per cent, then
the effective static load need be applied only over
150
that part of the structure over which the diameter is
within 10 per cent of the average for that part.
For tapered structures with a diameter variation
exceeding 10 per cent over the top third
C 1 = 3, and
C 2 = 0.6
and no increase in these coefficients is required for
low values of Vw
34. The recommendations of Paragraphs 32 and 33
apply to free standing structures vibrating in the
fundamental mode. For other mode shapes a dynamic analysis would be appropriate, although
Equation (11) may be used to determine the critical
speed. The application of Equation (12) will yield a
rough estimate of the effects of vortex shedding if the
load is applied over a length of up to one-third of the
total length and in a position centred upon the
location of the maximum displacement for the mode
of vibration in question. Slender structures with
cross-sections other than circular may also give rise
to vortex shedding, but data are limited and other
forms of across-wind motion may develop if the
wind speed, VII' is greater than about 7nD, where D
is the across-wind breadth. In such cases wind
tunnel tests provide the most satisfactory method of
estimating the likely response.
Pressure Coefficients
35. Pressure coefficients are the non-dimensional
ratios of wind-induced pressures on a building to the
dynamic pressure (velocity pressure) of the wind
speed at the reference height. Pressures on the
surfaces of structures vary considerably with the
shape, wind direction and profile of the wind velocity. Pressure coefficients are usually determined from
wind tunnel experiments on small-scale models,
although in a few recent instances measurements on
full-scale buildings have been used directly. In most
cases these pressures must be measured in a wind
tunnel in which the natural velocity profile and
turbulence are simulated; experiments in uniform
flow can be highly misleading.(13, 14)
I
pays
36. The information on external and internal
pressure coefficients given in Figures B-7 to B-24
covers the requirements for the design of the cladding and the structure as a whole for a variety of
simple building geometries. With the exception of B7 to B-10, the values of the pressure coefficients are
given as either time- and spatially-averaged pressure
coefficients, C p' or simply as time-averaged local
In Figures 8-7 to B-10,
pressure coefficients, ｃｾＮ＠
dealing with low rise structures, values of the product CpC g are given; this is the form in which they are
used, and of the basic wind tunnel data from which
they were derived.
Internal Pressures
37. The internal pressure coefficient, C i' defines
the effect of wind on the air pressure insiJe the
building and is important in the design of both
cladding elements and the primary structure. The
magnitude of this coefficient depends on the distribution and size of the leakage paths and openings
which vent the internal air space to the external wind
pressures. If the leakage is slow, through small
cracks and pores in the building envelope, and is
uniformly distributed, the internal pressures will
equilibrate to a pressure approximately equal to the
average external pressure over the exposed surface of
the building. With very small cracks and pores, the
influence of gusts will be attenuated. If the openings
are larger and more significant, on the scale of doors
or windows, the internal pressure will move closer to
that prevailing externally at the largest dominant
opening and gust pressures will be felt within the
interior. Because of the changeability and uncertainty of the size and distribution of these openings,
internal pressure coefficients can be influential and
wide ranging.
In the face of these uncertainties, an appropriate
treatment of internal pressure coefficients for both
high and low structures is to use the coefficients in
Figure B-12 in conjunction with the formula in NBC
Sentence 4.1.8.1.(3) and a C g of 1.0 or 2.0 as appropriate. This choice depends on whether there are
significant openings and whether small openings
producing background leakage are uniformly distributed. In this context, a large or significant opening is
a single opening or a combination of openings on any
one wall which offers a passage to the wind and
whose area exceeds the leakage area of the remaining
building surface, including the roof. Such a significant opening may be provided by main doors,
shipping doors, windows and ventilators if they are
open during a storm, either through expected usage
or through damage.
To handle the range of circumstances which may
prevail, three basic design categories are provided as
follows:
Category 1 (C ' = 0.0 to - 0.3; C g = 1.0)
ｾ＠
This category includes buildings without large or
significant openings, but having small uniformly
distributed openings (accumulating to less than
0.1 per cent of total surface area). The value of C i
should be 0.3 as given in Figure B-12, except where
such openings alleviate an external load, when
C,pi 0 should be used. Internal pressure fluctuates
even within buildings having small distributed
openings, and the pressure fluctuations occasionally
reach C,pi O. Such buildings would include most
high-rise buildings that are nominally sealed and
ventilated mechanically, and exceptional lower
buildings, such as windowless warehouses, with
door systems not prone to storm damage.
Category 2 (C pi
0.7 to - 0.7; C g = 1.0)
This category includes buildings in which significant openings, if any, can be relied on to be closed in
storms but in which background leakage may not be
uniformly distributed. Most low buildings fall into
this category provided that all elements (shipping
doors especially) are designed to be fully wind
resistant. In this category, the building should be
designed for the full range of C pi
0.7) given in
Figure B-12.
Category 3 (C pi' = 0.7 to
0.7; Cg = 2.0)
This category includes buildings with large or
significant openings through which gusts are trans151
pays
•
mitted to the interior. Normally the range of C pi =
± 0.7 should be used as given in Figure B-12, in conjunction with C g = 2.0. Such. buildings would include, for example, sheds WIth one or more open
sides, and industrial buildings with shipping doors,
ventilators or the like, having a high probability of
being open during a storm or not fully resistant to
design wind loads.
An ever-present threat in severe storms is the
breakage of large unprotected glass areas (and other
vulnerable components) by flying debris. Structures
required in post-disaster services should be capable
of withstanding all the consequences of failure of
glass and be included in Category 3. For other
structures, in which the glass is designed for wind
and there is adequate protection against roof uplift,
the contingency of glass damage due to debris is
covered by normal load factors for wind.
In most cases, there is no need to consider nonuniform internal pressures except in the design of
internal partitions, see Clause 4.1.8.4.(1 )(a). Thus, for
most structural design, the two limiting values of
internal pressure can be considered separately.
Exceptions might arise if interior compartments of
the building are well sealed and wind damage or the
like could expose one area of the building to Category 3 conditions while the rest of the building
remains Category 1 or 2, resulting in unbalanced
internal pressures.
Internal pressures are also affected by mechanical
ventilation systems and by the stack effect due to
different inside and outside air temperatures. Under
normal operations, mechanical systems create a
differential across walls of somewhat less than
0.1 kPa, but the stack effect for differences in temperature of 40° could amount to 0.2 kPa per 100 m of
building height (Reference (15».
38. Figures B-7 to B-l0 refer to low buildings and
present recent data obtained from systematic boundary layer wind tunnel studies. In several instances
these data have been verified against full scale
measurements. The coefficients are based on the
152
maximum gust pressures lasting approximately 1 s
and, consequently, include an allowance for the gust
factor, C g • The coefficients, therefore, represent the
product C C g • These figures refer to the tributary
area associated with the particular element or member over which the wind pressure is assumed to act.
In all cases these coefficients should be combined
with the appropriate internal pressures. Figures B-7
to B-l0 are most appropriate for buildings with
widths greater than twice their heights and a reference height that does not exceed 10 m. In the absence
of more appropriate data they may also be used for
buildings with H/W < 1 and reference height less
than 20 m. Beyond these extended limits, Figure B-ll
should be used. Further details of the work on which
these results are based are given in References (16)
and (17).
39. Figure B-7 presents values of C Cg applicable
to those primary structural actions affected by wind
pressures on more than one surface, such as in
framed buildings. These simplified load distributions were developed to yield as closely as possible
the structural actions (horizontal thrust, uplift and
frame moments) determined directly from experiment. These results make allowance for the partial
loading of gusts referred to in NBC Sentence
4.1.8.3.(1).
40. Figures B-8 to B-l0 are intended for those
actions influenced mainly by wind acting over single
surfaces, such as the design of cladding and secondary structural members. They should also be used
for design of primary structural elements of single
surfaces, for example, roofs for which moment
connections are not provided at the roof/wall
intersection. In this case, the edge region loads need
not be included around the entire perimeter of the
roof, but only adjacent to the windward edges. For
roofs exceeding 10° where edge regions are also
specified along the ridge, these increased loads need
only be included on the downstream side. The loads
on other edge regions can revert to the values specified for the interior regions.
pays
Wind direction
range
Building surlaces
Root slope
0 TO So
20
0
30 TO 45
90
0
0
Notes to Figure B·7:
The building must be designed for all wind directions. Each
corner must be considered in turn as the windward corner
shown in the sketches. For all roof slopes, Case A and
Case 8 are required as two separate loading conditions to
generate the wind actions, including torsion, to be resisted by
the structural system.
(2)
For values of roof slope not shown, the coefficient (C C )
may be interpolated linearly.
p9
(3)
Positive coefficients denote forces toward the surface,
whereas negative coeHicients denote forces away from the
surface.
(4)
Interior pressure coefficients C i are given in Figure 8-12.
(5)
The reference height, H, for ｰｲｾｳｵ･＠
is mid-height of the
roof or 6 m, whichever is greater. The eave height may be
substituted for the mean height if the slope of the roof is less
than 10°.
(6)
For the design of foundations, exclusive of anchorages to the
frame, only 70 per cent of the effective load is to be
considered.
(7)
End zone width "y" should be the greater of 6 m or 2 z, where
"z" is the gable wall end zone defined for Case 8 below.
Alternatively, for buildings with frames, the end zone "y" may
be the distance between the end and the first interior frame.
(8)
End zone width "z" is the lesser of 10 per cent of the least
horizontal dimension or 40 per cent of height, H, except that
"z" must be at least 4 per cent of the horizontal dimension
and at least 1 m.
(1)
Load case A. winds generally perpendicular 10 ridge
0.7S
IE
I.IS -1.3
2E
-2.0
-0.7
4
3E
-1.0 -0. SS
4E
-0.8
1.0
I.S
-1.3
- 2.0
-0.9
-1.3 -0.8
-1.2
I. OS
1.3
0.4
O. S
-0.8
-1.0 -0.7
-0.9
I. OS
1.3
I. OS
1.3
-0.7
-0.9 -0.7
-0.9
Load case 8' winds generally parallel 10 fldge
6E
Figure B·7 External peak pressure coefficients, CpC g, for
primary structural actions arising 'from wind load acting
simultaneously on all surfaces.
153
pays
-6.0
-5.0
-2.0
-4.0
-1.0
aa.
ocr>
､ｾ＠
0
t-----------I
-3.0
0
-2.0
(6)
*
1.0
-I
0
2 . 0 L....-L....-l---I.-.....L----L---L---L----J
o
1
2
5
10
20
50
100
Area.m2
+
Figure 8·8 External peak pressure coefficients, C C , on
individual walls for design of cladding and secondcfry gstructural
members
Notes to Figure 8·8:
(1)
These coefficients apply for any roof slope, a.
(2)
The abscissa area in the graph is the design tributary area
within the specified zone.
(3)
z = 10 per cent of least horizontal dimension or 40 per cent
of height, H, whichever is less. Also z ｾ＠ 1 m, z ｾ＠ 4 per cent
of least horizontal dimension.
(4)
Interior pressure coefficients C . are given in Figure 8-12.
(5)
The eave height may be substftuted for the reference height
(mean height) if the angle of the roof is less than 10°.
Notes to Figure 8·9:
Canopy coefficients include contributions from both upper
and lower surfaces. (28)
(2) sand r apply to both roofs and upper surfaces of canopies.
(3)
The abscissa area in the graph is the design tributary area
within the specified zone.
0
Area, m 2
Figure 8·9 External peak pressure coefficients, C C ,on roofs
of 10° slope or less for design of cladding and ｳ･｣ｯｨ､ｾｲｹ＠
structural members
(4)
(5)
(6)
(1)
154
1.0
(7)
Z = 10 per cent of least horizontal dimension or 40 per cent
of height, H, whichever is less. Also z ｾ＠ 1 m, z ｾ＠ 4 per cent
of least horizontal dimension.
Interior pressure coefficients Cpi are given in Figure 8-12.
For uplift on tributary areas in excess of 100 m2 on unobstructed nearly-flat roofs with low parapets where the centre
of the tributary area is at least two building heights from the
nearest edge, the value of C C may be reduced to -1.1 at
x/H = 2 and further reduced ｾｮ｡ｲｬｹ＠
to - 0.6 at x/H = 5, where
x is distance to the nearest edge and H is building height.(29)
For roofs having a perimeter parapet with a height of 1 m or
greater, the corner coefficients CpCgfor small tributary areas
can be reduced from - 5.4 to - 4.4. (30,31)
pays
l
ｾＭｕＢｦＧ＠
@
,
H
a :: 10
45
height
0
-5.0
-5.0
roofs
30° _ 45
roofs
-4.0
-4.0
-3.0
-3.0
0
Ol
()
0-
()
-2.0
-2.0
Ol
()
(:)
()
- 1 .0
1.0
®,CD
1.0
a.
and©
1.0
100
0
Area, m2
2.0
a
1
5
10
20
50
100
Area, m'
Figure 8-10 External peak pressure coefficients, CpC g, on roofs
of greater than 10° slope for design of cladding and secondary
structural members
Notes to Figure 8·10:
(1)
The abscissa area in the graph is the design tributary area
within the specified zone.
(2)
z =10 per cent of least horizontal dimension or 40 per cent
of height, H, whichever is less. Also z ;;:: 1 m, z ;;:: 4 per cent
of least horizontal dimension.
(3)
Interior pressure coefficients Cpi are given in Figure 8-12.
155
pays
41. Figures B-ll and B-12 are for use with taller,
rectangular structures for which H/W is greater
than 1. The pressure coefficients given are not yet
multiplied by a gust effect factor, C , because they are
intended for use either with those factors given in
NBC Sentence 4.1.8.1.(6) or with the detailed method
in which C g for the structure as a whole depends on
its dynamic properties as well as turbulence characteristics. A local pressure coefficient, C * = -1.0,
applicable to the design of small claddiri g areas
(about the size of a window), can occur almost
anywhere at any elevation, and is not limited to
corners. The simple procedure is mandatory for
calculating local cladding loads.
42. Figures B-13 to B-24 are based on wind tunnel
experiments in which the correct velocity profile and
wind turbulence were not simulated and should
therefore be regarded with caution. They are based
on the Swiss Association of Engineers and Architects
Standards, S.LA., No. 160, published in 1956.(18)
Protected Membrane Roofs
43. In the case of a protected membrane roof, with
insulation which is not bonded to the waterproofing
membrane, the insulation is not subjected to the same
uplift pressure as is applied through the depth of the
entire roof assembly, because of air leakage and
partial pressure equalization between the top and
bottom of the insulation boards. External pressure or
uplift due to wind is, therefore, applied to the membrane, which acts as an air barrier between the inside
and the outside and prevents pressure equalization.
Further information can be found in References (19)
and (20).
Rounded Structures
44. For rounded structures (in contrast to sharpedged structures) the pressures vary with the wind
velocity, depending on the Reynolds number, Re,
(defined following Equation (11». In Figures B-15, B16, B-19 and B-24, which have been translated and
reproduced from the Swiss tables,oS) the Reynolds
number is expressed by d VqC e , where d is the diameter of the sphere or cylinder in metres and q is
156
the velocity pressure in kilo pascals. To convert to Re,
multiply d VqC e by 27 X 10°.
45. The roughness of rounded structures may be
of considerable importance. Common well-laid
brickwork without parging can be considered as
having a "moderately smooth" surface (Figure B-15).
Surfaces with ribs projecting more than 2 per cent of
the diameter are considered "very rough." In case of
doubt, those C values which result in the greater
forces should b1e used. For cylindrical and spherical
objects with substantial stiffening ribs, supports and
attached structural members, the pressure coefficients depend on the type, location and relative
magnitude of these roughnesses.
Icing
46. In locations where the strongest winds and
icing may occur simultaneously, forces on structural
members, cables and ropes must be calculated
assuming an ice covering based on climate and local
experience. For the iced condition, values of C given
in Figure B-19 for thick wire cables for a "rough"
surface should be used.
Structural Members
47. In Figures B-20, B-21, B-23 and B-24 pressure
coefficients with the subscript are used to indicate
that they apply to structural members of infinite
lengths and this is multiplied by a reduction factor, k,
for finite lengths of members. If a member projects
from a large plate or wall, the reduction factor, k,
should be calculated for a slenderness based on twice
the actual length. If a member terminates with both
ends in large plates or walls, the reduction factors for
infinite length should be used.
00
Loads on Frames and Shielding
48. For framing members that are located behind
each other in the direction of the wind, the shielding
effect may be taken into account. The windward
members and those parts of the leeward members
that are not shielded should be designed with the full
pressure, q, whereas the shielded parts of the leeward
members should be designed with the reduced
pressure, qx' according to Figure B-22.
pays
Notes to Figure 8·11:
Wind perpendicular to one wall: for width, use the dimension
perpendicular to the wind direction.
(2)
Wind at an angle to the wall: this condition produces high
local suctions on the wall which is at a slight angle to the
wind. The coefficient Cp* may occur anywhere over the wall
area, but need not be considered in conjunction with the Cp
for over-all loading. The coefficients Cp* for the roof are
given in Figure 8-12.
(3)
End walls: pressure coefficients for end walls (parallel to
wind direction) are given in Figure 8-12.
(4)
Interior pressure: coefficients Cpi for interior pressures are
given in Figure 8-12.
(5)
Reference heights for exposure factor for the calculation of
both spatially-averaged and local pressures:
leeward walls
0.5 H
roof and side walls
H
in conjunction with Cp*
H
any area at height Z above ground
on the windward wall
Z
(6)
Height H1: the height to which Ce is constant is 10m for the
simplified method and exposure A, 12.7 m for exposure 8
and 30 m for exposure C.
(7)
Windward wall Cp: the pressure coefficient is 0.8 for the
entire height. The variation in the pressure distribution
shown is due to variation in exposure factor Ceo
(1)
cp = -1.0
Cp
-0.5
c·p = -1.0
pressure
distribution
pressure
distribution
(7)
H
z
H1
Elevation of building
Figure 8·11
width
Flat roofed buildings greater in height than in
157
pays
,
Notes to Figure 8·12:
Local maximum suctions: the coefficients Cp* for the roof
surface occur for wind at an angle to one corner, and are
used in the design of the roofing itself and its anchorage to
the structure. Cp* are not to be added to Cp for determining
total uplift on the roof.
(2)
End walls: the end walls are the ones parallel to the wind
direction; they have a uniform pressure distribution over the
whole building height, except for local maximum suction as
indicated in Figure B-11.
(3)
Reference height for exposure factor: for the calculation of
external pressures on end walls use H, the totailleight of
the building. For the calculation of internal pressures, use
one-half H; where there are dominant openings in the
windward wall, use Z, the height to the highest such
opening.
(4)
The value of C/ can be reduced from 2.3 to - 2.0 for roofs
with perimeter parapets having heights> 1 m.(30,31)
(1)
c· = -2.3
D
c·p = -1.5
I
0.2D
I
02D
II
•
!
ｾ］［ｩＱ＠
］ｲ［ｩｊｾ＠
Iw
C D = -0.7
Plan view of building
Interior pressures
1. Openings mainly in windward
wall
+0.7
2, Openings mainly in leeward
wall
-0.5
3. Openings mainly in walls
parallel to wind direction
-0.7
4. Openings uniformly distnbuted
in all 4 walls
-0.3
Figure 8·12 End wall pressure coefficients, local suction
maxima on the roof and interior pressures for use with Figures
B-7 to B-11
158
I
pays
A detailed discussion of the loads on unclad
building frameworks is given in Reference (21).
49. As the shape of a structure may change during
erection, the wind loads may be temporarily higher
during erection than after completion of the structure. (22) These increased wind loads should be taken
into account using the appropriate coefficients from
Figures B-7 to B-24.
50. For constructions made from circular sections
with ､ｶｱ｣ｾ＠
< 0.167 and As/ A ｾ＠ 0.3, the shielding
factors can be taken by approximation from Figure B22. If dV gCe > 0.167, the shielding effect is small and
for a solidIty ratio As / A ｾ＠ 0.3, it can be taken into
account by a constant shielding factor kx:::: 0.95.
Partial Loading and Torsional Loading
51. NBC Sentence 4.1.8.3.(1) requires all buildings
to be designed for partial loading as well as full
loading, as illustrated in Figure B-25. Removal of up
to 25 per cent of the load prescribed by the Code
from any part of the structure is intended to reflect
the observed behaviour of pressure patterns in
turbulent wind. Some structures, such as arch-type
roof systems, undergo larger stresses under partial
loading. Low buildings designed to the specifications of Figure B-7 do not need further unbalanced
loads (see Paragraph 39). Tall buildings should be
checked against partial loadings that produce
torsional effects. In wind tunnel testing, torsional
effects have sometimes been even greater than those
afforded by a 25 per cent removal of loads from
selected areas of the building. (14) Torsional effects are
enhanced when the centre of twist is eccentric from
the centre of gravity (inertial loading) or from the
centre of area (wind loading, full or partial).
52. The pressure coefficients in Figures B-11 and
6-12 refer to the pressures acting along the principal
axes of rectangular building forms. They are most
appropriate for buildings where H/W > 1 and H>
10 m. In some structural systems more severe effects
may be induced when the resultant wind pressures
approach the building diagonal. To account for this
and also the additional tendency for structures to
sway transversely to the wind direction, the structure
should be capable of resisting 75 per cent of the
maximum loads for each of the principal directions
applied jointly, as specified in NBC Sentence
4.1.8.3.(1). The influence of the 25 per cent removal
of load discussed in Paragraph 51 should also be
examined for combined loads for its influence on
torsion, as specified in NBC Clause 4.1.8.3.(1)(d).
Further discussion of combined loading effects can be
found in References (23) and (24).
Lateral Deflection of Tall Buildings
under Wind Loading
53. Lateral deflection of tall buildings under wind
loading may require consideration from the standpoints of serviceability or comfort. The general trend
is toward more flexible structures, partly because
adequate strength can now be achieved by using
higher strength materials that may not provide a
corresponding increase in stiffness.
54. One symptom of unserviceability may be the
cracking of masonry and interior finishes. Unless
precautions are taken to permit movement of interior
partitions without damage, a maximum lateral
deflection limitation of 1/250 to 1/1000 of the
building height should be specified. According to
Sentence 4.1.1.5.(5) of the 1990 NBC, 1/500 should be
used unless a detailed analysis is made.
Wind-Induced Building Motion
55. While the maximum lateral wind-loading and
deflection are generally in the direction parallel with
the wind (along-wind direction), the maximum
acceleration of a building leading to possible human
perception of motion or even discomfort may occur
in the direction perpendicular to the wind (acrosswind direction). Across-wind accelerations are likely
to exceed along-wind accelerations if the building is
slender about both axes, that is if VWD IH is less
than one-third, where Wand 0 are the across-wind
and along-wind plan dimensions and H is the height
of the building.
159
pays
56. Although treatment of this subject is somewhat tentative, the following guidelines may be of
assistance. A wide range of turbulent boundary layer
wind tunnel studies, have demonstrated that the
peak acceleration in the across-wind direction at the
top of the building can be found from the following:
58. Although many additional factors such as
visual cues, body positions and orientation and stateof-mind influence human perception of motion,
when the amplitude of acceleration is in the range of
0.5 per cent to 1.5 per cent of the acceleration due to
gravity, movement of the building becomes perceptible to most peopleY5-27)
(13)
59. Based on this and other information, a tentative acceleration limitation of 1 to 3 per cent of
gravity once every 10 years is recommended; for use
in conjunction with Equations (13) and (14) the lower
value might be considered appropriate for apartment
buildings, the higher value for office buildings. The
application of Equations (13) and (14) tends to give
conservative results insofar as they assume that the
wind always comes from the most sensitive direction;
this factor has also been considered in setting the
above limitation. A designer who has more detailed
information available can make suitable allowances.
57. In less slender structures or for lower wind
speeds, the maximum acceleration may be in the
along-wind direction and can be found from the
expression
(14)
where
across-wind and along-wind building
dimensions, m,
peak acceleration in across-wind and
along-wind directions,
m/s2,
=
78.5 X 10- 3
ar
PB
ｾｷＧ＠
ｾｯ＠
=
average density of the building, kg/ m:>,
=
fraction of critical damping in acrosswind and along-wind directions,
n w,no
fundamental natural frequencies in
across-wind and along-wind directions,
Hz,
maximum wind-induced lateral deflection at the top of the building in alongwind direction, m,
acceleration due to gravity = 9.81 m/ S2,
g
g p, K, s, F, Ce , C g are as defined previously in connection with Equation (9).
Note that
definitions.
160
ｾｯ＠
= ｾ＠
and no = no in terms of previous
60. Owing to the relative sensitivity of expressions
and (14) to the natural frequency of vibration,
and in (14) to the corresponding building stiffness,
these should be determined using fairly rigorous
methods, and approximate formulas should be used
with caution. For example, the adoption of a natural
frequency of 10/N, where N is the number of storeys,
may not be consistent with the assumption that the
displacement under wind loading is as large as H/
500.
(13)
61. If a more rigorous analysis is not available, the
maximum deflection resulting from the equivalent
static wind loading can be related to the fundamental
building frequency using modal representation of the
building motion. The following assumptions may be
acceptable:
(1)
Use first mode only, assumed linear
<j>(Z) = r 1Z
(2)
(15)
Uniform distribution of building mass
m(Z)
= WDP B
(16)
I
pays
r
As a consequence of modal representation
H
cp(Z)m(Z)$(Z)dZ
u(Z)
41t2ul> =
r 2 4>(Z)
r ＼ｉ＾ＨｚＩｾｐ＠
(18)
<I>(Z)dZ
H
u(Z)
.0
Jo
(17)
(19)
Z p( Z)dZ
(Ll
qC,CgC
2+a
rl'r 2
Ceq)
constants,
m(Z)
distribution of building mass, with
height Z, O<Z<H, kg/m,
acceleration due to gravity = 9.81 m/ S2,
g
u(Z)
displacement at height
P(Z)
distribution of equivalent static wind
pressure with height Z, O<Z<H, kPa.
O<Z<H, m,
e
Substituting Equations (22) and (23) into (14)
3.9 ) (
2+a DgpB
fundamental eigenvector,
=
(23)
where Cp = 0.8 -(- 0.5) = 1.3 and a is the appropriate
exponent from Equations (2), (3) and (4).
where
4>(Z)
p
(24)
62. Sample Calculation of aw and aD' A detailed
calculation for a wand a o using Equations (13) and
(24) will be made for the sample problem worked
earlier to illustrate the calculation of a gust effect
factor:
assume that nw = no = 0.2 Hz
ｾｷ＠
ｾｯ＠
= 0.015
PB = 176 kg/m3 •
Other symbols are as defined earlier.
Step 1: Calculate a r
From Equations (15), (16) and (17)
＼ｉ＾ＨｚＩ］ｾ＠
3
WDPBH
3
)z
ar
(20)
=
v:
32.1
Step 2: Calculate a w
From Equations (18), (19) and (20)
f2
= 78.5 x 10-3 [37.8/(0.2 x 30.5)]3.3
aw = 0.2 x 0.2 x 3.75 x 30.48 (
2
41t no
A
3
/
'V
3
WDPBH-
/' H
ZP(Z)dZ
(21)
0.69 m/s2
,0
7.1 per cent
Substituting Equation (21) into Equation (18), the
deflection at height H becomes
Step 3: Calculate q
H
3
ｾ］Ｍ
Ｔｾｮｬ＾ｄｰｂｈＲ＠
32.1
)
1730 "0.015
Z P(Z)dZ
q
(22)
= 0.00065 x 27.4 x 27.4
0.488 kN/m2
One possible expression for P(Z) assumes a power
law variation with a maximum at the top of qC eCgC p
161
pays
Step 4: Calcuiate a D / g
aD/g = 3.75
two other sample buildings. One is rectangular and
is examined in cases 1 and 2 for wind along both
axes. Results are given for three different terrains
and for three different wind pressures, corresponding to Montreal, Toronto and Vancouver. A tall
building with a waterfront location may be exposed
to all three terrain conditions for different wind
directions.
xO.ll xO.28 (3.9 ) (1.90X0.488)
2.50
30.5 x 1.73
1.90 x 0.015
= 3.4 per cent
63. In this example clearly the across-wind
accelerations overshadow the along-wind accelerations. Table B-2 gives the results of calculations for
Zone
Table B-2
Wind Induced Building Motions: Examples of Calculated Peak Accelerations (a)
in Along-Wind (D) and Across-Wind (W) Directions at Top of Building (H)
q 0.39 kPa
q =0.31 kPa
q =0.45 kPa
Exposure
(1/10 basis)
(1/10 basis)
(1/10 basis)
Factor
V (H),
V(H),
aw'
aw'
aD'
aD'
mls
mls
%g
%g
%g
%g
Ce
Ｇｾ＠
Case 1: 120 x 50 x 30 m building (1)
open
2.01
30.9
1.54
27.1
suburban
22.8
1.09
city
1.61
1.24
0.93
2.99(2)
1.93
1.08
34.7
30.4
25.5
2.30
1.78
1.33
4.38
2.82
1.58
37.3
32.6
27.4
2.87
2.22
1.67
5.55
3.52
2.01
Case 2: 120 x 30 x 50 m building (1)
open
2.01
30.9
1.54
27.1
suburban
city
1.09
22.8
1.80
1.40
1.07
1.84
1.18
0.66
34.7
30.4
25.5
2.53
1.98
1.51
2.69
1.73
0.97
37.3
32.6
27.4
3.12
2.45
1.88
3.41
2.19
1.23
38.2
36.1
32.8
6
2.45
2.24
2.01
7
4.73
3.92
2.83
8
41.1
38.8
35.2
9
3.01
2.75
2.48
10
5.99
4.96
3.59
11
Case 3: 240 x 50 x 50 m building (1)
2.43
34.1
1.75
open
3.23
suburban
2.17
32.2
1.59
2.68
1.94
1.79
29.2
city
1.43
2
4
Col. 1
5
3
Notes to Table B-2:
(1)
Full dimensions and properties of Cases 1 to 3 are
given in the following Table.
Case
1
2
3
Column 1
162
Height H
m
120
120
240
2
Weight
Density
kN/m 3
1.5
1.5
1.9
3
Dimen.
m
50
30
50
4
(2)
Bold faced values might exceed acceptable limits
and detailed wind tunnel tests might be warranted.
in D Direction
Frequency Damping
0.250
0.200
0.125
5
0.015
0.010
0.010
6
Dimen.
m
30
50
50
7
in W Direction
Frequency Damping
0.200
0.250
0.125
8
0.010
0.015
0.010
9
pays
Pressure Differences Across Interior Walls
and Partitions
64. Considerable pressure differences can result
across interior walls and partitions in high-rise
buildings and in low-rise buildings in exposed
locations, if windows are broken during a storm. In
certain locations almost the full pressure difference
between the windward and leeward sides of the
building could be applied across interior walls or
partitions. For example, a large window on the
windward side might be broken by flying debris and
the full positive pressure exerted on the walls of a
small room located at the broken window. Similar
conditions could prevail in an apartment building
with operable windows or doors. This pressure
difference could be aggravated by stack effects in a
tall building in the winter. On the other hand,
experience does not indicate many failures of interior
walls due to this cause, and thus interior walls and
partitions are not required to be designed for the
maximum possible pressure difference. A design
pressure difference of the order of 0.5 kPa may be
appropriate.
References
(1) Associate Committee on the National Building
Code, National Building Code of Canada 1990.
National Research Council of Canada, Ottawa,
NRCC 30619.
(2) E. Simiu and RH. Scanlan, Wind Effects on
Structures: An Introduction to Wind Engineering. John Wiley & Sons, New York, 1986.
(3) J.E. Cermak, Application of Fluid Mechanics to
Wind Engineering. Freeman Scholar Lecture,
Journal of Fluid Engineering, ASME, Vol. 97,
No.1, March 1975.
(4) D. Surry and N. Isyumov, Model Studies of
Wind Effects - A Perspective on the Problems
of Experimental Technique and Instrumentation. Int. Congress on Instrumentation in
Aerospace Simulation Facilities, 1975 Record,
pp.79-90.
(5) A.G. Davenport, Gust Loading Factors. Journal of Structural Division, Proc., Am. Soc. Civ.
Eng., Vol. 93, June 1967, pp. 12-34.
(6) D.R. Lemelin, D. Surry and A.G. Davenport,
Simple Approximations for Wind Speed-Up
Over Hills. 7th International Conference on
Wind Engineering, Aachen, West Germany,
July 6-10, 1987.
(7) p.s. Jackson and J.C.R Hunt, Turbulent Wind
Flow Over a Low Hill. Quart. Journal R. Met.
Soc., Vol. 101, 1975, pp. 929-955.
(8) J.L. Walmsley, P.A. Taylor and T. Keith, A
Simple Model of Neutrally Stratified Boundary-Layer Flow Over Complex Terrain With
Surface Roughness Modulations. BoundaryLayer Meteorology, Vol. 36, 1986, pp. 157-186.
(9) P. Sachs, Wind Forces in Engineering. Second
Edition, Pergamon Press, Toronto, 1978.
(10) L. Christensen and S. Frandsen, A Field Study
of Cross Wind Excitation of Steel Chimneys:
Safety of Structures under Dynamic Loading.
Norwegian Institute of Technology, Trondheim, June 1977, pp. 689-697.
(11) A.G. Davenport, Note on the Distribution of
the Largest Value of a Random Function with
Application to Gust Loading. Proc., Inst. Civ.
Eng., London, Vol. 28, June 1964, pp. 187-196.
(12) B.J. Vickery and RI. Basu, Simplified Approaches to the Evaluation of the Across-Wind
response of Chimneys. Journal of Wind Eng.
and Indust. Aerodynamics, Vol. 14, December
1983, pp. 153-166.
(13) M. Jensen and N. Franck, Model Scale Tests in
Turbulent Wind, Part II. Danish Technical
Press, Copenhagen, 1965.
(14) D. Surry, R.B. Kitchen and A.G. Davenport,
Design Effectiveness of Wind Tunnel Studies
for Buildings of Intermediate Height. Can. J.
Civ. Eng., Vol. 4, No.1, 1977, pp. 96-116.
(15) Y. Lee, H. Tanaka and C.Y. Shaw, Distribution
of Wind and Temperature Induced Pressure
Differences Across the Walls of a Twenty Story
Compartmentalized Building. Journal of Wind
Eng. and Indust. Aerodynamics, Vol. 10, 1982,
pp. 287-301.
(16) T. Stathopoulos, D. Surry, and A.G. Davenport,
Internal Pressure Characteristics of Low-Rise
Buildings Due to Wind Action. Proc. Fifth
International Conference on Wind Engineering,
Colorado State University, July 1979, Pergamon Press.
163
pays
(17) D. Surry, T. Stathopoulos and A.G. Davenport,
The Wind Loading of Low Rise Buildings.
Proc. Can. Struct. Eng. Conference, Toronto,
1978.
(18) Normen fur die Belastungsannehmen, die
Inbetriebnahme und die Uberwachung der
Bauten. (Standards for Load Assumptions,
Acceptance and Inspection of Structures).
Schweizerischer Ingenieur und Architekten
Verein (Swiss Association of Engineers and
Architects), No. 160, Zurich, Switzerland, 1956.
(19) RJ Kind and R.L. Wardlaw, Model Studies of
the \Nind Resistance of Two Loose-Laid RoofInsulation Systems. Laboratory Technical
Report, LTR-LA-234, National Aeronautical
Establishment, National Research Council of
Canada, Ottawa, May 1979.
(20) R.J. Kind and R.L. Wardlaw, Design of
Rooftops Against Gravel Blow-Off. National
Aeronautical Establishment, National Research
Council of Canada, Ottawa, September 1976.
NRCC 15544.
(21) P.N. Georgiou and B.J. Vickery, Wind Loads on
Building Frames. Proc. Fifth International
Conference on Wind Engineering, Colorado
State University, July 1979, Pergamon Press.
(22) D.E. Walshe, Measurements of Wind Force on
a Model of a Power Station Boiler House at
Various Stages of Erection. NPL Aero Report
1165, National Physical Laboratory, Teddington, England, September 1965.
(23) Wind Effects Committee, American Society of
Civil Engineers, Wind Loading and WindInduced Structural Response. ASCE, New
York,1987.
(24) N. Isyumov, The Aeroelastic Modelling of Tall
Buildings. International Workshop on Wind
Tunnel Modeling Criteria and Techniques in
Civil Engineering Applications, Gaithersburg,
Maryland, April 1982. Cambridge University
Press, 1982.
(25) P.W. Chen and L.E. Robertson, Human Perception Thresholds of Horizontal Motion. Journal
of Structural Division, Proc., Am. Soc. Civ.
Eng., VoL 98, August 1972, pp. 1681-1695.
164
(26) F.K. Chang, Human Response to Motions in
Tall Buildings. Journal of Structural Division,
Proc., Am. Soc. Civ. Eng., VoL 99, June 1973,
pp. 1259-1272.
(27) R.J. Hansen, J.W. Reed and E.H. Van Marcke,
Human Response to Wind-Induced Motion of
Buildings. Journal of Structural Division, Proc.,
Am. Soc. Civ. Eng., VoL 99, July 1973, pp. 15871605.
(28) T. Stathopoulos, Wind Loads on Eaves of Low
Buildings. Journal of Structural Division,
ASCE, Vol. 107, No. ST10, October 1981, pp.
1921-1934.
(29) D. Surry and E.M.F. Stopar, Wind Loading of
Large Low Buildings. Can. J. Civ.
Vol.
16, 1989, pp. 526-542.
(30) T. Stathopoulos and A. Baskaran, Wind
Pressures on Flat Roofs with Parapets. Journal
of Structural Division, ASCE, Vol. 113, No. 11,
Nov. 1987, pp. 2166-2180.
(31) T. Stathopoulos, Wind Pressures on Flat Roof
Edges and Corners. Proc. of Seventh International Conference on Wind Engineering,
Aachen, West Germany, July 6-10, 1987.
I
pays
hob
L=l·l·lO
C p : External pressure
coefficients
Internal pressure
coefficients
OPENINGS
Uniformly distributed
Figure 8·13
Predominating
side
"A"
+0.7
Predominating
,ide
"8"
-1.1
Predominating on side
"c"
-1.3
Closed passage between large walls
F =C · q · C · C .h·L
n
f
g
e
C
f
- FORCE COEFF. FOR
10+00
lEnd Walls
2.0
10
1.3
1. 15
1.6
1.8
C
f
- FORCE COEFF. FOR
WALLS ON THE GROUND
I
I
I
ｾ＠
Figure 8·14
F
n
ｾＬ＠
t"
1• 5
Free standing plates, walls and billboards
165
pays
= 25
TOTAL FORCE F =C • q • Cg • C e • A/where A ==d.h
f
C f : FORCE COEFFICIENT FOR
> 0.167
d
vqc:;
Slenderness hid
l'
II
V)
N
II
ｾ＠
11
-0--0
ｾ＠ hLP]
ｾ＠ t"- ＮｾＭ
II
"
d
a,
, ,. LE-6-<>
p
Cp
/'; P := Pi - Pe
Figure 8·15
7
1
0.7
0.6
0.5
0.9
):::,
""0
';-
surface
ribs h == 2%d)
25
1 .2
__
+1.0 +0.8 +0. I
Smooth and rough
surface sharp edges
-0.7 -0.6
-0.8 -0.6 -0.5
-1.7
+1.0 +0.8 +0. I -0.7 -1.2
C pi • q • Cg . Ce
-0.7 -0.5
Pi
Pe
=Cp . q • Cg • Ce
1 .4
Stack throttled C.
P'
-0.4
C . == +0.1
p'
- 0.8
Cylinders, chimneys and tanks
TOTAL FORCE F
d ｾ＠
for
=
C . q • C • C • A; A
f
9
e
> 0.8
=
i
rr
-4-
and moderately smooth surface
C ; FORCE COEFFICIENT
f
0.2
Cf
p. for closed tanks
Pi
=working
press.
p'=C ·q·C ·C
e
p
9
e
EXTERNAL PRESSURE COEFF. FOR
Figure 8·16
166
ｾ＠
>
0.8 and moderately smooth surface
Spheres
I
pays
EXTERNAL
RAD,
f
=5/6 b
h:b:L
PRESSURE
COEFFICIENTS
= 1 :12:12
=0° q,=30° q,=90°
:to.2 ±0.2 1:0.2
Window Y open on side "Au
+0.4 +0.
-1.0
-0. I +0.6 +0.8
All door; open on Side "C"
D
Only door X open On side "C"
Sf;oded Area to Scale
Figure B·17
Uniformly distributed
I .5 +0.7 +0.4
Hangar, curved roof with moderately smooth surface
1
I
1,5
Totol
Pi
pe
A
force
working
=
C
p
= .!!.4
on
pressure
. q . C
d
roof
in
• Ce
g
2
C
p
external
pressure
coefficient = -1.0
Figure B·18
Roof load on smooth closed tank
C
lid> 100
Total
force
F
=
C
f
q
C
f
g
= F ORC E COEFFICIENTS
Ce
A
d
-e
<0.167 >0.167
ｾＭ
Smooth wires, rods, pipes
A ;:; d
.L
Mod. smooth wires ond rods
Fine wire cobles
Thick wire cables
Figure B·19
0
@
•
1 .2
0.5
1 .2
0.7
I .2
0.9
1.3
1.1
Poles, rods and wires
167
pays
L = Length of member
A =h . L
Area
• q . Cg • C . A
axis of member: Normal force F = k ·C
e
n
nco
Tangential force Ft = k • C t co . q • Cg , Ce . A
For wind normal
Force coefficients for an infinitely long member
C nco and C I co
i
r
ｾｯ＠
H t
l
-o,1/ 2h
B ｾＺｏﾰ＠
jP
t--"1 +F
C noo I C t 00
a
. h 'it +F
\:
H
ｯＰｾﾢＫｌｴ＠
-+F t
ｾ＠
.
Ｋｆｾ＠
C noo C t
00
0° + 1. 9 +0.95 + 1.8 + 1.8
-+F
.h t'it
1
ＱＭｬＰＮＴＵｾ＠
i
.t
ｾ＠
h
I
+ 1.6
1+2.0
h:,X·
ＺｾＭ
ｾ＠
2/3h {t H t
ｾ＠
4-
a
I
C noo
0 0 1+1.4
45
0
90°
'fr +F
h
'II
f
0°
-
0
+2.05
¢H
c lOO c noo
0
+2.05
h
ｯｾｊＺｉｮ＠
0
ｾ＠
C t ao
c noo
0
+ 1.6
h
h
ｾ＠
0°
｜ｾＫｆ＠
+2.0
+2.2 :0.5
Ft
is to be used
,
,L
Figure 8-20
+0.9
ｯｾＩＭ［ＺＧ＠
0
F
+ 1.9
ha
f
t
c;>n
ｯｬｾﾢｮ＠
h
+0.1
0
{t +F I
\
+F
h
ｾ＠
C nao C t 00 Cnco C teo
0
+2.0
0
+ 1.4 -+0.7 + 1.55 + 1.55
0
+0.75
0
+2.0
k: Reduction faclor for members of finite
slenderness (in generol use full length
not panel length)
L/ha
0/
0
ｾＭＫｆ＠
+2.1
0
+ 1.2 + 1.6 + 1.95 -+0.6 + 1.5 + 1.5 + 1.8 +0.1
0
+0.4
...,0.5h......
O.lh
....JIoo-
C too C nro C too
0
ｾ＠
-1.7 ::!: 2. 1 -1.8
'If +F t
ｯｾｈ＠
0.48h
+ 1.2 +0.9 + 1.85 +0.6
+2.4
'fr +F t
h
I
....J I-
For slenderness,
ha
ｾＭｉｬ＠
-1.4 1-1.4 -1.75 -0.1 1-1.5
..J ,!43h
0
-1.9 -1.0 -0. I + 1.75 -0.95 +0.7 -1.6 +2.15
-2.0 +0.1
-+F
C too
90° +2.0 + 1.7
0
-I
Cnro C too C nro
+2. I -+ 1.8 +0.85 +0.85 + 1.5 1-0 I
180
1] c:;;
0;
C noo C t ao
0
+Ft{t
+F
ｯｲｾﾢ＠
r'O.lh
ｴｾ＠
45 ° + 1.8 -+0.8
135 0 : - 1.8 -0. I : - .0 +0.3 -0.75 +0.75
168
+F
+F
\
O.lh
I ｾｨ＠
ｾＮ＠
I
t
k
5
10
20
35
50
100
00
0.60 0.65 0.75 0.85 0.90 0,95
Structural members, single and assembled sections
I
pays
As
= Section area
A
h
As/A
t
•
l-
Solidity rotio
For wind normal to surface A: Normal force Fn
=k
• C
•
nro
q .C
. C
9
e
. As
Plane trusses made from sharp-edged sections
Figure 8·21
kx SHIELDING
FACTOR
0.6
0.8
1.0
0.440.30 0.30 0.30'
k
Figure 8·22
x
Shielding factors
169
pays
LB = Length of bridge
CASE I
k, C neo ' As' kx from Figs. B-20 & B-21
Windward girder FI = kCneo·q .C 'C e .A s
g
WITHOUT VEHICLES
Leeward girder FII = k C neo ' kxq· Cg . C e ' As
I'
ｾｈＺｐＧ＠
"I
Deck horiz. laad Fh = 1.0·q· C g ' Ce ' d .L
B
Deck vert. load Fvert. =0.6·q'C g ·C e ·b.L
B
L = Length af vehicle; A = h • L
v
1
v1 v
S v e r t. • 1
A
b
CASE II
Windward girder FI
2
=h
'L
v2
v
= k C noo ' q • Cg . C e
• As
Leeward girder FII = k C neo ' kxq • Cg . C e . As
WITH VEH ICLES
Deck horiz. load Fh = 1.2·q·Cg ·C e ·d·L
B
Deck vert. laad Fvert. =0.8·q·C g ·C e ·b·L
B
Traffic load FVI = Cnq . C . C . Al
g
e
F v = C n • 2/3 q . C . C • A2
g
e
2
3.8m
Figure 8·23
1.5
Highway vehicle
3.0 m
1.2
Pedestrian
1.7m
1.0
Truss and plate girder bridges
A=d'Lorh'L
ｾ＠
A/A
0.3
L = true length of member
/3 = angle formed by wind directian and
the normal ta member axis
k x = a function of A s/A and x/b
ICI
8l
ｘｾ｝｢＠
ｾ｢ＮＬ］＠
TOTAL LOAD IN WIND DIRECTION F =
b
O·
0
ｾｏＩＮ［＠
LF
m
F = FORCE ON MEMBER
m
/
Fm = k • C eo/3' q . Cg • Ce ' Acos/3
ｓｾｆｭ＠
(Shielded member Fm =
k • C eo /3' kxq· Cg ' C e ' Acos/3 )
- "ｾ＠ I Fnf3
-,,<
0 h{
Caeff. C eo /3: For sharp-edged members C eo /3 = k/3 • C neo and k/3 • C teo
Caeff. C eo /3' k/3' k, kx: SEE FIG. B - 20FOR C neo and C teo values
ROUND MEMBERS, SMOOTH & ROUND MEMBERS,
MODERATEL Y SMOOTH
ROUGH SURFACES
SURFACES, d vqc" < 0.167
0.167
SHARP·EDGED MEMBERS
kf3
e
00
1.00
15 0
30 0
45 0
0.98
60 0
0.80
0.93
0.88
Figure 8·24
170
fQC" <
d
/3
k
kx
C
oof3
-ｾ＠
k
kx
1.20
See
Fig.
See
Fig.
B - 20
B - 22
ｾ＠
-
0.85
0.60
ｾ＠
C
See
Fig.
B - 20
oof3
k
kx
0.58
0.9
0.95
See r--far
0.53
constont
Fig. r - - 0.42 L/d=25
B·22 r - - 0.28
Three-dimensional trusses
pays
Case (a)
ｾ＠ ｾ＠
Cs+
cs·C
Cs -
Case (b)
Cs-
Case (c)
Case (d)
Figure 8·25 Full and partial loads due to combined and
torsional loads (see Sentence 4.1.8.3.(1))
171
Commentary C
Structural Integrity
significant probability of occurrence (approximately
10-4 per year or more) should therefore be identified,
and measures taken to ensure adequate structural
safety.
1. The strength and stability of building structural
systems is addressed by Sentence 4.1.1.3.(1) and by
the specific requirements in Part 4 of the National
Building Code 1990 and in the CSA material design
standards referenced in Section 4.3 of the Code This
commentary provides guidance on additional considerations for structural integrity as addressed in Sentence 4.1.1.3.(1) and Appendix A.
Safety Measures
2. Structural integrity is defined as the ability of
the structure to absorb local failure without widespread collapse. For example, a cellular or frame arrangement of components well tied together in three
dimensions has good structural integrity.
3. Building structures designed in accordance
with the CSA design standards will usually possess
an adequate degree of structural integrity, generally
through detailing requirements for connections
between components. Situations where structural
integrity may require special attention include
medium/high rise building systems made of components of different materials, whose interconnection is
not covered by existing CSA design standards,
buildings outside the scope of existing CSA design
standards, and buildings exposed to severe accidental loads such as vehicle impact or explosion. The
following provides guidance for such situations.
4. A significant number of failures, many of them
progressive, occur during construction. The construction sequence should, therefore, be carefully
planned and monitored to ensure that partially completed structural systems have sufficient strength,
ductility and lateral stability to resist progressive
collapse if a construction accident causes significant
damage to a structural element or if local failure of a
permanent or temporary structural element occurs.
Identification of Hazard
(1'
5. The hazard is the risk of widespread collapse
with serious consequences arising from local failure
caused by accidental events not addressed by the
loads specified in Part 4. Key components which
can be severely damaged by an accident with a
172
6. Measures to prevent the occurrence of widespread collapse resulting from such accidental events
include:
(a) Control of accidental events. Such measures
include protective devices (curbs, guards)
against vehicle impact, inspection of key elements or ground conditions for deterioration
during use, and blow-out panels to reduce
explosion pressures.
(b) Local resistance. This consists of designing key
members to resist accidental events.(2) Some
major structural members, for example, are so
strong that most accidental events are unlikely
to cause serious structural damage. Ductility of
the key members and of their connections to the
structure can also provide substantial additional
resistance to accidents not normally considered
in design.
(c) Design of tie forces. Structural integrity can
often be achieved indirectly by providing certain
minimum vertical, horizontal and peripheral ties
in buildings (References 3, 4 and 5).
(d) Alternate paths of support. Here it is assumed
that the key member has failed, and the damaged building is checked to ensure tha t it can
support the dead load plus a portion of the live
load and wind load.
(e) Control of widespread collapse. This measure
consists of dividing the structure into areas separated by planes of weakness which prevent a
collapse in one area from propagating into
adjacent areas. This method is described in
Commentary M: Structural Integrity of Firewalls.
7. Any building system should be considered as a
whole, and effectively tied together in such a way as
not to be sensitive to local accidental failure.
8. Additional information for specific building
structural systems is contained in References (3) to
(9). Reference (6) includes additional references for
concrete building systems.
pays
-References
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
H. Griffiths, A. Pugsley and O. Saunders,
Report of the Enquiry into the Collapse of
Flats at Ronan Point, Canning Town. Her
Majesty's Stationary Office, London, 1968.
Dansk Standard DS 410 - English Translation.
Loads for the Design of Structures: Chapter 17
- Accidental Action. Dansk Ingeniorforening,
Copenhagen, 1983.
J.E. Breen, Developing Structural Integrity in
Bearing Wall Buildings. Journal of the
Prestressed Concrete Institute. Vol. 25, No. I,
January-February 1980, pp. 42-73.
M. Fintel and G. Annamalai, Philosophy of
Structural Integrity of Multistorey Loadbearing Concrete Masonry Structures. Concrete International, VoL I, No.5, May 1979.
I.J. Speyer, Considerations for the Design of
Precast Concrete Bearing Wall Buildings to
Withstand Abnormal Loads. Journal of the
Prestressed Concrete Institute, VoL 21, No.2,
March-April 1976.
Canadian Portland Cement Association. Structural Integrity. Concrete Design Handbook,
Ottawa, 1985, pp. 1-25 to 1-30.
British Standards Institute. BS 5628: Code of
Practice for the Structural Use of Masonry:
Part 1 Unrein forced Masonry: Section 5
- Design: Accidental Damage, London, 1978.
B.R. Ellingwood and E.V. Leyendecker, Approaches for Design Against Progressive
Collapse. Journal of Structural Division, Proc.,
Am. Soc. Civ. Eng., March 1978, pp. 413-423.
D.A. Taylor, Progressive Collapse. Can. J. Civ.
Eng., Vol. 2, No.4, December 1975.
173
Commentary D
Effects of Deformations
in Building Components
Structural Effects
1. When building materials expand and contract
due to temperature changes, considerable forces may
be produced in restrained structural elements, i.e.,
those elements that are not free to expand and
contract with the changes in temperature. Often
these forces are compounded by those produced by
shrinkage, creep and moisture content changes and
are therefore difficult to analyse or predict. In many
situations, however, the structural designer must
consider the probable structural effects of the forces
produced by temperature changes along with all
other forces; indeed the designer is required to do so
by Sentence 4.1.2.1.(1) of the National Building Code
of Canada 1990.
2. In addition to expansion and contraction, temperature changes may produce differential deformation or warping of materials as a result of a gradient
in temperature through the thickness of materials or
assemblies. Again this may complicate the assessment of deformations or stresses, but a rational
judgment must be made in design if building elements are to perform in a satisfactory manner.
3. If these forces are not properly considered, the
stresses resulting from such forces can lead to serious
failures (usually cracking) in materials and structural
members. Failures occur when clearances are
insufficient, when fasteners do not allow movement
or deformations, or, in the case of restrained elements, when the elements are not strong enough to
withstand the stresses induced. An elementary
review of thermal and moisture deformations in
building materials is given in Reference (1), from
which Table 0-1 has been adapted, to indicate the
order of magnitude of movement to which various
materials are liable.
Design Temperature Ranges
4. In a country like Canada, with its many climatic
regions, the extremes of air temperature that have to
174
be considered in the design of exteriors of buildings
vary greatly. One way of approaching this problem is
to use temperature maps like those given in the
Ontario Highway Bridge Code (2) giving maximum
summer and minimum winter air temperatures.
Such a detailed approach may not be necessary for
buildings. Instead, the 2.5 per cent July and January
air temperatures for the design of cooling and heating systems in the Table "Design Data for Selected
Locations in Canada" in Chapter 1 of this Supplement are suggested. This will be illustrated by the
three examples below.
5. Because of solar heat gain in summer and radiation heat loss in winter, the range of temperatures
that building elements undergo is greater than the
ambient air temperature. Tables 0-2 and 0-3 show
typical annual ranges of temperature differences
between such elements and ambient air temperatures
due to these effects. (3)
6. The values in Table 0-2 will depend on the
colour, slope, orientation and insulation backing of
the surface.
Examples: For a horizontal dark-coloured surface in
three typical climate regions (coastal, central and
interior), the range of temperatures for design
purposes might be as follows:
Coastal (Victoria): (24(1) + 25(2) (- 5(3) 10(4» = 64°C
Central (Ottawa): (30(1) + 25(2» - (-25(3) -10(4» = 90°C
Interior (Regina): (31(1) + 25(2) - (-34(3) - 10(4» = 100°C
7. Except for the very temperate parts of Canada
referred to as Coastal, as a simple rule, one may
assume a range of exterior surface temperatures of
about 100°C for a horizontal relatively dark material.
Because of thermal insulation, thermal inertia and
other factors, however, the range of extreme temperatures in structural components of a certain thickness
will often be somewhat smaller than those in the
preceding examples.
8. Temperature variations can be particularly
significant in multi-storey apartment and office
(1) July 2.5 per cent temperature.
(2) Dark metal temperature gain.
0) January 2.5 per cent temperature.
(4) Dark metal temperature loss.
pays
Table D·1
Typical Deformation Properties for Some Common Building Materials
I
Material
Plain concrete (4)
normal weight
Glass
Masonry
clay
Shrinkage, mm/m
Thermal
Movement
mm/m per
100°C
1.0
0.9
1
Creep
Coefficient, (1)
<I>
0.5
±O.1
a
30
70
a
±O.1
20
1
1.0
1.0
-0.2
(expansion)
0.2
0.4
±O.1
±0.2
15
15
2
2
1.0
0.7
±0.2
10
2
2.4
1.7
3.0
1.2
a
a
a
a
a
a
a
a
70
110
14
200(5)
a
a
a
a
0.4
0.5
1.2
-
±O.1
±0.1
0.1
60
35
20
a
a
a
4.0
6.0
0.4
30(2)
50(2)
1(2)
2
3
Notes to Table D·1:
Deformation under sustained loading = short term deformation based on modulus of elasticity x (1 + <\».
(2)
Initial drying from green condition to equilibrium is assumed
to be 12 per cent; ｾｭ｣＠
=per cent change in moisture
content from 12 per cenU 21 )
(1)
Modulus of
Elasticity
MPa x 103
a
0.7
calcium silicate
concrete (normal weight)
concrete (autoclaved
lightweight
Metal
aluminum
copper
lead
steel
Natural Stone
limestone
marble
sandstone
Wood (spruce-pine-fir)
across grain
radial
tangential
parallel to grain
Cyclical
Change
Initial
Drying
ﾱｾｭ｣ｻＲＩ＠
1
0.5
10
ﾱＲｾｭ｣ＨＩ＠
ﾱｾｭ｣ＯＳＰＨＲＩ＠
4
5
3
(3)
(3)
1
6
Such application is usually avoided.
For reinforced concrete see CAN3-A23.3-M84, "Design of
Concrete Structures for Buildings."
(5) For cold-formed steel see CAN/CSA-S136-M89, "Cold
Formed Steel Structural Members."
(3)
(4)
175
pays
Table D·2
Temperature Increase in Excess of Ambient
Air Temperature due to Solar Radiation
Tel11perature Gain, °C
Surface
Dark roofing
20-40
Steel and other metal
15-25
Concrete and masonry
10-15
Column 1
2
Table D·3
Temperature Decrease below Ambient Temperature
due to Radiation Loss into a Dark Clear Sky
Surface
Dark roofing
Steel and other metal
Concrete and masonry
Column 1
Temperature Loss, °C
10
5-10
5
2
buildings with exterior columns partially, and in
some cases fully, exposed to the weather. Exposed
columns, when subjected to seasonal temperature
variations, change their length relative to interior
columns, which remain unchanged in a controlled
environment. Although in low buildings this causes
insignificant structural problems, in tall buildings
temperature stresses become significant and must be
investigated thoroughly.
9. Dimensional changes occur not only as the
result of temperature changes, but also from shrinkage, moisture content changes, chemical processes
and creep deformation in the component materials of
a building. If the building or component is not free to
contract or expand, tensile or compressive stresses
result. These stresses can be relieved or reduced to
tolerable limits by contraction and expansion joints.
Such joints are particularly important to allow
contraction to take place along certain preselected
lines rather than to produce cracks along accidental
lines of least resistance.
lengthening of columns due to temperature and
shrinkage effects and creep can crack, buckle or
otherwise overstress cladding materials and their
fastenings. Deflections and linear movements of
beams and spandrels and building sidesway can have
similar effects. Failure to consider these differential
movements has caused many cases of cladding
damage. For example, spalling, cracking and bulging
have occurred to brick and stone veneer on a number
of tall concrete buildings, (2]) necessitating extensive
repairs. The phenomenon is not, however, limited to
concrete frames, nor are the effects limited to stone and
brick cladding. References (6) and OS) to (20) discuss
these effects in greater detaiL
Bibliography of Temperature Effects
on Structures
0)
(2)
(3)
(4)
(5)
(6)
Effects on Cladding
10. In the design of all buildings, but particularly
very long and very high buildings, the effects of
movements of the structural members on the cladding elements should be considered. Shortening and
176
(7)
M.C. Baker, Thermal and Moisture Deformations in Building Materials. CBD 56, Division of
Building Reseach, National Research Council
Canada, Ottawa, August 1964.
Ontario Highway Bridge Design Code 1984.
Ontario Ministry of Transportation and Communications, Toronto, 1984.
Estimation of Thermal and Moisture Movements
and Stresses. Parts 1 and 2, British Building Research Establishment Digests No. 227 and 228.
Building Research Station, Garston, Watford,
Great Britain, August 1979.
Principles of Modern Building, VoL I. Building
Research Station of DSIR. Her Majesty's Stationery Office, London, 1959 (in particular see
Chapter 2 on Dimensional Stability).
D.G. Stephenson, Extreme Temperatures at the
Outer Surface of Buildings. CBD 47, Division of
Building Research, National Research ｾｯｵｮ｣ｩｬ＠
Canada, Ottawa, November 1963.
F.R. Khan and M. Fintel, Effects of Column
Exposure in Tall Structures. Paper in three
parts. (a) Temperature Variations and Their
Effects, (b) Analysis of Length Changes in
Exposed Columns, and (c) Design
Considerations and Field Observations of
Buildings. Journal of American Concrete Inst.,
Vol. 63, No.8, August 1966 and Vol. 65, No.2,
February 1968.
P. Weidlinger, Temperature Stresses in Tall
Reinforced Concrete Buildings. Civil Engineering, New York, Vol. 34, No.8, August 1964.
pays
....
(8) K. Jones, Restraint of Structures Attached to
Mass Concrete. Journal of Structural Division,
Am. Soc. Civ. Eng., Vol. 87, No. ST8, December
1961.
(9) W.T. Marshal, Shrinkage and Temperature
Stresses in Reinforced Concrete. Civil Engineering, London, Vol. 56, No. 665, December
1961.
(0) P. Fisher, Differential Temperature Movements in Rigid Frame. Journal of American
Concrete Inst., VoL 59, No.6, June 1962.
(1) D.W. Allen, The Calculation of Temperature
Stresses. Concrete & Constructional Engineering, VoL LVII, No.9, September 1962.
(2) G.L. England and A.D. Ross, Reinforced Concrete under Thermal Gradients. Magazine of
Concrete Research, Vol. 14, No. 40, March
1962.
(13) Principles of Modern Buildings. Vol. 1, British
Building Research Station, HMSO, London,
1959.
(14) J.H. Slack and MJ Walker, Movement Joints
in Concrete. Concrete Society Limited,
Grosvenor Gardens, London, Technical Paper,
1967.
(15) Deflections of Reinforced Concrete Flexural
Members. Report of ACI Committee
ACI
Manual of Concrete Practice 1970, Part 2.
(16) H. Mayer and H. Rusch, Building Damage
Caused by Deflection of Reinforced Concrete
Building Components. Deutsher Ausschuss
fur Stahlbeton, Heft 193, Berlin 1967, National
Research Council Technical Translation
TT1412.
(17) W.G. Plewes, Cladding Problems Due to Frame
Movements. CBD 125, Division of Building Research, National Research Council Canada,
Ottawa, May 1970.
(18) R.E. Copeland, Flexible Anchorage of Masonry
Walls. Concrete Products, Vol. 71, No.7, 1968,
p.54.
(19) M. Fintel and F.R. Khan, Effects of Column
Creep and Shrinkage in Tall Structures
Prediction of Inelastic Column Shortening.
Journal of American Concrete Inst., December
1969, Proc. V66, No. 12, p. 957.
(20) D. Foster, Some Observations on the Design of
Brickwork Cladding to Multi-storey RIC
Framed Structures. BOA Tech. Note, Vol. I,
No.4, September 1971, The Brick Development
Association, 3-5 Bedford Row, London WCl
4BU.
(21) W.G. Plewes, Failure of Brick Facing on HighRise Buildings. CBD 185, Division of Building
Research, National Research Council Canada,
Ottawa, April 1977.
177
Ｍｾ＠
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ｾ＠
Commentary E
Load Combinations
Introduction
1. Subsection 4.1.3. and Article 4.1.4.2. of the National Building Code of Canada 1990 are intended to
provide an acceptable and relatively uniform degree
of safety in the design of structural members. under
different load combinations. The rules pertam to the
ultimate limit states (allowable stresses, required
structural resistance) and not, in general, to serviceability considerations such as deflection. The rules
take into consideration the probability of simultaneous occurrence of the design loads stipulated in
NBC Subsections 4.1.5. to 4.1.10. They do not take
into account the change in material strengths with
changes in duration of loading.
Load Combinations
2. As dead load is nearly constant throughout the
life of a structure, a combination of dead load with
any other load constitutes a combination in which ｴｾ･＠
basic safety or load factors apply. When dead load IS
combined with two or more other loads, the full
design values of each of the ｬｾ｡､＠
･ｦ｣ｴｾ＠
are ｬ･ｳｾ＠
ｬｩｫｾｹ＠
to occur simultaneously than IS the basIc combmatIon
above. Sentences 4.1.3.2.0) and 4.1.4.2.(4) of the NBC
take this into consideration by allowing reductions in
the total effect due to combinations of the dead load
with two or more other loads.
3. Because of the very short duration of some
design loads, the probability of their simulta.neous
occurrence is extremely small. Thus, accordmg to
NBC Sentence 4.1.2.1.0), earthquake load does not
need to be considered simultaneously with wind
load. When L includes horizontal loads caused by
crane operations, the load combination factor of 0?5
is intended to be applied when a single crane only IS
in operation. For industrial ｢ｵｩｬ､ｮｧｳＮｷｴｾ＠
multiple
crane operations, the same load combmatIon factor
for horizontal crane loads should be applied on the
basis that the largest crane only is operating at
maximum capacity in the most critical location.
4. For building structures subjected to unusual
load combinations, for example those involving the
178
use of heavy equipment or the storage of liquids, the
simple rules of NBC Subsection 4.1.3. or Article
4.1.4.2. may not apply. In such cases the rule for
determining load combinations can be determined by
the following principle.(l) Each load can be separated
into two components, one a sustained or frequently
occurring component (e.g., dead load, storage), the
other a transient component which acts rarely, for a
short time only (e.g., impact, wind, earthquake, rare
accumulation of people or equipment). Since transient loading components are unlikely to occur
simultaneously, the critical load combination for any
structural effect can be estimated by combining the
load having the largest transient component with the
sustained or frequent components of all other loads.
This principle can be applied in place of the load
combination factor both for limit states design, where
the loads are factored, and for working stress design,
where the loads are not factored.
Counteracting Loads
5. Counteracting loads cause overturning, uplift,
sliding of structures as a whole and stress reversal in
structural members. For these cases, the dead load
acts to resist failure and deviations which decrease
rather than increase the dead load are critical. For
limit states design, an underload factor of 0.85 is,
therefore, applied in accordance with NBC Sentence
4.1.4.2.(2) as follows:
<!> R ｾ＠ 1.5 (Q or L) - 0.850
0)
where <!>R is the factored resistance of the anchorage
or member component.
6. Working stress design does not take into
account the need for an underload factor for dead
load and, therefore, special rules are required to
provide sufficient safety.(2, 3) NBC Article 4.1.3.4.
requires a safety factor of not less than 2.0 on loads
tending to cause overturning or sliding. In cases of
uplift or stress reversal, special rules may be required
which essentially reflect Equation 0).
7. With regard to overturning, the designer should
consider that: 0) unless the foundation material has
a high strength, the point of overturning is not at the
toe of the building, and (2) for flexible structures the
dead load acts through the centre of gravity of the
deflected structure.
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8. A special situation arises in the case o! overturning or sliding during an earthquake. Smce the
lateral earthquake force depends on the combined
weight of the structure and its contents, two cases
should be considered in applying Equation (1): one
with the structure empty, where dead load only acts
to resist overturning, and one with the structure full,
where dead load plus the contents act to resist
overturning. In the latter case, D in Equation 0)
should also include the contents.
Full and Partial Loading
References
0) C.J. Turkstra, Theory of Structural Safety. SM
Study No.2, Solid Mechanics Division, University of Waterloo, Waterloo, Ontario, 1970.
(2) D.E. Allen, Safety Factors for Stress Reversal.
Publications, International Association for
Bridge and Structural Engineering, Vol. 29/ II,
1969.
(3) Report of the Committee of Inquiry into
Collapse of Cooling Towers at Ferrybridge,
Monday, 1 November 1965. Central Electricity
Generating Board, London.
9. Full and partial loading considerations are
required in accordance with NBC Article 4.1.6.3. for
floor live load and Sentence 4.1.7.2.(2) for snow load.
For limit states design, such pattern loading requirements should be considered in conjunction with the
dead load multiplied either by 1.25 on all spans or
0.85 on all spans, whichever produces the most
unfavourable effect.
179
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Commentary F
Limit States Design
1. Subsection 4.1.4. of the National Building Code
of Canada 1990 allows the use of limit states design
as an alternative to existing procedures for design
calculations of building structures. This Commentary describes what is meant by limit states design
and the reasons for introducing it into the National
Building Code and associated CSA Structural Standards. In addition, a background explanation is given
of the safety and serviceability criteria contained in
NBC Subsection 4.1.4. The criteria were produced by
a CSA/NBC Joint Liaison Committee on Limit States
Design, which represented all structural and foundation standards used by the National Building Code of
Canada.
Limit States
2. All building structures have the same basic
functional requirements, namely that they should be
safe from collapse during construction and that they
should be safe from collapse and be serviceable
during the useful life of the building. The onset of
various types of collapse and unserviceability are
called limit states. Those concerning safety are called
ultimate limit states and include the exceeding of
load-carrying capacity, fracture, overturning, sliding
and large deformation. Those concerning serviceability are called serviceability limit states, and include
excessive deflection, permanent deformation, cracking and vibration.
3. The primary aim of limit states design is to
prevent the attainment of limit states, that is to
prevent various kinds of failure. This should be
clearly understood by the designer when reading and
interpreting structural standards, since any detailed
requirement is aimed at preventing the attainment of
a particular limit state.
4. Limit states design is not new; it is basically a
clarification of well-known principles. There is,
however, a change of emphasis.
5. Existing design methods - allowable stress
design, plastic design, ultimate strength design - put
the main emphasis on a particular structural theory
180
such as elastic or plastic theory. No particular theory,
however, applies universally to all limit states and all
types of construction. Elastic theory is generally
applicable for serviceability limit states and fatigue,
plastic theory for ultimate limit states in some cases, a
stability analysis for overturning. The appropriate
theory will either be indicated in the structural
material standard or chosen by the designer.
6. Furthermore, existing design methods emphasize only one limit state, usually associated with a
limiting stress or member strength. Due to changes to
lighter composite-acting construction with less in the
way of stiffening and damping from curtain walls and
partitions, serviceability requirements such as deflection and vibration are becoming more critical in
structural design, and deserve the same consideration
as strength requirements. In contrast to existing
design methods, limit states design applies to all
kinds of failure such as collapse, overturning and
vibration, and to all materials and types of construction.
7. In summary, limit states design provides a
unified rational basis for design calculations of
building structures of all materials. This is the main
reason that it is being adopted for international
standardization. (l)
Safety and Serviceability Criteria
8. As already stated, the aim of limit states design
calculations is to prevent failure, that is the attainment
of a limit state. Unpredictable factors such as loads
and workmanship enter into the calculations, however, and so the further qualification is added "that
the probability of failure be sufficiently small." The
more serious the consequences of failure, the smaller
should be the probability. Satisfactory failure probabilities are achieved through the use of reliable
materials, through competent structural engineering,
manufacture and erection, and by the use of safety
and serviceability criteria in the design calculations.
The safety and serviceability criteria should provide
adequate human safety and serviceability on the one
hand, and economy on the other hand, Le., optimum
or smaller failure probabilities.(2) This is achieved in
limit states design through the statistical definition of
specified loads and material properties and the use of
partial factors.
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9. The general form of safety and serviceability
criteria contained in NBC Subsection 4.1.4. can be
expressed as follows:
<j>R 2:: effect of [aDD + )'\jJ(aLL + aQQ + arT)]
(1)
where
0, L, Q and T are the specified loads (dead, live,
wind or earthquake, temperature, etc.) defined in
NBC Sentence 4.1.2.1.(1),
a = load factor applied to one of the specified
loads which takes into account variability of
the load and load patterns and, to some
extent, inaccuracy in the structural analysis,
'"
load combination factor applied to loads
other than dead load to take into account
reduced probability of simultaneous occurrence of loads from different sources,
y = importance factor applied to loads other than
dead load which takes into account the consequences of collapse as they relate to the use
and occupancy of the building, i.e., the
danger to human safety and the economic
loss,
R
calculated resistance of a member, connection or structure based on the specified
material properties,
<j>
resistance factor applied to the resistance or
specified material property which takes into
account variability of material properties and
dimensions, workmanship, type of failure
(e.g., brittle versus ductile) and uncertainty
in the prediction of resistance.
10. When the specified loads and resistances are
multiplied by the appropriate partial factors, the
prod ucts are called the factored loads and factored
resistances. The load factors, load combination factor
and importance factor in the right side of Equation
(1) are given in NBC Subsection 4.1.4., the same for
all building structures. The resistance and resistance
factor in the left side of Equation (1) are contained in
the appropriate structural standard, different for
different materials, type of structural element and
type of behaviour.
11. In the case of the ultimate limit states, Equation (1) states that the factored resistance must be
greater than or equal to the effect of factored loads. A
special situation arises in cases of overturning, uplift
and stress reversal, where the load effects tending to
cause failure are counteracted by the dead load effect.
For such cases positive anchorage is required if the
factored load effects tending to cause failure are
greater than the stabilizing effect of the dead load
multiplied by a dead load factor of 0.85.
12. For the serviceability limit states, instead of a
factored resistance, <j>R represents a criterion such as
an allowable deflection, acceleration or crack width.
Equation (1) therefore results in serviceability
requirements of the same type as in the past. It is
important, however, to understand which limit state
a particular criterion is attempting to prevent.
Definition of Speci'fied Loads
and Resistances
13. For limit states design, specified loads and
specified material properties used to calculate
resistance are defined on the basis of probability of
occurrence. Values so defined are called characteristic values. Material properties are controlled by
statistical sampling and the characteristic value
corresponds to a limiting probability of unfavourable
test values. Climatic loads are based on measurements taken at weather stations, and the characteristic value corresponds to a return period. Characteristic values for material properties and loads used in
the National Building Code are given in Table F-1.
Where statistical information is lacking, e.g. for live
loads, the specified values correspond to the existing
nominal values.
14. For new materials or new control methods,
material resistance should be defined on the basis of
the 5 per cent probability level and material stiffness
on the basis of the 50 per cent probability level;
where statistical sampling is used, a 75 per cent
confidence level is recommended.
15. Since the characteristic values in Table F-1
refer to standard tests or measurements (for example
the standard cylinder test for concrete, hourly wind
speed at an airport), the probability levels cannot be
directly applied to what happens in the structure
without further considerations.
181
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Table F·1
Characteristic Values for Loads and Material
Properties in the National Building Code
Materials
Concrete (cylinder test)
Wood (tests on small clear specimens)
Steel (yield in tension)
Masonry (for prism tests)
Load
Dead
Floor
Snow
Wind - ultimate limit states
- serviceability limit states
Earthquake
- ultimate limit states
Column 1
Probability Level
10 per cent
5 per cent
Not defined
(-1 to 2 per cent)
10 per cent
Return Period
Not defined
Not defined
30 years
30 years
10 years
(See Commentary J)
2
Partial Factors
16. To provide sufficiently small failure probabilities for the limit state under consideration, limit
states design makes use of partial factors in contrast
to the total safety factor used by existing design
methods. The use of partial factors gives more
consistent safety for different load combinations as
well as for different combinations of materials, with a
consequent economy of materials. It also provides a
better basis for development of new types of construction or for unusual situations, since all partial
factors, including resistance factors for the wellknown basic structural materials, will either be
known or can be established on a rational basis.
17. The partial factors contained in NBC Subsection 4.1.4. were determined on the following basis:
Load factors were first chosen on the basis of variability of the loads and load patterns only, excluding
approximations in structural analysis. Based on the
probabilistic assumptions given in Reference (3) for a
30-year life, the following load factors were obtained,
corresponding to a probability level three standard
deviations above the mean: 1.2 for dead load and 1.4
for live load and wind load.
182
To take into account approximations in structural
analysis, these load factors were increased to 1.25 for
dead load and 1.5 for live load and wind load. The
load factor for imposed strains (temperature, shrinkage, differential settlement) was taken as 1.25, the
same as for dead load. As a general rule, however,
inaccuracy in structural analysis should be taken care
of by means of conservative assumptions in the
analysis. Inaccuracies in member resistance are taken
into account in the factored resistance.
The load combination factor, 'V, was determined on
the basis of a probabilistic study for the combination
of dead, live and wind loads for office or residential
buildingsY) These studies indicate that 'V = 0.7 gives a
safety consistent with that for the basic combination of
dead load plus live load. The same studies also
indicate that for overturning, uplift and stress reversal,
safety consistent with that for dead load plus live load
is obtained when aD = 0.85.
For buildings of normal human occupancy the
importance factor was taken equal to 1.0 for practical
purposes, since this classification corresponds to most
buildings. For post-disaster buildings, importance
factors greater than 1.0 are applied to wind load in
NBC Subsection 4.1.8. (by means of increased return
period) and earthquake load in NBC Subsection 4.1.9.
The reason for retaining this approach is that the
importance factor should be applied only to those
loads which can cause a disaster. For buildings of low
human occupancy, such as farm buildings or storage
sheds, an importance factor less than 1.0 applied to
loads other than dead load is justified on the basis of
reduced risk to humans. The factor 0.8, along with the
reduction in dead load factor from 1.5 to 1.25, closely
corresponds to the 25 per cent increase in allowable
stress contained for some years in the ACNBC
Canadian Farm Building Code.
For the serviceability limit states, in accordance
with NBC Article 4.1.4.3., the partial factors are
generally taken as 1.0; an exception is the reduction for
load combinations. Two reasons for continuing this
traditional approach are: the consequences of serviceability failure are considerably less serious than for
collapse, and therefore the partial factors are closer to
1.0; since the criteria for serviceability failures cannot
be accurately defined, only simple empirical rules
which absorb safety factors are justified.
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18. The live load factor 1.5 applies to live loads for
most buildings. For live loads whose uncertainty
deviates considerably from those specified in NBC
Article 4.1.2.1., the load factor should be adjusted
accordingly. For example, the uncertainty in weight
or pressure of fluids in storage tanks is similar to uncertainty in dead load, and a load factor of 1.25 may
be appropriate in some cases. Design of such structures is often governed by a serviceability limit state
of water tightness or by differential settlement.
19. The dead load factor of 1.25 does not take into
account any increase in dead load as a result of
alterations (e.g., to the roof or floor) during the life of
the building.
20. During construction all permanent and temporary structural members should have sufficient
factored resistance to carry the effect of factored
construction loads. Adequate load factors not less
than 1.25 (greater if the construction load is more
uncertain than the dead load), with the importance
factor equal to 1.0, are recommended.
Resistance Factors
21. The resistance factors will be determined by
each structural materials standard as it develops limit
states design. Guidance on the determination of
resistance factors is given in Reference (4).
References
General Principles on Reliability for Structures.
International Standard ISO 2394. Geneva, 1986,
18 pp.
(2) M.K. Ravindra and N.C. Lind. Theory of Structural Code Optimization. Journal of Structural
Division, Proc. Am. Soc. Civ. Eng., Vol. 99, ST7,
July 1973, p. 1541.
(3) D.E. Allen. Limit States Design - A Probabilistic Study, Can. J. Civ. Eng., Vol. 2, No.1,
March 1975, p. 36.
(4) Guidelines for the Development of Limit
States Design. CSA Technical Publication
S408-1981. Canadian Standards Association,
Rexdale, Ontario.
(1)
183
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Commentary G
Tributary Area
1. Because live loads are generally given as uniformly distributed loads over a floor area, and
because dead loads can usually be considered as
uniform loads, either over an area or along the length
of a flexural member, design engineers have for years
used the concept of tributary area to determine the
loads that beams, girders and columns carry. Once
the concept is applied to any floor, it is easily extended for multi-storey columns to any number of
floors.
2. Earlier design standards recognized that the
probability that all the floors of a multi-storey building would be loaded to the full live load simultaneously was very remote. Therefore, to design the
columns for the full live load of a number of floors
was unduly restrictive, and reductions in the live
load were devised as a function of the number of
floors supported by the columns.
3. In the 1960 edition of the National Building
Code, with the recognition that the average live load
was a function of the area supported, the rationalization was carried one step further and a reduction of
15 per cent was allowed for beams, girders and
trusses supporting areas greater than 20 m 2 •
4. In subsequent editions, provisions have been
included for live load reduction based on tributary
areas with two different expressions, one for office
and apartment buildings and the other for storage or
similar areas.
5. Therefore, for determining the total dead load
to be supported by a given member, and to determine what live load reduction factor should be
applied, a clear definition of tributary area, about
which some confusion existed, is needed.
6. In the case of a member which supports the
load directly, such as a slab, the tributary area is
defined as the area supported by the member
bounded by the lines of support. In the case of a
member which does not support the load directly but
supports other members, the tributary area is defined
as the area bounded by the lines of support of the
member and the lines of zero shear in the members
184
supported, assuming a uniformly distributed load is
acting on the structure. These definitions, which for
continuous construction require a structural analysis
to determine locations of zero shear, should be
followed when determining the forces that members
carry. In determining live load reduction, however,
the following simplifications are recommended.
Decks and Slabs
7. No live load reduction factors should be
applied to wooden or sheet metal decks, precast units
or one-way slabs because of the uncertainty of the
degree of lateral distribution of loads.
8. The tributary area for a flat slab or the slab
portions of two-way slabs with beams is the area
bounded by column lines or by a combination of
column lines and lines of supporting members such
as beams and girders, whichever is the lesser, as
shown in Figures G-1, G-2 and G-3.
Beams and Girders
9. The tributary area for a member supporting a
portion of a floor is the area enclosing the member
and bounded by the lines of zero shear in the members supported. For buildings with fairly regular
bays the lines of zero shear in the members supported can be assumed to be half-way between lines
of support. Figures G-2 and G-3 illustrate the tributary area of beams supporting two-way slabs. Figures G-4 and G-5 illustrate the tributary areas for
joists, beams and girders supporting a one-way slab.
Negative Moments in Continuous
Members
10. Tributary area for negative moment over a
support may be taken as the sum of the tributary
areas of the beams on either side of the support.
Columns
11. For a column the tributary area per floor is the
area of floor supported, bounded by the lines of zero
shear. For buildings with fairly regular bays these
can be assumed to be half-way between the column
lines, as shown by the dotted area in Figures G-1 to
G-5. In structures with beams, joists or girders the
pays
Flat and
two-way slabs
ｾ＠
mmIIJ]
Joist, beam or ｾ＠ ｾ＠
girder
1<-:: ｾＺ｟ｊ＠
Column
1.
..l.
-
-
........ｾ＠
--
......
.. !""
-,-
-
-:-
Ｑｾ＠
-:-Joi
:-.,.;
T ｾｴ＠
,
_...
... !""
,
I
Figure G-1
and girders
,...
I
....
ｌｾ＠
2
II
Figure G·3 Tributary areas for a two-way slab with joists,
beams and girders
ｉｾＬＮ＠
,--
"-
ｾ＠
..,.....
l2-J
2
l2
Tributary areas for flat slabs without beams
Figure G-4
Tributary areas for a one-way slab with girders
Joist
girder
beam
Figure G·2
Tributary areas for a two-way slab with beams
.1
Figure G-S Tributary areas for a one-way deck or slab with
joists, beams and girders
185
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tributary area per floor is half the sum of the
tribu tary areas of each of the floor members framing
into it.
12. In multi-storey buildings the tributary area for
a column supporting one use and occupancy is the
sum of the tributary areas per floor for that column
on all levels above the storey in question.
13. For a column supporting more than one use
and occupancy, NBC Article 4.1.6.9. requires that the
tributary area for each use and occupancy be considered separately for determining reduction in live load
and that the area supporting snow load, which has
no reduction, not be included.
186
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f
Commentary H
Snow Loads
1. Snow loads on roofs vary according to geographical location (climate), site exposure, shape and
type of roof, and also from one winter to another. To
account for these varying conditions, the specified
snow load, S, on a roof or other surface is expressed
in Subsection 4.1.7. of the National Building Code
1990 as the sum of two components, one being the
prod uct of a series of factors
S = Ss (C b• C w• C s • C) + Sr
where
S5 = ground snow load in kPa with a 1-in-30
probability of exceedence per year
Sr
the associated rain load in kPa. However,
the rain load at any location on a roof need
not be taken greater than the load due to
snow (Le., Sr -::; Ss(CbCwCsC).
the basic roof snow load factor,
the wind exposure factor,
Cw
the roof slope factor, and
Ca
the accumulation factor.
The factors are discussed separately in this Commentary and a series of figures are provided to illustrate their application to various shapes of roofs. The
factors are based on measurements obtained during
surveys of snow on roofs, and on judgment. Since
surveys of sufficient length (about 10 years or more)(l)
cover only a limited selection of the most common
and simplest roof shapes, the factors are of limited
accuracy and may be subject to change as more data
become available.
Snow Loads on the Ground
2. In Canada, ground snow loads are used as a
basis for the determination of roof snow loads.
Therefore, they form part of the basic climatic information needed for building design and are given in
Chapter 1 of this Supplement in the Table "Design
Data for Selected Locations in Canada." Each ground
snow load is composed of a load due to the snow
load with a 1-in-30 annual probability of exceedence,
based on measured depths and densities and a
load, Sr' due to the associated rain which may fall
into the snow cover (not including any rainfall that
exceeds the weight of the snow cover)Yl (See Paragraph 5.)
The snow loads for a given town or city are for the
exact latitude and longitude defined in the Canada
Gazetteer en for that town or city. In cities having a
large change in elevation, snow loads may vary
within the city. Maps from which S5 and Sr can be
obtained for locations not listed in Chapter 1 of the
Supplement are available from the National Climatalogical Information Services, Environment Canada,
4905 Dufferin Street, Downsview, Ontario, M3H 5T4.
Variations with Climate
3. The wide climatic variations across the country
produce large variations in snow conditions. The
heaviest snow loads occur in the mountainous
regions of British Columbia and Alberta; they last the
entire winter and vary considerably with elevation.
In certain limited coastal locations of British Columbia, little drifting of snow occurs. The Prairie provinces, Yukon and the Northwest Territories have very
cold winters, with small annual snowfalls but
frequent strong winds, which cause considerable
drifting of snow on roofs and on the ground. The
region that includes Ontario, Quebec, and interior
regions of the Atlantic provinces is marked by
moderate winds and snowfalls, and sufficiently low
temperatures in most places to allow snow accumulation all winter. In this region, moderate uniform and
high drift loads occur. Also, cold northwesterly
winds often cause locally heavy snowfalls to the lee
of bodies of water such as the Great Lakes and the
Saint Lawrence River, which lead to increased snow
loads.
Local Variations - Mountainous Areas
4. In mountainous areas ground snow loads increase with elevation. Observations by the Institute
for Research in Construction of the National Research
Council on a number of mountains in British Columbia indicate significant increases in ground snow load
with increases in elevation, depending on the local
topography and climate.(4) Individual mountains or
groups of mountains may cause Significant changes
in local or micro climate within short distances.
Hence, snow loads listed in Chapter 1 of this Supplement apply only at a particular elevation at the
187
individual location as defined by the name and
latitude/longitude coordinates given by the Gazetteer of CanadaY) For locations not listed, the Atmospheric Environment Service should be consulted for
specific recommendations as stated in Chapter 1.
Unit Weight of Snow on the Ground
5. Falling snowflakes usually consist of very large
complex ice crystals. Because of their large surface
area to weight, they fall to the ground relatively
slowly. On arrival, this snow accumulates in a loose
and fluffy layer with a unit weight of about 0.5 to
1.0 kN /m 3 . Immediately, however, the snow crystals
start to change: the thin, lacy needle-like projections
begin to sublime and the crystals become smaller
irregularly shaped grains. Settlement of the snow
results and the unit weight, y, increases after a short
time to about 2.0 kN/m 3 or greater, even at below
freezing temperatures. The unit weight of the
snowpack continues to increase with age, ranging
from 2.0 to 5.0 kN/m 3 • As explained in Chapter 1 of
this Supplement, average values for the seasonal
snow pack have been derived for different regions
across the country for use in the ground snow load
calculations.(2) The snow surveys from which the unit
weight is derived are made four times per month (at
most). While the survey measurements reflect to
some extent the portion of rainfall that is trapped in
the snowpack over a period of time, only a small
proportion of measurements would have been made
directly after a rainfall. Therefore, the measurements
probably do not adequately represent the short term
density increase due to the wetting of snow by rain,
and for this reason, the rain load, S , is included in
the calculation of roof snow loads. (2)
Snow Loads on Roofs
Unit Weight of Snow on Roofs
6. In calculation of loads due to snow on roofs a
measurement or good estimate of the unit weight is
necessary. The unit weight of snow on roofs, y ,
obtained from measurements at a number of stations
across Canada varied from about 1.0 to 4.5 kN/m 3 .
An average value for use in design in lieu of better
local data is y= 3.0 kN/m 3 • (5) In some places, where
the maximum roof load is reached only after contributions from many snowstorms, a unit weight as
high as 4.0 kN /m 3 may be appropriate.
188
Solar Radiation and Heat Loss
7. Some factors which modify snow loads occur
only under special conditions. For example, solar
radiation has little effect in reducing loads in cold
weather. Similarly, during cold weather, heat loss
from roofs is not very effective in melting the snow,
particularly on well insulated and well ventilated
roofs. These two factors cannot, therefore, be relied
upon to reduce the snow load significantly during
the colder periods. During thaws and toward the
end of winter, however, when air temperatures
approach the freezing point, solar radiation and heat
loss do result in melting.
Roof Snow Load Factors
8. The factors C b , C w ' C" and Ca were not obtained
by rigorous statistical analyses due to the lack of
data, but they have been found to give acceptable
and conservative designs.
9. Basic roof snow load factor, C b • The basic roof
load has been set at 80 per cent of the ground load
(i.e., C b = 0.8). This figure is based on the results of a
countrywide survey of snow loads on roofs carried
out by the Institute for Research in Construction and
a number of volunteers.
10. Wind exposure factor, Cwo Observations in
many areas of Canada have shown that where a roof
or a part of it is fully exposed to wind, some of the
snow is blown off or prevented from accumulating
and the average snow load is reduced.
11. Therefore, for roofs fully exposed to the wind
(though not for very large roofs where it may be
inappropriate) the wind exposure factor, C w ' may be
taken as equal to 0.75 rather than 1.0 (or 0.5 rather
than 1.0 for exposed sites north of the treeline). This
substitution applies under the following conditions:
(a) the building is in an open location containing
only scattered buildings, trees or other such obstructions, so that the roof is exposed to the
winds on all sides and is not shielded by
obstructions higher than the roof within a
distance from the building equal to 10 times the
height of the obstruction above the roof level;
(b) the area of roof under consideration does not
have any significant obstructions such as
parapet walls within a distance of at least
］ｾ＠
pays
f
e
10 times the difference between the height of the
obstruction and C bC wSs iy, m; and
(c) the loading case under consideration does not
involve accumulation of snow due to drifting
from adjacent surfaces such as, for example, the
other side of a gable roof.
A value for C wof 1.0 must be applied to other than
the loadings marked Case 1 in Figures H-1 to H-3.
12. The value CbCwSs iyis obtained by assuming
that the snow will drift to the top of the parapet. Then
hdrift hparapet = CbCwS s iyon the exposed roof (Le., 0.6
S5 iy normally or 0.4 S5 iy north of the treeline).
13. In practice it is sometimes difficult to make a
clear distinction between roofs that will be fully
exposed to the winds and those that will not. The
designer should, in consultation with the owner,
weigh the probability of the roof becoming sheltered
by an addition to the building or by adjacent higher
buildings or trees. Such changes could cause either
drift loads or higher average loads. In considering
drift loads, which are the more serious, a minimum
distance of at least 5 m should be maintained from
another existing or future building or from the property line to justify disregarding drift loads. This
corresponds to the distance used in NBC Sub-clause
4.1.7.1.(7)(b)(iji) for multi-level roofs. With regard to
higher average loads, it is important to use a wind
exposure factor, C w' equal to 1.0 for any roof area
whose exposure may decrease.
14. The designer should also be aware that the
snow loads on the roof of an existing building on the
same or adjacent property may also be affected by the
location of a new higher building or other obstruction.
15. The installation of solar collectors on roofs
may result in reduced exposure similar to that around
obstructions unless the clear gap under them is
sufficiently large to allow scouring and ren-lOval by
the wind rather than deposition.(6,7)
16. Regional variation in Cw ' For the exposure
factor to have any application there must be wind.
Therefore, designers should use C w 1.0 in the few
areas of Canada, such as winter-calm mountain
valleys, where winter winds are not strong or frequent enough to produce significant reductions in
roof loads.
17. Roof slope factor, Cs ' Snow loads on a sloping
surface act on the horizontal projection of the surface.
Under most conditions, less snow accumulates on
steep roofs than on flat and moderately sloped roofs,
because of sliding, creep, better drainage and saltation.(S-lO) The coefficient, C ,as defined in NBC
Sentence 4.1.7.1.(4) accounts for these effects by
reducing the snow load linearly from full snow load
at 30° slope to zero at 70°. A lesser value of C s is
permitted in Sentence 4.1.7.1.(5) for unobstructed
smooth, slippery roofs such as glass or metal. In this
case, the load may be reduced linearly from full load
at 15° to zero at 60°. In order for the designer to use
the full reductions as described in either of these
relationships, the snow should be able to slide
completely off the roof surface under consideration.
18. Situations in which public safety may be compromised by snow and ice falling from roofs should
be avoided. If snow fences or barriers are required to
keep snow and ice on roofs, they should be designed
to transmit the substantial forces involved into the
building structure.{S,9) Heat-traced gutters, heated
drips or some other means to prevent the growth of
dangerous icicles due to meltwater from the snow
retained on roofs may also be required. Snow and ice
falling from the roof of a building may be deflected
against the building, causing damage.
19. Accumulation factor, Ca' The accumulation
factors, Ca, are described in Figures H-1 to H-6 for a
number of different roof shapes. For cases where
Figures H-1 to H-6 do not apply, accumulation
factors should be determined by the designer based
on applicable field observations, special analyses
usually accounting for local climate effects Ol -13) or on
model tests. (6) In an effort to provide guidance, the
Institute for Research in Construction has published
two collections of interesting non-uniform snow
loads as case histories.(14,lS)
20. Effect of wind on snow accumulation on roofs.
When the wind encounters obstructions, regions of
accelerated and retarded flow result. The regions of
retarded flow are said to be regions of "aerodynamic
shade."(16) Since a minimum velocity is required to
transport the snow, it settles out where the flow
velocity is too low and forms drifts whose shapes are
indicated by Ca'
189
21. Roofs situated below adjacent roofs are particularly susceptible to heavy drift loads, because the
upper roofs can provide a large volume of snow to
form drifts.(S,17,lS) Canopies, balconies and porches are
similarly susceptible. The drifts that accumulate on
these roofs depend mainly on the difference in
elevation and on the size of the upper roof.(17)
linearly to zero at 22.5° beyond the sector
boundaries and with no snow on the remaining
225° sector.
Local experience should also be considered. Snow
accumulations due to sliding and drifting occur
regularly at the bases of domes where they meet the
ground. These should not be neglected.
22. Projections such as penthouses or parapet
walls on flat roofs may collect triangular snow drifts
that reach the tops of the projections, but the magnitude of the loads is usually less than on roofs
situated below adjacent roofs.
25. In completely calm areas, snow covers roofs
and ground in uniform layers. For these locations,
the design load can be considered as a uniformly
distributed load equal to some suitable fraction of the
ground snow load if sliding is not a factor. Truly
uniform loads, however, are rare and have been
observed only in certain mountain valleys of British
Columbia and occasionally in other parts of the
country, on roofs that are well sheltered on all sides
by high trees. Generally, the winds which usually
accompany or follow snowfalls transport new snow
from exposed to protected areas. Hence, the probability that high uniform loads will occur on exposed
roofs is reduced and the probability that drifts will
form is increased. Drifting does not occur in certain
local areas on the B.C. coast where heavy snowstorms
invariably consist of wet snow. In these specific
locations, the drift requirements of Sentence
4.1.7.1.(7) may be overly conservative. Where the
authority having jurisdiction is convinced that
drifting will not occur, drift effects need not be
considered. However, the influence of creep and
sliding snow causing unbalanced loads should be
considered on gable roofs of slope >15°, arches with
rise to span, h/b greater than 0.1, and other roofs of
significant slope.
23. Wind flow over gable, or arch roofs, is accelerated by being deflected upwards on the windward
sides. On the leeward sides, velocities drop and the
snow entrained in the wind and scoured from the
other side is deposited. Heavy unbalanced loads
often occur as a result of the transfer of snow from
one side to the other. (lY,2()) This unbalance is especially important for domes and also for buildings
such as arenas, which have long spans and in which a
collapse might be catastrophic. (1) Lightweight curved
structures, such as cold-formed metal arch buildings,
are particularly sensitive to unbalanced snow loads,
as the self-weight of the structure is relatively small.
These structures can generally be analyzed as arches.
However, the flexibility of such arches suggests that a
second-order analysis is likely to be required to
predict the structural behaviour.(lH,lY) The structures
can also be analyzed as shells when special consideration is given to shear transfer and to the axial
capacity of longitudinal stiffeners. Load tests may be
needed to assess the behaviour and load carrying
capacity of the structural elements, especially when
transverse corrugations are present.
24. When the wind flows over peaked or smooth
domes, unbalanced snow load will also occur. Data
on snow load distributions on domes are not available and wind tunnel or water flume tests are therefore recommended to assist in the selection of appropriate design loads. In the absence of such tests, the
following approximate distributions may be considered; in plan view:
(a) a uniformly distributed load (adjusted for slope)
over the whole dome, and
(b) the Case II loading (Figures H-2(a) and
H-2(b», applied over a 90° sector, tapering
190
26. Redistribution of load due to melting. Redistribution of loads may occur as a result of snow or ice
melting and flowing or sliding to other areas where it
refreezes, or falling to a lower roof where it accumulates as slush or ice. On sloped roofs, meltwater from
warm, perhaps poorly insulated, parts may refreeze
on colder areas or on the eaves and cause high ice
loads and also ice damming, water back-up under
shingles and danger from falling icicles. These can be
alleviated by taking steps to decrease heat loss from
the warm surfaces.
27. Since drainage under the snow cover on flat or
nearly flat roofs is not generally as good as on those
with slopes, meltwater, slush and ice may be retained
pays
longer. Also snow accumulations near projections
can melt as a result of heat loss through the roof or
solar radiation or exhausted warm air. The resulting
meltwater may migrate to the lower areas causing
heavy loads. The centres of bays are particularly
vulnerable if the drains are located at the columns
(high points). This redistribution of load may cause
further deflection and lead to an instability similar to
that produced by rain ponding (see Commentary I).
shown in Figure H-l. Where both slopes are equal to
or less than 15°, the load distribution is determined
by Case I, but is also subject to the general requirements of NBC Article 4.1.7.2. for "full and partial
loading" which now apply to the Case I loading only.
On slopes over 15°, Case II, which accounts for
unbalanced loading, and Case I both apply. Case II
loading is intended to account for snow blown from
the windward over to the leeward side as well as
snow removed by sliding from one side. Flat and
shed (single sloped) roofs are subject to Case I and
"full and partial" loading only.
Detailed Explanations of Figures H·1
to H·6
28. In the following, Figures H-l and H-2 apply to
the basic shapes: the simple flat and shed roofs, the
simple gable roofs and the simple arch and curved
roofs. More complex shapes can often be considered
as combinations of these. When the roofs shown in
Figures H-l and H-2 are adjacent to higher roofs or
have projections or are combined to form valleys,
reference should also be made to Figures H-3 to H-6.
For all these simple and complex roofs, the basic
snow load coefficient, C b , is 0.8 in all loading cases.
30. Arch roofs (Figures H-2a and H-2b). Uniform
and unbalanced load distributions are particularly
important for the design of curved roofs. (1,18-20) In
addition, where the rise to span ratio (h/b) is equal to
or less than OJ, the requirements for "full and partial
loading" apply. On large span buildings with low
h/b ratios designed for locations having low ground
snow loads, the total snow load in Case II may
exceed a load equal to half the ground snow load (or
36 per cent of the ground snow load for unobstructed
slippery roofs) uniformly distributed on the roof. In
this situation, Case III may be used in the calculation
of the unbalanced snow load instead of Case II.(20)
29. Gable, flat and shed roofs (Figure H-I). On
gable roofs both uniformly distributed and unbalanced loads should be considered for all slopes less
than 70° (or 60° for unobstructed slippery roofs), as
Roof profile
_ ..,
_-
I
LD
I
I
I
I
I
i
Factors
Roof
slope
Load
case
Cw
0.
Distribution of snow load, S
I
Case I
o . 75(3)
I
I I II II
I II I II
Ca
Cs
ｏｯｾ｡ＹＰﾰ＠
I
(a
OR
)(1)
1.0
1.0
I
i
I
Case
11(2)
_I____I ",. .J.-IＮｊｉＭＧｾ＠
II
15'5a520'
ＲＰｯｾ｡ＤＹﾰ＠
Figure H·1 Snow distributions and snow loading factors for
gable, flat and shed roofs
Notes to Figure H·1 :
(1)
Varies as a function of slope a as defined in NBC Sentences
4.1.7.1.(4) and (5).
j
1.0
f ( a ) (1)
1.0
f ( a ) (1)
0.25
20
1 .25
I
(2)
(3)
Case II loading does not apply to gable roofs with slopes of
15° or less or to single-sloped (shed) roofs or to flat roofs.
Cw = 0.75 may be reduced to 0.5 for exposed areas north of
the treeline as defined in NBC Sentence 4.1.7.1.(3).
191
Case II loading may also be used for the design of
domes (see Paragraph 24).
wrinkles and layers at the bottom of the valley, the
loads on the upper slopes are reduced. Since Cases II
and III describe the worst loads due to drifting and
slope effects, the C, factor is taken as equal to 1.0.
31. Snow accumulations caused by wind and by
snow sliding off the surface regularly occur on either
or both sides of arches where they meet the ground
and should not be neglected. (19)
32. Valleys in curved or sloped roofs (Figure H-3).
In the design of roofs with valleys, uniform loads and
loads accounting for drifting, sliding or creep, and
the movement of meltwater are important. A reduction due to slope is allowed for Case I loading,
because as the snow creeps down the slope and
33. Multi-level roofs, obstructions and parapets.
Multi-level roofs, obstructions and parapets are all
"bluff objects" creating turbulent wakes downwind,
where snow accumulates in drifts. Such roofs and
obstructions can be considered as geometrical variations of a rectangular object situated on or adjacent
to a lower flat roof. If the object is narrow and lower
than the design depth of uniformly distributed snow
wind ------.
Roof profile
a
I
I
< 30°
Load
case
I
Distribution of snow load, S
I
Case I
I
I
I
S ｾ＠
2 S5 + Sr
MAX.= ,
S
2 S5
t
I
I
I
+
Ｇｾ＠
I
I
I
Factors
C
All
I
C
w
0.75
OR
C
s
f( a)
(5)
11(1)
h
- > 0.1
1.0
b
1.0
Y hx
(5)
f( a)
ｾ＠
For 0
f (a)
S:
I
a
(3)
1.0
I,
MAX·'::1j"lnr
*
I
Case III
f( a)
nllllllllllllI11
I
Case II
I
Range
of
application
I I 1(1)
but not more than2Cb
< x<
x3
C = l..
a Cb
h
- > 0.1
1.0
b
f (a
)(5)
For x
30
s:
d
4
)
x
x
30
x
C=2..
a Cb
Figure H-2(a) Snow distributions and snow loading factors for
simple arch or curved roofs
Notes to Figure H-2(a):
(1)
If the total load per unit length of building perpendicular to
span b exceeds 0.5 (Ss + Sr)b, Case III may be used instead
of Case II. For circular curved roofs Case III may be used if
b > 3.0 Ss + Sr ( 17 + 7 Cos 4 Oe)
(2)
(3)
(4)
Y
(5)
192
Max S =2S s+ Sr occurs at u =30° or at the edge of the roof
if u e < 30°.
Cw = 0.75 may be reduced to 0.5 for exposed areas north of
the treeline as defined in NBC Sentence 4.1.7.1.(3).
X30 = value of x where u = 30° or value of x at edge of roof if
u e < 30°.
Varies as a function of slope u as defined in NBC Sentence
4.1.7.1.(4).
I
pays
Roof profile
Distribution of snow
01
Load
case
1
I
1
Factors
Range
of
i application
Cw
(3)
(5)
All
Case I
f( 0
OR
1.0
i
LO
Case II
h
- > 0.1
but not more than 2/C b
1.0
b
I
I
max.
Case III
S.$l..
. ＭｾＮ＠
ｾ＠
o<
' : . f(n)
C
a
x
<
f (a)
1.0
For x
30
a
I
Figure H-2(b) Snow distributions and snow loading factors for
simple arch or curved roofs with unobstructed slippery surfaces
Notes to Figure H-2(b):
(1)
If the total load per unit length of building perpendicular to
ｾｰ｡ｮ＠
b exceeds 0.36 (Ss + Sr)b , Case III may be used
Instead of Case II. For circular curved roofs Case III may be
used if
b> 3.0 ＿ＮﾧＱﾷｾＡ＠
17 + 7 Ca; 4
(leI
(2)
x
30
C :::
,4 )
=2-.-'2Cb x
(5)
0.1
'30
2
Cb
.
Max S 1.7S5 + SI occurs at the edge of the roof if
22.6° (i.e., h/b = 0.1)
Cw =0.75 may be reduced to 0.5 for exposed areas north of
the treeline as defined in NBC Sentence 4.1.7.1.(3).
X30 = value of x where C1 = 30° or value of x at edge of roof if
C1e < 30°.
Varies as a function of slope C1 as defined in NBC Sentence
4.1.7.1.(5).
C1e =
(3)
(4)
(5)
193
pays
Distribution of snow load, S
Factors
Roof
slope
Load
case
Cw
ex
ca
Cs
I
0.75 (2)
Case I
I
Case II
II
o
ｾ＠
90
OR
0
f (0
1.0
)(1)
1.0
or Ｐ＼ｸｾ｢ＯＴＺ＠
10
<a
:5. 90
0
1.0
1.0
Co
For
Co
l/C b
b/4<x5b/2:
O. 5/C b
For 0<x:5:b/8:
Case III
III
10
0
<0'::;90°
1.0
Co
1.0
C
Figure H-3 Snow distributions and snow loading factors for
valley areas of roofs
Notes to Figure H-3:
e (1) Varies as a function of slope a as defined in NBC Sentence
4.1.7.1.(4).
on the roof it is, for the purposes of this Commentary,
a "non-obstructing" parapet; if higher, it is an obstruction; if higher than a "non-obstructing" parapet
and wide enough to provide a significant source of
snow on its upper surface, it is an "upper level" roof.
34. The lower roof (Figure H-4). The load distribution on roofs adjacent to higher ones should be
a triangular shape with the maximum load near the
higher roof equal to the unit weight of snow
(3.0 kN / m 3) times the difference in roof elevation (in
metres). The triangular snow drift is presumed to
extend to the level of the higher roof, except that an
upper limit equivalent to 3 Ss + Sr has been suggested
in Figure H-4. The accumulation factor in Figure H-4
is based on observations taken on roofs with a difference in elevation of about 1 storey (2 to 5 m) and
194
(2)
1.5/Cb
For b/8<x:5.b/2:
0
Cw = 0.75 may be reduced to 0.5 for exposed areas north of
the treeline as defined in NBC Sentence 4.1.7.1.{3).
where the upper roofs were usually less than 75 m
long measured parallel to the wind direction. (5,21)
Drifts produced by snow blown from larger roofs may
exceed the suggested limits in Figure H-4, but not
enough data exist about such roofs to make definite
recommendations. On the other hand, for relatively
short upper roofs (less than 15 m), loads less than
those calculated from Figure H-4 may be judged
adequate by the designer. Drifts deposited as a result
of a change in elevation occur not only when the
upper roof is part of the same building but also when
it is on an adjacent building not more than 5 m away,
as shown in Figure H-4. Where the drift obtained
from Figure H-4 is longer than the lower root the drift
should be truncated at the edge of the lower roof.
Further, where the difference in elevation between
two roofs is small (less than about 1.5 m) and the
pays
J
Factors
x
Cw
J
Ｍｬｯｾ＠
0
Distribution of snow load, S
I
Ca (2)
Cs
1.0
f (a )(1)
1.0
f (a )(1)
C
00
I
[ttl! I I II I I I b-n
ｾ＠
, : 1Oh'
0< x
.1
xd
S xd
< x S 10 h'
1.0
C
00
-
(Coo
1) x
xd
f(a
t)
1.0
f (a
/1)
1.0
Value of xd :
xd=2h but 3ms;xd
9m
Value of h':
0.75(3)
> 10 h'
h' = h·
Value of Ca 0
OR
1.0
:
when C a 0 < 1,0 use 1,0, when C a 0>
Figure H·4 Snow distributions and snow loading factors for
lower levels of adjacent roofs
Notes to Figure H·4:
(1)
Varies as a function of slope a as defined in NBC Sentences
4.1.7.1.(4) and (5).
upper roof is long, drifts up to twice as long as those
obtained using Figure H-4 have been observed.
35. The wind exposure factor, C w ' should be taken
e as equal to 1.0, for those areas of the lower roof
sheltered by the upper roof. The width of the sheltered area is 10 times the difference between the
elevation of the upper roof and the elevation of the
uniformly distributed snow on the exposed lower
roof (Le., 10 (h 0.6 SJy) or 10 (h 0.4 SJy) north of
the treeline).
36. Multi-level roofs with the upper roof sloped (Figure
H-5). A lower roof should be designed for the loads
provided in Figure H-4 plus an additional load
(2)
(3)
If a > 5 m or h ｾ＠ 0.8S s drifting need not be considered.
y
Cw =0.75 may be reduced to 0.5 for exposed areas north of
the treeline as defined in NBC Sentence 4.1.7.1.(3).
produced by the snow that may slide from an upper
roof. The following guide is recommended. Because
of the low probability that both upper and lower
roofs will have the full load over their entire areas
simultaneously when sliding occurs, the lower roof
should be assumed to carry its full load according to
Figure H-4 plus 50 per cent of the total weight of the
Case 1 snow load from the upper roof. The distribution should be made depending on the relative sizes,
slopes and positions of the two roofs. If all the
sliding snow cannot be retained on the lower roof
because it is too small, appropriate reductions may be
made. A profile of the snow depth on the roof should
be drawn to confirm that the loading is reasonable.
195
e
pays
Figure H·5 Snow distributions on lower roof with sloping upper
roof
Notes to Figure H·5:
(1)
Lower roof is designed for drift load (see Figures H-3 and
H-4) and sliding snow load (see Paragraph 36).
(2)
Upper roof is designed in accordance with NBC Subsection
4.1.7. (see Figures H-1, H-2{a) and H-2(b)).
Roof profile
Distribution of snow load(1·2), S
Figure H·6 Snow distribution and snow loading factors for
areas adjacent to roof obstructions
Notes to Figure H·6:
(1)
Varies as a function of slope a as defined in NBC Sentences
4.1.7.1.(4) and (5).
(2)
If b is less than 3Ss 1y, m the effect of the obstruction on the
snow loading can be ignored.
(3)
Cw =0.75 may be reduced to 0.5 for exposed areas north of
the treeline, as deIined in NBC Sentence 4.1.7.1.(3).
sliding snow load
drift load
e
Roof projection
b,
Factors
x
metres
(2)
<
0.75 (3)
3 Ss
--y-
Distribution of snow
f (a
OR
ALL
)(1)
1.0
1.0
S
>
rrIDlllllllltr
＾ｾ＠
C, 10 h'----J
>
1.0
C
00
(Coo -
1.0
y
Xd
< x$.
10 h'
1.0
f(
a
)(1)
f(
a
t)
1.0
Value of
0.75
> 10
Value of h':
ｾＭ＠
:
ca 0= 0.67
when C a 0 < 1.0 use 1.0, when C a 0 > ｾ＠
196
OR
1.0
h' = hValue of Ca 0
h'
use
b
(3)
1.0
l)x
pays
37. Areas adjacent to obstructions (Figure H-6). Consideration should also be given to triangular drift
loads adjacent to significant vertical obstructions,
such as elevator, air conditioning and fan housings,
small penthouses and wide chimneys. The peak load
adjacent to the obstruction in Figure H-6 is assumed
equal to 0.67 yh + Sr' where h is the obstruction
height in metres and y the unit weight in kN I m 3 • It
decreases to the design roof load at a distance of 2 h
from the obstruction. The peak load need not be
larger than 2 S5 + Sr (Ca ::; 2/C b ) nor is it necessary to
consider the drift load if the width, b, of the obstruction in Figure H-6 is less than 3.0 SJy.
supporting members is generally too remote to be
considered in design. (22) On most of the roofs in
Figures H-l and H-2 a number of separate cases of
full and partial loading will be required to ensure
proper design of all elements.
41. The reason for these requirements is that snow
seldom accumulates according to the simple configurations in Figures H-l and H-2. Consequently, full
and partial loading must be considered for the
design of structural members which are sensitive to
changes in load distribution (e.g., truss diagonals and
cantilevers) and which would not otherwise be
designed for unbalanced loads.
Unusual Roofs
Snow Removal
38. In some cases, particularly roofs of unusual
shapes, exceptionally large roofs and roofs over
which the air flow is significantly affected by other
buildings or topographic features, the prediction of
snow loads is difficult. In such cases, the designer
should calculate and plot the snow depths to scale
applying a unit weight of 3.0 kN 1m3 to judge
whether the distributions look reasonable. In some
circumstances wind tunnel or water flume tests
might be used to assist in the evaluation.
42. Although it is fairly common practice in some
areas to remove snow from roofs after heavy snowfalls, the National Building Code does not allow a
reduction of the design load to account for this
because:
(a) snow removal cannot be relied upon. Experience in several countries has shown that during
and after extreme snow storms, traffic is immobilized and snow removal crews cannot be obtained,
(b) snow cannot be effectively removed from the
centre of large roofs, and
(c) unbalanced loading can occur as a result of
certain patterns of snow removal.
Parking Decks
39. Roofs used as parking decks should be designed for the loads noted in NBC Tables 4.1.6.A and
4.1.6.B. or the roof snow loads, whichever are greater.
Where snow removal may occur, consideration
should be given to the loads due to snow removal
equipment and to the weight of piled snow.
Full and Partial Loading
40. All roof areas, including those to be designed
for increased or decreased loads according to Figures
H-l to H-6, must be designed for the full specified
load given in NBC Article 4.1.7.1. over the entire area.
However, only the flat, shed, low slope gable «15°)
and curved roofs (h/b < 0.1) of Figures H-l and H-2
need be designed for Case I loading distributed on
one portion of the area and half of this on the remainder of the area, the location and size of such partial
areas being chosen to give the greatest effects in the
members and joints concerned. These requirements
do not imply checkerboard loading because the
probability that checkerboard loading will occur in
such a way as to give the worst conditions for
43. In special cases, roofs have been designed with
reduced design loads because of the incorporation of
melting systems which periodically clear them of
snow. Decisions to use such systems should be
considered carefully, because adequate energy for
melting may not be available when required. Further, as the years pass, the importance of keeping the
system functioning (perhaps at great cost) may be
forgotten.
Ice Loading on Structures
44. Loads due to ice accretion on exposed surfaces
of superstructure members, railings, lattice towers
and signs are described in References (23) and (24).
The Atmospheric Environment Service, Downsview,
Ontario has a modeL based on climate data at
weather stations, to compute ice loading on vertical
and horizontal surfaces and cables.
197
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Minimum Roof Load
45. Articles 4.1.6.3. and 4.1.6.10. of the National
Building Code provide for a minimum uniform roof
load of 1 kPa and a minimum concentrated load of
1.3 kN. These loads are "use and occupancy loads"
intended to provide for maintenance loadings, workmen and so forth. These loads are not reduced as a
function of area or as a function of the roof slope.
History of Snow Loads in the
National Building Code
46. In the 1953 National Building Code of Canada,
design snow loads were equal to the ground snow
load, with reductions allowed for sloped roofs only.
Such values were very approximate and resulted in
overdesign in some roofs while allowing underdesign in others, particularly in areas subject to high
drift loads. Information on which to base a more
refined assessment of the loads was not available,
however, until a countrywide survey of snow loads
on roofs was undertaken by the Institute for Research
in Construction with the help of many volunteer
observers. This survey provided evidence on the
relationship between ground and roof loads and
enabled the committees responsible for the 1960
edition of the National Building Code to make
changes. The roof load was set at 80 per cent of the
ground load and the ground load was based on a
return period of 30 years and adjusted to allow for
the increase in the load caused by rainwater absorbed
by the snow.
47. With the introduction of the 1965 Code and its
Commentary, further changes made by the Revision
Committee on Structural Loads and Procedures led
to a more rational approach to design loads. All roof
loads were directly related to the snow load on the
ground and, consequently, the roof snow loads were
removed from the table of Design Data for Selected
Locations in Canada in Chapter 1. The basic load
remained at 80 per cent of the ground load, except
that a snow load of 60 per cent of the ground load
was allowed for roofs exposed to the wind. This
reduction was made because at the same time allowance was made for a variety of influences causing
accumulations of snow on roofs. This was done by
means of "snow load coefficients" or shape factors,
which were shown in the form of simple formulas
198
and diagrams similar to Figures H-1 to H-6. In
addition, the slope red uction formula was changed
from the step function used in 1960 to a linear
function.
48. In the 1970 Code and Commentary, minor
changes were made to the provisions for gable and
arch roofs and more severe "full and partial loading
provisions": "full and zero loading" rather than "full
and half."
49. In the 1975 Code and Commentary, few
changes were made, except that the requirement for
full and partial loading was considered too severe at
"full and zero" and was changed back to "full and
half" loading.
50. In the 1977 and 1980 Commentaries, the provisions for loads on arch roofs were changed/and a
number of rationalizations made as an aid to better
understanding of snow loads on roofs.
51. The 1985 Code and Commentary provisions
were rewritten to simplify the presentation and
to clarify the intent of the minimum roof loading of
1.0 kPa. Further, the minimum roof loading
was made independent of slope, the unit weight
of roof snow was increased 1.9 per cent to give
y = 2.4 kN 1m3, "full and partial loading" was
restricted to Case I loadings on buildings in Figures
H-1 and H-2, and the unbalanced loading on arches
was simplified.
52. In the 1990 Code and Commentary a new
slope reduction formula is given for unobstructed
slippery sloping roofs, the unit weight of roof snow is
increased to y = 3.0 kN 1m 3, the need for unbalanced
snow loads on domes is emphasized, the minimum
C is reduced to 0.5, rather than 0.75, for exposed
ｲｯｾｦｳ＠
north of the tree line, and design roof snow
loads are separated into snow and rain components
consistent with the new ground snow loads given in
Chapter 1 of this Supplement.
References
D.A. Taylor, A Survey of Snow Loads on the
Roofs of Arena-Type Buildings in Canada.
Can. J. Civ. Eng., Vol. 6, No.1, 1979, pp. 85-96.
(2) M.J. Newark, L.E. Welsh, R.J. Morris and W.V.
Ones, Revised Ground Snow Loads for the
(1)
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(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11 )
(12)
1990 National Building Code of Canada. Can.
J. Civ. Eng., VoL 16, No.3, June 1989, pp. 267278.
Canadian Permanent Committee on Geographical Normes, Gazetteer of Canada (12 Volumes
by Province and Territory). Surveys and Mapping Branch, Dept. of Energy, Mines and
Resources, Available from Mail Order Services,
Canadian Government Publishing Centre,
Dept. of Supply and Services, Ottawa, Ontario
K1A OS9.
B.R. Claus, S.O. Russell and P.A. Schaerer,
Variation of Ground Snow Loads with Elevation in Southern British Columbia. Can. J. Civ.
Eng., VoL 11, No.3, September 1984, pp. 480493.
D.A. Taylor, Snow Loads on Multi-Level Flat
Roofs in Canada. Proc. 55th Western Snow
Conf., Vancouver, April 14-16, 1987, pp. 133141. NRCC 28486.
Ontario Ministry of Municipal Affairs, Housing, Research and Development Section. Prevention of Excess Snow Accumulation due to
Roof Mounted Solar Collectors. (Report prepared under contract by MHTR Ltd., Guelph,
Ontario) Toronto, December 1981, 76 pp.
D. Nixon, Solar Collectors Briefing Document
S-2. Public Works Canada, Design/Construction Branch, Sir Charles Tupper Building,
Ottawa, March 1981, 25 pp.
D.A.Taylor, Snow Loads on Sloping Roofs.
Two Pilot Studies in the Ottawa Area. Can. J.
Civ. Eng., Vol. 12, No.2, 1985, pp. 334-343.
D.A. Taylor, Sliding Snow on Sloping Roofs.
CBD 228, Division of Building Research, National Research Council Canada, Ottawa, 1983,
4pp.
R.L. Sack, Snow Loads on Sloped Roofs. ASCE
Journal of Structural Eng., Vol. 114, No.3,
March 1988, pp. 501-517.
N. Isyumov, Roof Snow Loads - Their Variability and Dependence on Climatic Conditions.
Symposium on the Structural Use of Wood in
Adverse Environments, 15-18 May 1978,
Vancouver, Van Nostrand Reinhold, 510 pp.
N. Isyumov and M. Mikitiuk, Climatology of
Snowfall and Related Meteorological Variables
with Application to Roof Snow Load
(13)
(14)
(15)
(16)
(17)
(18)
(19)
(20)
(21)
(22)
(23)
(24)
Specifications. Can. J. Civ. Eng., VoL 4, No.2,
1977, pp. 240-256.
N. Isyumov and A.G. Davenport, A Probabilistic Approach to the Prediction of Snow Loads.
Can. J. Civ. Eng., VoL 1, No.1, 1974, pp. 28-49.
W.R. Schriever, Y. Faucher, and D.A. Lutes,
Snow Accumulation in Canada: Case Histories:
1. Division of Building Research, National
Research Council Canada, Ottawa, January
1967. NRCC 9287.
D.A. Lutes, and W.R. Schriever, Snow Accumulation in Canada: Case Histories: II. DBR
Technical Paper 339, Division of Building
Research, National Research Council Canada,
Ottawa, March 1971. NRCC 11915.
J.T. Templin and W.R. Schriever, Loads due to
Drifted Snow. Journal of Structural Division,
Proc., Am. Soc. Civ. Eng., VoL 108, No. ST8,
August 1982, pp. 1916-1925.
M.J. O'Rourke and E. Wood, Improved Relationship for Drift Loads on Buildings. Can. J.
Civ. Eng., Vol. 13, No.6, 1986, pp. 647-652.
D.A. Taylor, Roof Snow Loads in Canada. Can.
J. Civ. Eng., VoL 7, No. 1, 1980, pp. 1-18.
D.A. Taylor, Snow Loads for the Design of
Cylindrical Curved Roofs in Canada 1953-1980.
Can. J. Civ. Eng., VoL 8, No.1, 1981, pp. 63-76.
T.H.R. Kennedy, D.J.L. Kennedy, J.G. MacGregor and D.A. Taylor, Snow Loads in the 1985
National Building Code of Canada: Curved
Roofs. Can. J. Civ. Eng., Vol. 12, No.3, 1985,
pp.427-438.
D.A. Taylor, Snow Loads on Two-Level Flat
Roofs. Proc. 41st Eastern Snow Conf., Washington, D.C., June 7-8, 1984, pp. 3-13. NRCC
24905.
R.L. Booth, and D.A. Taylor, Discussion,
Design of Light Industrial Buildings. Can. J.
Civ. Eng., Vol. 7, No.4, 1980, pp. 660-661.
Ontario Ministry of Transportation and Communications, Highway Engineering Division,
1983 Ontario Highway Bridge Design Code,
Toronto, p. 46.
Canadian Standards Association CAN ICSAS237-M86. Antennas, Towers and AntennaSupporting Structures. Rexdale, Ontario, 1986,
73pp.
199
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Commentary I
Rain Loads
1. In accordance with National Building Code
Sentence 4.1.7.3.(1), any roof which can accumulate
water must be designed for the load that results from
a 24 h rainfall on the horizontal projected area of the
roof. This requirement applies whether or not the
surface is provided with drainage, such as rainwater
leaders. The distribution of rain load should be
determined by the designer, who should take into
account the shape of the roof, including camber, with
or without creep deflection due to dead load, and
also deflection due to rain.
2. Notwithstanding the above requirement, it is
considered good practice in the location of roof
drains to take into account not only the roof slope but
also deflection of the roof due to creep, snow and
rain. Drains should be provided with suitable
devices to prevent clogging by leaves or, when
appropriate, suitable overflows should be provided
through parapet walls.
Ponding Instability
3. If a flat roof is too flexible, rainwater will not
accumulate evenly over the roof but will flow to form
ponds in a few local areas. This may lead to an
instability similar to buckling, which can result in
failure of the roof due to local overloading. In the
case of one-way roof beams or decking simply
supported on rigid supports, ponding instability will
occur when the beam or decking stiffness is less than
Elcrit given by
4
(1)
EI cit = pgS ＨｾＩ＠
where
E =
I
L
S
P
200
modulus of elasticity,
moment of inertia of the beam or decking,
span,
spacing of the beam or decking,
mass density of water, kg/m 3•
4. In the case of a two-way system of roof joists on
girders, the critical stiffness can be approximated by
+ ｅｉｧｾ＠
1
(2)
Elj
where EIcrit and EIgcrit are given by Equation (1) for
joists and girders, respectively.
5. Even if the roof system is stiffer than the critical
values determined by Equations (1) and (2), calculated moments and deflections may be amplified due
to ponding effect. A practical criterion is to require
roof stiffness to be at least twice the critical stiffness.
In the case of a one-way system on rigid supports, in
terms of existing deflection requirements, this can be
expressed as follows:
w> lS.4L ＨｾＩ＠
(3)
L allowable
where w is the design load in kilopascals specified
for deflection calculation and ＨｾＩ｡ｬｯｷ｢･＠
is the allowable deflection to span ratio (see Table A-l, Commentary A, "Serviceability Criteria for Deflections
and Vibrations"). If for a one-way system the design
load w is less than the critical value given in Table
1-1, the effects of ponding should be considered. This
applies particularly to large flat roofs in areas of
heavy rainfall. Further information is given in
References (1) to (7).
Table 1-1
Critical Values of w for Ponding, kPa
{one-way system - Equation (3))
Deflection/Span I
Requirement L = 5 m L = 10 m
.
1:180
0.43
0.86
1:240
0.32
0.64
Column 1
2
3
i
I
L 20 m L =30 m
1.71
2.57
1.28
1.93
4
5
References
(1) D.A. Sawyer, Ponding of Rainwater on Flexible
Roof Systems. Journal of Structural Division,
Proc. , Am. Soc. Civ. Eng., Vol. 93, ST1, February 1967, p. 127.
(2) R.W. Haussler, Roof Deflection Caused by
Rainwater Pools. Civil Engineering, VoL 32,
October 1962, p. 58.
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t
(3) F.J. Marino, Ponding of Two-Way RoofSysterns. Engineering Journal Am. Inst. of Steel
Construction, Vol. 3, No.3, July 1966, p. 93.
(4) Commentary on the Specification for the
Design, Fabrication and Erection of Structural
Steel for Buildings. Am. Inst. of Steel Construction, New York, February 1969.
(5) A.E. Salama and M.L. Moody, Analysis of
Beams and Plates for Ponding Loads. Journal
of Structural Division, Proc., Am. Soc. Civ.
Eng., Vol. 93, ST1, February 1967, p. 109.
(6) J. Chinn, A.H. Mansouri and S.F. Adams,
Ponding of Liquids on Flat Roofs. Journal of
Structural Division, Proc., Am. Soc. Civ. Eng.,
Vol. 95, ST5, May 1969, p. 797.
(7) D.A. Sawyer, Roof-Structural Roof-Drainage
Inter..actions. Journal of Structural Division,
Proc., Am. Soc. Civ. Eng., Vol. 94, ST1, January
1969,p.175.
201
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Commentary .J
Effects of Earthquakes
Objectives of EarthquakeResistant Design
1. The earthquake-resistant design requirements
of the National Building Code of Canada 1990
provide an acceptable level of public safety, which is
achieved by designing to prevent major failure and
loss of life. Structures designed in conformance with
these provisions should be able to resist moderate
earthquakes without significant damage and major
earthquakes without collapse. For the purpose of
this section, collapse is defined as the state at which
exit of the occupants from the building becomes
impossible because of failure of the primary structure.
2. Structures could be designed to resist major
earthquakes without damage; this, however, would
be uneconomical and unwarranted because of the
relatively small likelihood of such events in Canada.
Instead, the objective of the NBC provisions is to
reduce the probability of fatalities to an appropriately
small value and to accept some structural damage in
major earthquakes. Damage caused by landslides
such as have occured in Anchorage, Alaska, (1) or
damage due to earth consolidation or liquefaction as
in Niigata, Japan}2l will not be prevented by conforming to the seismic requirements of the NBC. The
NBC regulations provide buildings with resistance to
earthquake ground motions but not to slides, subsidence, or active faulting in the immediate vicinity of
the structure; such cases require special study.
3. To design an earthquake-resistant structure, one
needs to know the characteristics and probability of
occurrence of the "design" seismic ground motion,
the characteristics of the structure and the foundation, the allowable stresses in the materials of construction, including the foundation soils, and the
amount of damage that is tolerable. The design must
provide not only sufficient structural strength to
resist the ground motion, but also the proper stiffness
to limit the lateral deflection or drift. Damage to
nonstructural elements may be minimized by proper
limitation of distortions and by attention to the
202
details of their connection to the primary structure.
The minimum requirements given in the NBC
incorporate the above considerations. This commentary elaborates on the quantitative and qualitative
bases for the NBC requirements, and in some cases,
recommends procedures.
4. It is beyond the scope of the NBC to cover the
entire range of problems involved in the earthquakeresistant design of all structures. Unusual structures,
highly irregular buildings and special-purpose
industrial structures such as nuclear reactors, power
plants and stacks should be treated as special problems with special design criteria in each instance,
including possibly a dynamic analysis. Likewise,
tanks, piping and structures whose failure constitutes
an unusually high involuntary hazard to health or
life as a result of emission of toxic or explosive
substances must be designed to standards determined by an evaluation of the probabilities of failure
and their consequences. Some of these structures
have earthquake-resistant design provisions identified in other standards, e.g., CANDU nuclear power
plantsYl liquefied natural gas facilities(4) and fixed
offshore production structures.(5) The advice of an
experienced engineer should be sought to arrive at
suitable design criteria.
Seismic Regionalization
5. Earthquake-resistant designs should be considered for structures built in all regions of Canada,
although the severity of expected earthquake effects
varies considerably across the country. Detailed
information on earthquakes that have occurred in
Canada is contained in the publications of the Geological Survey of Canada, Energy, Mines and ResourcesY,·lOl From these studies, the present seismic
zoning maps for Canada have been developed.(11-15)
6. The seismic zoning maps (Figures J-1 and J-2)
are based on a statistical analysis of the earthquakes
that have been experienced in Canada and adjacent
regions. These ma ps differ from the previous (1970)
seismic zoning map employed in the 1980 and earlier
editions of the NBC in that
(a) the data were analyzed using a method proposed by Cornell(16) and a seismic risk computer
program developed by McGuire,(17) instead of
the extreme-value method. The new method
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provides for inclusion of geological and tectonic
information in support of the seismic data,
(b) new strong seismic ground motion attenuation
relations(12l were employed,
(c) both peak horizontal acceleration and peak
horizontal velocity have been mapped, and
(d) the probability of exceedance of the seismic
ground motion parameters has been changed to
10 per cent in 50 years (which is mathematically
equivalent to a probability of exceedance of
0.0021 per annum) from the previous value of
0.01 per annum.
The probability of exceedance of 10 per cent in
50 years for the ground motion parameters is considered to be more appropriate than the previously
employed 0.01 per annum for the objectives of earthｱｵ｡ｫ･Ｍｲｳｩｾｴｮ＠
design described in Paragraph 1.
However, on average across the country, the calculation of minimum lateral seismic forces has not
changed relative to the NBC 1980, although at any
geographical location the forces will vary in some
detail from previous values because of the improved
estimates of seismic risk and the adoption of the
second ground motion parameter, peak horizontal
velocity.(1S)
7. The range of the ratio, a, of peak horizontal
ground acceleration to the acceleration due to gravity
(taken nominally as 10 m/s2) and of the ratio, v, of
peak horizontal ground velocity to a velocity of
1 m/s and the zonal ratios associated with each zone
Acceleration-Related or
Velocity-Related
Seismic Zone
Za' Zv
0
1
2
3
4
5
6
Column 1
are given in Table J-1. Table J-2 includes representative values of acceleration and velocity ratios for
several levels of probability of exceedance for a
number of Canadian cities. Similar calculations for
any site in Canada may be obtained at cost by writing
to Geophysics Division, Geological Survey of Canada, 1 Observatory Crescent, Ottawa, Ontario K1A
OY3, or the Pacific Geoscience Centre, P.O. Box 6000,
Sidney, B.C. V8L 4B2.
8. The zonal acceleration and velocity ratios for
Zone 6 (a = v 0.40) should be considered nominal
values. These ratios may be applicable for derivation
of design loads for structures, but it should be
recognized tha t
(a) site specific values of the acceleration and
velocity ratios in Zone 6 can exceed 0.40 by
substantial margins, and
(b) depending on the type of structure, it may be
necessary to characterize more explicitly the
nature of expected ground motion in the dominant frequency range of structural response. In
the latter case, the advice of an experienced
engineering seismologist should be sought to
arrive at suitable design seismic ground motion.
9. There is, and always will be, an inherent
uncertainty in the appropria te seismic ground
motions to be used in earthquake-resistant design.
Because of the nature of earthquakes, their size and
location and the ground motion effects that they will
produce cannot be accurately defined. The ground
Table J-1
Definition of Seismic Zones
Range of Peak Horizontal Ground Acceleration, g,
or Peak Horizontal Ground Velocity, mIs,
for 10 per cent probability of exceedance in 50 years
Equal to
Less than
0.00
0.04
0.04
0.08
0.11
0.08
0.11
0.16
0.16
0.23
0.23
0.32
0.32
or greater
2
3
Zonal Acceleration,
Ratio, a
Zonal Velocity
Ratio, v
0.00
0.05
0.10
0.15
0.20
0.30
0040
4
203
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Table J-2
Peak Horizontal Ground Acceleration (PH A, g) and Peak Horizontal Ground Velocity (PHV, m/s)
for Selected Localities and Probabilities of Exceedance
Probability of Annual Exceedance
0.0021 (2)
Locality (1)
0.01
0.005
PHV
PHA
PHV
PHA
PHV
PHA
I
Inuvik
(68.30, 133.48)
Prince Rupert
(54.30, 130.43)
Victoria
(48.65,123.43)
Vancouver
(49.18, 123.17)
Calgary
(51.10, 114.02)
Toronto
(43.67,79.63)
Ottawa
(45.32,75.67)
Montreal
(45.47,73.75)
Quebec City
(46.80,71.38)
Fredericton
(45.87,66.53)
Halifax
(44.88,63.52)
St. John's
(47.61,52.75)
Column 1
0.033
0.052
0.043
0.066
0.060
0.083
0.074
0.13
0.096
0.20
0.13
0.27
0.12
0.088
0.18
0.15
0.28
0.26
0.089
0.077
0.13
0.12
0.21
0.21
0.011
0.026
0.014
0.032
0.019
0.040
0.029
0.014
0.039
0.023
0.056
0.038
0.084
0.031
0.12
0.054
0.20
0.098
0.078
0.031
0.11
0.053
0.18
0.097
0.075
0.035
0.11
0.066
0.19
0.14
0.046
0.020
0.066
0.036
0.096
0.066
0.027
0.016
0.038
0.030
0.056
0.056
0.013
0.033
0.026
0.054
0.052
7
0.022
2
i
3
Notes to Table J-2:
Geographical coordinates (ON, OW) used for the computation
are indicated.
(2)
Equivalent to the probability of 10 per cent in 50 years
employed for Figures J-1 and J-2.
P(50 yrs) = 1 - (1 - p(per annum))50.
(1)
204
4
5
I
6
pays
D
g
Zo
0
.04
.08
0
I
.11
.16
.23
.32
4
5
6
ｾ＠
/J
--- ｾＱ［ｑＭ
Ｇｕｾ＠
km
Figure J-1 Contours of peak horizontal ground accelerations,
in units of g, having a probability of exceedance of 10 per cent in
50 years.
motions computed to produce Figures J-1 and J-2 are
the current best estimates for building code purposes.
Estimates of seismic ground motions at lower levels
of probability of exceedance than those given in Table
J-2 would require additional investigations.
Direction of Earthquake Motions
[NBC 4.1.9.1.(3)]
10. In general, ground motion in an earthquake is
multidirectional. This complex motion is imparted to
the supports of a structure; the structure then responds according to its stiffness and inertial properties. At any instant during the earthquake, the
state of stress in the structure is a function of the
inertial forces and the deformations of the structure.
In the most general case, seismic analysis would
involve the simultaneous translation along the two
horizontal axes, rocking plus vertical and torsional
motions. For normal buildings, however, independent design about each of the horizontal axes
together with the associated torsional forces is
considered to provide adequate resistance against
earthquake motions applied in any direction. This
simplification forms the basis for the earthquake requirements in the NBC. Particular attention should
be paid, however, to the effect of the combined
stresses at the external and re-entrant corners, which
are especially vulnerable to the effect of concurrent
translational and torsional motions. O)
Vertical Accelerations
11. The multi-directional ground motion during
an earthquake may contain a substantial vertical
component. The ratio of vertical to horizontal motion
varies widely depending on site conditions; an
average value for this ratio is 2/3 to 3/4.
205
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D
m/s
0
.04
.08
v
Zv
0
0
.05
.11
.16
.23
.32
.30
5
.40
6
Figure J·2 Contours of peak horizontal ground velocities, in
mis, having a probability of exceedance of 10 per cent in
50 years.
12. Under abnormally high vertical accelerations,
columns at the upper floors, especially at the roof
level, could be adversely affected. However, there is
usually sufficient reserve strength in vertical loadcarrying members that vertical accelerations can be
safely neglected. In certain special structures, (lll)
these accelerations may have led to instability or
unusual reductions in the factors of safety. Cantilevered structures or cantilevered building components
are also sensitive to vertical accelerations. When this
becomes a governing design consideration, dynamic
analysis should be employed.
fundamental period and the damping characteristics
of the system, and on the frequency content and
amplitude of the ground motion. The base shear
which can be used as a measure of this response is
expressed as the product of the mass of the system
and the spectral acceleration as given by the response
spectrum.
The acceleration response spectrum reflects the
dependence on the natural period, T, the damping of
the system and also the characteristics of the ground
motion. Details of its derivation can be found in
Reference (19).
Structural Response to Ground
Motion [NBC 4.1.9.1.(4)]
14. This concept of calculating base shear can be
applied to multi-storey buildings having many
modes of vibration. For usual buildings of low or
moderate height, the principal earthquake response
is due to the fundamental mode of vibration. For
13. The elastic response of a single-degree-offreedom system to ground motion depends on the
I
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taller structures, some allowance for contributions of
the higher modes is made in the base shear calculations in most building codespOl including the NBC.
15. With the onset of inelastic material behaviour,
the base shear induced by earthquakes is reduced as
compared to that of elastic behaviour. Such a reduction in base shear is implicit in the provisions of most
building codes, including the NBC. The lower base
shears, however, are justified only if a structure possesses ductility, i.e., the capacity to deform beyond
the yield point without major structural failure.(21-23)
Minimum Design Earthquake
Forces [NBC 4.1.9.1.(4)]
16. The NBC specifies that a structure should be
designed for a minimum base shear, V, given by
V = (V/R) V
(1)
where Ve is the equivalent lateral seismic force
representing elastic response, R is the force modification factor, and V = 0.6 is a calibration factor. This
calibration factor is applied to maintain the design
base shears at the same level of protection for buildings with good to excellent capability of resisting
seismic loads consistent with the R factors used.
Each of these factors will be discussed in greater
detail.
17. The base shear, V, corresponds to that at the
ultimate limit state, where the structure is assumed to
be at the point of collapse. For 1990 NBC, the seismic
load factor in Subsection 4.1.4. has been separated
from that of wind and assigned a value of 1.0, in
contrast to 1.5 for the 1985 NBC. This follows from
the argument that the seismic ground motions
specified in the NBC should be considered to be
extreme or accidental actions, rather than live loads
or variable actions, as for example, live or wind
loads. (24) Although the load factors have changed,
the factored base shear has remained approximately
constant compared to the 1985 NBC.
Equivalent Lateral Seismic Force
Representing Elastic Response, Ve
[NBC 4.1.9.1.(5)]
18. The lateral force
Ve
vSIFW
(2)
is a good approximation of the base shear of an
elastic structure having nominal damping and subjected to a seismic ground motion characterized by
peak ground velocity, for which S represents an
idealized elastic response spectrum. (24) This is a useful reference in terms of the response of a structure
having period T. Therefore, in the 1990 NBC, Ve is
taken as the "equivalent lateral force representing the
elastic response." This elastic response parameter is
then modified by R to account for various forms of
energy dissipation and by the calibration factor V, to
arrive at the base shear force, V.
Zonal Velocity Ratio, v
19. The zonal velocity ratio, v, is derived from the
probabilistic study of ground motions in the 1 s
period range, normalized to a spectral velocity of
1.0 m/ s. Similarly, a zonal acceleration ratio, a, was
obtained from probabilistic evaluation of the ground
motions in the 0.2 s period range, normalized to 1.0 g.
At any location, the two ground motion parameters,
a and v, affect the behaviour of structures in the short
period and intermediate period range, respectively.
In the formulation for the NBC seismic provisions,
only the zonal velocity ratio, v, is specified explicitly,
whereas the zonal acceleration ratio, a, is used
implicitly via the seismic response factor, S.(15) Values
for v and the corresponding velocity-related seismic
zone, Zv' and accceleration-related seismic zone, Z""
are given in Chapter 1 of this Supplement.
20. The seismic hazard maps for peak ground
acceleration and for peak ground velocity having a
probability of exceedance of 10 per cent in 50 years
are shown as Figures J-l and J-2. The correspondence
between zone boundaries, zone numbers and zonal
acceleration and velocity ratios is presented in
Table J-1.
207
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Seismic Response Factor, S
[NBC 4.1.9.1.(6)]
Fundamental Period, T
[NBC 4.1.9.1.(7)]
21. The seismic response factor, Sf is plotted in
Figure J-3. The factor is a function of the fundamental period, T, of the structure, and the relative values
of the velocity-related and acceleration-related
seismic zones, Zv and Za' pertaining to a particular
geographical location. This factor represents the
idealized elastic response of 5 per cent damped
multi-degree-of-freedom systems, for unit values of
the zonal velocity ratio, v, and weight, W. Research
assessing the validity of 5, on the basis of dynamic
response studies using a number of representative
earthquake records, is reported in Reference (25).
23. The following empirical formulas are to be
used for the determination of the fundamental
period, T, for buildings:
22. For the case where Za> Zv' the maximum
value of 5 in the short period range, T < 0.25, has
been limited by the multiplier 1.4 relative to the case
where Z Z, whereas for Z < Z the minimum
value is ｦｩｭｴｾ､＠
by the multiplier 0.71. This is for
code purposes, to prevent extreme variations in lateral force due to differing velocity and acceleration
zones. The evolution of the seismic response factor,
5, over the last few decades is reviewed in Reference (23).
(/)
4.2
ｦＭｾ
......
t5
ｾ＠
c
T
O.lN
(3)
for all others
(4)
where h n and Ds must be expressed in metres. Other
symbols are defined in Sentence 4.1.9.1.(2) of the
NBC. Period calculations based on these formulas
give values that for the most part are in reasonable
agreement with measured values. (26) However, variations in the order of 50 per cent have been observed
when these formulas are used.
24. For pure shear wall structures, the natural
period is generally closer to the true building period
when Ds rather than D, also expressed in metres, is
used in Equation (4). However, when the length of
the lateral force resisting system is not well defined,
then the Code requires that D shall be used instead of
D.s
25. The period, T, for a structure may be determined by more refined methods of calculation. One
such method is to use the following expression,
which represents the Rayleigh approximation for
determining the natural period of the fundamental
mode:
c5
ｾ＠
for moment resistant space frames only,
(5)
3.0 1 - - - -.......
o
a.
(/)
ｾ＠
u
2.1
where 8. (i = 1 ... n) are the elastic deflections in
storeys Ldue to the forces Wi applied horizontally at
storeys i. Wi is as defined in Sentence 4.1.9.1.(2), g is
the acceleration due to gravity and the units used
must be consistent.
E
(/)
'Q)
(/)
0.25
0.50
0.75
1.00
Period. T, S
Figure J-3 SeIsmIc response factor S for 1990 NBC
1.25
26. When the fundamental period is calculated by
the Rayleigh method or any other analytical method,
the NBC requires the period used to be less than or
equal to 1.2 times the period, T, calculated from
Equations (3) or (4). The reason for limiting the period deviation is that the Code is primarily calibrated
on the period calculation of Equations (3) and (4).
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r,..
Large deviations of T resulting in significant reductions in base shear are undesirable.
Force Modification Factor, R
[NBC 4.1.9.1.(8)]
27. The force modification factor, R, aSSigned to
different types of structural systems reflects design
and construction experience, as well as the evaluation
of the performance of structures in major and moderate earthquakes. It endeavours to account for the
energy-absorption capacity of the structural system
by damping and inelastic action through several load
reversals. Types of construction that have performed
well in earthquakes are assigned higher values of R.
The values of R in Table 4.1.9.B. of the NBC recognize
the following:
(1) The capability of a structure to absorb
energy, within acceptable deformations and without
failure, is a very desirable characteristic of any earthquake-resistant design.
(2) The existence of alternate load paths or
redundancy of a structural system is a desirable
characteristic. It increases the locations where energy
can be dissipated and reduces the risk of collapse
when individual members should fail or become
severely damaged.
(3) A building designed with a value of R
greater than 1.0 is presumed to be capable of undergoing inelastic cyclic deformations. Members and
connections in such systems must therefore be detailed to accommodate these deformations in a
ductile manner.
(4) Buildings are normally endowed with a
multiplicity of nonstructural elements and resisting
elements not considered in the analysis. Furthermore, buildings generally have higher damping
values during large amplitude vibrations than do
mere skeleton structures.
28. The R values for structural systems need to
reflect the
of continuity and ductility provided. A building with a value of R equal to 1.0 corresponds to a structural system exhibiting little or no
ductility. Values of R higher than 1.0 reflect the fact
that structures can be designed and detailed to
accommodate the corresponding inelastic cyclic
deformations. The definitions, together with the
minimum design and detailing requirements for each
of the specific cases in Table 4.1.9.B., are given in the
corresponding material standards.
29. In choosing the structural system for a building, large dissimilarities in the stiffness and ductility
characteristics of framing systems in the orthogonal
directions should be avoided. For example, a moment-resistant ductile frame in one direction and
reinforced masonry walls in the other would be
unsuitable, whereas reinforced concrete ductile
flexural walls and reinforced concrete walls with
nominal ductility in orthogonal directions would be
acceptable. The reason for this recommendation is
that seismic displacements induced in flexible
framing systems would probably cause failure in the
relatively brittle and weak directions of elements that
resist the load in the orthogonal direction.
30. Internal structures such as multi-storey racks
that are free-standing on the ground but are surrounded by, but not otherwise connected to, the
building structure should be analyzed as separate
structures. Separation by Sentence 4.1.9.2.(5) must
also be satisfied. Appropriate R values need to be
chosen in accordance with the structural system
employed, and adequate resistance to the lateral
forces needs to be provided throughout the height of
the structure. When connections are made between
the racks and the enclosures, the combined system
has to resist the lateral seismic forces in proportion to
the relative stiffnesses of the components.
Importance Factor, I
[NBC 4.1.9.1.(10)]
31. Normally, structures are assigned an I factor of
1.0. For school buildings, which are usually well
distributed throughout a community and whose
grounds and buildings may be needed for postdisaster services, the importance factor is assigned a
value of I 1 which gives an increased degree of
life safety for schools.
32. Some structures are designed for essential
public services, and these post-disaster structures
should be operative immediately after an earthquake.
Examples of such structures are buildings that house
209
.,
pays
1
or control electrical generating and distribution
systems, fire and police stations, hospitals, radio
stations and towers, telephone exchanges, water and
sewage pumping stations, fuel supplies and civil
defence buildings. Such structures are assigned an
importance factor of I 1.5. However, the mere
application of I = 1.5 will not necessarily assure
operational readiness of a facility after an earthquake.
The requirements for a functional survival would
entail a detailed study of the anticipated behaviour of
equipment and structural components. Building
contents, such as equipment and services, which are
required to remain functional immediately after an
earthquake, should be capable of accommodating the
deflections specified in Sentence 4.1.9.2.(2). These
more stringent drift requirements, coupled with the
factor I = 1.5 for post-disaster structures and for parts
and portions of such structures, are intended to
provide a higher probability of maintaining these
functional requirements immediately after a major
earthquake.
33. The factor I 1.5 is not intended to cover the
design considerations associated with special purpose structures whose failure could endanger the
lives of a large number of people or affect the environment well beyond the confines of the building.
These special purpose structures would include, for
example, facilities for the manufacture or storage of
toxic materials and may require more sophisticated
analysis.
Foundation Factor, F
[NBC 4.1.9.1.(11)]
34. The soil conditions at a site have been shown
to exert a major influence on the type and amount of
structural damage resulting from an earthquake. (27-30)
As the motions propaga te from bedrock to the
surface, the soil may amplify the motions in selected
frequency ranges around the natural frequencies of
the surficial layer. In addition, a structure founded
on the surficial layer, with some natural frequencies
close to those of the layer, may undergo even more
intense shaking due to the development of a state of
quasi-resonance between structure and foundation
soil. Direct calculation of these effects by suitable
e mathematical models such as lumped masses, wave
propagation and by two-dimensional finite element
210
models using realistic soil properties is possible with
the assumption that the earthquake motions are shear
waves propagated vertically from bedrock. This
simplified model of wave transmission ignores the
source mechanism of the earthquake, the geology of
the travel path and the effect of surface waves.
Because of the uncertainties and complexities in the
realistic estimation of site effects on the seismic
response of structures and ground, only a rough
allowance for site effects can be made at this time.
35. The seismic provisions of the NBC incorporate
site effects by categorizing the wide variety of
possible soil conditions into four types and assigning
values to a foundation factor, F, as per Sentence
4.1.9.1.(11), depending on soil type and depth. The
factor, F, reflects experience with these soil conditions
in the field, and in an approximate way integrates the
effect of possible soil amplification and soil-structure
resonance into the estimation of the seismic design
forces for buildings having no unusual structural
characteristics.
36. Sites underlain by deposits of very soft to soft
fine-grained soils with depths greater than 15 mare
assigned a foundation factor F 2.0. This provision
is based on the observation of large amplifications of
incoming earthquake motions in the clay deposits
of Mexico City during the September 19, 1985 earthquake. (27,30,31)
37. When a site is underlain by a number of
different soil layers, an F value appropriate to some
average conditions may be used. However, when
substantial layers of soft clay are present, F = 1.3
should be used if the total thickness of clay is less
than 15 m and F = 2.0 when the thickness is 15 m or
greater.
38. The seismic design procedures outlined in the
NBC are based on the assumption that the structures
are founded on a rigid base moving with the ground
surface motion. Real foundations possess both
flexibility and damping capacity, which alter structural response. The flexibility of the foundation
increases the fundamental period of a structure, and
the damping capacity arises from dissipation of
energy by radiation away from the structure and by
hysteretic damping in the foundation, thus increasing
the effective damping of the structure. These effects
are described as soil-structure interaction and are not
I
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considered explicitly in the NBC. For most buildings
covered by the NBC, neglecting soil-structure interaction results in conservative design.
Dynamic Analysis
[NBC 4.1.9.1.(13)(b)]
39. Liquefaction potential of foundation soils
may be assessed as outlined in References (32), (33)
and (34).
42. Sentence 4.1.9.1.(13) states that the distribution
of forces over the height of a building may also be
determined by a dynamic analysis. This would
apply especially to buildings with significant
irregularities, either in plan view or elevation,
buildings with setbacks or major discontinuities in
stiffness or mass, and those with large or irregular
eccentricities between the centre of mass and the
centre of stiffness. An independent determination of
base shear using a dynamic analysis is not intended
with this procedure, since various assumptions of
structural behaviour that cannot always be substantiated can result in much lower base shears than those
prescribed by the Code. This is undesirable, since the
Code values are already minimum values commensurate with an acceptable level of public safety. For
this reason, the following simplified procedure is
recommended.
(a) Determine modes of vibration, modal periods
and participation factors for the building.
(b) Multiply the normalized design distribution
spectrum in Figure J-4 by the peak ground
velocity, v, and determine the modal response
for each mode. At least the lowest five modes or
the number of storeys, whichever is less, should
be used in each of the two principal or major
coordinate directions.
(c) Determine the total probable modal base shear,
V m' by combining the individual modal base
shears. For most structures, a root-sum-square
(r.s.s.) method will be satisfactory. When closely
spaced modes are present, other methods of
combining modal responses should be used.
See for example Reference (36).
(d) Scale all modal contributions by the ratio of the
Code base shear, V, (obtained by the method in
Subsection 4.1.9. of the NBC) to the total probable base shear, V .
(e) Obtain design sto;'ey shears and other design
quantities of interest by summing the scaled
modal quantity of each contributing mode using
the root-sum-square method or other methods
as in (c) above.
Lateral Force Distribution
[NBC 4.1.9.1.(13)]
40. For translational vibrations, the Code formula
assumes that the building response is primarily due
to its fundamental mode and the mode shape is
assumed to be linear. As the inertial forces, F ,induced at any level, x, are proportional to the weight, W x'
at that level, the distribution of seismic forces is
approximated by
Fx
v(
Wxhx
n
)
IWihi
(6)
i=l
For a lumped mass system the use of this equation
is reasonable for structures with fundamental periods
less than about O.7s. For buildings having longer
periods, higher forces are induced at the top portion
of the structure due to increasing contributions to top
storey amplitudes by all the contributing modes.(21,35)
This redistribution of forces is accounted for by
applying part of the base shear as a concentrated
force, Ft' to the top of the structure, in which case V
e in Eq. (6) is replaced by V - Ft' The top force,
increases with the period of the structure, starting at
T = 0.7s and reaching a maximum of 25 per cent of
the base shear. This is considered a more rational
approach to account for the effects of higher modes
in tall structures than the criterion of slenderness
employed in the 1985 NBC.
41. Vn' the shear force for the top storey, and Vx'
the shear force transmitted to the supporting structure just below the level i = x, are given by
Vn=Ft+Fn
(7)
(8)
211
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ｾ＠
E
1
0.8
0,6
">
(/)
.i-
0.4
'0
0
Q)
>
ｾ＠
0.2
t)
0.1
0.08
0.06
Q)
0..
(/)
0.04
ＰＮＱＭＴａｾＫＲｏＶＸｙ＠
0.01
O. 1
10
100
Period T, S
Figure J-4 Normalized design distribution spectrum for peak
horizontal ground velocity v =1 m/s
43. Methods of determining modal properties and
combination of modes can be found in standard
references (e.g., 37, 38, 39).
44. The normalized design distribution spectrum
shown in Figure J-4 was derived from a response
spectrum for 5 per cent damping and assuming
Z = Z . These simplications are introduced since the
ｶｾｲｴｩ｣［ｬ＠
distribution of shear forces is not sensitive to
variations in damping or to relative shifts of velocity
and acceleration zones.
45. For cases where more detailed knowledge of
the building motion or forces near the ultimate limit
state is required, a non-linear step-by-step approach
is indicated, with consideration of a number of appropriately selected ground motions. These motions
might be chosen from both historical records and
artificially generated ones which incorporate the
desired characteristics pertaining to the site and
seismological considerations. A comprehensive
treatise on aspects of earthquake engineering and determination of seismic response is presented in Reference (40).
212
Machinery, Equipment and
Components of Buildings
[NBC 4.1.9.1.(15)]
46. Architectural components, machinery and
electrical and mechanical equipment mounted within
buildings should be designed to withstand the forces
and displacements that arise from the seismic response of the structure. Elevators and their counterweights are vulnerable to large structural displacements as well as lateral forces. Guide rails should be
designed to accommodate these effects and to
prevent derailment of the components. The mountings and supports of motors, fans and other machinery and equipment need sufficient strength to resist
the seismic forces transmitted through these components. In order to prevent injury to persons and to
avoid secondary damage to the structure, stops need
to be provided on resilient machinery mounts to keep
the component from jumping off the springs during
an earthquake. Minimum design forces for equipment and parts and portions of buildings are given in
pays
NBC Sentence 4.1.9.1.(5). For the 1990 NBC, values
of Sp for architectural components are given in Table
4.1.9.D. (See NBC 4.1.9.1.(6) and (8).) Category 1
of the Table does not include walls forming part of
the main structural lateral force resisting system.
50. For solid components, T can be obtained from
experiments, refined calculatiohs, or from the singledegree-of-freedom relationship
ｲｾﾷＭ
Mechanical and Electrical Components
[NBC 4.1 .9.1.( 17)]
Tp=21tVMp/Kp
47. For the design of mechanical and electrical
components, values of S are obtained by multiplying three factors: Sp C pAr A.x C p depends on the
relative sensitivity of components to dynamic excitation and on their relative importance, given in Table
4.1.9.E. Ar is a response amplification factor that
depends on the flexibility of the component or the
mounting and Ax is a height factor that accounts for
the larger accelerations that can occur in the upper
storeys of a building. The distinction between the
values of Ar is whether sympathetic resonance can
exist between the component and the building that
houses it.
48. For many situations the meaning of "rigid,"
"rigidly connected," "flexible" or "flexibly connected" is quite clear and needs no special analysis. For
example, an electric motor or internal combustion
engine, a circulation pump or a tank completely filled
with liquid, all firmly bolted to a stiff slab, can be
considered as rigid. The same motor or pump on
spring supports with seismic limiting stops would be
considered flexibly mounted without further analysis. Free-standing racks bolted to the floor, or piping
that spans long distances, will often be considered
flexible without additional analysis, since they
exhibit considerable flexibility of their own. Because
tanks that are partially filled with liquids can develop
sloshing motions in resonance with the building, they
also need to be considered "flexible."
49. For a more refined analysis of equipment and
where some doubt exists as to the proper classification according to Sentence 4.1.9.1.(7), the following
analytical or experimental verification can be carried
out. A condition of sympathetic resonance is said to
exist whenever the fundamental period of the component, T ,relative to the building period, T, falls
within thG range
0.7::; Tp/T::; 1.5
The component is then classified as being "flexible"
or "flexibly connected."
(9)
(0) e
where
mass of component, kg,
M=
p
Kp
stiffness of component including that of the
supports (e.g., springs), N/m,
load per unit deflection at centre of gravity
of component, N 1m.
51. The sloshing period, T ,of liquids in partially
filled circular tanks is given iIi Reference (41). For
other shapes, the methods given in Reference (42) can
be employed.
52. Equipment whose periods fall outside the
range of 0.7 ::; T IT::; 1.5 can be considered to be rigid
or rigidly conn:cted. T and T need to be measured
in the same direction relative to the mounted equipment, and the same equipment located in different
buildings or on different mounts might require
different values of S . Seismic design of ground
supported circular ｴｾｮｫｳ＠
is dealt with in Reference
(41); mounting details and other aspects of seismic
response of equipment are treated in Reference (43).
53. Some suggested design considerations and
details are presented in References (44) to (50). The
failures of interior partitions, finishes and hung
ceilings also pose hazards to occupants.
Overturning Moments
[NBC 4.1.9.1.(20), (21)]
54. The lateral forces induced in a structure by
earthquakes give rise to moments which are the
product of the induced lateral forces times the
distance to the storey level under consideration,
where they have to be resisted by axial forces and
moments in the vertical load-carrying members.
While the base shear contributions of modes higher
than the fundamental can be significant, the corresponding modal overturning moments for the higher
modes are small. As the equivalent static lateral base
shear in the NBC also includes the contributions from
213
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higher modes for moderately tall and tall structures,
a reduction in the overturning moments computed
from these lateral forces appears justified. This is
achieved by means of the multiplier J as given in
NBC Sentence 4.1.9.1.(20). If, however, a structure
did respond exclusively in its fundamental mode, the
overturning moment at the base would be the sum of
the moments corresponding to the forces, Fx ' about
the base without any J-factor reductions. A more
refined method of accounting for the maximum overturning moments is through dynamic analysis.
Torsional Moments
[NBC 4.1.9.1.(22)-(24)]
55. The inertial forces induced in the structure by
earthquake ground motions act through the centre of
gravity of the masses. If the centre of mass and the
centre of rigidity do not coincide because of asymmetrical arrangement of structural elements or
uneven mass distributions, torsional moments will
arise. The designer should endeavour to make the
structural system as symmetrical as possible and
should consider the effect of torsion on the behaviour
of the structural elements.
56. A realistic approach to aseismic torsional
design should consider the effect of the dynamic
magnification of the torsional moments/ 51 -54 ) the
effect of simultaneous action of the two horizontal
components of the ground disturbance, and accidental torsion. Accidental torsion moments are intended
to account for the possible additional torsion arising
from variations in the estimates of the relative
rigidities, uncertain estimates of dead and live loads
at the floor levels, addition of wall panels and partitions after completion of the building, variation of the
stiffness with time, and inelastic or plastic action.
The effects of pOSSible torsional motion of the ground
should also be considered. For most practical
situations, however, these concepts and effects can
only be accounted for by the use of adjustment
factors.
57. The torsional provisions of the NBC deal with
the complex nature of torsion by increasing or decreasing the computed torsion by 50 per cent, whichever produces the worst effect in a member. The part
played by accidental torsion and torsional ground
motion is recognized by specifying an additional
214
torsion due to an eccentricity of 0.10 times the plan
dimension in the direction of the computed eccentricity.
58. For cases where the location of the centre of
rigidity and centre of mass vary substantially from
one storey to the next, approximate static analyses
cannot adequately encompass the torsional effects. A
dynamic analysis is then required.
59. For structural elements to resist torsional
moments most effectively, they should be located
near the periphery of the building,
some distance
from the centre of rigidity. Wall elements that are
intended for resisting torsional forces should be
oriented so that their in-plane forces are associated
with as large a moment arm as possible about the
centre of rigidity. In buildings with complete diaphragms, such as complete reinforced concrete floor
slabs, all elements interconnected by such members
can be counted on to resist torsional forces.
60. In core-type buildings, where all stiffening
elements are located in a central core away from the
periphery, accidental torsion and torsional ground
motion are particularly significant. In odd- and
irregularly-shaped buildings (e.g., L-shaped), and in
buildings with the core located at one side or corner,
large torsional oscillations are induced by horizontal
ground motion. These are examples of torsion
situations that should be avoided in building layouts.
Torsional effects should also be evaluated for parts of
structures relative to the whole. For example, the
torsional effects of projecting wings on buildings
should be considered in relation to the motion of the
building as a whole.
Setbacks
[NBC 4.1.9.1.(25)]
61. A setback is a sudden change in plan dimension or a sudden change in stiffness along the height
of a building. The effects of major changes in stiffness and geometry are best investigated by dynamic
methods (see Paragraph 42). For moderate or small
changes, the equivalent static procedure in the NBC
usually gives acceptable lateral forces. However,
some refinement may have to be applied to the determination of the period, T, by using Rayleigh's
method or some other procedures.
I
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F
Structural Requirements for Setbacks
62. In addition to the determination of the seismic
loads on the building, the "notch" effect must be
considered in design, particularly where the tower
framing does not extend downward through the
base. A shear wall type of design for both a tower
and base could produce severe stresses at and about
the 90° notches.
63. Some setbacks may consist of simple onestorey penthouses, whereas others may constitute
substantial portions of the entire building. In view of
the dynamic and also the notch effect phenomena
that may occur, the lateral load resisting elements
should be vertically continuous through the setback
portion. If the lateral load resisting elements are not
vertically continuous through the setback portion
and all the way to the foundations, a special analysis
should be carried out to demonstrate that the offsets
are fully compatible with the setback conditions.
Deflection and Separation of
Buildings [NBC 4.1.9.2.(1 )-(9)]
64. Deflection refers to the lateral deflection at any
point in the structure relative to the ground. Incremental deflection or interstorey deflection refers to
the lateral deflection of a storey relative to the one
just below it. The calculations of deflections are
intended to be based on accepted practice and should
include such items as P - A effects, foundation
rotations, and the effects of cracked concrete sections,
when these have an important effect on the structure.
65. The requirement to calculate deflection as R
times the elastic deflection resulting from the design
earthquake forces as specified in the NBC includes
allowance for some plastic deformation to occur in
the structural system.
66. Deflection limitations have been established in
consideration of the acceptable damage to the nonstructural components. Current state-of-the-art
shows that the specified deflections appear reasonable approximate limits for the control of damage to
structures and their contents/55 ) Significantly lower
deflection limits are required for post-disaster buildings to ensure a higher probability of functioning
after an earthquake.
67. The separation of two adjacent structures is
required to prevent collision of buildings in an earthquake. Collision of buildings was observed to be
destructive, particularly when adjacent buildings
have different heights or different storey heights.
These clauses also apply to the expansion joints
within buildings. Such joints could be connected for
seismic forces, or special details could be developed
to ensure local failure without damage to the principal structural elements.
68. Sentence 4.1.9.2.(6) is inserted to ensure
consistency with Clause 4.1.9.1.(9)(c).
69. Gravity loads acting through a displaced
shape can have a profound effect on the behaviour
of a structure. This is commonly referred to as the
P A effect. For seismic loading, the probable dead
and live gravity loads will act through large inelastic
displacements as defined in Sentence 4.1.9.2.(2) and
this must be accounted for in the design. For the
calculations of P - A effects, specified gravity loads
should be used for defining P. Live load reduction as
listed in the Code may be used. The reason for the
use of specified loads is that factoring of the loads in
the calculations of the P - A effect has already been
introduced through the use of the limit state value for
seismic effect. This should not be cumulated with
another multiplication factor> 1, which would
happen if factored gravity loads were used.
70. Both structural and non-structural components should either be isolated or be accounted for in
the design. The nonstructural components of the
structure should be detailed so as not to transfer to
the structural system any forces that are not accounted for in the design. If nonstructural members are
designed as isolated units, their connections should
be detailed so as to be capable of accommodating the
anticipated movement due to drift and temperature
changes. (56) If, on the other hand, these components
are rigidly attached to the structure, then their
effect on the behaviour of the structure should be
considered and allowed for in the elastic, plastic and
fracture stages. An example is the stair that may act
as a stiffening element. Failures of some buildings in
the Caracas 29 July, 1967 earthquake were caused by
the partition tile walls, which acted as shear walls,
thus changing the relative rigidity of the bents from
that assumed in the design.(57)
215
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Special Provisions
[NBC 4.1.9.3.(1 )-(6)]
tanks have been separated from Table 4.1.9.B., since
they are not buildings in the sense of the other
structures referred to in that Table.
71. Unreinforced masonry buildings have fared
badly when subjected to earthquakes.(1) The,presence
of reinforcing embedded in mortar or grout Increases
ductility and reduces the likelihood of brittle failure,
Examples and detail sheets for the seismic design of
reinforced masonry can be found in References (56)
and (58).
74. The structural configuration should be such
that elastic-plastic action in the members or failure of
individual elements will not produce instability or
initiate progressive collapse. Abrupt changes in
geometry, stiffness and mass are generally undesirable from the point of view of seismic response;
yielding tends to concentrate at such discontinuities
and, therefore, such configurations require special
attention.
72. The NBC specifies that, except in velocity- or
acceleration-related seismic Zones 0 and I, buildings
shall have structural systems as described by Cases 1
through 16 in Table 4.1.9.B. For velocity-related Zone
4 and higher, buildings over 60 m high having a
structural system of R == 1.5 or 2.0 shall increase V
by 50 per cent. Analyses of buildings approximately
60 m high have shown that if damage is to be minimized in a moderate earthquake, the structure must
incorporate ductile features that are associated with
these high R values. (21) Alternatively, extra strength is
to be provided by increasing the design base shear, V.
The height limitations associated with the provisions
of NBC Article 4.1.9.3. and the cases described in
Table 4.1.9.B. are summarized in Table J-3.
73. The category of "elevated tanks on 4 or more
cross-braced legs" in the 1985 NBC has been
broadened to include all elevated tanks, since they
can be classed as inverted pendulum structures,
which are sensitive to seismic excitation. Elevated
75. Sentence 4.1.9.3.(6) of the NBC requires that
masonry in velocity- or acceleration-related zones of
2 and higher be reinforced. These elements include
exterior loadbearing and non-Ioadbearing walls,
parapet walls, interior loadbearing walls and nonloadbearing partitions that weigh more than
200 kg/m2 or are more than 3 m high. Masonry
elements around stair and elevator shafts are required to be reinforced to ensure a safe exit from the
structure.
Foundation Requirements
Mismatch of Strength between Structure
and Foundation [NBC 4.1.9.4.(1)]
76. Conventional seismic structural design is
based on acceptance of damage without collapse in
the event of a severe earthquake. This implies that
Table J-3
Summary of Cases Permitted by NBC Article 4.1.9.3.
e
Height of Building
Up to 3 storeys in
building height
Greater than 3 storeys
but not more than 60 m
in building height
Greater than 60 m in
building height
Column 1
216
Velocity- or AccelerationRelated Seismic Zones
oand 1
Velocity- or AccelerationRelated Seismic Zones
2 and 3
Velocity-Related
Seismic Zones 4
and Higher
1 -18
1 - 18, except
unreinforced masonry
1 - 18, except
unreinforced masonry
1 -18
1 - 5,7 -10,
12 -14, or 16
1 - 5,7 -10,
12 -14 or 16
1 -18
1 - 5,7 -10,
12 -14 or 16
2
3
1-5,7-10,12-14
or 16; if R =1.5 or 2.0
increase V by 50%
4
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;.a
plastic deformation (defined loosely to include
cracking of reinforced concrete, yielding of steel, etc.)
is permitted to occur at suitable locations in the
structure. The maximum earthquake loads that are
transmitted by the structure to its foundation are,
therefore, governed not by the design loading, but by
the load levels at which yielding takes place in the
structural elements that transfer the lateral loads to
the foundation, such as bracing members, frame
members and shear walls.
77. This load transfer can result in an overload of
the foundation during an earthquake if the structure
does not yield at the expected lateral load level
because some of its elements are stronger than required. In this case, the foundation will be forced to
receive that higher seismic load and consequently
suffer additional distress or damage as compared to
the case where the structure yields at a lower lateral
load level. The problem of mismatch in strength
between the structure and the foundation requires
continual liaison between the structural and foundation designers to ensure that the foundation elements
are designed to be compatible with the earthquake
loads transmitted from the structure.
78. If the designer intends to provide energy
dissipation mechanisms in the foundation rather
than in the superstructure, the areas of yielding in the
foundation must be defined clearly. The ductility
imposed on the potential plastic hinges in the
foundation system should be checked.
Soil Pressures on Basement Walls
[NBC 4.1.9.4.(5)]
79. Basement wall pressures arising from ground
shaking may be determined according to procedures
described in References (59) and (60) or by other
generally accepted methods.
Design Considerations
80. Most failures in structures subjected to seismic
loading can be traced to poor detailing, especially at
beam and column connections. This becomes the
governing factor in good aseismic behaviour of
buildings built of precast elements. m
81. Floor systems that act as diaphragms
should be studied to ensure that they are capable of
distributing the loads to the various elements.
82. When the shear wall contains numerous
openings, the design should account for its real
behaviour under lateral loads, Le., whether the wall
acts as a unit or as a number of units because of the
reduced rigidities due to the openings. Overstress at
the openings should be examined. This is a common
cause of damage to lintels above door openings and
to piers between window openings. O) Suggested
design details are also given in Chapter 21 of
CAN3-A23.3-M84, "Design of Concrete Structures for
Buildings."
83. Special mechanical protection systems such as
base isolation or controlled friction damping devices
can significantly alter the seismic response of buildings.(61-64) It must be demonstrated through nonlinear analysis and representative experimental data
that the building so equipped will perform at least
equally well in seismic events as the same building
designed following the NBC seismic requirements.
84. The fact that the design forces for wind are
greater than the seismic design forces (Le., wind
"governs" the design) does not obviate the need for
seismic detailing. While wind forces govern, the
design must provide at least the type of seismic
detailing that corresponds to the seismic forces
calculated for that building.
85. Parking garages used for storage of cars or
parking need not be considered as storage areas in
calculating W.
References
The Prince William Sound, Alaska, Earthquake
of 1964 and Aftershocks. Vol. II, Research
Studies, Seismology and Marine Geology.
Department of Commerce, Environmental
Science Services Administration, Coast and
Geodetic Survey, U.S. Government Printing
Office, Washington, 1967.
(2) The Niigata Earthquake, 16 June 1964, and
Resulting Damage to Reinforced Concrete
Buildings. International Institute of Seismology and Earthquake Engineering, Tokyo,
February 1965.
(3) Canadian Standards Association, General Requirements, Ground Motion Determination,
Design Procedures, Testing Procedures, and
Seismic Instrumentation Requirements for
(1)
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Seismic Qualification of CANDU Nuclear
Power Plants. CSA Standards CAN3-N289.1,
N289.2, N289.3, N289.4 and N289.5, Rexdale,
Ontario.
Canadian Standards Association, Liquefied
Natural Gas (LNG) - Production, Storage and
Handling. CSA Standard Z276-M1981,
Rexdale, Ontario.
Canadian Standards Association, Code for the
Design, Construction and Installation of Fixed
Offshore Production Structures. Preliminary
Standard 5471, 1987, Rexdale, Ontario.
P.W. Basham, D.A. Forsyth and R.J. Wetmiller,
The Seismicity of Northern Canada. Can. J.
Earth Sci., Vol. 14, 1977, pp. 1646-1667.
W.G. Milne et aI, Seismicity of Western Canada. Can. J. Earth Sci., Vol. 15, 1978, pp. 11701193.
R.B. Horner and H.s. Hasegawa, The Seismotectonics of Southern Saskatchewan. Can. J.
Earth Sci., Vol. 15, 1978, pp. 1341-1355.
J. Adams and P.W. Basham, The Seismicity and
Seismotectonics of Canada East of the
Cordillera. In Geoscience Canada. Vol. 16, No.
1, Geological Assoc. of Can. 1989, pp. 3-16.
G.C. Rogers and R.B. Horner, An Overview of
Western Canadian Seismicity. In Decade of
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Geotectonics of North America, Geological Soc.
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D.H. Weichert and W.G. Milne, On Canadian
Methodologies of Probabilistic Seismic Risk
Estimation. Bull. Seism. Soc. Am., Vol. 69,
1979, pp. 1549-1566.
H.s. Hasegawa, P.W. Basham and M.J. Berry,
Attenuation Relations for Strong Seismic
Ground Motion of Canada. Bull. Seism. Soc.
Am., Vol. 71, 1981, pp. 1943-1962.
P.W. Basham et al., New Probabilistic Strong
Seismic Ground Motion Maps of Canada: A
Compilation of Earthquake Source Zones,
Methods and Results. Earth Physics Branch
Open File Report No. 82-33, Energy, Mines and
Resouces Canada, 1982, 205 pp.
P.W. Basham et al., New Probalistic Strong
Seismic Ground Motion Maps of Canada. Bull.
Seism. Soc. Am., Vol. 75, 1985, pp. 43-75.
A.C. Heidebrecht et al., Engineering Applications of New Probabilistic Seismic Ground
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Motion Maps of Canada. Can. J. Civ. Eng., Vol.
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C.A. Cornell, Engineering Seismic Risk Analysis. Bull. Seism. Soc. Am., Vol. 58, 1968, pp.
1583-1606.
R.K. McGuire, FORTRAN Computer Program
for Seismic Risk Analysis. U.S. Geol. Survey
Open File Report 76-67, 1976,90 pp.
L.G. Jaeger and A.D.S. Barr, Parametric Instabilities in Structures Subjected to Prescribed
Periodic Support Motion. Proc., Symposium
on Design for Earthquake Loadings, McGill
University, September 1966.
G.W. Housner et al., Spectrum Analysis of
Strong Motion Earthquakes. Bull. Seism. Soc.
Am., Vol. 43, No.2, 1953, pp. 97-119.
Earthquake Resistant Regulations, A World
List 1984. Compiled by International Association for Earthquake Engineering, Tokyo.
R.W. Clough and K.L. Benuska, FHA Study of
Seismic Design Criteria for High Rise Buildings. Report prepared for Technical Studies
Program and Federal Housing Administration,
HUD TS-3, August 1966.
J. Penzien, Dynamic Response of Elasto-Plastic
Frames. Trans. Am. Soc. Civ. Eng., Paper 3284,
Vol. 127, Part II, 1962.
S.M. Uzumeri, S. Otani and M.P. Collins, An
Overview of Canadian Code Requirements for
Earthquake Resistant Concrete Buildings. Can.
J. Civ. Eng., Vol. 5, No.3, September 1978, pp.
427-441.
J.H. Rainer, Force Reduction Factors for the
NBCC Seismic Provisions. Can. J. Civ. Eng.,
Vol. 14, No.4, August 1987, pp. 447-454.
A.C. Heidebrecht and C.Y. Lu, Evaluation of
the Seismic Response Factor Introduced in the
1985 Edition of the National Building Code of
Canada. Can. J. Civ. Eng., Vol. 15, No.3, June
1988, pp. 382-388.
A. Anderson et al., Lateral Forces of Earthquake and Wind. Paper No. 2514, Trans. Am.
Soc. Civ. Eng., Vol. 117, 1952, pp. 716-780.
W.D.L. Finn and A.M. Nichols, Seismic Response of Long Period Sites, Lessons from the
September 19, 1985 Mexican Earthquake. Can.
Geotech. J" February 1988, pp. 128-137.
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World Conf. on Earthquake Engineering,
Santiago, 1969, Session J-2, Vol. 3, pp. 75-86.
H.B. Seed et al., Soil Conditions and Building
Damage in 1967 Caracas Earthquake. J. Soil
Mech. Found. Div., Am. Soc. Civ. Eng., Vol. 98,
No. SM8, August 1972, pp. 787-806.
D. Mitchell, J. Adams, R.H. DeVall, R.C. Lo and
D. Weichert, Lessons from the 1985 Mexican
Earthquake. Can. J. Civ. Eng., Vol. 13, No.5,
1986, pp. 535..557.
The Mexico Earthquakes - 1985: Factors Involved and Lessons Learned. Proc. of the
International Conf., Mexico City, 1986. M.A.
Cassaro and E.M. Romero, Eds., Am. Soc. Civ.
Eng., New York, 1987.
H.B. Seed and I.M. Idriss, Ground Motions and
Soil Liquefaction During Earthquakes. Monograph Series, Vol. 5, Earthquake Engineering
Research Institute, Berkeley, 1982, 134 pp.
H.B. Seed, Soil Liquefaction and Cyclic Mobility Evaluation for Level Ground During Earthquakes. J. Goetech. Eng. Div., Am. Soc. Civ.
Eng., Vol. 105, No. GT2, 1979, pp. 201-255.
H.B. Seed, I.M. Idriss, and I. Arango, Evaluation of Liquefaction Potential Using Field Performance Data. J. Geotech. Eng. Div., Am. Soc.
Civ. Eng., Vol. 109, No.3, March 1983, pp. 458482.
J.A. Blume, Structural Dynamics of Cantilever
Type Buildings. Proc., 4th World Conf. on
Earthquake Engineering, Santiago, 1969,
Session A-3, Vol. 2, pp. 1-16.
E.L. Wilson, A. Der Kiureghian and E.P. Bayo,
A Replacement for the SRSS Method in Seismic
Analysis. J. Earthquake Eng. Struct. Dyn., Vol.
9, 1981, pp. 187-194.
A. Capra and V. Davidovici, Calcul Dynamique des Sructures en Zone Sismique.
Editions Eyrolles, Paris, 1980, 164 pp.
N.M. Newmark and E. Rosenblueth, Fundamentals of Earthquake Engineering. PrenticeHall, Englewood Cliffs, NJ, 1971.
R.W. Clough and J. Penzien, Dynamics of
Structures. McGraw Hill, New York, 1975,
634 pp.
V. Davidovici, Ed., Genie Parasismique.
Presses de l' ecole national des points et
chaussees, Paris, 1985, 1105 pp.
(41) M.A. Haroun and G.W. Housner, Seismic
Design of Liquid Storage Tanks. J. Tec. Councils, Am. Soc. Civ. Eng., Vol. 107, TC1, April
1981, pp. 191-207.
(42) Nuclear Reactors and Earthquakes. TID-7024,
U.s. Atomic Energy Commission, Washington,
1963, pp. 376-390.
(43) G.L. McGavin, Earthquake Protection of Essential Building Equipment. John Wiley and Sons,
New York, 1981,464 pp.
(44) J.M. Ayres and T.Y. Sun, Criteria for Building
Services and Furnishings. Building Science
Series 46, National Bureau of Standards,
February 1973, pp. 253-285.
(45) Anonymous, Design Could Mitigate Disaster
Results. Engineering News Record, November
15,1973, p. 13. See also November 29, 1973,
p.64.
(46) C. Nguyen, A. Ghobarah and T.s. Aziz, Inelastic Response of Tuned Equipment-Structure
Systems, Proc., 5th Canadian Conf. on Earthquake Engineering, Ottawa, July 6-8, 1987, pp.
571-576. A.A. Balkema, Rotterdam/Boston,
1987,882 pp.
(47) American Society of Civil Engineers, Structural
Analysis and Design of Nuclear Plant Facilities.
Manual No. 58, New York, 1980.
(48) Canadian Standards Association, Design Procedure for Seismic Qualification of CANDU
Nuclear Power Plants. CSA Standard
CAN3-N289.3-M81, Rexdale, Ontario.
(49) Canadian Standards Association, Testing Procedures for Seismic Qualification of CANDU
Nuclear Power Plants. CSA Standard
CAN3-N289.4-M85, Rexdale, Ontario.
(50) T.s. Aziz, Coupling Effects for Secondary
Systems in Nuclear Power Plants. ASME
Special Publication PVP-Vol. 65, American
Society of Mechanical Engineering, July 1982.
(51) G.W. Housner and H. Outinen, The Effect of
Torsional Oscillations on Earthquake Stresses.
Bull. Seism. Soc. Am., Vol. 48, No.3, July 1958,
pp.221-229.
(52) J.1. Bustamante and E. Rosenblueth, Building
Code Provisions on Torsional Oscillations.
Proc., 2nd World Conf. on Earthquake Engineering, Japan, 1960, Vol. 2, pp. 879-892.
(53) W.K. Tso, and K.M. Dempsey, Seismic
Torsional Provisions for Dynamic Eccentricity.
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Seismic Design for Buildings. Dept. of Army
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February 1982.
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Caracas Earthquake of 29 July, 1967. National
Academy of Sciences, Washington, 1968.
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Handbook. Masonry Institute of America, Los
Angeles, 1978, 445 pp.
N. Mononobe and H. Matsuo, On the Determination of Earth Pressures During Earthquakes.
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Retaining Structures for Dynamic Loads. Am.
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Stresses in the Ground and Design of Earth
Retaining Structures, Cornell University, Ithaca,
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1986 (ATC-17). Redwood City, CA, 1986,478
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Earthquake Engineering, Ottawa, 6-8 July 1987,
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1987,882 pp.
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University Library Building. Proc. 5th Canadian Conference on Earthquake Engineering,
Ottawa, 6-8 July 1987, pp. 191-200. A.A.
Balkema, Rotterdam/Boston, 1987,882 pp.
I.D. Aiken, J.M. Kelly and A.S. Pall, Seismic
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pays
Commentary K
Glass Design
The following Commentary has not been updated
to reference or reflect the latest information on glass
design. The 1990 NBC references the new standard
CAN/CGSB 12.10-M89, "Structural Design of Glass
for Buildings." Users are cautioned, therefore,
concerning the use of this Commentary in specific
applications since it is retained for general information only. The future of this Commentary will be
considered during preparation of the next edition of
the Supplement.
Introduction
1. Article 5.7.1.2. of the National Building Code of
Canada 1990 requires exterior cladding, including
glass, to be designed to resist the loads specified in
Section 4.1 and installed according to good engineering practice.
2. Glass panels in curtain walls function as structural elements insofar as they resist wind pressure or
suction and transfer wind forces to the building
frame. Just as roof decks must be designed to carry
snow loads and resist wind uplift, or floor slabs to
carry occupancy loads, so must windows and
spandrel panels be designed to withstand the lateral
forces of wind.
3. Windows, glass spandrel panels and sometimes
even glass mullions combine to form a large percentage of the cladding of many modern buildings. For
reasons of public safety, and economy as well,
everyone connected with glass selection should have
a clear understanding of its structural function and
its response to various stress-producing phenomena.
The proper design, installation and operation of glass
in buildings involves the coordination of activities
among architects, engineers, manufacturers, glazing
contractors, building officials and, of course, building
owners. The role and area of responsibility of each
participant must be clearly defined.
Professional Practice
4. Because the architect and the engineer are
responsible for providing performance criteria
(design loads, probability of failure), their judgments
and actions are highly important. Manufacturers'
data and recommendations to support the design
professionals are a key element in the proper usage of
glass in buildings. The purpose of this commentary
is to provide an additional information base so that
architects and engineers may duly function in their
areas of responsibility and professional practice.
Flat Glass Manufacture
5. In preparation for a discussion of glass strength,
a brief explanation of how the glass commonly used
in building is made may be helpful. Glass is an
inorganic product of fusion, which has been cooled to
a rigid condition without crystallization. The approximate percentages of the main ingredients of
soda-lime glass are: silica sand (Si02, 72 per cent),
soda and potash (Na 20,K20, 13 per cent), lime (CaO,
11 per cent), magnesia (MgO, 3 per cent) and alumina
(AI20 3,1 per cent). They are thoroughly mixed and
heated with waste glass (called cullet) to a melting
temperature at the glass surface of about 1 500°C.
After the removal of scum and bubbles, then cooling
to the required viscosity, flat glass is taken from the
melt either by "drawing" into sheets or by "floating"
on a bed of molten tin.
6. Drawn sheet glass, or common window glass, is
normally used only for smaller areas and nominal
thicknesses less than 6 mm. The drawing process
leaves a slightly wavy surface, and where a greater
degree of flatness is required, float glass is used.
Float glass, first introduced in 1959, has for the most
part replaced plate glass.
7. The rate of cooling determines the level of
residual compressive stress in the glass surfaces. To
make cutting and handling easy, the most commonly
used sheet and plate are annealed after forming by
controlled cooling beginning at 550°C to keep surface
stresses low. Where high mechanical strength is
required, however, tempered glass is produced by
rapid, controlled cooling after reheating, "freezing
in" high surface compressive stresses balanced by
internal tensile stresses. In general, the nominal
tensile breaking stress can be said to increase by the
amount of compressive "prestress" developed in the
heat treatment. Surface stress for heat strengthened
glass is usually in the range from 25 to 70 MPa and
221
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for fully tempered glass, above 70 MPa. Compared
to annealed glass, heat strengthened or partially
tempered glass is about twice as strong, and fully
tempered glass is about four times as strong. Annealed and heat strengthened glasses tend to break
into large pieces, while fully tempered glasses break
into smaller, cube-like pieces.
Characteristics of Glass Strength
8. Although known to have a theoretical strength
of over 7 000 MPa, annealed glass fails in practical
situations at a nominal stress of approximately
30 MPa because of various surface discontinuities
ranging from visible abrasions to submicroscopic
flaws. Failure begins not necessarily at the location
of maximum stress but at some defect where the
stress is often considerably lower. Surface flaws have
as much influence on the fracture origin as the
applied stress, and what is observed as the strength
of glass in engineering applications is related more to
the condition of the surface than to any intrinsic
strength of glass as a material.
9. It is useful to think of a flaw as a very sharptipped crack with a stress concentration factor of
several hundred, making the effective stress at the tip
of the flaw of the order of 7 000 MPa, consistent with
the average breaking stress of carefully prepared
glass fibres free of flaws. The stress concentration
factor increases with the ratio of flaw depth to tip
radius, which lowers the nominal surface stress at
which fracture will occur.
10. Many of the unusual characteristics of glass
strength can be explained in terms of the changes that
surface flaws undergo with tensile stress application
and weathering or aging. According to one theory,
based on the concept of stress corrosion, the application of high tensile stress greatly accelerates the rate
of corrosion at the flaw tip, making the flaw deeper
but not appreciably wider. This would steadily
increase the stress concentration factor under sustained load and could account for delayed failures,
i.e., decreasing breaking strength with increasing duration of stress. Under zero to moderate tensile
stress, however, ordinary corrosion rounds out the
sharp flaw tip to reduce the stress concentration
factor, which could explain why glass specimens can
withstand moderate stresses indefinitely.
Influence of Glass Area and Load
Duration on Strength Testing
11. For geometrically similar specimens of different sizes, various lab tests on plate glass have shown
that the average breaking stress,S, varies with the
area of the specimen, A, according to the formula:
5
K + A lin
(1)
where K and n are factors found by experiment for a
given lot of glass and test procedure. Typically, n is
about 5 to 7. For n = 6, the formula suggests that a
1 m 2 plate should be about 12 per cent stronger, and a
4 m 2 plate 11 per cent weaker, on average, than a 2 m 2
plate. Assuming a random distribution of surface
flaws, there is a greater chance of a severe flaw
coinciding with a high tensile stress for larger plates
than for small ones.
12. Many lab tests of the effect of duration on
average breaking load, L, can be summarized by the
formula:
L = K'
T
1/m
(2)
where K' and m are factors determined from the lab
tests and T is load duration. For soda-lime glass, m is
most often around 16, although in some cases values
as low as 12 or as high as 20 fit the data better.
According to the formula for m = 16, the 3 s breaking
load should be about 21 per cent higher and the 1 h
breaking load about 23 per cent lower than the 1 min
breaking load. Equation (2) is consistent with the
stress corrosion theory, which states that the rate at
which the stress concentration increases at a flaw is
proportional to some high power of the applied
stress.
13. One important feature to be emphasized about
the testing of glass is the wide scatter of test results.
Even when specimens are chosen from the same lot
of glass, carefully inspected to eliminate visible
surface damage and tested under identical loading
and environmental conditions, the coefficient of
variation of the breaking load for annealed soda-lime
glass is about 25 per cent.
14. The conditions listed above point to the
primary influence of surface defects on the practical
strength of large glass plates. The severity of randomly distributed flaws and the level of residual
I
.
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...
ｾ＠
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compressive surface stress are far more important
than variations in the chemical composition of the
glass.
Flexibility of Glass Retaining
Members
15. The performance of the glass retaining members used in service may have a bearing on the actual
load carrying capacity of the window if they are
significantly more flexible than the support provided
in strength tests. Furthermore, relatively large lateral
deflections may occur under design loads, resulting
in in-plane movements and a tendency for the glass
to "walk" out of its retaining frame.
16. The most commonly recommended deflection
limitation is 1:175 of the span. The manufacturers
point out, however, that stiffer supports may be
required for acceptable weather-tightness, durability
of seals or appearance. In many modern glazing
situations, one or more sides may not have adequate
support and will require special design consideration, either by going to a separate chart or by consultation with the manufacturer's technical advisor.
17. Control of deflections from a performance
point of view, visual as well as weather-tightness and
durability, is important and there is a growing
tendency to perform mock-up tests. The advice of
the manufacturer regarding such details and installation procedures should be followed.
Manufacturers' Thickness
Selection Charts
18. Glass design from a structural point of view
usually consists of selecting an appropriate thickness
for a given area and design pressure from a chart
based on tests to destruction of full-sized plates. The
number of samples in various tests has ranged from
about 20 to over 2 500. At least 20 to 30 samples of
each configuration are required for reliable
information about the mean strength and the variation about the mean.
19. The charts produced by the three largest flat
glass manufacturers active in Canada have much in
common, but some differences are worth noting. In
dealing with aspect ratio for rectangular plates firmly
supported on four sides, two of the three manufacturers make no distinction for ratios of long side
divided by short side up to 3:1 or 5:1. The third
manufacturer allows a linear increase up to about
30 per cent in load bearing capacity for aspect
ratio increasing from 1:1 to 3:1. As can be seen in
Table K-1, showing the range of wind pressures
recommended for five different glass thicknesses by
the three manufacturers, there is significant divergence at large aspect ratios. Aspect ratio does
influence glass behaviour and the designer should be
aware of the importance of aspect ratio when specifying glass.
!
Table K·1
Range of Wind Pressure Resistance Quoted by
Three Glass Manufacturers for Annealed Float Glass
Supported on Four Sides, Area 4m2 (1,2)
Aspect ratio
1:1
2:1
2.99:1
Thickness
Min. Max. Min. [ Max. Min. Max.
mm
Kilopascals
0.77 0.81
5
0.77 0.96 0.77 1.05
1.15 1.29 1.15 1.39 1.15 1.58
6
10
2.15 2.44 2.15 2.63 2.15 3.02
12
3.21
3.54 3.21
3.78 3.21 4.40
4.21
15
5.17 4.21
6.03 4.21 6.89
Column 1
2
4
3
7
5
6
!
Notes to Table K·1:
(1)
For glass areas other than 4 m2 multiply by 4 + area.
(2)
This chart does not take into account any modification
introduced by manufacturers since 1 January 1979.
20. A common feature of all three manufacturers'
charts for four-edged support is that thickness, hI is
approximately proportional to some power of the
total load, LI where L is the product of uniform
pressure times the area:
h
K" x La
(3)
where K" and a are factors found by fitting the chart
data to Equation (3); a varies with the manufacturer
from about 0.56 to 0.72. This formula implies that
any combination of pressure and area producing the
same totalload L, requires the same glass thickness.
l
223
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The factor K" also varies with aspect ratio in the case
of the manufacturer who allows increased loadbearing capacity for increasing aspect ratio.
21. Two manufacturers supply charts for plates
supported on two opposite edges only, and for all
three manufacturers, recommended thicknesses are
proportional to the maximum bending stress for a
uniformly loaded, simply-supported beam. The
working stresses used for this purpose by the
various manufacturers range from about 9 to 23 MPa
for 8 mm and 6 mm glass, and from 11 to 15 MPa for
thicker glass.
22. For two-edged support, glass thickness is
proportional, not to some power of total load (see
Equation 3) but to the load per unit of length raised to
the power 0.5, where the length is the dimension
perpendicular to the span between supports. One
manufacturer recommends using the chart for
two-edged support for aspect ratios of 3:1 or greater,
which would result in an allowable load of only
2.1 kPa for 12 mm glass of area 4 m 2, about two-thirds
the allowable load in the four-edged support chart. In
Table K-l the aspect ratio of 2.99:1 is given as a
column heading instead of 3:1 to avoid this situation.
23. Separate charts are also provided by two manufacturers for sealed double-glazed units, while the
third provides a multiplying factor of 1.5 to be used
with the chart for single glass supported on four sides.
Specification of Design Wind
Pressures
24. The correct application of manufacturers' data
requires a matching of the specified design wind
pressure with the loads quoted in the glass thickness
selection charts. In the National Building Code 1990
the use of a gust effect factor of 2.5 for cladding design
implies an averaging time of 1 or 2 s when considering wind fluctuations over open country (Exposure A)
at a height of 10m.
25. Descriptions of the loads quoted in the charts
vary with the manufacturer; one states 3 s mean wind
loadings, another specifies 1 min wind loads, and in
the third case, "the graphs are based on actual tests to
destruction in which the glass was exposed to uniform loads increased in increments and held static for
1 min."
26. Where a code or standard specifies loads
averaged over a few seconds rather than 1 min,
current practice in Canada and the U.S. is to ignore
the difference and use them directly with the manufacturers' charts. According to Equation (2) in
Paragraph 12, the increased capacity for the 3 s load
over that for the 60 s load would be about 20 per cent.
27. The specified design wind pressure is intended to represent the most severe loading that can
reasonably be expected to occur during the useful life
of the cladding element being deSigned. Many
interrelated factors must be considered in arriving at
such a representative design pressure, and a simple
procedure such as that followed in the Code should
not be expected to provide a very precise solution.
28. The principal factors involved are the building
site exposure, shelter or channelling created by
neighbouring buildings, position of the cladding
element on the building and the wind direction and
speed when the most severe loading occurs. To be on
the safe side, the simple procedure assumes an open
exposure, no shelter from other structures and
coincidence of the maximum wind speed with the
most critical wind direction.
29. There are two situations in which the simple
procedure may not be the best approach: firstly, on
large projects the expense involved in using design
loads thought to be overly conservative may be too
high, and secondly, unusual building shapes, groupings or exposures may give rise to higher loadings for
certain areas of the building than the simple procedure states. In both situations the recommendation
in Commentary B (Wind Loads) is to provide for
special wind tunnel tests in which all the above
factors are taken into consideration.
30. High local suctions are often found at corners
for "glancing winds," where the flow first breaks
away from the building and then reattaches to the
wall some distance downstream. This condition is
reflected in the simple procedure by the use of local
pressure coefficients of 1.0 near corners, but a more
complete analysis (taking into account frequency of
occurrence of strong winds from critical directions)
may present a different picture in which corners are
no longer the most critical areas on the surface.
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r
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Sometimes the largest design pressures are found
from wind tunnel tests to occur fairly low on a building, in line with the roof tops of adjacent buildings
rather than near the top of the building itself. The
critical area for cladding design in such situations
might be overlooked unless adequate testing is
carried out.
Wind-Borne Missiles and
Thermal Stresses
31. J.W. Reed investigating window damage from
the Lubbock (Texas) tornado of 11 May 1970 found
that only upper floors appeared to be damaged by
wind forces alone. He concluded that 80 per cent of
window damage to large buildings during that storm
was probably caused by wind-borne missiles, mostly
in the first five floors, decreasing exponentially up to
about the 15th floor.
32. Subsequent surveys and research were carried
out by Minor and Beason at Texas Technical University in which roof gravel was found capable of
breaking window glass at mean minimum impact
velocities of 10-20 m/s. Minor concluded that loose
roof gravel endangers glass in multi-storey buildings
because it is often present in locations where it can be
lifted and propelled by winds with sufficient momentum to break windows.
33. Thermal stresses arise from differential heating
of the glass. The potential for thermal breakage is
measured by the difference between the mean
temperature of the glass and the minimum edge
temperature. J.R. Sasaki has measured the potential
for thermal breakage of sealed double-glazing units,
and in one study found temperature differences of up
to 27°C. The technical literature indicates that glass
with clean-cut undamaged edges can withstand a
temperature difference of up to 30°C, but that breaks
have been known to occur at lower than 15°C with
abraded, nipped or otherwise damaged edges. Heat
absorbing and heat reflecting glass have higher
potentials for breakage than clear glass, and in
double-glazed units, either the outer or the inner
pane can be subject to breakage.
34. Thermal breakage usually can be distinguished from the wind effect because it almost
always originates at an edge, whereas wind damage
almost never does, unless the edge is inadequately
supported. Careful inspection, particularly during
the first few months or a year after installation, is
recommended so that glass with visible cracks may
be replaced. If glass is not inspected and damaged
glass is not replaced, failures may eventually occur,
and these could be incorrectly attributed to wind
forces alone unless examined by a glass technologist
familiar with the distinctive characteristics of thermal
breakage on the fracture faces.
Probability of Breakage
35. From the preceding section it is clear that a
distinction must be made between breakage by wind
pressure alone and breakage to which other factors
contribute. The probability of wind pressure blowing
out (or in) a window already cracked by flying gravel
or by thermal stresses is obviously much higher than
the probability for an undamaged window.
36. Where special wind tunnel tests have been
done, incorporating climatological information on
wind direction as well as wind speed, useful estimates of the probability of failure of previously
undamaged windows will be feasible. When the
simple procedure has been used, an estimate is still
possible, but in general it will be conservative
because the reduced probability of occurrence of the
maximum wind from the most critical direction (as
compared to any direction) cannot easily be assessed
at the present time.
37. As the manufacturers themselves point out,
the structural behaviour of glass due to brittle failure
and randomly distributed surface flaws is such that
glass cannot be guaranteed against breakage. By
selecting an appropriate safety factor on the glass
strength or an appropriate probability of exceedance
of the specified design wind pressure, the risk of
breakage can be reduced to an acceptable level. In
current practice, and under normal circumstances,
the minimum acceptable level is met by using the
simple procedure of the Code, with an annual probability of exceedance of 1/10 for design wind pressure.
Where special circumstances such as sloped or
overhead glazing give rise to unusual hazards, such
as increased risk of injury to occupants or the general
public, the provision of safety glass may be required.
225
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Future Developments
38. In current practice the designer must rely to a
greater extent on technical advice from individual
manufacturers when dealing with glass than with
most other common building materials. Some of the
reasons for this situation are apparent from the sections on "Characteristics of Glass Strength" and
"Influence of Glass Area and Load Duration on
Strength Testing"; the manufacturing process and the
handling of the product from the time of manufacture
to the time of installation have a significant influence
on surface condition and hence the structural strength.
39. At present no generally agreed-upon strength
testing procedure has been formulated, a fact that has
probably contributed to some of the differences in the
charts of different manufacturers. The influence of
aspect ratio on the strength of large glass plates
requires further investigation, as does the effect of
load duration for peak loads down to less than 1 s.
40. Research is now under way to develop a testing
apparatus and procedure to investigate the strength of
large glass plates under dynamic loading representative of the wind gust pressures measured on real
buildings.
Bibliography
Glass Strength Characteristics
(1) W.B. Hillig, Sources of Weakness and the Ultimate Strength of Brittle Amorphous Solids.
Modern Aspects of the Vitreous State, Vol. 2,
J.D. MacKenzie, Ed., Butterworths, London,
1962, pp. 152-194.
(2) R.J. Charles, Static Fatigue of Glass II. Journal of
Applied Physics, Vol. 29, No. 11, November
1958, pp. 1554-1560.
(3) S.M. Wiederhorn, Influence of Water Vapor on
Crack Propagation in Soda-Lime Glass. Journal
of the American Ceramic Society, Vol. 50, No.8,
August 1967, pp. 407-414.
(4) L. Orr, Engineering Properties of Glass. Conference on Windows and Glass in the Exterior of
Buildings, Publication 478, Building Research
Institute, Washington, March 1957.
(5) E.B. Shand, Glass Engineering Handbook.
Second edition, McGraw-Hill Book Company
Inc., 1958.
(6) C.R. Frownfelter, Structural Testing of Large
Glass Installations. Symposium on Testing
Window Assemblies, ASTM Special Technical
Publication No. 251, July 1959, pp. 19-30.
(7) R. Bowles and B. Sugarman, The Strength and
Deflection Characteristics of Large Rectangular
Glass Panels Under Uniform Pressure. Glass
Technology, Vol. 3, No.5, 1962,
pp.156-170.
(8) J.D. Gwyn, Factors Affecting Structural Performance of Glass. Building Research, Building Research Institute, U.s.A., May-June, 1967,
pp.36-38.
(9) W.G. Brown, A Load Duration Theory for
Glass Design. Research Paper No. 508, Division of Building Research, National Research
Council Canada, Ottawa, January 1972. NRCC
12354.
(10) L. Orr, Practical Analysis of Fractures in Glass
Windows. Materials Research and Standards,
January 1972, pp. 21-23 and 47.
(11) R.L. Hershey and T.H. Higgins, Statistical
Prediction Model for Glass Breakage from
Nominal Sonic Boom Loads. Technical Report
to Federal Aviation Administration, BoozAllen Applied Research Inc., Bethesda, Maryland, NTIS AD-763-594, January 1973.
(12) J.E. Minor, Window Glass in Windstorms.
Civil Engineering Report Series CE74-01, Texas
Technical University, May 1974.
(13) L. Orr, Strength and Fracture of Glass in Buildings. American Society of Civil Engineers
Annual Convention, Session 32, Building Code
Requirements for Wind Loading, November 5,
1975, Denver, Colorado.
Wind Pressures on Buildings
(14) W.A. Dalgliesh, Statistical Treatment of Peak
Gusts on Cladding. Journal of Structural
Division, Proc., Am. Soc. Civ. Eng., Vol. 97, No.
ST9, September 197t pp. 2173-2187.
(15) D.E. Allen and W.A. Dalgliesh, Dynamic Wind
Loads and Cladding Design. Research Paper
No. 611, Division of Building Research, National Research Council Canada, Ottawa, 1973.
NRCC 14056.
(16) W.A. Dalgliesh, Comparison of Model/Full
Scale Wind Pressure on a High-Rise Building.
pays
Journal of Industrial Aerodynamics, Vol. 1,
No.1, 1975, pp. 55-66.
(17) J.K. Eaton, Cladding and the Wind. Building
Research Establishment, Current Paper CP47,
Building Research Station, Garston, Watford,
WD2 7JR, U.K., May 1975.
(18) J.A. Peterka and J.E. Cermak, Wind Pressures
on Buildings - Probability Densities. Journal of
Structural Division, Proc., Am. Soc. Civ. Eng.,
Vol. 101, No. ST6, June 1975, pp. 1255-1267.
(19) A.G. Davenport, D. Surry and T. Strathopoulos, Wind Loads on Low Rise Buildings:
Final Report of Phases I and II, Part I-Text and
Figures. BL WT-SS8-1977. Faculty of
Engineering Science, University of Western
Ontario, London, Ontario, 1977.
No. 423, Division of Building Research, National Research Council Canada, Ottawa,
August 1974. NRCC 14167.
(27) J.E. Minor and W.L. Beason, Window Glass
Failure During Windstorms. The Glass Industry, February 1975, pp. 12-15 and 32.
(28) H. Ishizaki, S. Miyoshi and T. Miura, On the
Design of Glass Pane Against Wind Loading.
Fourth International Conference on Wind
Effects on Buildings and Structures, 8 -12
September 1975, London.
(29) J.R. Mayne and G.R. Walker, The Response of
Glazing to Wind Pressure. Building Research
Establishment Current Paper 44/76, Building
Research Station, Garston, Watford, WD2 7JR,
U.K., June 1976.
Glass Design and Behaviour in Service
Building Codes and Industry Publications
(20) L.E. Robertson and P.W. Chen, Glass Design
and Code Implications for Extremely Tall
Buildings. Building Research, Building Research Institute, U.S.A., May-June 1967, pp. 611.
(21) F.R. Khan, Optimum Design of Glass in Buildings. Building Research, Building Reseach
Institute, U.s.A., May-June 1967, pp. 45-48.
(22) F.R. Khan, A Rational Method for the Design of
Curtain Walls. In Proceedings of Design Symposium, Wind Effects on High-Rise Buildings,
Northwestern University, Evanston, Illinois,
March 1970, pp. 145-174.
(23) J.W. Reed, Window Damage Study of the
Lubbock Tornado. Report No. SC-TM-70-535,
Sandia Laboratories, Albuquerque, New
Mexico, August 1970.
(24) J.R. Sasaki, Potential for Thermal Breakage of
Sealed Double-Glazing Units. CBD 129,
Division of Building Research, National Research Council Canada, Ottawa, September
1970.
(25) J.R. Sasaki, Measurement of Thermal Breakage
Potential of Solar-Control Sealed Glazing
Units. Research Paper No. 617, Division of
Building Research, National Research Council
Canada, Ottawa, NRCC 14259. Reprinted from
Specification Associate, Vol. 16, No.3, pp. 1122, May-June 1974.
(26) K.R. Solvason, Pressure and Stresses in Sealed
Double Glazing Units. Technical Paper
(30) Installation Recommendations for Tinted
Glass. PPG Industries, Inc., Glass Division
- Technical Services, TSR 104D, Toronto.
(31) Installation Recommendations for Twindow.
PPG Industries, Inc., Glass Division Technical
Services, TSR 104C, Toronto.
(32) External Environment. Wind Loadings, Pilkington Brothers Limited, St. Helens, Lancashire, England, August 1971, pp. 1-7.
(33) The Application of Solar Control Glasses, Glass
and Windows. Bulletin No. 10, Pilkington
Technical Advisory Service, Pilkington Brothers (Canada) Ltd., 101 Richmond St. W.,
Toronto, Ontario, January 1972.
(34) Recommended Glazing Practices for Reflective
Insulating Units Over 20 Square Feet in Area.
PPG Industries, Inc., Glass Division - Technical
Services, Toronto.
(35) Building Code Requirements for Minimum
Design Loads in Buildings and Other Structures. ANSI A58.l, American National Standards Institute, Inc., New York, 1972.
(36) Code of Basic Data for the Design of Buildings.
British Standards Institution, CP3, Chapter V,
Part 2, Wind Loads, London, 1972.
(37) Glass Product Recommendations: Wind Load
Performance. Technical Service Report No.
lOlA, Glass Division/PPG Technical Services,
PPG Industries, Pittsburgh, PA.
(38) Glass for Construction. Libbey-Owens-Ford
Company, Toledo, Ohio, January 1976.
227
pays
(39) Design Wind Loads for Aluminum Curtain
Walls. Publication No. AAMATIR-A2-1975,
Architectural Aluminum Mfgrs. Assoc.,
Chicago, 1975.
(40) Metal Curtain Wall, Window, Store Front and
Entrance Guide Specifications Manual, Architectural Aluminum Mfgrs. Assoc., Chicago,
1976.
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..
Commentary L
Foundations
Introduction
1. The purpose of this Commentary is to suggest
reasonable guidelines, compatible with sound engineering practice, to provide compliance with the
requirements of Section 4.2 (Foundations) of the National Building Code of Canada 1990. Much of the
material herein is simple, intended as a first approximation dealing with routine problems of foundation
design and construction. Neither this material nor
the papers or texts to which it refers should substitute for the experience and judgment of a person
competent in dealing with the complexities of
foundation practice.
2. The Commentary falls into three principal
parts: Temporary Excavations, Shallow Foundations
and Deep Foundations. The text in these parts refers
to relevant paragraphs of the National Building
Code, Section 4.2.
3. The Commentary does not deal specifically
with the identification and classification of soils and
rocks, with subsurface investigations, with swelling
and shrinking clay, nor with frost action as related to
foundations; these topics are included in the "Canadian Foundation Engineering Manual, 1985" published by the Canadian Geotechnical Society, available from BiTech Publishers, Suite 801, 1030 West
Georgia St., Vancouver, B.C., V6E 2Y3.
Temporary Excavations
Unsupported Excavations
4. The safety and stability of unsupported excavations depends on the soil and groundwater conditions and on the depth and slope of the cut. In
granular materials slope failure will generally be
fairly shallow; in clays deep rotational failures
involving not only the sides but also the base of the
excavation are possible. The length of time the cut
will remain unsupported must also be considered.
5. Guidelines for treatment of open cuts in broad
soil categories are included in Table L-l. The selec-
tion of stable slope angles for Categories C and D
requires that stability analyses be carried out. The
selection of appropriate design shear strength parameters for such analyses requires a careful assessment
of imposed shear stress levels, time effects, soil directional properties and uniformity, and should be
carried out by a person qualified in this work. The
influence of groundwater conditions within the
slope, or piezometric levels at or below the toe of the
proposed slope, should also be investigated, as the
resisting shear strength along a potential failure
surface may be greatly reduced by hydrostatic
pressures.
Supported Excavations
6. Temporary shoring support of vertical excavation faces requires an assessment of a number of
factors, including the length of time the excavation is
to be supported, earth pressures, pressures from frost
action or corrosion from aggressive soil or groundwater. The shoring wall elements may be either open,
permitting full drainage, or closed, providing an
impermeable barrier, depending mainly on the soil
permeability and groundwater conditions. Closed
systems are designed for soil and full groundwater
pressures, whereas hydrostatic pressures are not
included in open systems, where seepage through the
wall can take place.
Design earth pressures
7. For flexible and semi-flexible shoring walls
commonly used for support of vertical faces of
excavations, and which may have a variety of
support conditions, no satisfactory general theoretical
solutions for prediction of earth pressures are available. The design earth pressure must take into
account the method and sequence of construction
and the tolerable deformation limits of the sides or
faces of the excavation.
8. The yield of one part of a flexible wall throws
pressure onto the more rigid parts. Hence, pressures
in the vicinity of supports are higher than in unsupported areas, and the loads on individual supports
vary, depending largely on the stiffness characteristics of the supports themselves and the construction
technique.
229
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Table L·l
Open Cut Excavation Guidelines (1,2)
Typical
Failure
Time to
Mode
Failure
Remarks
Category
Soil Type
Ground
water
A
Freedraining,
granular,
non-plastic
silts
Below
cut or
controlled
by advance
de-watering
Shallow
surface
or slope
wedge
Generally
rapid
Rarely a problem if groundwater under
control and slope angle does not exceed
Iriction angle of soil. Unsaturated
temporary steeper cuts rely on apparent
cohesion and may slough with time; cuts
steeper than 45° are not recommended;
vertical cuts more than 1.2 m in depth
should never be used.
(1)
B
As for
Category
A
Cut
below
groundwater
Sloughing
to flow
Rapid
Uniform fine soils may flow for
considerable distances if pumping
from within excavation is attempted.
Slopes are controlled by hydraulic
effects and may range from 1/3 or less
to full value of friction angle.
As for
Category
A
C
Non-sensitive
clays.
Plastic and
cohesive silts
Saturated
(see also
Note 3)
Rotational.
Plane of
weakness
or composite
surface
Rapid or
delayed
depending
on per cent
of operational
soil shear
strength
mobilized
Analytical methods generally reliable
for prediction of stability in soft to firm
clays.
As for
Category
A
D
Sensitive
clays
Saturated
(see also
Note 3)
Rotational.
Retrogressive
slides and
as per (C)
As per (C):
little advance
little
warning
Extreme caution required; once initial
failure is provoked, retrogressive action
may affect wide area; reliability of
analytical prediction methods generally
poor.
-
Column 1
2
3
Notes to Table L·l :
Mixed soils such as glacial tills should be classified into
Category A, B, or C, depending on grain size, plasticity and
permeability, and treated accordingly.
(2)
The stability of an open cut slope which is only marginally
stable at the end of excavation may be adversely affected by
such factors as the nature and magnitude of crest loading,
vibrations, rainfall, the length of time the cut remains open or
disturbance of the soil in the vicinity of the toe of the slope.
(1)
230
4
5
(3)
References
6
Excavations through alternate layers of cohesive and
granular soils or excavations terminated within a cohesive
soil underlain by granular strata require an investigation of
groundwater conditions in each layer, and the factor of safety
against excavation base heave or slope failure as a result of
upward water pressure should be assessed.
Ij
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9. The pressure envelopes representing the
pressures that would normally be anticipated can be
represented in triangular, trapezoidal or rectangular
form, and the applicable design earth pressure
coefficients will range between the active KA* case
and the earth pressure at rest Ko '" depending on
permissible wall and soil movements.
10. Non-cohesive (granular) soils. As a first
approximation the guidelines in Table L-2 are suggested in essentially granular soil such as fills, sands,
silts, sandy silts, gravelly sands, sands and gravels or
alternate layered conditions composed of such strata.
11. Cohesive soils. For cohesive soils a distinction
must be made between soft to firm clays and stiff to
very stiff clays. The effects of clay sensitivity and the
factor of safety against base heave must also be
accounted for.
12. For stiff clay soils (C u > SO kPa)*** including
silty clays, sandy clays and clayey silts, the guidelines in Table L-3 are suggested. Similarly, for soft to
firm clays (Cu > 12 kPa < SO kPa), reference should be
made to Table L-4.
'K
_
A -
UK
1 sin<\>'
1 + sin <\>'
=
1
=
12
,
I
where <I> = effective ｦｲｩ｣ｴｾｯｮ＠
｡ｾｧｬ･＠
of soil
and the ground surface IS hOrIzontaL
sin <\>'
unconfined compressive strength.
Table L·2
Envelope of Earth Pressure for Design of Temporary Supports for Granular Soils
Restraint
Design
Total
Pressure (1)
Envelope of
Pressure
Distribution (2)
Cantilever
1.0 PA
Triangular
Braced
1.2 to 1.3 PA
or
trapezoidal
Rectangular
or
trapezoidal
Generally poor where control of groundwater
inadequate or where workmanship poor; can
be moderate to good where these factors are
properly controlled and bracing properly
designed and tightly wedged or preloaded
Tied-back
1.1 to 1.4 PA
Rectangular
or
trapezoidal
Generally good where high total pressures
are used; movements usually less than for
braced walls and dependent on degree of
prestressing, workmanship and wall stiffness
Column 1
2
3
Notes to Table L·2:
PA = theoretical total active pressure =0.5 pgH2 x KA
where
p
density of soil (submerged if below ground
water), kg/m 3,
H
depth of cut, and
g
acceleration due to gravity, m/s2.
The figure of 0.2 is suggested as a lower bound for KA even in
dense soils. Surcharge pressures and hydrostatic water
pressures should be added where appropriate.
(1)
Ability to Restrict
Adjacent Soil Movements (3)
Generally very poor unless wall extremely
stiff and embedded in dense soil
4
(2)
(3)
After increasing PA by the appropriate multiplier, distribute
total pressure over depth of cut as indicated in this column:
triangular limits of trapezoid generally taken as 0.2H to 0.25H
at top and bottom.
Where greater control of adjacent ground movements is
required, earth pressure should be computed using the at
rest Ko earth pressure coefficient with prestress in struts or
tie-backs to the full design load. Additional measures would
include choice of a stiff wall and close vertical spacing of
struts or tie-backs.
231
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I
Table L·3
Envelope of Earth Pressure for Design of Temporary Supports for Stiff Cohesive Soils
Design
Total
Pressure
Envelope of
Pressure
Distribution (3)
Cantilever
1.0 PA
but not less than
0.15pgH2 (1)
Triangular
Braced or
tied back
0.15pgH2
to
0.4pgH2(2)
Rectangular
or
trapezoidal
Column 1
2
Restraint
.
Ability to Restrict
Adjacent Soil Movements
May be poor depending on length of
cantilever, wall stiffness, embedment conditions and clay sensitivity (4.5)
Depends on soil strength, sensitivity, effective
preloading or prestressing and wall stiffness
4
3
Notes to Table L·3:
PA may be computed using short term strength, i.e.,
PA = pgH - 2Cu if excavation open for limited period. Regardless of whether pressures are negative or zero,
minimum positive pressures indicated must be used.
(2)
Use higher range where clay is of high sensitivity. If the
construction sequence or workmanship allow significant
inward movement during any stage of excavation, pressures
may build up to essentially fluid soil values in very sensitive
clays. With good workmanship, clay pressures are similar to
those given in Table L-2. Strength tests taken on intact
samples of stiff clays which are jointed or fissured may
(1)
(3)
(4)
(S)
over-estimate the strength characteristics and thus lead to an
under-estimation of earth pressures.
Surcharge pressures should be added where appropriate;
hydrostatic pressures need not be included; total density of
soil, p, is to be used in calculations.
Computed passive pressures below the base of the excavation should be reduced by 50 per cent to account for
unavoidable disturbance due to strain effects and stress
release.
The factor of safety against base heave in stiff overconsolidated clays, as a result of high locked-in lateral stresses,
should also be investigated.
Movements Associated with Excavations
13. Movements associated with excavations are
primarily related to construction technique and
commonly consist of lateral yield of the soil and
support system towards the excavation, with corresponding vertical movement adjacent to the excavation walls. Both lateral and vertical movements due
to yield are generally of the same order of magnitude;
however, if very flexible vertical wall elements are
used, lateral movements can be grossly increased.
Where construction technique is poor, erratic movements can also occur due to loss of ground or erosion
behind the wall.
14. Movements due to yield of cantilever walls are
related to the wall and soil stiffness. For most flexible
or relatively flexible wall types the lateral deformations will exceed values required for mobilization of
active soil pressures. For most soils and particularly
232
cohesive soils, therefore, there is a danger that a
further build-up of lateral pressures beyond active
values will take place as a result of loosening due to
strain effects. An exception would be where design
soil pressures of an at rest Ko magnitude or greater
are used in design, and an appropriately stiff wall,
such as large diameter cylinder piling, is provided,
embedded in competent soil.
15. Movements due to yield in strutted excavations are, to a large extent, unavoidable, since they
are controlled not by design assumptions but by
construction details and procedures. Such movements develop in each excavation phase before the
next level of struts is installed.
16. The yield movements of anchored walls are
controlled by design methods more than is the case
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r
Table L·4
Envelope of Earth Pressure for Design of Temporary Supports for Soft to Firm Clays
I
Restraint
Cantilever
Design
Total
Pressure
Envelope of
Pressure
Distribution (4)
Ability to Restrict
Adjacent Soil Movements (5.6)
Triangular
Very poor; this type of support generally to be
in soft, sensitive clays
4
Notes to Table L·4:
PA may be computed using short term strength, i.e.,
PA =pgH 2C u if the excavation is open for a limited period.
Regardless of whether pressures are negative or zero,
minimum positive pressures indicated must be used.
(2)
Higher range should be used where clay is of soft consistency, and lower range where clay is of firm consistency.
This value may be conservative for non-homogeneous, nonsensitive sandy-silty cohesive soils of firm consistency. If
..
pgH +surcharge
stability number N = Ｍｾ｣
approaches 5 to 6, use
the higher range. At this ､ｾｰｴｨ＠
base heave may also take
place and therefore suitable precautions should be taken.
(3)
Design of a suitable shoring and bracing system in soft to
firm clay conditions is not a routine matter, and the advice of
a specialist should be obtained to establish design pressures,
(1)
(4)
(6)
to check overall stability and base heave and to predict
adjacent soil movements.
Essentially fluid soil pressures in very sensitive clays may be
realized as a result of unavoidable wall movements prior to
insertion of restraint supports.
Computed passive pressures below the base of the excavation should be reduced by at least 50 per cent to account for
unavoidable disturbance due to strain effects.
Additional precautions in soft to firm sensitive clays would
include (a) insertion of the top strut or anchor prior to excavation beyond 1.5 to 3 m depth, and (b) where the excavation area is of limited size, placing of a 150- to 300-mm thick
concrete mat at the base of the excavation, where practical,
immediately on completion of excavation.
Underpinning
with strutted walls. The number of anchors and the
vertical spacing of such anchors, playa significant
part in controlling the degree of lateral deformation.
In normal practice, movements due to the yield of
anchored diaphragms, sheeted or soldier pile walls
are usually less than for strutted walls for the same
depth of excavation.
17. For general guidance Table L-5 summarizes
the approximate range of vertical and lateral movements to be expected. In certain cases, more favourable results may be achieved with proper design,
good construction workmanship and careful field
supervision, including monitoring the behaviour of
the excavation.
18. Structures adjacent to excavations frequently
need to be supported. The need for underpinning
depends on the location of the structure, the details of
its foundation support, its sensitivity to settlement
and lateral deformations, the cost of underpinning or
provision of extra excavation face support and other
precautions, and the cost of repairs or the consequences if the structure is not underpinned.
19. The geometry of zones within which support
for adjacent structures is usually considered necessary, as a result of adjacent excavation through soit is
shown in Figure L-1. Where adjacent structures are
founded on bedrock and excavation is through rock,
less underpinning and more face support should be
considered.
233
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Wall Details
Restraint (5)
Table L-S
Vertical and Lateral Movements Associated with Excavation (1,2)
Granular
Soft to
Firm Clay, (3)
Remarks
Soils,
Stiff Clay,
% depth
% depth
% depth
Conventional
stiffness
Moderate
to large
Moderate
May
collapse
Movements related to wall,
soil stiffness and
embedment condition
Soldier piles or
sheet piles
0.2 to 0.5
0.1 to 0.6 (4)
1to 2 (4)
Struts installed as soon as
support level reached and
prestressed to 100 per cent
design load
Rakers or struts
loosely wedged
0.5 to 1.0
0.3
Soldier piles or
sheet piles
0.2 to 0.4
0.1 to
Concrete
diaphragm walls
< 0.2
< 0.1 to 0.5
Tied-back
Column 1
2
3
4
Cantilever
Braced
loo.sl
Notes to Table L-S:
Movements indicated apply directly behind wall; for granular
soils and stiff clays, movements would feather out in
approximately linear fashion over horizontal distance of 1.0 to
1.5 depth of excavation (H). For soft to firm clays, and
assuming average workmanship, this distance increases to
2.0 to 2.5H, and with poor workmanship to greater than 3H.
(2)
If groundwater is not properly controlled in granular strata,
movements may be much larger than indicated, and loss of
ground could also result.
(1)
234
Poor workmanship would
result in greater values
>2
2
<1 to 2
5
(3)
(4)
(5)
Prestressed to pressure
between active and at -rest
Prestressed as above, since
wall stiffness and design
earth pressures are normally
greater, movements generally are
less than for soldier piles or sheet
piling; little data available
6
If the factor of safety against base heave for soft to firm clays
is low, large deformations will result.
Upper range of movements usually applies for highly
sensitive clays in either stiff or soft to firm category.
Experience indicates that movements are reduced by using
close vertical spacing between strut or tie-back levels and by
careful attention to prestress details.
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tightly braced/tied
excavation wall
base of excavation
T
600mm
Zone A
Foundations within this zone often require underpinning. Horizontal
and vertical pressures on excavation wall of non-underpinned
foundations must be considered.
Zone B
Foundations within this zone often do not require underpinning.
Horizontal and vertical pressures on excavation wall of non-underpinned foundations must be considered
ZoneC
Foundations within this zone usual!y do not require underpinning.
Figure L·1
Requirements for underpinning
20. The general order of magnitude of movements
as a result of excavation with various support
methods in different soil conditions has been summarized in Table L-S. This table may also be used to
assist in judging the necessity for underpinning.
Factors to be Considered with Soil and
Rock Tie-Back Anchors
21. Anchors are usually inclined downwards,
transmitting the vertical component of the anchor
force into the anchored vertical member. This force
should be considered in design, together with the
weight of the vertical member itself.
22. Forces which resist downward movement due
to the inclined anchor load are skin friction and the
reaction at the base of the vertical member. When
soldier piles are used, vertical forces are concentrated
in the piles. Only minimal friction, if any, can be
mobilized. Such vertical forces must therefore, be
supported at the base of the pile. The vertical and
horizontal base capacity of the pile must be checked;
otherwise, unacceptable vertical and horizontal
deformation may take place.
23. Settlement of vertical members produces some
reduction in anchor loads, with a consequent tendency for outward displacement of the supported
face. Therefore, vertical and horizontal movements
at the top and bottom of the excavation must be
monitored at regular intervals throughout the course
of the work.
24. The performance of soil and rock anchors
depends, not only on minor variations in soil and
groundwater conditions, but also on construction
techniques and details. Consequently, the prediction
of anchor capacity by theoretical calculations is not
reliable. Anchorage capacities must be established by
test taking into account the load deformation and
"creep" properties of the soit and each anchor must
be proofloaded during construction.
25. The overall stability of a soil anchorage system
should be checked by analyzing the stability of the
block of soil lying between the wall and the anchorages. In generat the anchors should be extended
beyond a 1:1 line drawn from the base of the excavation, and no allowance for any load carrying support
should be assumed within this line.
Design and Installation of Members
26. Members such as walers, struts, soldier piles
and sheeting should be sized in accordance with the
structural requirements of Part 4 of the National
Building Code of Canada 1990.
27. The depth of penetration of the vertical wall
member should be 1.5 times the depth required for
moment equilibrium about the lowest strut.
28. For driven soldier piles, the maximum horizontal force on the flange of the soldier pile below the
bottom of the excavation may be taken as 1.5 times
the values computed for the width of the flange,
providing that the pile spacing is not less than five
times the flange width.
29. For piles placed in a concrete base, the diameter of the concrete filled hole may be used in place of
the flange width as discussed in the preceding
paragraph.
30. The selection of material and sizes of timber
planks or lagging should conform with good practice, and the lagging should be of good quality
235
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hardwood. Lagging is installed by hand after a
depth of about a metre is excavated. The maximum
depth made each time before a section of lagging is
placed depends on the soil characteristics. Soft clay
and cohesion less soils must be planked in short
depths to reduce the amount of soil moving into the
excavation. The depth of excavation below any
lagging boards that have not yet been placed should
not exceed 1.2 m. Lagging must be tightly backfilled
or wedged against the soil.
31. To minimize the possibility of erratic loss of
ground in local areas when excavating sands and silts
below original groundwater, straw packing, burlap
or in extreme conditions, grouting must be used
behind the lagging as it is installed.
32. The design of all members including struts,
walers, sheetpiling, walls and soldier piles should be
checked for several stages of partial excavation when
the wall is assumed to be continuous over the strut
immediately above the excavation level and supported some distance below the excavation level by
the available passive resistance. This condition could
produce the maximum loading in struts and walers.
33. Where excessive stresses or loads would result
(b)
(c)
(d)
(e)
(f)
(g)
(h)
from interim construction conditions using regular
construction procedures, trenching techniques can be
employed to advantage.
34. The design of members should also be checked
for the condition when portions of the building
within the excavated area are completed and lower
struts are removed. Consideration must be given to
the possible increase in loading on the upper struts
remaining in place; also the span between that
portion of the building that has been completed and
the lowest strut then in place must be considered in
relation to flexural stresses.
Control of Groundwater in Excavations
35. Good practice requires that the following
conditions must be fulfilled when dewatering excavations:
(a) A dewatering method must be chosen that will
not only assure the stability of the sides and
236
(0
bottom of the excavation but will also prevent
damage to adjacent structures, such as by settlement.
The lowered water table must be kept constantly
under full control, and fluctuations liable to
cause instability of the excavation must be
avoided.
Effective filters must be provided where necessary to prevent loss of ground.
Adequate pumping and standby pumping
capacity must be provided.
Pumped water must be discharged in a manner
that will not interfere with the excavation or
cause pollution.
For most soils the groundwater table during
construction must be maintained at least 600 to
1 500 mm below the bottom of the excavation so
as to ensure dry working conditions. It should
be maintained at a somewhat lower level for silts
than for sands in order to prevent traffic from
pumping water to the surface and making the
bottom of the excavation wet or "spongy."
Adequate monitoring of groundwater levels by
piezometers or by observation standpipes
should be maintained.
Where impermeable strata are underlain by
pervious water-bearing layers, depending on the
depth of excavation and the hydrostatic head in
the pervious strata, it may be necessary to lower
the head in the pervious stratum in advance of
excavation, to prevent a "blow" or excessive
disturbance of the base as a result of upward
hydrostatic pressure.
Pumping from sumps or ditches inside the excavation is normally carried out where dense low
permeability soils, such as certain glacial tills or
cohesive soils, are present or where the excavation is in bedrock; this method is not recommended for excavation in semi-pervious or pervious soils, such as silts or fine sands, since it
often leads to extensive sloughing of the excavation sides and disturbance of the bottom.
Shallow Foundations
General
36. A shallow foundation means a foundation unit
which derives its support from the soil or rock close
to the lowest part of the building which it supports.
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The depth of the bearing area below the adjacent
ground is usually governed by the requirement to
provide adequate protection against climatic or frost
effects; vertical loads on the sides of the foundation
due to adhesion or friction are normally neglected.
Bearing Capacity and Settlement
37. The design of a foundation unit normally
requires that both bearing capacity and settlement be
checked. While either bearing capacity or settlement
criteria may provide the limiting condition, settlement
normally governs. Distress from differential settlement, as evidenced by cracking and distortion of
doors and window frames, is common. The drastic
effects of a bearing capacity failure are rare, except
perhaps during construction, where shallow temporary footings are frequently used with falsework.
38. The bearing capacity of both cohesive and noncohesive soils can be determined with reasonable
reliability by assuming that the strength parameters
for the bearing soil are accurately known within the
depth of influence of the footing.
39. Cohesive soil. The settlement of a structure on
cohesive soil can be calculated with less accuracy than
the bearing capacity. Such a calculation is affected by
a number of complicating factors usually requiring
judgement to assess. The most important of these is
an estimate of the preconsolidation pressure, that is,
the maximum past consolidation pressure on the in
situ soiL Because of the various uncertainties, errors of
a factor of 2 should be expected in the calculation of
settlement.
40. Non-cohesive soil. The settlement of a structure on non-cohesive soil can normally only be
estimated by empirical methods. Such an estimate is
usually taken to mean the settlement directly related
to the load, but this settlement generally occurs quite
rapidly, often during the construction period. Post
construction settlement in such a case will be negligible and may be considerably less than predicted.
41. Post construction settlement can occur for a
considerable period after construction, even after a
period of successful performance of the structure, as
the result of vibrations or changes in the groundwater
conditions, whether natural or man-made, due to
earthquake or blasting, flooding or groundwater
lowering. Settlement of this nature is not usually
included in an empirical estimation, but should
be assessed.
Design Bearing Pressure
42. The design bearing pressure is limited by two
considerations:
(a) the foundation must be safe against shear
failures of the supporting soil, and
(b) settlement must not be excessive.
43. The design bearing pressure is the lesser of the
values dictated by these two requirements.
44. A detailed flow diagram for the design of
shallow foundations is shown in Figure L-2. In many
cases this can be simplified; however, it illustrates the
factors affecting the choice of design bearing pressure
for most structures.
Estimates of Allowable Bearing Pressure
45. Universally applicable values of allowable
bearing pressure cannot be given. Many factors
affect bearing capacity, and the allowable load will
frequently be controlled by settlement criteria.
Nevertheless, allowable bearing pressure for the
preliminary design can usefully be estimated on the
basis of the material description; such values should
be recalculated for the final design in keeping with
good geotechnical practice and normal analytical
proced ures. (1 )
46. Estimated values of presumed allowable
bearing pressure and notes are given in Tables L-6,
L-7, L-8 and L-9. Such pressures should be considered as the maximum permissible under the total
dead and live loading and treated as first approximations only.
Frost Penetration
47. The best indication of frost penetration in a
particular locality is local experience. In the absence
of local experience, however, daily air temperature
measurements can be used to estimate the combined
effects of both depth and duration of freezing. The
cumulative total of the difference between daily
mean air temperatures and the freezing point is
known as the "Freezing Index," and is expressed in
237
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Flow diagram for foundation design
Shallow foundations
Field Investigation
- boreholes
.
Factors affecting depth
of footing: - frost
protection, slope
stability, erosion
topography, sOil
I
I
conditions, water level
sweillng(?)
I
I
...
I
I
I
I
+
I
I
I
I
I
I
I
I
I
I
+
I
I
I
yes
yes
L_+_
238
:
____ -. ___ L ___ -'
-These factors frequently control foundation design
Figure L-2
I
Flow diagram for design of shallow foundations
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f
Table L·6
Estimates of Allowable Bearing Pressure on Rock
ｲＭｾ
Rock Conditions (1)
Rock Type
(a)
(b)
Massive igneous and
metamorphic rocks in
sound condition:
granite, diorite, basalt
and gneiss
Foliated metamorphic
rocks in sound
condition: slate and
schist
(c)
(d)
Sedimentary rocks in
sound condition:
cemented shale or siltstone, sandstone,
limestone, dolomite
and heavily cemented
conglomerate
Compaction shale and
other argillaceous
rocks in sound
condition
1----------
(e)
All closely jOinted
rocks including thinly
bedded limestones and
shales
(f)
Heavily shattered or
weathered rocks
Discontinuities (joints,
minor cracks) at wide
ｳｾｰ｡ｃ｟ｩｮｧＨ＾ＱｭＩ＠
________ｾ＠
Discontinuities at moderate
spacing (300 ｭ｟ｴｯＱｾＩ＠
Ｍｉｾｴ＠
(i)
Discontinuities at
wide spacing (>1 m)
(ii) Discontinuities at
moderate spacing
(300 mm to 1 m)
iii) Foliations tilted to the
horizontal
__--_____
2 to 5
r '_ _
,
,
,
,
r
I
ｾＭｲＫ＠
Allowable
Bearing
Pressure (2)
MPa
Discontinuities at wide
spacing (>1 m)
3
Remarks
1
I
Foliations approximately
horizontal
Foliations approximately
horizontal
Potential sliding along
foliations. Potential lack of
support adjacent to cuts on
excavations See Reference (2),
Strata approximately
r-________ＭＫＺｨｾｯＬＮ｣ｲｩｺ［ＰＧ｟Ｗｮｴ｡Ｑ＠
ｾＭ｟［Ｚｬ＠
Potential solution cavities in
limestone, dolomite.
Variability in cementation of
conglomerates. See (b) (iii)
-
ＭｲＫＮｾ＠
0.5 to 1
Discontinuities at wide
spacing (> 1 m)
ｾ
Discontinuities at spacing
less than 300 mm apart.
Random joint or crack
patterns
ＭＱ｟ｾｨｏｲｩｺｯｮｴ｡ｬＧ＠
i
Strata approximately
-Argillaceous shales are subject to
some swell on release of stress.
All shales tend to soften on
exposure to water and certain
shales swell markedly
Can only be assessed by detailed
investigations and examination
in situ, including loading tests if
I
i
I
i
'V"''''' "" .."A , J
See!e)
i
Column 1
Notes to Table L-6:
Spacing of discontinuities is critical to the bearing pressure
allowable on a rock mass. Discontinuities, such as joints or
cracks, are considered widely spaced if greater than 1 m apart
and moderately spaced when greater than 300 mm. The
thickness or width of such discontinuities is presumed to be less
than 5 mm (or less than 25 mm if completely filled with soil or
(1)
(2)
rock debris). Where such conditions do not exist, Types (e) or (f)
must be assumed.
Values of bearing pressures given above, except for (f), are based
on the assumptions that the foundations are close to the rock
surface but carried down to unweathered rock with adequate frost
protection and that the foundation is greater than 300 mm wide.
239
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Table L-7
Estimates of Allowable Bearing Pressure on Non-Cohesive Granular Soils
Soil Type and
Conditions (1)
Allowable
Bearing
Pressure (2)
kPa
Potential Problems (3)
Remarks
For general reference see
References (1) and (4)
(a) Dense well-graded
sands, dense sand and
gravel
400 to 600
Density of sands containing
large sizes or gravels is
frequently overestimated when
(b) Compact well-graded
sands, compact sand
and gravel
200 to 400
inferred from standard or cone
penetration tests only, See
Reference (3)
(c) Loose well-graded
sand, loose sand and
gravel
100 to 200
Potential settlement when subject
to shock or vibrations. See (f)
(d) Dense uniform sands
(e) Compact uniform
sands
300 to 400
100 to 300
Density usually better
defined by standard or cone
penetration tests, as compared
to (a) to (c). Considerable
caution required in interpretation
of test data
See References (5) - (7)
(f) Loose uniform sands
<100
Even where very low bearing
pressures are used, settlement
can occur due to submergence,
vibrations from blasting machine
operation or earthquake
See Reference (8)
-
Subject to possible liquefaction.
Should never be used for support
of foundations
(g) Very loose uniform
sands, silts
Column 1
2
Notes to Table L-7:
Density condition of the soil is assumed to be established in
conformance with good geotechnical practice.
(2)
Values 0", bearing pressure are based on the assumptions
that the foundation (B) is not less than 1 m wide and that the
groundwater level will never be higher than a depth, B, below
the base of the foundation. When the groundwater level is,
3
(1)
240
(3)
4
or could be, higher than such depth, the values listed should
be divided by a factor of 2.
Long term settlement of foundations on compact to dense
non-collesive deposits is normally modest, provided such
deposits are not underlain by compressible cohesive
deposits at depth.
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Table L-8
Estimates of Allowable Bearing Pressure on Cohesive Soils (for sensitive clays, see Table L-9)
ｾｓＱ＠
Soil Type and
Allowable
Bearing
Pressure (2)
kPa
(a) Very stiff to hard clay,
heterogeneous clayey
deposits or mixed
deposits such as till
300 to 600
(b) Stiff clays
(c) Firm clays
100 to 200
(d) Soft clays
oto 50
(e) Very soft clays
Column 1
50 to 100
-
Applicability for Support
of Shallow Foundations (2)
I
Good
Normally estimated on the basis of
investigations, sampling
and laboratory test data
Fair to good
Poor -- except for minor
structures little affected by
distortion
For general reference see
References (1) and (9) (11 )
Very poor - not
recommended
i
No
2
Notes to Table L-8:
Strength of cohesive soils is assumed to be established in
conformance with good geotechnical practice.
(2)
Cohesive soils are susceptible to long term consolidation
settlement. For Types (b) to (d) inclusive, such settlement
( 1)
Settlement (2)
3
4
often governs the applied pressure rather than bearing
pressures based on soil strength. In the case of Type (a)
soils, heave can take place with excavation and consequent
relief of stress.
241
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Table L·9
Problem Soils, Rocks or Conditions (1)
References
(12)
Type or Condition
Organic soils
Examples
Muskeg terrain: estuarine organic silts
and clays
Normally consolidated
clays
Lacustrine deposits and varved glaciolacustrine deposits in Manitoba, Northern
Ontario, Northern Quebec
(13)
Sensitive clays
Marine clay deposits in St. Lawrence
River Valley, Eastern Ontario, Quebec
(14)-(16)
Swelling/shrinking clays
Clay-rich deposits in Alberta,
Saskatchewan, Manitoba
(17)
Metastable soils
British Columbia loess
(18)
Expansive shales
Western Canada - Bearpaw and
Cretaceous deposits
Eastern Canada - weathering of sulphide
minerals accelerated by oxidizing bacteria
(19,20)
Permafrost
Northern Canada, Arctic
(21,22)
Column 1
2
3
Note to Table L·9:
No bearing pressure can be presumed without detailed
investigations.
(1)
242
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degree days. Freezing indices for a large number of
weather stations in Canada have been published by
the Atmospheric Environment Service.(23) As a
general guideline the variation in freezing indices
across Canada is illustrated in Figure L-3. Information on how the "Freezing Index" may be used to
estimate depth of frost penetration is given in References (24) to (27).
Insulated Shallow Foundations
48. In recent years lightweight plastic insulation
has been used to reduce the loss of ground heat and
thereby reduce the depth of frost penetration. Insulation should be used for this purpose only after
careful examination of the pertinent conditions and
with a thorough understanding of its effect on the
temperature at the soil-foundation interface.(27)
Insulation is of particular advantage in the design of
unheated buildings such as warehouses, garages and
refrigerated buildings used for food storage. It is also
used to restrict the depth of frost penetration beneath
artificial ice surfaces.
49. Insulation can be obtained with relatively high
compressive strengths, so that slabs of these materials
can be placed directly below the bearing surfaces of
foundations. Substantial economic advantages may
accrue where such designs are used, because foundations can be located closer to the ground surface,
thereby reducing the costs of providing granular fill
to replace frost-susceptible soil.(27)
Figure L-3 Normal freezing index in degree days Celsius,
based on the period 1931 to 1960
243
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Deep Foundations
Introduction
50. A deep foundation is a foundation unit that
provides support for a building by transferring loads
either by end-bearing to a soil or rock at considerable
depth below the building, or by adhesion or friction,
or both, in the soil or rock in which it is placed. Piles
are the most common type of deep foundation.
51. Piles can be premanufactured or cast-in-place;
they can be driven, jacked, jetted, screwed, bored,
drilled or excavated. They can be of wood, concrete
or steel or a combination thereof. (Drilled shafts of
diameter greater than about 750 mm are frequently
referred to as caissons in Canada.).
52. Loads which may be applied to a deep foundation depend not only on the properties of the
foundation as a structural unit (e.g., the shaft
strength of a drilled shaft determined on the basis of
CAN3-A23.3-M84, "Design of Concrete Structures for
Buildings"), but also on the properties of the foundation soil (or rock) and of the soil/ foundation system
(e.g., pile capacity as a function of soil strength,
settlement of a drilled shaft as a function of contact
pressure). Thus, the designer must distinguish the
structural from the geotechnical capacity of a deep
foundation unit or system, analyze each very carefully and define application of loads which may be
carried safely, both from a structural and a geotechnical point of view. In many applications,
geotechnical considerations limit the permissible
loads to levels well below those which might be
arrived at on the basis of structural considerations
alone.
53. Geotechnical criteria for assessing permissible
loads on a deep foundation are determined on the
basis of site investigations and geotechnical analyses.
However, in most cases, the quality of a deep foundation is highly dependent on construction technique, equipment and workmanship. Such parameters cannot be quantified nor taken into account in
normal design procedures. Consequently, as implied
in NBC Subsection 4.2.7., deep foundations should be
designed on the basis of in situ load tests on actual
foundation units.
54. Criteria relating to structurally permissible
loads are defined in the design sections of the National Building Code applicable to the structural
materials used in the deep foundation unit. However, the standards referenced in the NBC were
written mainly for the purpose of designing elements
and assemblies in the superstructure. A structural
consultant involved in the design of deep foundations must recognize that installation and quality
control conditions below grade differ from those
above grade; the permissible loads determined by the
usual structural design methods may have to be
reduced, sometimes to a marked degree, to account
for these differences. Permissible loads can only be
selected on the basis of close co-operation between
the geotechnical and structural consultants for the
project.
55. In this section of the Commentary, suggested
values of permissible loads are given for several
kinds of foundation units. These values are listed
solely to provide a first approximation of the probable loads which, under routine conditions, might be
applied safely to a given kind of unit. In each case,
both geotechnical and structural evaluation and
analysis is mandatory. However, as discussed above,
since construction procedures often have a dominant
influence on the load/ deformation behaviour of the
deep foundation, the choice of a permissible load is
always subject to judgment and experience and to the
provision that appropriate review is carried out as
specified in Article 4.2.2.3. of the NBC. Review must
be considered an integral part of the design process.
Geotechnical Requirements
of Deep Foundations
Deep foundations end.bearing on rock
or highly competent deposits
56. Deep foundations which are placed on rock or
on a dense basal deposit, such as till or hard clay, are
bored, drilled or excavated and cast-in-place, and are
commonly referred to as drilled shafts. In this case,
the area of end-bearing contact is known and,
provided this area and the character of the foundation stratum can be defined by inspection, the
geotechnical capacity of the deep foundation can be
evaluated on the basis of the allowable bearing
pressure of the foundation stratum. (Refer to Tables
L-6, L-7 and L-8, on shallow foundations.)
I
I
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•
provide base fixity and resistance to horizontal
movement. (28,29)
57. Rock sockets. Frequently, cast-in-place foundations are socketed into rock, either to obtain higher
end bearing capacity at depth or to transfer load to
the rock by adhesion or bond along the walls of the
socket. Adhesion is highly dependent on the rock
ｴｹｰｾ＠
and on the socket wall condition after drilling.
DesIgn values used for adhesion in sound rock lying
below weathered or shattered rock range from 0.7
MPa to 2.0 MPa; however, much lower values have
been observed in practice, where the construction
methods used have produced a poor contact area.
Careful inspection of all rock sockets prior to concreting is essential. Socketing may also be employed to
Pile Type
(a) End-bearing on
rock, dense till
or other similar
materials
(b) Piles driven
into dense sand,
, sand and gravel
(c) Piles driven
into loose to
compact sand,
sand and gravel
I
(d) Piles driven
into compact to
dense silts
(e) Piles driven
into cohesive
soils
58. Deep foundations may also be driven to rock or
into dense basal deposits. In this case, which includes H-piles, pipe piles driven closed-end or
precast concrete piles, the exact area of contact with
the foundation stratum, the depth of penetration into
it or the quality of the foundation stratum are largely
unknown. Consequently, the load capacity of such
driven deep foundations should be determined on
the basis of observations during driving, load tests
and local experience. (Refer to Table L-IO.)
Table L·10
Load Capacities of Driven Piles
Load Capacity
Recommendations
High to very high, but
Ultimate pile capacity
dictated by driving
usually high but load/
conditions, conditions of
deformation can only be
basal deposits, pile types
assessed by load test
and stiffness
(ASTM 01143-81,
Method A)
See (a)
See (a)
Medium to high, part pOint
resistance, part skin
friction
Medium, but "relaxation"
effects must be checked
Low to medium,
susceptible to long term
settlement
I
Column 1
2
I
References
-
(30) (31)
First approximation to load
capacity, use skin friction
(kPa) =50 ± 25. Define by
load test (ASTM
01143-81, Method A)
See (c). Essential to define
by load test
See references
above. See also
References (32)
and (33)
First approximation, use
skin friction. Soft cohesive
soil, 0 - 30 kPa. Firm to
stiff cohesive soil, 30
60 kPa. Define by load test
(ASTM 01143-81,
Method B)
3
(35) (36)
(34)
4
245
pays
Piles in granular soils (Refer to Table L-10)
59. Piles which are driven into granular soils
derive their load carrying capacity from both point
resistance and shaft friction. The relative contributions of point resistance and shaft friction to the total
capacity of the pile depend essentially on the density
of the soil and on the characteristics of the pile.
60. It is commonly assumed that pile driving in
granular soils increases the density of the deposit.
Because of this, piles in granular soils should be
driven to the maximum depth possible, without
causing pile damage, in order to obtain the maximum
working load on the pile. However, in some granular
soils, such as fine sands or cohesionless silts, the pile
capacity may decrease after driving. This effect is
known as "relaxation." In contrast, in some coarse
sands or other coarse grained deposits, the load
capacity of piles may increase after driving. This
effect is known as "freeze." Neither of these effects
can be assessed quantitatively, except on the basis of
red riving and load testing.
61. Compacted concrete piles. Compacted or
rammed concrete piles in granular soils derive their
load capacity mainly from the densification of the soil
around the base. The capacity of such piles is,
therefore, entirely dependent on the construction
technique and can only be assessed on the basis of
load tests and detailed local experience.
Piles in cohesive soils (Refer to Table L-10)
62. The load capacity of piles driven into cohesive
materials is governed by the adhesion between the
pile and the soil and, to a much lesser extent than in
granular soils, by the point resistance. This is particularly true for soft to firm clays.
63. The adhesion is not always equal to the
undrained shear strength of the soil since, in some
circumstances, the effect of pile driving markedly
changes the character of the soil. In soft sensitive
clays, complete remoulding of the soil may occur on
driving. This effect diminishes with time following
driving, as the soil adjacent to the pile consolidates.
In some cases, soil strength has not returned to the
original undisturbed value even after a considerable
period of time.(37)
246
64. Because of the slow rate of regain of strength
in certain cohesive soils, load testing should sometimes be delayed until several weeks have elapsed
after driving.
65. In stiff to very stiff cohesive soils, evidence
indicates that, in driving, a gap is formed between
the pile and soil; this gap is not always fully closed
with time, thus minimizing the adhesion to the pile
relative to the high shear strength of the soil. For this
reason, an approximate limit of 60 kPa has been
suggested for the adhesion value, even for stiff clays
(Table L-10).
66. Drilled shafts in cohesive soils. Except for
shafts drilled through stiff or very stiff cohesive
deposits, the major portion of drilled shaft capacity is
derived from the bearing capacity of a hard or dense
stratum at the base. For a first approximation of
bearing capacity, Tables L-6 and L-7 should be used.
For a more detailed assessment of bored piles, see
Reference (38).
Spacing and arrangement of piles and
drilled shafts
67. The following should be considered during the
spacing and arrangement of piles and drilled shafts:
(a) the overlap of stresses between units, which
influences total load capacity and settlement,
(b) overstressing of weaker zones at depth, and
(c) installation difficulties, particularly the effects
on adjacent piles or drilled shafts.
68. In most cases the spacing, D, between the
centres of driven piles of average diameter, d, should
not be less than 2.5 d.
Settlement and group effects in piles
69. In practice, piles are frequently used in groups;
however, most of the published literature deals with
the behaviour of single piles. Leonards (39) states that,
"there is no consistent relationship between the
settlement of a single pile and the settlement of the
pile group at the same load per pile. Therefore,
selecting a design load on the basis of the load at a
given gross or net deflection, or at a given fraction of
the ultimate pile capacity, is equivalent to accepting
an unknown factor of safety with respect to satisfactory performance of the foundation." This statement
is certainly valid for all piled foundations where the
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,...
piles derive their support from skin friction, or from
combined skin friction and end-bearing; however,
group effects may be less critical where piles derive
all of their support or the major portion of it from
end-bearing on a relatively incompressible stratum.
An example of such support is where piles are driven
through weak deposits to end-bearing on rock. For
this case, the engineer normally relies on some means
of assessing the dynamic resistance during pile
driving complemented by load tests to define the
deformation characteristics of the piles under load.
70. In contrast to true end-bearing pile foundations, where the load/ deformation characteristics of
individual piles are significant, the use of friction pile
foundations is generally governed by considerations
of group action and, for cohesive soils, long term
consolidation settlement. The actual capacity and
load / deformation characteristics of individual piles
are not significant in this case. The purpose of
friction piles in the upper part of a deep deposit of
cohesive soils or of granular soils (or silts) is to
reduce the intensity of pressure acting at ground
level and to shift the zone of maximum stress to the
lower levels, where less settlement will result.
71. In the case of an individual pile or where the
building is narrow in relation to the depth of piles,
the zone of pressure increase is spread over a large
area in comparison with the width of the foundations; in contrast, where the building is wide, friction
piles spread the load out very little, and the effect of
the pile foundation on the soil is practically the same
as that of a raft foundation without piles. In this case,
the total bearing value of the piles in the foundation
bears no relation to the carrying value of an individual pile by itself; the settlement of the foundation is,
therefore, governed by the character of the subsoil,
not by the load capacity of the piled foundation.
Load tests on deep foundations
72. Use of load tests. As previously indicated,
load testing of piles, as specified in NBC Sentence
4.2.7.2.(2), is the most positive method of determining
load capacity. Depending upon the type and size of
the foundation, such load tests may be performed at
different stages during design and construction.
73. Load tests during design. The best method of
designing a pile foundation is to perform pile driving
and loading tests. The number of tests, the type of
pile tested, the methods of driving or of installation
and of test loading should be selected by the engineer
responsible for the design. The following points
should be considered:
(a) The test program should be carried out by a
person competent in this field of work.
(b) Adequate soil information should be obtained at
the test location.
(c) The piles, the equipment used for driving or
other method of installation and the procedure
should be those intended to be used in the
construction of the foundation.
(d) As a minimum, the head of a pile should be
instrumented to record the total pile and soil
deformation. Where possible, deformation
measurements should also be made at the tip of
the pile and at intermediate points to allow for a
separate evaluation of point resistance and skin
friction.
(e) The driving process should be observed in detail
and, wherever possible, stress levels in the pile
assessed (e.g., by means of the wave equation
method of analysis).
(f) The piles should be loaded to at least twice the
proposed working load and preferably to
failure.
74. Routine load tests during construction. Load
tests should be performed on representative deep
foundation units at early stages of construction. The
purpose of such tests is to ascertain that the allowable
loads obtained by design are appropriate, and that
the installation procedure is satisfactory.
75. The selection of the test piles should be made
by the engineer responsible for the design on the
basis of observed driving behaviour or installation
features.
76. Load tests for control. Where full advantage
is to be taken of Clause 4.2.4.1.(1)(c) and Sentence
4.2.7.2.(2) of the NBC, a sufficient number of load
tests must be carried out on representative units to
ascertain the range of the pile performance under
load. Load tests for control should be performed on
one out of each group of 250 units, or portion thereof,
of the same type and capacity. Load tests should also
be performed on one out of each group of units
where driving records or other observations indicate
247
pays
that the soil conditions differ significantly from those
prevailing at the site. Selection of the deep foundation units to be load tested is the responsibility of the
design engineer.
Installation and Structural Requirements of
Deep Foundations
77. In most cases, the maximum allowable load on
a deep foundation unit is governed by geotechnical
considerations. The design capacity of a deep
foundation unit determined from structural considerations represents the maximum axial load which
theoretically could be carried; however, this load is
generally less than could be applied to a comparable
unit used in the superstructure of a building because
(a) the actual placing of deep foundations frequently deviates from the position and alignment assumed in design,
(b) once in place, deep foundation units often can
neither be inspected nor repaired, and
(c) the placement of concrete in cast-in-place deep
foundations frequently cannot be done with the
same degree of control as in structural columns.
78. In Tables L-ll to L-13 guidelines are given to
assist in determining a reasonable axial design
capacity for deep foundation units under common
conditions. These tables are not a substitute for
structural analysis and design, but only provide a
conservative guide for routine situations which may
confront a designer, where a unit may be considered
as a short column and where axial load governs the
design.
79. The flexural capacity and ductility of piles
should be considered when, under certain soil
conditions, the soil either does not provide lateral
support or could cause lateral loads to be applied to
the piles.
80. Frequently, economies can be made by using
higher capacities or different techniques. Such higher
capacities should only be used in conditions where
they can be justified as suitable and when quality can
be ensured by an adequate program of inspection
and load tests.
Driven piles
81. This type of deep foundation unit may suffer
structural damage when being driven. Determina248
tion of capacity is generally made by comparing
driving resistance (blows per 30 cm) with the energy
or size of hammer blow and relating these figures to
previous experience or to the behaviour of similar
piles subjected to static load tests. For this purpose,
observations of pile driving must include:
pile length and weight,
hammer type (e.g., drop, diesel, ram weight),
hammer energy applied,
type and thickness of packing, and
blows per 30 cm and elastic rebound of pile, or
acceleration and stress at head of pile.
82. The assessment of pile stresses during driving
by the theory of wave propagation or by the "wave
equation" method of pile analysis is useful. By
assigning appropriate elastic properties to such
parameters as the pile/cushion system and the pilei
soil system, the penetration per blow and pile
stresses for a given hammer energy can be computed;
however, these results and the extrapolation of the
penetration per blow to a definition of ultimate pile
capacity are, at best, only approximations. The
"wave equation" method, in common with all
empirical dynamic pile formulae, calls for the exercise of judgment and experience. No method, in
itself, can provide definitive values either for driving
criteria or load/ deformation characteristics of a
driven pile. Pile load tests are essential to confirm
the driving criteria used and to assess load/ deformation performance.
83. Damage to driven piles. Piles may be damaged by attempting to drive to an excessively small
"set" per blow or to an excessively large number of
blows at high resistance. This is known as "overdriving." The driving set should be established so as to
achieve a reasonable performance under load without incurring the risk of serious damage. Driving
stresses depend upon the hammer, blows, size and
type of pile, length of pile, cushion material and soil
conditions. These factors must be examined for each
situation and acceptable "set" criteria determined on
the basis of previous experience and load testing.
84. Piles may also be damaged by driving through
obstructions, such as boulders or fill material, or by
sloping rock surfaces which may deflect the pile or
create high local stresses leading to serious deformation or breakage.
pays
Table L·11
Guidelines for Driven Piles
.
· Normal
Size
Type of
Pile . Range
(a) Timber I 180 to
250mm
tip
Typical
Pile Load
kN
180 to
450
(b) Steel
sections
{H, WF}
200 to
350mm
350 to
1800
(c) Pipe
sections
200 to
600 mm
diam
350 to
1800
200 to
300 mm
300 to
900mm
350 to
1 000
900 to
2500
2
3
(d) Precast
concrete
sections
!
i
Structural
Considerations
Must be checked in
accordance with NBC
Subsection 4.3.1.
Installation
Considerations
Cannot be inspected.
Susceptible to damage
during hard driving.
Tip reinforcement
recommended where
driven to end bearing
Notes
Must be checked in accordance
with NBC Subsections 4.3.3.
and 4.3.4. End bearing
allowable working stresses
usually i> 0.3fy when driven
to end bearing refusal on
rock or dense strata;
higher stresses possible under
specific controlled conditions.
Friction: working stresses
usually governed by
geotechnical considerations
and rarely exceed 80 MPa.
In pipe piles, concrete
strength does not normally
contribute to pile capacity
unless the pile is driven to
end bearing
May be damaged during
driving but load
capacity not
necessarily reduced
Tip points often required
for hard driving.
Average thickness of
flange or web,
t ｾ＠ 1 cm.
Projection of flange ｾ＠ 14t
Suitable for
inspection after
driving. Concrete
quality highly
dependent on
placement method
Normally driven closedend. Tip reinforcement
or drive shoe required
when driven open-end.
Pipe thickness >5 mm,
but 10 mm recommended
End bearing: capacity must
be checked in accordane
with NBC Subsection 4.3.3.
Normally ｦｾ＠ > 27.5 MPa
Friction: the capacity of
friction piles is normally
governed by both installation
method and geotechnical
considerations; average
compressive stress under load
rarely exceeds 10 MPa
Cannot be inspected.
Careful selection and
driving method
required to prevent
damage
Refer to ACI 543R-1980
Possible tensile stresses
in concrete during 'soft'
driving. High compressive
stresses in concrete during
'hard' driving. Tip
reinforcement usually
essential
Preservative treatment
normally required.
(CAN/CSA 080-M89)
•
Column 1
4
5
6
249
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85. Excessive bend or sweep may be experienced
when driving long piles (30 m or more). A discussion
of allowable bending of piles is given in Reference
(41).
86. The use of steel reinforcing tips is strongly
recommended whenever ends may be damaged. Tip
reinforcement may also reduce damage incurred
through overdriving.
87. Movement of adjacent piles during driving.
Where a group of piles is to be placed through silt or
clay, measures shall be taken to indicate any movement of each pile during the installation of adjacent
piles. Horizontal and vertical movement should be
recorded.
88. Piles which have suffered vertical movement
should generally be redriven. Piles which have
suffered horizontal displacement must be investigated for structural damage.
89. Jetting or pre-excavation. When jetting,
predrilling or other pre-excavation methods have
been used during pile installation, the pile tip should
be driven below the depth of pre-excavation to the
required bearing. Care must be taken to avoid
jetting, pre-driving or pre-excavating to a depth or in
a manner that will affect the design capacity of piles
previously placed. This is discussed in detail in ACI
543R-1980. (40)
Cast-in-place deep foundations
90. Cast-in-place deep units can be divided into
two main categories: compacted expanded base piles
(Table L-12) and drilled shafts (Table L-13).
91. The placement of the materials forming such
units is cruciaL It is difficult, if not impossible, to
ensure the same level of quality in placing concrete in
such units as in a building superstructure. Careful
attention must be given to the methods of installation, concrete mix proportions and placement methods, and to the degree of inspection possible. The
allowable loads on such units must be adjusted
accordingly, in keeping with sound design, engineering experience and judgement.
92. Concrete cast in place. The placing of concrete in pipe piles, expanded base pile shafts and in
drilled shafts can be classified in two categories:
(a) Concrete placed in the dry should be placed by
250
guided free fall, bucket or chute. Segregation
may occur if concrete is allowed to fall through a
reinforcing cage or similar obstruction.
Concrete of more than 100 mm slump placed by
free fall of 5 m or more in non-reinforced or
lightly reinforced shafts receives adequate
compaction and does not require vibration.
Placement by tremie methods is necessary when
a considerable inflow of groundwater is present
or when there is standing water in the hole.
(b) Concrete placed under water should be placed
through a tremie pipe or by pump in such a way
as to eliminate any contamination, washing or
dilution of the concrete by the water. It should
have a 150 to 200 mm slump and vibration
r
should not be applied. (Refer to CAN/CSAA23.1-M90, "Concrete Materials and Methods of
Concrete Construction.")
93. Reinforcing steel for cast-in-place units.
Reinforcing steel is generally placed pre-assembled
as in a cage. During placement, the steel may be
subjected to severe handling and placement stresses
and to impact. Placement cannot be made with as
high a degree of accuracy as in a superstructure, nor
can it be easily checked.
94. For the design of cast-in-place foundations, the
provisions of CAN3-A23.3-M84, "Design of Concrete
Structures for Building" should, therefore, be
amended in the following respects:
(a) Reinforcing steel assemblies should be designed
and constructed so as to withstand all handling
and placing stresses without deformation which
would impair the structural performance of the
unit.
(b) Weldable steel should be employed, in most
cases, to permit construction of rigid and strong
assemblies.
(c) The clear distance between longitudinal bars
should not be less than 75 mm.
(d) Ties or spirals may be welded to the longitudinal bars. Welding should be in accordance with
CSA W59-1989, "Welded Steel Construction
(Metal-Arc Welding)." Welded spirals or ties
should be of wire not less than 7.0 mm in diam,
with pitch not more than 300 mm and with not
less than 75 mm clear space between ties or
spirals.
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Table L·12
Guidelines for Compacted, Expanded Base Piles
Type of
Pile
ITypical I
i
i
Load
kN
!
Structural
Considerations
Installation
Considerations
I
Notes
i
350 to
600
450 to
1350
Concrete quality highly
dependent on technique
Cannot be inspected.
Contamination of
concrete. 'Necking' of
shafts. Possible damage
by adjacent piles.
Allowable load frequently
determined on the basis of energy
required to expel measured
volumes of concrete at base.
Highly dependent on judgement and
experience. Possible heave of all
piles must be continuously
monitored.
(b) Steel
300 to
pipe sl1aft, 500
concrete
filled
450 to
1 550
Where the pipe wall
thickness < 5 mm, the
structural contribution
of the pipe should be
disregarded
Less subject to
damage than (a)
above. Shaft can be
inspected prior to
filling
See (a) above
(a) Rammed
shaft
Column 1
(e)
(f)
Normal
Size
Range
mm
2
3
4
The possibility of misplacing the reinforcing
bars should be allowed for in the design, and
reasonable tolerances established for field performance: e.g., ± 75 mm of correct bar location
in plan, ± 150 mm of correct bar location in elevation.
Generally, longitudinal steel should be uniformly distributed around the cross-section, as
an assembly may become twisted during placement.
Location and alignment
95. The exact location of each deep foundation
unit should be staked in advance and checked
immediately prior to installation of each unit. After
completion of the installation the location of each
unit should be checked against design location and
permissible deviation as indicated on the design
documents.
96. As required in NBC Article 4.2.7.5., permissible
deviations from the design location shall be determined by design analysis. In practice, piles and
shafts can usually be positioned within a tolerance of
5
6
80 mm; for practical reasons smaller tolerances
should not be specified.
97. As required in NBC Article 4.2.7.6., where a
deep foundation unit is wrongly located, the condition of the foundation shall be assessed by the person
responsible for the design and the necessary changes
made.
98. During and after installation of any deep
foundation unit, its alignment should be checked
against the design alignment and the permissible
deviation as indicated on the design documents.
99. Current practice is to limit the total deviation
from design alignment to a percentage of the final
length of the deep foundation unit; 2 per cent is a
common value. However, such practice does not
ensure proper structural behaviour of the unit since it
does not take into account the length over which this
deviation is distributed.
(a) The total deviation from alignment of a deep
foundation unit has little influence on its geotechnical capacity unless it reaches values
greater than 10 per cent of the length of the unit.
251
pays
Table l·13
Guidelines for Drilled Shafts
Normal
Size
Range
Typical
Load
kN
30 to
700mm
diam
shaft
250 to
450
(b) Uncased. 750 to
Reinforced 1 500
or plain
mm
concrete.
diam
Undershaft
reamed
or straight
(c) Cased.
450 to
Permanent 1500
mm
steel pipe
lining
diam
shaft
Type of
Shaft
(a) Uncased
plain
concrete
Column 1
2
Installation
Considerations
Notes
Good concrete quality
not always possible
Where shaft diameter
<700 mm normally
cannot be inspected,
thus permitting only
low allowable loads
< 450 kN.
Not recommended for normal
application where caving can occur
450 to
45000
Generally good
concrete quality
possible with
ｦｾ＠
> 20 MPa < 35 MPa
Can normally be
designed in
accordance with
NBC Subsection
4.3.3. (CAN3A23.3-M84)
Can be inspected.
Where temporary
casing is used to retain
wet, caving soil,
high slump concrete
may be required.
Precautions should be
taken to prevent
contamination of concrete
Usually under-reamed to provide
belled base. Bell sides typically at
2(V) to 1(H). Often not underreamed where bearing on sound
rock.
450 to
45000
See (b) above. Must
be checked as
composite unit in
accordance with
NBC Subsections
4.3.3. (CAN3A23.3-M84) and 4.3.4.
Can be inspected
Usually not under-reamed.
Generally socketed where taken to
rock. Design for complete load
transfer through socket. Essential
to seat liner on rock bearing
surface. Drive shoe usually fitted
to pipe liner
Structural
Considerations
4
5
6
Permafrost
(b) Practically all piles, particularly when driven,
are more or less out of design alignment. A
straight pile is a theoretical concept seldom
achieved in practice.
(c) Only the radius of curvature of a deep foundation unit is important for its structural and geotechnical behaviour. The maximum allowable
radius of curvature should be determined by
design whenever such radius is required to be
measured during inspection. A discussion of
allowable bending of piles is given in Reference
(40).
252
100. The lines on Figure L-4 indicate the
approximate southern limit of permafrost and the
boundary between the discontinuous and continuous
permafrost zones in Canada. The distribution of
permafrost varies from continuous in the north to
discontinuous in the south. In the continuous zone
permafrost occurs everywhere under the ground
surface and is generally several decametres thick.
Southward, the continuous zone
way gradually
to the discontinuous zone, where permafrost exists in
combination with some areas of unfrozen material.
The discontinuous zone is one of broad transition
pays
t
between continuous permafrost and ground having no
permafrost. In this zone, permafrost may vary from a
widespread distribution with isolated patches of
unfrozen ground to predominantly thawed material
containing islands of ground that remain frozen. In
the southern area of this discontinuous zone!
permafrost occurs as scattered patches and is only a
few metres thick.
101. The lines on this map must be considered as
the approximate location of broad transition bands
many kilometres wide. Permafrost also exists at high
altitudes in the mountains of Western Canada a great
distance south of the southern limit shown on the
map. Information on the occurrence and distribution
of permafrost in Canada has been compiled by the
Institute for Research in Construction, National
Research Council Canada.(42,43)
References
(1)
(2)
(3)
(4)
(5)
K. Terzaghi and R.B. Peck! Soil Mechanics in
Engineering Practice. J. Wiley & Sons! New
York! 1967.
E. Hoek and J.W. Bray! Rock Slope Engineering. Inst. of Mining and Metallurgy! 1972.
G.F.A. Fletcher! Standard Penetration Test: Its
Uses and Abuses. Journal of SoiL Mech.
Found. Div.! Proc.! Am. Soc. Civ. Eng.! Vol. 9L
SM4! 1965! pp. 67-75.
R.B. Peck! W.E. Hanson and T.H. Thornburn!
Foundation Engineering. J. Wiley & Sons! New
York, 1974.
J.W. Gadsby, Discussion of the !The Correlation of Cone Size in the Dynamic Cone Penetration Test with the Standard Penetration Test.'
Geotechnique, Vol. 20, 1971, pp. 315-319.
Figure L·4 Permafrost region. 1 - Discontinuous zone,
2 - Continuous zone.
253
pays
(6) EA. Tavenas, Difficulties in the Use of Relative
Density as a Soil Parameter. ASTM, STP 523,
1973.
(7) F.A. Tavenas, R.s. Ladd and P. LaRochelle, The
Accuracy of Relative Density Measurements:
Results of a Comparative Test Programme.
ASTM, STP 523, 1973.
(8) K. Terzaghi, Influence of Geological Factors on
the Engineering Properties of Sediments. Economic Geology, 5th Anniv. Volume, 1955,
pp.557-618.
(9) L. Bjerrum, Engineering Geology of Norwegian
Normally-consolidated Marine Clays as
Related to Settlements of Buildings, Seventh
Rankine Lecture. Geotechnique, Vol. 17, 1967,
pp.83-117.
(10) C.B. Crawford, Interpretation of the Consolidation Test. Journal of Soil Mech. Found. Div.,
Proc., Am. Soc. Civ. Eng., Vol. 90, SM5, 1964,
pp.87-102.
(11) J.H. Schmertmann, Estimating the True Consolidation Behavior of Clay from Laboratory
Test Results. Proc., Am. Soc. Civ. Eng., Vol. 79,
Separate 311, 1963.
(12) I.C. MacFarlane, Ed., Muskeg Engineering
Handbook. Univ. of Toronto Press, Toronto,
1969.
(13) V. Milligan, L.G. Soderman and A. Rutka,
Experience with Canadian Varved Clays.
Journal of Soil Mech. Found. Div., Proc., Am.
Soc. Civ. Eng., Vol. 88, SM4, 1962, pp. 31-67.
(14) C.B. Crawford, Engineering Studies of Leda
Clay. In Soils in Canada. RE Legget, Ed., Roy.
Soc. Can., Spec. Publ. No.3, 1961, pp. 200-217.
(15) C.B. Crawford, Quick Clays of Eastern Canada.
Eng. Geol., VoL 2, No.4, 1968, pp. 239-265.
(16) P. LaRochelle, J.Y. Chagnon and G. Lefebvre,
Regional Geology and Landslides in Marine
Clay Deposits of Eastern Canada. Can. Geotech. J., VoL 7, No.2, 1970, pp. 145-156.
(17) J.J. Hamilton, Shallow Foundations on Swelling
Clays in Western Canada. Proc. Intern. Res.
Eng. Conf. Expansive Clay Soils, Texas A&M
Univ., Vol. 2, 1965, pp. 183-207.
(18) R.M. Hardy, Construction Problems in Silty
Soils. Eng. Journal, VoL 33, No.9, 1950,
pp.775-782.
254
(19) R.M. Quigley and RW. Vogan, Black Shale
Heaving at Ottawa, Canada. Can. Geotech. L
Vol. 7, No.2, 1970, pp. 106-112.
(20) R.M. Hardy, Engineering Problems Involving
Preconsolidated Clay Shales. Trans. Eng. Inst.
Can., VoL 1, 1957, pp. 5-14.
(21) R.J.E. Brown, Permafrost in Canada. Univ. of
Toronto Press, Toronto, 1970.
(22) EJ. Sanger, Foundation of Structures in Cold
Regions. Cold Reg. Res. Eng. Lab., Cold Reg.
Sci. Eng. Monogr., VoL 111-C4, 1969.
(23) Normal Freezing and Thawing Days for
Canada 1931-1960. Atmospheric Environmental Service, 4905 Dufferin Street,
Downsview, Ontario M3H 5T4.
(24) U.s. Army Corps of Engineers. Report on Frost
Investigations, 1944-1945. Corps Engrs., New
England Division, Boston, 1947.
(25) G.H. Argue, Frost and Thaw Penetration of
Soils at Canadian Airports. Can. Dept. Trans.,
Air Services, Constr. Eng., Arch. Branch, Rep.
CED-6-163,1968.
(26) W.G. Brown, Difficulties Associated with
Predicting Depth of Freeze or Thaw. Can.
Geotech. J., Vol. t pp. 215-226, 1964. (Also
NRC 8276, Division of Building Research,
National Research Council Canada, Ottawa.)
(27) L. Robinsky and K.E. Bespflug, Design of Insulated Foundations. Journal of Soil Mech.
Found. Div., Proc., Am. Soc. Civ. Eng., Vol. 99,
SM9, 1973, pp. 649-667.
(28) D.E Coates, Rock Mechanics Principles. Mines
Branch Monograph 874, Queen's Printer,
Ottawa, 1967, p. 358.
(29) EA. Tavenas, Controle du roc de fondations de
pieux fores a haute capacite. Can. Geotech. J.,
Vol. 8, 1971, pp. 400-416.
(30) G.G. Meyerhof, Penetration Tests on Bearing
Capacity of Cohesionless Soils. Journal of Soil
Mech. Found. Div., Proc., Am. Soc. Civ. Eng.,
VoL 82, SM1, Paper No. 866, 1956.
(31) V.G. Berezantsev, V.s. Kristoforov and V.N.
Golubkov, Load Bearing Capacity and Deformation of Pile Foundations. Proc. Intern. Conf.
Soil Mech. Found. Eng., Paris, Vol. 2, 1961, pp.
11-15.
I
!
,
I
pays
(32)
(33)
(34)
(35)
(36)
(37)
(38)
(39)
(40)
(41)
(42)
(43)
AS. Vesic, Tests on Instrumented Piles,
Ogeechee River Site. Journal of Soil Mech.
Found. Div., Proc., Am. Soc. Civ. Eng., Vol. 96,
SM2, 1970, pp. 561-584.
E.E. De Beer, The Scale Effect in the Transposition of the Results of Deep Sounding Tests on
the Ultimate Bearing Capacity of Piles and
Caisson Foundations. Geotechnique, Vol. 13,
1963, pp. 39-75.
N.C. Yang, Relaxation of Piles in Sand and
Inorganic Silt. Journal of Soil Mech. Found.
Div., Proc., Am. Soc. Civ. Eng., Vol. 96, SM2,
1970, pp. 395-410.
M.J. Tomlinson, The Adhesion of Piles Driven
in Clay Soils. Proc. Intern. Soc. Soil Mech.
Found. Eng., London, Vol. 2, 1957, pp. 66-7l.
P. Eide, J.N. Hutchinson and A. Landva, Short
and Long Term Loading of a Friction Pile in
Clay. Proc. Intern. Conf. Soil Mech. Found.
Eng., Paris, Vol. 2, 1961, pp. 45-53.
M.J. Tomlinson, Foundation Design and Construction. John Wiley & Sons, New York, 1963.
J.D. Burland, EG. Butler and P. Dunican, The
Behavior and Design of Large Diameter Bored
Piles in Stiff Clay. Proc. Symp. Large Bored
Piles, Inst. Civil Eng., London, 1966, pp. 51-7l.
G.A. Leonards, Summary and Review of Part II
of the Symposium on Pile Foundations. Hwy.
Res. Record No. 333, Highway Research Board,
Washington, 1970, pp.55-59.
ACI Committee 543. Recommendations for
Design, Manufacture and Installation of
Concrete Piles. ACI 70-50, ACI Manual of
Concrete Practice, Part 3, Detroit, 1974.
B.H. Fellenius, Bending of Piles Determined by
Inclinometer Measurements. Can. Geotech. J.,
Vol. 9, 1972, pp. 25-32.
Permafrost Map of Canada (a joint production
of the Geological Survey of Canada and DBR/
NRC). August 1967. NRC 9769.
R.J.E. Brown, Permafrost Map of Canada.
Canadian Geographical Journal, February 1968,
pp.56-63. NRC 10326.
255
pays
Commentary M
Structural Integrity of
Firewalls
1. Sentence 3.1.10.1.(1) of the National Building
Code requires that, where framing members are
connected to or supported on a firewall and such
members have fire-resistance ratings less than that
required for the firewall, the connections and supports for such members must be desi9ned S? ｴｨ｡ｾ＠
the
collapse of the framing members dunng a fIfe wIll
not cause collapse of the firewalL Sentence
4.1.10.3.(1) requires that the firewall be designed to
resist a factored lateral load of 0.5 kPa under fire
conditions.
2. These requirements, along with others in
Subsection 3.1.10., form part of a general requirement
that the fire not spread between compartments
separated by a firewall within the ｲ･ｱｾｩ､Ｎ＠
fireresistance rating for the wall (4 h for hIgh fIre hazard
occupancies and 2 h for other occupancies). To
achieve this the wall must not be damaged to the
extent that it allows fire spread during this time.
3. In order to meet the requirement for structural
integrity of firewalls the following loading conditions
apply.
Lateral Loads on Firewalls
4. To prevent collapse of the firewall during the
fire from explosion of unburned gases, glancing
blows from falling debris, force and thermal shock of
fire-hose stream and wind pressure, Sentence
4.1.10.3.(1) requires that the firewall be designed for a
factored lateral load of 0.5 kPa. If the structure
exposed to the fire has less fire resistance than .
required for the firewall, it is assumed to have faIled
and therefore to provide no lateral support to the
firewalL
5. Sentence 4.1.10.3.(1) also requires that the
firewall be designed for the normal structural requirements for interior walls for wind and earthquake, including that for pounding damage.
6. The building structure, including the firewall,
should also be designed to provide structural
256
integrity in accordance with the recommendations of
Commentary C Structural Integrity.
Thermal Effects
7. Thermal expansion of the structure exposed to a
fire must not cause damage to the firewall which
would allow premature fire spread through the walL
8. To assess the potential for such damage, thermal expansion of the structure should be estimated
on the basis of a SOO°C temperature increase in
combination with the thermal coefficients given in
Table 0-1 of Commentary D. The expansion of the
structure toward the firewall can be assumed to
begin at a vertical plane in the fire compartment 20 m
from the firewall or half the width of the fire compartment, whichever is less.
9. In assessing thermal effects, attention should be
given to the effect on the stability of the firewall from
distortion due to temperature differential through the
wall.
10. If thermal movements are sufficient to damage
the firewall, either adequate clearances should be
provided or the firewall and structure on both sides
should be detailed to prevent wall damage.
Design Approaches
11. Design approaches to satisfy the general
requirements for structural integrity of firewalls
include the following.
Double Firewall
(3.1.10.1.(2))
Here the structure on each side is tied to a separate
wall in such a way that, when the structure exposed
to fire fails, only one wall collapses without damaging the remaining walL A schematic example is
shown in Figure M-1. Each wall should have at least
half the total required fire-resistance rating. The
separation between the walls must satisfy the above
requirements for thermal expansion and earthquake.
Cantilever Firewall
Here the structure on either side is not connected
to the wall, so that collapse of the structure exposed
to the fire does not collapse the fire wall. A schematic example is shown in Figure M-2. Reinforcement of the cantilever wall and foundations for
pays
beam or joist
beam or joist
t
--beam or truss
beam or truss
column
column
ｾＫＭ＠
v...."q-f----+I---
firewall
(1)
firewall (1)
separation (2)
ａｾＷＧＱＭｴｈ
separation (2)
Figure M·1 Schematic example of double firewall
Notes to Figure M·1:
(1)
Each firewall must be tied to the adjacent structure in
accordance with Paragraph 11 and reinforced in accordance
with Paragraphs 4 and 5.
(2)
Firewalls must be separated in accordance with Paragraphs
5 and 10.
Figure M·2 Schematic example of cantilever firewall
Notes to Figure M·2:
(1)
Firewall is not tied to the structure and is designed as a
cantilever from the foundation with reinforcement and
pilasters in accordance with Paragraphs 4, 5, 10 and 11.
(2)
Separation may be required in accordance with Paragraphs 5
and 10.
overturning will generally be required to resist the
lateral loads specified in Sentence 4.1.10.3.(1). Pilasters will frequently be needed to provide the requisite
lateral load capacity.
non-fire side does not. This approach has traditionally been used in timber construction, where timber
beams or joists bear without anchors into pockets of
firewalls and can twist free when they collapse.(1)
Figure M-4 shows a more recent technique for block
wall construction. If this technique is used, care must
be taken to provide adequate anchorage for wind
uplift and earthquake.
Tied Firewall
Here the structure to each side of the wall provides
lateral support to the wall and is tied together in such
a way that lateral forces resulting from collapse of the
structure exposed to the fire are resisted by the
structural framework on the other side. Lateral
forces are recommended in Paragraphs 12 and 13.
Suitable provisions must be made to transmit these
forces to members on opposite sides of the firewall.
A schematic example is shown in Figure M-3.
Weak-link Connections
Here structural components are supported by the
fire wall in such a way that the failing structure
collapses without causing the firewall to be severely
damaged. As with a tied firewall, the structure may
also provide lateral support to the wall. If a weak
link is provided on each side of the firewall, the link
on the fire side must break away while the link on the
Tied Firewalls: Horizontal Forces
from Collapsing Structure
12. Where a structure of fire resistance less than
that required for the firewall is tied through the wall
to the structure on the other side of the wall, the
supporting structure and tie should be designed for a
factored horizontal force equal to wBL2/8S, where w
is the dead weight plus 25 per cent of the specified
snow load, B is the distance between ties, L is the
span of the collapsing structure between columns
perpendicular to the wall and S is its sag, assumed to
be 0.07L for steel open-web beams and O.09L for steel
solid-web beams. The supporting structure should
be capable of resisting the recommended forces for
257
pays
structural
､ｩ｡ｐｨｲｾ＠
/
beam or
truss
ties (2)
ＫＭｈｾ＠
firewall
(3)
Figure M·3 Schematic example of tied firewall
Notes to Figure M-3:
(1)
Structural diaphragm resistance may be required in accordance with Paragraphs 11, 12 and 13.
(2)
Ties must be located and detailed in accordance with
Paragraphs 11, 12 and 13.
(3)
Firewall must be reinforced and detailed in accordance with
Paragraphs 4, 5 and 10.
Figure M·4 Example of a weak-link connection used in wood
frame construction
Notes to Figure M·4:
(1)
Blocking connection to woodframe must be detailed to act as
a weak link in accordance with Paragraph 11.
(2)
Firewall must be reinforced and detailed in accordance with
Paragraphs 4, 5, 10 and 11.
Plan
ties within a 10m length of firewall; the other ties are
assumed to carry no force (see Figure M-S). The
factored resistance of the tie should include a reduction factor of 0.5 to take account of reduced yield
strength at high temperature.
..,.....--
13. Alternatively, if the firewall is located so that
area of
equal
heat
intensity
the roof structure has the same resistance to horizontal forces on either side of the firewall (e.g., the
firewall is located mid-way between end walls or
expansion joints of a structurally symmetric building), only the tie need be designed for the factored
horizontal force wBL2/8S.
Reference
(1)
258
Canadian Wood Council. Fire Separations and
Firewalls - Commentary on NBCC 1990, Subsections 3.1.8., 3.1.9. and 3.1.10., CWC Datafile
FP-S, Ottawa, 1990.
---
"-
..
..
J
"-I-
..,/-
..,.....
Section
supporting
structure
Figure M·5
Sketch to show principles of Paragraph 12
pays
Appendix A to Chapter 4
List of Referenced Standards
r
Issuing
Agency
Standard
Number
ASTM
Title of Standard
Supplement Reference
01143-81 (1987)
Piles Under Static Axial
Compressive Load
Commentary L, Table L-1 0
ACI
543R-1980
Commentary L, Table L-11
CSA
CAN/CSA-A23.1-M90
CSA
CAN3-A23.3-M84
Recommendations for Design,
Manufacture and Installation
of Concrete Piles
Concrete Materials and Methods
of Concrete Construction
Design of Concrete
Structures for Buildings
CSA
CSA
CAN/CSA-080-M89
CAN3-086-M84
CSA
CAN/CSA-086.1-M89
CSA
CAN/CSA-S16.1-M89
CSA
CAN/CSA-S 136-M89
CSA
W59-M1989
Wood Preservation
Engineering Design in Wood
(Working Stress Design)
Engineering Design in Wood
(Limit States Design)
Steel Structures for Buildings
(Limit States Design)
Cold Formed Steel
Structural Members
Welded Steel Construction
(Metal Arc Welding)
Commentary L, Para 89
Commentary L, Para 92
Commentary A, Para 2
Commentary A, Table A-1
Commentary 0, Table 0-1
Commentary J, Para 82
Commentary L, Para 52
Commentary L, Para 94
Commentary L, Table L-13
Commentary L, Table L-11
Commentary A, Table A-1
Commentary A, Table A-1
Commentary A, Table A-1
Commentary 0, Table 0-1
Commentary L, Para 94
i
Column 1
2
3
4
259