ICS 91.010.30; 91.080.01
ISBN 0-626-09815-7
SABS 0160-1989
(As amended 1990, 1991 and 1993)
SOUTH AFRICAN STANDARD
Code of practice for
The general procedures and loadings
to be adopted in the design of buildings
Reprint 1994
First Revision
Published by
THE COUNCIL OF THE SOUTH AFRICAN BUREAU OF STANDARDS
Gr18
SABS 0160-1989
Amdt No.
Date
Text affected
I
I
I
I
SABS 0160-1989
ICS 91.010.30; 91.080.01
(As amended 1990,1991 and 1993)
SOUTH AFRICAN BUREAU OF STANDARDS
CODE OF PRACTICE
for
THE GENERAL PROCEDURES AND LOADINGS TO BE ADOPTED
IN THE DESIGN OF BUILDINGS
Obtainable from the
South African Bureau of Standards
Private Bag X191
Pretoria
Republic of South Africa
0001
Telephone
Fax
E-mail
Website
: (012) 428-791 1
(012) 344-1568
: sales@sabs.co.za
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COPYRIGHT RESERVED
Printed in the Republic of South Africa by the
South African Bureau of Standards
SABS 0160-1989
2
(As amended 1991 and 1993)
NOTICE
This code of practice was approved by the Council of the South African Bureau of Standards on
7 November 1989.
In terms of the regulations promulgated under the Standards Act, 1982 (Act 30 of 1982), it is a
punishable offence for any person to falsely claim compliance with the provisions of a code of practice
published by the South African Bureau of Standards.
Authorities who wish to incorporate any part of this code of practice into any legislation in the manner
intended by section 33 of the Act should consult the South African Bureau of Standards regarding the
implications.
This code will be revised when necessary in order to keep abreast of progress. Comment will be
welcomed and will be considered when the code is revised.
First Revision November 1989
Incorporating Amendment
No. 1: 15 May 1990
Reprint incorporating Amendment No. 2: 15 November 1991
No. 3: 18 October 1993
This code of practice supersedes SABS 0160-1980
ISBN 0-626-09815-7
3
SABS 0160-1989
(As amended 1990 and 1993)
CONTENTS
........................................................
6
SECTION 1.
SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
SECTION 2 .
DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
SECTION 3
GENERAL DESIGN CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . .
10
3.1
Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
3.1.1
3.1.2
3.1.3
3.1.4
3.1.5
3.1.6
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Design procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Deformations under service loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Integrity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
10
11
14
15
15
COMMITTEE
SECTION 4 .
GENERAL GUIDANCE ON LIMIT-STATES DESIGN LOADS . . . . . . . . . . 17
4.1
4.2
4.3
4.4
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Limit-states Criterion of Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Limit-states Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Uniform Load Factors and Load Combinations . . . . . . . . . . . . . . . . . . . . .
17
17
18
18
4.4.1
4.4.2
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Limit-states design loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18
19
4.5
Design Codes for Individual Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
4.5.1
4.5.2
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23
Assessment of partial material factors for material codes . . . . . . . . . . . . . 23
LOADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
5.1
5.2
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Load Factors and Load Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
24
5.2.1
5.2.2
Limit-states design methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Working stress design methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24
25
5.3
5.4
NominalPermanentLoadsG, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
NominallmposedLoadsQ, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
25
5.4.1
5.4.3
5.4.4
5.4.5
Nominal imposed floor loads in buildings containing occupancies
other than industrial and storage occupancies . . . . . . . . . . . . . . . . . . . . .
Nominal imposed floor loads in buildings containing storage and
industrialoccupancies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Load reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nominal imposed roof loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forces on walls, balustrades and glazing . . . . . . . . . . . . . . . . . . . . . . . . . .
29
30
31
32
5.5
Wind Loads W, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
5.5.1
5.5.2
5.5.3
Determination of nominal wind loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nominalwindspeed V, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nominal wind pressures and forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
34
36
41
SECTION 5 .
5.4.2
Amdt 3.
Oct . 1993
25
Amdt 3.
993
SABS 0160-1989
Blank
4
5
SABS 0160-1989
(As amended 1990)
CONTENTS (continued)
5.5.4
5.5.5
5.5.6
Pressure and force coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dynamiceffects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Simplified wind load design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
64
66
5.6
EarthquakeLoads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67
5.6.1
5.6.2
5.6.3
5.6.4
5.6.5
5.6.6
5.6.7
Seismic hazard zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Design considerationsfor multistorey buildings in Zone I and Zone II . . . .
Planning considerations for low-rise housing in Zone II . . . . . . . . . . . . . . .
Design load effect and load combinations . . . . . . . . . . . . . . . . . . . . . . . . .
Seismic base shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Distribution of seismic forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Structural component load effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
67
70
71
72
72
76
77
5.7
Loads due to Overhead Travelling Cranes . . . . . . . . . . . . . . . . . . . . . . . . .
78
5.7.1
5.7.2
5.7.3
5.7.4
5.7.5
5.7.6
5.7.7
5.7.8
5.7.9
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Classification of travelling cranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vertical wheel loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Horizontal transverse forces. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Horizontal longitudinal force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Forcesonendstops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Position of crane and crab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
More than one crane in a building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Combination of crane lateral forces and wind load . . . . . . . . . . . . . . . . . . .
78
78
79
80
82
82
82
82
82
5.8
Otherloads
.................................................
82
5.8.1
5.8.2
5.8.3
5.8.4
5.8.5
Provision for impact and vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lifting and handling equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lateral and uplift forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inertia sway forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ceilings, skylights and similar structures . . . . . . . . . . . . . . . . . . . . . . . . . .
82
83
83
83
83
IN-SITU LOAD TESTING OF BUILDINGS AND BUILDING
ELEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
6.1
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
6.1 .1
6.1.2
Types of full scale load tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
83
84
6.2
6.3
Testing Authority . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Testprocedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
84
84
6.3.1
6.3.2
6.3.3
Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conducting of tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Test precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
84
85
85
APPENDIX A .
APPLICABLE PUBLICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
88
APPENDIX B.
NOMINAL UNIT MASSES CIF MATERIALS . . . . . . . . . . . . . . . . . . . . . . . .
90
APPENDIX C.
NOMINAL IMPOSED LOADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
95
APPENDIX D.
WIND FORCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
97
APPENDIX E.
DEFORMATION OF BUILDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
105
APPENDIX F.
RAINFALL INTENSITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
119
SECTION 6.
SABS 0160-1989
6
COMMITTEE
South African Bureau of Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bruinette, Kruger, Stoffberg Incorporated
...........................
Concrete Masonry Association . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CSlR
Division of Building Technology
..................................
RH Watkins
(Chairman)
I Jablonski
(Standards Writer)
A van Wyk
(Committee Clerk)
HJ Maoc
JW Lane
JAP Laurie
RV Milford
Division of Processing and Chemical Manufacturing Technology . . . . . . . . MR Newham
South African Transport Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
J Geldenhuys
Steel and Engineering Industries' Federation of South Africa . . . . . . . . . . . .
FH Pienaar
The South African Association of Consulting Engineers . . . . . . . . . . . . . . . .
DJW Wium
University of Pretoria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BWJ van Rensburg
University of the Witwatersrand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
AR Kemp
A Goldstein
7
SABS 0160-1989
SOUTH AFRICAN BUREAU OF STANDARDS
CODE OF PRACTICE
for
THE GENERAL PROCEDURES AND LOADINGS
TO BE ADOPTED IN THE DESIGN OF BUILDINGS
1.
SCOPE
1.I
This code of practice details the general structural design procedures and the minimum
design loads to be adopted in the design of buildings or their structural members.
1.2
This code of practice does not cover the following:
a) Detailed design appropriate to particular construction materials or methods;
b) loads on bridges;
c) loads on earth-retainingstructures and on structures subject to internal pressure from
the contents (e.g. bunkers, silos, water tanks, etc.); and
d) dynamic loadings due to plant and machinery (other than loadings covered in 5.4.2.3,
5.7, 5.8.1 and 5.8.2).
1.3
Loads incidental to construction c:annot, because of the wide variety and nature of the
combinations, be specified. It is necessary, however, that the designer give consideration to the effects of such loads on a partly completed structure. (See also 5.1.2(b).)
NOTE
a) The standards referred to in the code are listed in Appendix A-1 , and references that may be consulted
for additional information are listed in Appendix A-2.
b) Nominal unit masses of materials that may be used in the calculation of loadings are given in
Appendix B.
c) The assessment of floor loads in factories and warehouses is covered in Appendix C .
d) Further information on wind forces is given in Appendix D.
e) Guidance on acceptable limits for deformations of various types of buildings is given in Appendix E.
f) Guidance on the design of rainwater disposal from roofs is given in Appendix F.
2.
DEFINITIONS
NOTE: Where it is desired to use t e r m in addition to the terms listed below, these terms should be
selected from IS0 8930.
2.1
For the purposes of this code of practice the following definitions shall apply:
Act. The National Building Regulations and Building Standards Act, 1977 (Act 103 of
1977).
Action. Any cause (load or imposed deformation) leading to internal forces in, or
deformation of, the members of a structure, or the structure as a whole. It may be
a) a set of concentrated or distrihuted forces acting on the structure (direct action), or
b) imposed or constrained deforrnations within the structure (indirect action). Symbols
such as a, a, E, etc., must be chosen to designate each particular indirect action.
NOTE: The term "load" may be used with essentially the same meaning as "action".
Combination of actions. A set of values for the actions occurring in a structure, that is
used for the verification of the structural reliability of a structure for a limit state under the
simultaneous influence of differerit actions.
Free action. Action which may have any distribution in space over the structure, within
certain limits, e.g. action of vehicles on a bridge.
Permanent action. Action which is likely to act throughout a given design situation
and for which the variation in magnitude with time is negligible in relation to the mean
value, or for which the variation is always in the same direction until the action attains a
certain limit value, e.g. self-weight, prestressing force.
SABS 0160-1989
8
Sustained action/Transient action. Terms used for a qualitative classification of actions,
e.g. in a floor loading, the weight of the furniture represents the "sustained" action, and
the weight of persons represents the "transient" action.
Building. As defined in the Act.
Code of practice. As defined in the Act.
Deflection. Movement of a defined point in a defined direction.
Medial deflection (Fig. 1). Deflection of the middle of a member relative and normal to
the line joining its ends.
Terminal deflection (Fig. 2). Deflection of the end of a member relative and normal to
the line through the opposite end parallel to its undeflected position.
Desiqner. In relation to the erection of a building or of part of a building, a competent
person appointed by the owner to be responsible for the design of such building or part.
Deviation. The distance of a defined point from a defined datum.
Medial deviation (Fig. 1). Deviation of the middle of a member from the straight line or
plane joining its ends.
Terminal deviation (Fig. 2). Deviation of the end of a member from the straight line or
plane, horizontal or vertical (as relevant) through the opposite end.
Durabilitv. Ability of the structure and its members to maintain adequate performance in
time.
Dwellincl house. A building, together with any outbuildings appurtenant thereto, situated
upon its own site and designed for occupation as a separate dwelling for one or more
persons forming a household.
Dwellins unit. A dwelling other than a dwelling house comprising one or more rooms
which have living, sleeping, eating, cooking and sanitary facilities for one or more
persons forming a household.
Ground movement. Disturbance of foundations by influences not dependent on the loads
applied by the building.
Limit states. States beyond which the structure no longer satisfies the design
(performance) requirements.
Serviceabilitv limit states. Limit states related to normal use (often related to function).
Ultimate limit state. Limit state corresponding to the maximum load-carrying capacity of
a structure or of a part of the structure.
Load (see also Action)
Desian load. Design value of load.
Imposed load (The term Preferred to "live load"). Load due to intended occupancy
(includes loads due to movable partitions and loads due to cranes), snow, ice and rain,
earth and hydrostatic pressures, and horizontal components of static and inertia forces.
Nominal load. Nominal value of load.
Point-in-time load. The most-likely load which is on the structure at any instant in time
(not the lifetime maximum value).
Self-weiqht (The term preferred to "dead load"). Load consists of the weight of all the
members of the structure itself, plus the weight of all finishes, including permanent
partitions, which are to be supported permanently by any member of the structure.
Load arranqement. Arrangement of loads introduced into a calculation to allow for the
variation in space of a free action, e.g. arrangement of traffic loads on a bridge.
Load case. A load case is determined by fixing the arrangement of each of the free
actions.
Local authoritv. As defined in the Act.
National Buildinq Reaulations. As defined in the Act.
OccuDancv. The use or purpose to which a building or site is normally put or intended to
be put. (See the National Building Regulations for clarification of the various types of
occupancies.)
Owner. As defined in the Act.
Partition. An internal vertical structure that is employed solely for the purpose of
subdividing any storey of a building into sections, and that supports no load other than
its own weight.
SABS 0160-1989
9
Undef lected
A
Deflected
SABS 0160
Org.11902-EC/00-07
i
a and b a r e medial deviations b e f o r e and a f t e r deflection
a
+
b
is m e d i a l deflection
Fig. 1 - Medial Deflection and Deviation
Vertical line representing t h e
i n t e n d e d p o s i t i o n o f t h e member
(column)
a = T e r m i n a l d e v i a t i o n in n o - l o a d
condition
b = T e r m i n a l d e v i a t i o n in l o a d e d
condition
c = Terminal d e f l e c t i o n o r
movement o f t h e member,
c a u s e d b y the l o a d
\
i
'1/
F r e e - s t a n d i n g (no l o a d ) p o s i t i o n
o f the member
New p o s i t i o n o f the member
under l o a d
I
Fig. 2 - Terminal Deflection and Deviation
SABS 0160-1989
10
Serviceability. Ability of the structure and structural elements to perform adequately in
normal use (serviceability limit-states related).
Settlement
Differential settlement. Relative displacement of different parts of foundations under the
action of loads applied by the building.
The effective span of horizontal or inclined members, assuming conditions of
simple support. (For cantilevers - the overhang. For two-way spanning slabs - the shorter
span.)
Standard specification. As defined in the Act.
Storev heiaht. The vertical distance between the points of support of horizontal
supporting members at successive floor levels.
Structural safety. The capacity of a structure to resist all the actions, and also certain
specified accidental phenomena, which it will have to withstand during construction and
anticipated use (ultimate limit-state related).
Value (of a Darameter)
Characteristic value. Value fixed on statistical bases to correspond to a prescribed
probability of not being exceeded on the unfavourable side during the lifetime of the
structure. (See also Nominal value.)
Combination values. Values associated with the use of combinations of actions to take
account of a reduced probability of simultaneous occurrence of the most unfavourable
values of several independent actions. They may be expressed as a certain part of the
nominal value by using a factor y,, I 1.
Desian values. Values obtained by application of partial safety factors to the relevant
nominal values.
Partial safetv factor. This term describes all the y factors, which are principally
a)
?,factors (applicable to actions), the value of which reflects the uncertainties of
the actions;
b) the ym factors (applicable to materials), the value of which reflects the uncertainties
of the material properties.
Nominal value. The principal representative value of a parameter (either an action, or
a property of a member or of a material), fixed on non-statistical bases, for example on
experience acquired or on physical constraints.
m.
3.
GENERAL DESIGN CONSIDERATIONS
3.1
DESIGN REQUIREMENTS
3.1.1
General. Ensure that any building or any part of a building is designed to possess
sufficient structural capacity to resist safely and effectively all loads and influences that
may reasonably be expected to act upon it, having regard to the expected service life of
such building.
3.1.2
Desian Procedure. In order that the design of a building or of part of a building may
comply with the provisions of the National Building Regulations’), ensure that
a) the procedures adopted in such design are in conformity with this code and with any
other code of the South African Bureau of Standards that is relevant to the materials used
in such building or in part of such building; or
b) the design is in accordance with the empirical rules contained in SABS 0400, relevant
to specific elements of a building; or
c) the design is in accordance with one of the following alternative methods:
1) A code of practice other than prescribed above;
2) an analysis based on generally established theory;
3) an evaluation of a full-scale building or a prototype by test loading;
1) Published by Government Notices 1211 of 6 July 1977, R441 of 1 March 1985, 729 of 18 April 1986 and
798 of 25 April 1986.
11
SABS 0160-1989
4) studies of model analogues; or
5) an authoritative document covering in detail the design of a building or a structural
member for a specific purpose or a specific material or both, provided that where a
material is used for which there is no SABS specification, the design is in accordance
with a safe method applicable to such material.
In terms of the National Building Regulations,alternatives (a) and (b) above are deemed
to satisfy the regulations and therefore must in all cases be accepted by the local
authority. A design based on one of the methods given in (c) above may have to be
justified by the designer to prove that it will ensure the level of safety and performance
implicit in the regulations. The deemed-to-satisfy requirements for the use of specific
materials employed in the construction of a building or of part of a building are given in
SABS 0100 for structural concrete
SABS 0137 for glazing
SABS 0161 for foundations
SABS 0162 for structural steel
SABS 0163 for structural timber
SABS 0164 for structural masonry
The empirical rules contained in SABS 0400 relate to
Foundations
Floors
Walls
Roofs
Glazing
3.1.3
(see Part H)
(see Part J)
(see Part K)
(see Part L)
(see Part N)
Deformations under Service Loads. So design structural members that their deformations under expected service loads will be acceptable with regard to
a) the intended use of the building or member;
b) possible damage to non-struct.uralmembers and materials; and
c) possible damage to the building itself, taking account, where significant, of the
additional effects of loads acting on the deformed building or member; and
d) possible damage to the adjacent buildings.
NOTE: Table 1 is a summary of suggested deformation limits and should be read in conjunction with
Appendix E.
TABLE 1 - SUMMARY OF SUGGESTED DEFORMATION LIMITATIONS
(To be read in conjunction with Appendix E)
1
4
5
6
a
7
~~
Actions
Type of
deformation
Particular deformation
Medial deflection of floors
I
Suggested limiting value
Critical elements and criteri:
Stability
Damage at supports
Ceiling damage
Partition damage
Span1300
Span1300
Varies with construction (usually less critical than
partitions)
Span1500 to span1300 (floor beneath partition)
10 mm if Clh < 3,5 (floor below partition)§
10-15 mm if Qlh< 3.5 (floor above partition)§
Stability
Damage at supports
Ceiling damage
Partition damage
Roof covering damage
Span1300
Span1300
Varies with construction
10-15 mm if Qlh < 3,5511
Span1250 to span1125
Terminal deflection of
cantilever floors
Ceiling damage
Partition damage
Varies with construction
Span1500 to span1300 (floor beneath partition)
Terminal deflection of
cantilever roofs
Ceiling damage
Partition damage
Varies with construction
10-15 mm§//
Span1250 to span1125
Medial deflection of roofs
or roof members
Deflection
Terminal deflection of noncantilevered horizontal
members
Terminal deflection of
vertical members
Damage at supports
Span1100
Span1500
Damage at supports
Storey height1100
Storey height1500
Construction deviation*
Diff.
settlements+
-
I displacements involvc
load$
C
C
9
10
iail or
snow
load
Nind
load
---
I
E
I
**EC
** E
**E
"E
**E
**E
C
EC
EC
EC
-
KEY:
Q = length or span of member. h = height of element. C = creep deflection. E = elastic deflection.
Thermal and moisture movements may also be involved according to the construction arrangement and the environment.
'Taking account of any camber provided.
+Under all appropriate actions.
$Includes the self-weight load of the structure, cladding, finishes, partitions and also pre-stress where this contributes to the deformation under consideration
§In this case the floor or roof is considered to be isolated from the partition in question.
/I Deflection at the nodes in the case of a roof truss.
**The creep component need only be included if the imposed loads are long-term actions. Hail and snow are not normally long-term actions in South Africa.
++If acting eccentrically.
E
*'EC
1
TABLE 1 (continued)
1
Type of
deformation
I
4
Particular deformation
Medial deviation of floors
I
Suggested limiting value
Critical elements and criteria
5
Visible length1250, or 30 mm
Span1300
Yes
Medial deviation of roofs
and roof members
Appearance
Visible length/250, or 30 mm
Yes
Terminal deviation of
cantilever floors
Appearance
Use (curvature)
Visible length1250, or 15 mm
Span1125
Use (rotation)
Span1100
Yes
Terminal deviation of
cantilever roofs
Appearance
Visible length1250, or 15 mm
Yes
Terminal deviation of noncantilevered horizontal
members
Use (slope)
SDan1lOO
Terminal deviation of
vertical members
Stability
Appearance
Oscillations of members
Resonance
Use
Oscillations of the building
as a whole
Use
Oscillations
7
0
9
++EC
++EC
**++EC
**++EC
"++E
**++E
Construction deviation"
Appearance
Use (curvature)
Deviation
6
I
I
Yes
Yes
yes
KEY:
P = length or span of member. h = height of element. C = creep deflection. E = elastic deflection.
Thermal and moisture movements may also be involved according to the construction arrangement and the environment.
'Taking account of any camber provided.
+Under all appropriate actions.
$Includes the self-weight load of the structure, cladding, finishes, partitions and also pre-stress where this contributes to the deformation under consideration.
§In this case the floor or roof is considered to be isolated from the partition in question.
I/ Deflection at the nodes in the case of a roof truss.
**The creep component need only be included if the imposed loads are long-term actions. Hail and snow are not normally long-term actions in South Africa.
++If acting eccentrically.
10
SABS 0160-1989
14
Commentary:
The deformation of a building or of any part of a building should not
adversely affect the appearance or proper functioning of the building. The
designer must satisfy himself that the deformations under service conditions
will not be excessive, having regard to the particular characteristics of the
building, including its size, type of cladding, partition construction, finishes
and occupancy, as well as the foundation conditions and environmental
conditions to which it is subject.
This consideration should cover the possible effects of differential axial
deformations of members as a result of temperature, moisture and shortterm or long-term loading effects, as well as effects due to deflection of
members.
Where experience or analysis shows that movement or stress relief joints
are necessary to avoid damage, overstressing or instability of elements of
the building, such joints must be designed and suitably described in the design documents.
Note that the deformation in question in a particular case is that due to the
relevant portion of the loading or environmental effect, e.g. for control of
cracking in partitions, it would be that portion of the elastic and creep deflection of the supporting floor that occurs after construction of the partition
(this will also depend on when the floor props are removed). Note also that
a distinction is made in Table 1 between deflection, which is the movement
of a defined point in a defined direction, and deviation, which is the distance
of a defined point from a defined datum (e.g. out of straightness or out of
plumbness, whether due to deflection or to initial distortion). Deviation limits
are generally related to appearance factors but may in some cases involve
use and stability.
Whilst it is undesirable that the deformations of a building damage adjacent
buildings, or inconvenience their occupants or other members of the public,
such matters are normally the subject of legislation and are not appropriate
to this code. Nevertheless, attention may be drawn to the fact that the provision of movement joints between adjacent buildings and the avoidance of
interference with neighbouring foundations are normal good building practice.
3.1.4
Vibration
a) Give special consideration to floor systems susceptible to vibration, to ensure that
such vibration is acceptable for the intended occupancy of the building.
b) Investigate unusually flexible buildings and, where necessary, check lateral
accelerations of the building to ensure that such accelerations are acceptable for the
intended occupancy of the building.
commentary:
a) In the majority of buildings, the stiffness provided to conform to the
deformation limit state will be such that no further consideration of vibration
is necessary. Where specific consideration of vibration is required by virtue
of known repeated loading, the following should be taken into account (See
also Table 1.):
1) The damping characteristics of the material;
2) the dynamic magnification effects on the structural members; and
3) the sensitivity of human beings to vibration.
15
SABS 0 160-1989
b) Two types of vibration problems require attention in building construction, i.e. continuous vibration and transient vibration. Continuous vibration
results from the periodic forces of machinery or of certain human activities
such as dancing. These vibrations can be considerably amplified by
resonance when the periodic forces are synchronized with a natural
frequency of vibration of a building. Transient vibrations are caused by
footsteps or other impiactsfollowed by decay at a rate which depends on the
available damping.
The undesirable effects of continuous vibrations caused by machines can
be minimized by special design provision, such as location of machinery
away from sensitive occupancies, vibration isolation, or alteration of the
natural frequency of the structure. Human beings can create periodic forces
in the frequency rartge of approximately 1-4 Hz, and floor resonant
frequencies of less than about 5 Hz should be avoided for light residential
floors, schools, auditoria, gymnasia and similar occupancies. For very
repetitive activities such as dancing, some resonance is possible when the
beat is on every second cycle of floor vibration, and it is therefore
recommended that the resonant frequency of such floors be 10 Hz or more,
unless there is a largo amount of damping.
3.1.5
Stability. Ensure that adequate provision is made for the stability of a building as a whole
and for that of its elements against overturning, uplift, sliding, foundation failure and
stress reversal.
This requirement may be deemed to have been met if
a) in analysis according to the (ultimate) lirnit-state method: The sum of the effects of the
destabilizing nominal loads multiplied by the appropriate partial load factors that exceed
unity as specified in 4.4.2, combined with the effects of the stabilizing component of
self-weight load multiplied by the load factor less than or equal to unity as specified in
4.4.2, does not exceed the ultimate resistance of the relevant parts of the structure and
its foundations; or
b) in analysis according to the permissible working stress method: The sum of the effects
of the destabilizing design loads combined with 0,7 times the effects of the stabilizing
component of the self-weight load does not exceed the design resistance of the relevant
parts of the building and its foundations.
Commentary:
The adoption of the passive resistance of the soil as part of the resistance
to sliding should be carefully considered, as full passive resistance generally comes into play only after movement has taken place.
3.1.6
lntearity (See also 4.3)
a) The degree of safety of a structure depends not only on the strength of the
load-bearing members and of the structure as a whole but also on the integrity of the
structure, i.e. its ability to withstand local damage without it causing or initiating
widespread collapse. Adequate structural integrity may be achieved by
1) designing the structure in such a way that, if any single load-bearing member
becomes incapable of carrying load, this will not cause collapse of the whole structure
or any significant part of it within a period of time sufficient to make the necessary repairs
(method of alternative paths of support); or
2) minimizing by design or by protective measures the probability of failure of a
load-bearing member whose failure is likely to result in widespread collapse (method of
local resistance).
SABS 0160-1989
16
b) Design every building to withstand, at any level, a horizontal force acting on the
portion of the building above that level and acting in any plan direction, the magnitude
of the force being at least equal to the greater of
1) the wind load acting above that level; or
2) 1 o/' of the total nominal self-weight load above that level, including that due to
unlocated partitions exerting a force exceeding 3 kN/m of length.
This force may be shared between the elements of the structure, depending on their
stiffness and strength.
c) Traditional structures, particularly building structures, often possess an adequate
degree of structural integrity. When a review of a structure's integrity indicates that the
consequences of failure could be widespread or otherwise very serious or when the
structural integrity of a new or unusual form of construction is being evaluated, specific
provisions for structural integrity as indicated above should be incorporated in the design.
Commentary:
The following is intended to give guidance when progressive collapse is
considered:
a) It is clearly not feasible to design all buildings for absolute safety nor is
it economical to design for abnormal events unless there is a reasonable
chance that they will occur. However, when there is a reasonable chance of
abnormal occurrences, the designer must, in terms of 3.1.6, consider
rational means of limiting the spread of local failure to an extent
disproportionate to the initial cause of local damage.
Some abnormal events that can occur are explosions due to gas, boiler
failures or ignition of industrial liquids, vehicle impact, falling or swinging
objects, adjacent excavation or flooding causing severe local foundation
failure, or very high winds such as cyclones or tornadoes.
Most of the foregoing events would not in general be considered in design,
but events such as fires, earthquakes (in certain areas of South Africa), and
corrosion, which are taken into account in the normal course of design,
should also not cause progressive collapse.
Although a building should have resistance to progressive collapse caused
by "accidental" abnormal events, it is accepted that well-placed explosives
could bring down any such building.
In some traditional construction systems there is inherent structural integrity,
a tying together of elements and an ability to redistribute overloads. This
inherent integrity is frequently overlooked in new systems and, as a
consequence, prefabricated systems in particular are often designed to
resist the primary gravity and lateral forces only. The resistance to
progressive collapse should be fully evaluated for any new system and if
such resistance is not inherent in the system, it should be provided by other
means.
b) There are four general considerations that can be used in designing to
prevent progressive collapse:
1) Reduction of the probability of the occurrence of an abnormal event;
2) design using ductile connection;
3) design to resist abnormal loads;
4) design for alternative load paths in the event of a local failure.
17
SABS 0160-1989
(As amended 1993)
c) It is difficult to apply limits to collapse resulting from an abnormal event;
however, it is suggested that collapse be limited,
1) where progressionis vertical, to the storey where the event occurred and
to the storeys immediately above and below;
2) where the progression is horizontal,
i) to the truss, beam, precast strip floor, or roof panel damaged, and to the
one on either side;
ii) to a single bay of a full bay-sized floor or roof slab except that where the
principal support at one end of a slab is removed, two bay-sized panels may
act together as a catenary.
d) Severe deformation is temporarily acceptable in the vicinity of the local
failure at the ultimate conditions.A load combinationof self-weight load plus
one-third of the total of the specified imposed load plus wind load should be
used in evaluating the ultimate stability and ultimate strength of the
damaged building after the event.
4.
GENERAL GUIDANCE ON LIMIT-STATES DESIGN LOADS
NOTE
a) This section is not to be used unless there is a reference to it in the material code.
b) See NOTE (b) to Section 5.
4.1
GENERAL. This section describes a standardized formulation for preparing limit-states
codes for different structural materials. This is achieved through a two-phase process:
a) Acceptance of a set of partial load factors and a uniform system for defining load
combinations which would be applicable to all structural materials, as described in 4.4.2.
b) Subsequent evaluation of partial material factors, and resistance (or performance)
factors appropriate to each limit state in each material code in order to achieve a
consistent level of reliability, as described in 4.5.
4.2
LIMIT-STATES CRITERION OF FAILURE. The criterion of fitness for purpose is:
Rd = design resistance
Qd = design load or action effect
where
and Rd and Qd are given by
where R( ) = a function defining the resistance of the structure for a particular limit
state
fk
= the characteristic:material strength
ym
= the partial material factor which allows for uncertainty in the material
strength
@Q
= the resistance (or performance) factor which allows for all other
uncertainties in modelling the as-built structure by equation 4(a) for the
limit state under [consideration,and for brittle modes of failure
Amdt 3,
Oct. 1993
Amdt 3,
Oct. 1993
SABS 0160-1989
18
QnI
YI
v/I
4.3
= the effect of the nominal action or load defined in the loading code; the
summation reflects the combination of self-weight, imposed, wind or
other types of load effect appropriate to that limit state
= the partial load factor defined for the type of action or load i which
allows for variability in the action and an average uncertainty over all
materials and limit states in the process of modelling the effect of the
action
= the load combination factor applicable to action or load i which allows
for the probability of simultaneous occurrence of different load types in
a particular load Combination.
LIMIT-STATES APPROACH. Astructure, or part of a structure, is considered unfit for use
or to have failed when it exceeds a particular state, called a limit state, beyond which its
performance or use is impaired. The limit states are classified into the following two
categories:
a) Ultimate limit states are those concerning safety, and correspond to the maximum
load-carrying capacity. They include:
1) Loss of equilibrium of the whole or of a part of the structure considered as a rigid body
(e.g. overturning, uplift);
2) loss of load-bearing capacity of members, due to exceeding material strength,
buckling, fracture, fatigue, fire or deformation;
3) overall instability of the structure;
4) very large deformation, e.g. transformation into a mechanism.
b) Serviceability limit states are those which restrict the normal use and occupancy or
affect durability. They include:
1) Excessive deflection or rotation that affects the use of the structure, the appearance
of structural or non-structural elements or the operation of equipment;
2) excessive local damage (cracking or splitting, spalling, local yielding, slip of
connections) that affects the use, durability or appearance of the structure;
3) excessive vibration that affects the comfort of the occupants or the operation of
equipment.
All relevant limit states should be considered in the design; the usual approach, however,
will be to design on the basis of the expected critical limit state and then to check that the
remaining limit states will not be reached.
4.4
UNIFORM LOAD FACTORS AND LOAD COMBINATIONS
4.4.1
General. It is intended that future issues and revisions of design codes for structural
materials in South Africa will, whereverfeasible, be expressed in a limit-states format and
will conform to a single set of partial load factors and a uniform system for defining load
com binations.
Cornrnentary:
The uniform set of partial load factors and load combination factors defined
in 4.4.2 is based on the assumption that the following two-stage procedure
is a legitimate approach:
a) Identification of partial load factors and load combination factors from
available statistical data on common types of loading that give consistent
combinations of design load effects possessing a maximum probability of
occurrence comparable with existing practice. (The results of this analysis
are defined below.)
SABS 0160-1989
19
(As amended 1991 and 1993)
b) Identification of partial material factors for each structural material and
partial resistance factors for each limit state that, from available statistical
data on resistance of different limit states, give consistent probabilities of
failure, using the loading information obtained from (a) above. (This
assessment will be undertaken by the individual code committees for the
different structural codes.)
This is different from the approach adopted in North America and Australia,
where the assessment of each limit state and load combination is undertaken ab initio, allowing for variability in both load effect and resistance. A
practical problem associated with a full reliability analysis of this type is that
the statistics of both the load effect and the resistance of the member are
required. In South Africa, statistics for member resistance, related to the
relevant materials codes, are largely unavailable at present and it would be
a lengthy process to collect the necessary information.A further problem is
that several of the materials codes are still in the process of preparation and
it is also anticipated that some of the existing codes may undergo major
revisions in the future.
In terms of the above, the partial load factors and load combination factors
defined subsequently were therefore selected in order to achieve a
consistent value of a load index a, calculated as follows:
where
Qd = the design load effect = Z(wiyiQni)
PQ = the curnulative probability of the load exceeding the design
value
The target value of the load index a used in this assessment is 2,O at the
ultimate limit state (equivalent to a 1 % probability of exceeding the design
value in the 50-year life of the structure) and 1,O at the serviceability limit
state (equivalent to a 10 % probability of exceeding the design value). The
actual minimum values of a at the ultimate limit state over a practical range
of load combinations range from 1,6 to 2,0,
owing to a desire to deviate from
existing practice as little as possible.
4.4.2
Limit-states Desian Loads
NOTE: The partial load factors and load combination factors described in this section are to be used only
in cases where the relevant material design code has been drafted or modified to be compatible with these
provisions.
The design load effect Q pertaining to the ultimate and serviceability limit states is
obtained from equation 4(e) or 4(f), as the case may be, by multiplyingthe effects of the
nominal loads by the partial load factors given in Column 2 or 3 of Table 2, as applicable,
and by the relevant load combination factors given in Column 4 of Table 2 or derived
from the recommendationsgiven in Table 3 (depending on the time-dependent nature
of the additional load and its correlation to the dominant load).
SABS 1060-1989
20
(As amended 1991 and 1993)
where
yi
= the partial load factors given in Table 2
D, = the nominal permanent load effect
Q, = the dominant imposed load effect for the load combinations and limit state
under consideration
Qni = additional imposed load effects relevant and significant to the load
combination and limit state under consideration
t,ui
= the load combination factors given in Tables 2 and 3
The design point-in-time value of the load effect Qdpisobtained from equation 4(f) as
follows:
Qdp
= YD Dn +
2 (ViYiQnJ
4(9)
The design point-in-time value obtained from equation 4(g) may be required in the
following design situations:
Amdt 3,
Oct. 1993
-
determination of the sustained load contribution for analysis of time-dependent
behaviour of materials at the serviceability limit state
-
analysis of stability of structures with localized accidental damage at the limit state
of accidental damage
-
analysis of residual strength of structures at the limit state of progressive collapse.
For self-weight D,, imposed floor loads Q, and wind loads W,,the following combinations can be used at the ultimate limit state:
Amdt 3,
Oct. 1993
with the exception that the load factor 0,5 for imposed loads must be replaced by 1,Ofor
garages, filing areas and storage areas and by 0,O for roof loads, and the load factor 1,3
for wind loads must be replaced by 1,5 for chimneys and free-standing towers.
The following combinations can be used at the serviceability limit state:
Amdt 3.
Oct. 1993
171Dn + 1,OQn
l,lD,
+ 0,3Q, + 0,6W,
with the exception that the load factor 0,3 must be replaced by 0,6 for garages, filing
areas and storage areas and by 0,Ofor roof loads.
NOTE: The 0,6 serviceability wind load factor should be used in conjunction with the 50-year mean
return period of wind speed only.
Amdt 2,
Nov. 1991
SABS 0160-1989
21
(As amended 1991 and 1993)
The sustained portion of the loads at the serviceability limit state is obtained from
Amdt 3,
Oct. 1993
1,lQ + 0,3Qn
with the same proviso on the factor 0,3 as above.
The design load effect may be adjusted at the discretion of the designer by multiplying
the design load effect in equation 4(e) and 4(f) by an importancefactor yc to allow for the
consequences of failure. In the case of critical structural members of structures in which
large numbers of the public gather and where there would be "very serious" consequences of a failure, a value of yc in the range 1,1-1,2 should be used. For structures
with a very low degree of hazard to life and "not serious" consequences of failure, a value
of yc of 0,9 would be appropriate.
TABLE 2 - PARTIAL LOAD FACTORS AND LOAD COMBINATION FACTORS
I
4
1
Partial load factor Y;
Type of load
Ultimate limit state
Serviceability limit
state
Load
combination
factor i,ui
Permanent loadinq
a) Maximum self-weight load acting in
isolation (eqn 4(e))
b) Maximum self-weight load acting in
combination with other loads (eqn 4(9)
c)Minimum self-weight load
1,o
1,o
Imposed loading
0
d) Wind load
e) Loads on floor (other than garages,
filing or storage areas)
f) Loads on floor for garages, filing or
storage areas
g) Loads on roof (other than those in (d)
and (h)-(l))
1) Inaccessible roof
2) Accessible roof
h) Earthquakes
i) Loads from fluids
j) Imposed deformations
1) Temperature, settlement, etc.
2) Prestressing
k) Accidental loads
I) Other types of imposed loads not
considered above (e.g. material loads,
cranes) in the absence of more detailed
information
0.3
0,6
1,o
1.o
1.o
See Table 3
1,o
0
See Table 3
1 3 for slender non-redundant structures such as chimneys and free-standing towers that exhibit significant
cross-wind response.
SABS 1060-1989
22
(As amended 1991 and 1993)
It is necessary for the designer to assess the degree of dependence or correlation
between the dominant load and the additional load, and the variation of the additional
load with time. For example, for a single crane where horizontal crane load is the
dominant load and vertical crane load an additional load, a value of cy = 0,75 would
frequently be appropriate. For two cranes working in tandem, cy = 1 would apply. For
cranes in adjacent bays that operate completely independently, cy = 0,5 may be applied
to the additional load from the second crane. Examples of the influence of the time
variation of loads are implied by the values of cy = 1 in Table 2, for imposed loads of a
semi-permanent nature such as storage loads or loads from fluids, where the additional
load is assumed to be uncorrelated to the dominant load. In addition, it is expected that
the designer would not include as additional loads those types of load that, when
factored, contribute in an insignificant manner to the total load.
Amdt 3,
Oct. 1993
TABLE 3 - RECOMMENDED LOAD COMBINATION FACTORS FOR
TYPES OF IMPOSED LOADINGS NOT COVERED BY TABLE 2
I
I
3
Correlation between
dominant imposed
load and additional
imposed load
None
Variation of additional load
with time, i.e. the ratio:
Arbitrarv point-in-time value
Lifetime maximum value
Load combination factor
'+"i
0,s
1,o
Partial
03
Examples of common applications of Tables 2 and 3 are:
Amdt 3,
Oct. 1993
1 3 (PERMANENT)
1,2 (PERMANENT) + 1,6 (FLOOR)
0,9 (PERMANENT) + 1,3 (WIND) + 0,8 (CRANE HORIZONTAL) + 0,8 (CRANE
VERTICAL)
1,2 (PERMANENT) + 1,6 (CRANE VERTICAL) + 0,5 (FLOOR) + 1,2 (CRANE
HORIZONTAL)
Commentary:
No provision has been made for pattern loading of permanent loads. North
American practice is adopted in which this effect is apparently absorbed in
the portion of the partial load factors that allows for modelling uncertainties
and in terms of the definition of permanent loading.
Considering Tables 2 and 3, at the ultimate limit state, the factored values
of the self-weight and dominant load effects reflect the lifetime maximum
load effects, and the factored value of the additional load effect reflects the
instantaneous or arbitrary point-in-time value which is likely to occur
simultaneously with the lifetime maximum of the dominant load.
At the serviceability limit state, the factored value of the self-weight and
dominant load effects and the factored value of the additional load effect
may be compared to the mean point-in-time value of the sustained portion
of the load effect.
SABS 0160-1989
23
It should be emphasized that appropriate statistical information is not
available for types of loading other than self-weight, wind and office floor
loading. Load factors for other types of loading (vehicles, material storage,
retail and residential, crane and temperature) should therefore be based
either on the partial load factors and load combination factors given in
Tables 2 and 3 or, where it is apparent that these are inappropriate, on the
judgement of the designer.
The load factor of 1,3 for wind loads is increased to 1 3 for chimneys and
free-standing towers that exhibit significant cross-wind response, owing to
the greater uncertainty in the structural response. The wind load factor is
also increased to take into account the likelihood that the maximum
cross-wind response due to vortex shedding occurs at a relatively low wind
speed, and not at an extreme wind speed, and therefore has a greater
probability of occurrence.
A specified magnitudeof importancefactory, has a greater influence on the
probability of failure for a limit state with a small coefficient of variation and
is therefore material dependent.
4.5
DESIGN CODES FOR INDIVIDUAL MATERIALS
4.5.1
General. It is intended that codes for each structural material will include appropriate
values for the partial material factors, and resistance (or performance)factors applicable
to the limit states in such codes, in accordance with equation 4(b). Partial factors will be
established on a consistent basis, using a procedure that involves identifying values for
these partial factors that achieve probabilities of failure for different limit states over the
practical range of properties, dimensions and loads which are consistent with existing
practice.
5 for reinforcement and 1,075 for strucPartial material factors of 1,50 for concrete, 1,I
tural steel are likely to be adopted in codes applicable to those materials. In the
assessment of individuallimit states, an appropriate resistance or performancefactor (@@
in equation 4(b)) will be determined allowing for these partial material factors so that at
least the following target values of safety index@are achieved:
Ductile, gradual modes of failure
: J'= 3,O
Brittle, sudden modes of failure
: @=4,0
Connection details between components : @ = 4 3
The safety index@is the inverse of the cumulative normal distribution function @-' of the
probability of failure pfwhich is defined as the probability of the effect of the actions or
loads exceeding the resistance of a particular limit state (equation 4(a)), i.e.
4.5.2
Assessment of Partial Material Factors for Material Codes. It is clearly desirable that
consistent partial material factors be adopted in different structural codes to allow for
uncertainties in material strengths (for example, the factors for composite beams should
correspond to those in the concrete and steel codes). These partial material factors
should correspond to existing practice in SABS codes.
It has been shown that for material strengths and resistances with a coefficient of
variation in the range 0,lO-0,30 (which covers most materials used in construction), a
safety index of@= 3,O (required for ductile failure modes) will be achieved if the partial
material factors and partial resistance factors are selected on the basis of achieving a
1 % resistance fractile (i.e. the resistance of not more than 1 % of members will be
less than the design resistance). This is therefore a suitable definition of a design
strength for ductile members. For members with a coefficient of variation in the range
SABS 1060-1989
24
(As amended 1991 and 1993)
0,lO-0,15 (which is typical of structural steel and reinforced concrete), a safety index
ofJ = 4,O(required for brittle failure modes) will be achieved if the partial resistance
factor forJ = 3,O is reduced by a factor of about 0,7-0,8, whereasp = 4,5 (required
for steel connections) will be achieved if the partial resistance factor forJ = 3,O is
reduced by a factor of about 0,6-0,7.
5.
LOADS
NOTE
a) Since in general practice nominal values of loads are used more often than characteristic values
in 2.1.)
of loads, the term "nominal" will be used in relation to load values. (See definition of
b) Take the nominal values of loads given in this section for use with limit state design methods to
be synonymous with the design or service loads for use with the permissible working stress methods
of design .
5.1
GENERAL
5.1 .I
Ensure that, except as provided for in 5.1.2, the following loads, forces and other
effects are, where relevant, considered in the design of a building and its structural
members and connections:
a) Self-weiuht loads G, as provided for in 5.3.
b) ImDosed loads Q, due to intended occupancy (includes loads due to movable
partitions and loads due to cranes), snow, ice and rain, earth and hydrostatic
pressures, and the horizontal component of static or inertia forces, as provided for
in 5.4.
c) Wind loads W, or earthuuake loads E,, whichever produces the more unfavourable
effect, as provided for in 5.5 and 5.6.
d) Loads due to overhead cranes and other loads applicable to special conditions,
as provided for in 5.7 and 5.8.
e l Deformations due to one or more of the following:
1) Temperature changes, shrinkage, moisture changes;
2) creep in component materials;
3) movement due to differential settlement or heave.
5.1.2
a) Where a building or structural member can be expected to be subjected to loads,
forces or other effects not listed in 5.1 . I , or where the loads or forces listed in 5.1 . I
differ significantlyfrom those given in the relevant tables, ensure that these are taken
into account in the design, using the most appropriate information available.
b) Precautions must be taken in the design to ensure that, during all stages of
construction, the building or any part of the building is not damaged, distorted or
made unserviceable owing to the application of excess loads in the construction
process.
c) If it can be shown by the application of engineering principles, or if it is known from
experience, that disregard of some or all of the effects resulting in deformations (as
listed in 5.1 . I (e)) will not affect the safety and serviceability of the building or of any
part of the building, calculation for these specific effects may be omitted.
5.2
LOAD FACTORS AND LOAD COMBINATIONS
5.2.1
Limit-states Desian Methods. In limit-states design procedures, use the most adverse
combinations of the various types of loads as specified in the appropriate limit-states
material design codes of practice, and factored according to the partial load factors
specified in such codes of practice for each load combination and limit state under
consideration.
25
SABS 0160-1989
(As amended 1993)
5.2.2
Workina Stress Desian Methods.
a) Where the design is to be executed by the permissible working stress method, use
the following loads and load combinations:
Self-weight load G;,
self-weight load plus imposed load (G, + Q,J;
self-weight load plus wind load or earthquake load (G, + W,) or (G, + En);
self-weight load plus imposed load plus wind load or earthquake load
(Gn+ Qn + W,J or (Gn+ Qn + E,);
5) any one of (1)-(4) above, together with those dimensional change effects not
exempted in terms of 5.1.2(c).
1)
2)
3)
4)
b) Where the effects of self-weight loads counteract those of other loads or load
combinations in any of (a) above, the value of the self-weight load to be used in this
case is the nominal self-weight load multiplied by a reduction factor of 0,7
(see 3.1.5(b)).
5.3
NOMINAL PERMANENT LOADS G,
5.3.1
The nominal permanent load for a building or for a structural member of the building
consists of
a) the weight of the building or rnember itself, plus
b) the weight of all finishes and materials of construction which are incorporated into
the building or member and which are to be supported permanently by the building
or member, including permanent partitions, but excluding movable or unlocated
partitions (see 5.4.1.3), domestic appliances and sanitary appliances, which are
treated as imposed loads.
Commentary:
Designers and owners are advised to give special thought to the likely
types and positions of partitions, since insufficient provision for
partitioning may reduce the future utility of the building.
5.3.2
Calculate nominal permanent loads from the actual known masses of the materials
to be used. Where there is a reasonable possibility of a significant change in mass
owing to the absorption of moisture by porous materials, make due allowance for
such increase when calculating permanent loads.
Commentary :
Where the unit masses of materials are not known or where
approximations are sufficient for a preliminarydesign, use may be made
of the data given in Appendix B.
5.4
NOMINAL IMPOSED LOADS Q,,
5.4.1
Nominal Imposed Floor Loads in Buildinas Containinq Occupancies other than
Industrial and Storaae Occupancies
5.4.1.1
Occupancies included in Table 4. Where a building or part of a building contains a
class of usage listed in Column 2 of Table 4, for the design of its floors use nominal
imposed loads of at least
a) the appropriate uniformly distributed floor load given in Column 3, such load being
applied over either the entire floor area or such part of the floor area as will produce
the most severe effects on the element under consideration;
Arndt 3,
Oct. 1993
SABS 0160-1989
26
(As amended 1993)
b) the appropriate concentrated load given in Column 4, applied over the plan area
given in Column 5 and placed in the position that produces the most severe effects
on the element under consideration.
NOTE
1) The loads in Columns 3 and 4 should not be considered as acting simultaneously;
2) the loads in Column 3 may be reduced in accordance with 5.4.3.
5.4.1.2
OccuDancv classes not included in Table 4. Where the category of usage of a floor
area is not provided for in Table 4 or where it is desired to determine the intensity of
a nominal imposed floor load (or floor loads) because of special circumstances, such
load(s) may be determined from an analysis of the likely loads and their effects for
the particular occupancy. Generally, the imposed floor loads should be applied as in
5.4.1 .I.
The values so obtained should be in appropriate relationship to those in the
most relevant categories of usage in Table 4.
TABLE 4 - INTENSITY OF NOMINAL IMPOSED FLOOR LOADS FOR OCCUPANCIES OTHER THAN INDUSTRIAL AND STORAGE
Load
category
I
I
1
I
Minimum uniformly
distributed imposed
floor load, kN/m2
Occupancy class of building or floor zone
(description of room or floor use')
All rooms in a dwelling unit and a dwelling house including corridors, stairs and lobbies to a dwelling
house
Bedrooms. wards, dormitories, private bathrooms and toilets in educational buildings, hospitals,
hotels and other institutional occupancies
Access catwalks in buildings
I
I
1.5
0 , l x 0,l
2
Classrooms, lecture theatres
X-ray rooms, operating theatres
2,o
3
Garages and parking areas for vehicles of gross weight less than 25 kN excluding garages where
mechanical parking or stacking devices are employed
2,o
A
Offices for general use*
23
€3
offices with data-processing and similar equipment*
4
5
Cafes, restaurants
Dining rooms, dining halls, lounges, kitchens, communal bathrooms and toilets in educational
buildings, hotels and offices
Entertainment, light industrial and institutional occupancies
15
5,O
10,o
0,75x 0,75
9,o
3,O
ro
-4
3,O
5,O
0,l x 0,l
'For uses not listed in Column 2, refer to 5.4.1.2.
+Offices where small printing presses, collating machines, etc., are installed.
In the case of assembly areas with fixed individual seating, it is implied that
a) the number of occupants is controlled, and
b) the removal of the seating and the use of the space for other purposes is improbable.
$Attention is drawn to the possible need to increase floor ioadings where compacted filing systems are used.
NOTE: Attention is drawn to the fact that it is possible for loading intensities to reach as much as 7 kNlm2 when large numbers of people are forced by panic or other urgencies to crowd together to the point
where free movement is impossible and acute discomfort is experienced.
These extreme loadings would tend to be confined to limited areas in the vicinity of points of congestion such as exit gates, stair landings, subways or foot-bridges at railway stations. The highest prescribed
crowd loading of 5,O kN/mz in the table is based on a more probable level of loading consistent with the philosophy that the code of practice loadings are not the maximum attainable values. It alSO takes
account of the history of satisfactory performance of public assembly buildings that have been designed for this level of loading in many countries. Where public assembly type structures are PartiCUlarlY
sensitive to overloads (such as might be the case with light foot-bridges or temporary grandstands), the designer should consider designing or checking the relevant portions of the structure for an imposed
load of 7 kN/m2.
,cn
2g
:a
$6
Q?
TABLE 4 (continued)
Load
category
Minimum uniformly
distributed imposed
floor load, kN/m2
Occupancy class of building or floor zone
(description of room or floor use*)
Area over which
concentratedload in
Minimum concentrated load
(applied over the area
given in Column 5), kN
6
Assembly halls, theatres, cinemas, sports complexes, grandstands, all with fixed individual seating
4.0
3,O
7
Light laboratories
Sales and display areas in retail shops and departmental stores
Banking halls
4,O
5.0
0
Assembly halls, sports complexes, grandstands, all without fixed individual seating
Stairs, corridors, landings and individual components of grandstands
Public and assembly areas of airports, railway stations, and terminals
Stages to assembly halls, theatres and cinemas
Cantilever balconies accessible to the public
5.0
3,O
Co'umn
is to be
applied, m
0,l x 0 , l
9
10
11
I
Filing and storage areas to offices, institutional occupancies, and hotels*
Shelved areas to libraries
Exhibition halls
Corridors, stairs and lobbies to all buildings other than dwelling houses (where Category 1 applies)
Cantilever balconies, loggias and canopies irrespective of whether they are normally accessible to
the public or not
50
I
5,O
The same as the zone that they serve but not less
than:
The same as the zone that they serve but not less
than:
4,O
3,O
I
29
SABS 0160-1989
(As amended 1993)
5.4.1.3
Partitions. Where provision is to be made for unlocated or movable partitions, allow
for the following nominal imposed floor loads for such partitions, in addition to the
loadings in Table 4:
a) Where the partitions have a weiaht Der unit lenqth not exceedina 3 kN/m and are
SUDDOrted on a floor svstem with adeauate load-distributina DroDerties:An equivalent
uniformly distributed floor load (in kilonewtons per square metre) of 0,5times the
weight per unit length of the partition (in kilonewtons per metre), but with a minimum
of 1 kN/m2.
b) Where the Dartitions have a weiqht Der unit lenqth exceedina 3 kN/m: A series of
line loads, spaced at a maximum of 2,5 m centres, placed in any position and
direction and having a weight per unit length equal to that of the partitions.
Commentary:
For serviceability limit-states analysis, it is often only the permanent or
long duration or regularly acting component of the imposed floor load
that is of consequence, e.g. where creep deflection is a factor. The
proportion of the nominal imposed load which may be considered as
being of long duration varies with the type of usage. As a guide, the
following proportions of the specified nominal distributed imposed loads
may be taken as being of long duration:
Floors in the following:
Residential buildings;
offices ;
wards, corridors ancl theatres in hospitals;
schools;
assembly buildings.
)
)
) 0,3
)
)
Floors used for storage and floors in
laboratories and in storage and
industrial buildings.
)
) 0,6
)
Owners and designers are advised to give special thought to the
possibility of later changes of occupancy involving loading heavier than
was originally contemplated. They should not necessarily in every case
select the lower loading appropriate to the first occupancy. In doing this,
they may considerably restrict the use of the building at a later date, and
thereby reduce its utility. Attention is drawn also to the possibility of
temporary changes in the use of a building, as in the case of a dormitory
being cleared for a dance or other recreational purpose and in the case
of an institutional dining hall being used also as an assembly area.
5.4.2
Nominal Imposed Floor Loads in Buildinas Containina Storage and Industrial
OccuDancies
5.4.2.1
Storaae OccuDancv. Determine the nominal imposed floor loads in a building or in
part of a building, of storage occupancy, taking into consideration the type of stacked
materials and methods of storage. Take into account the greatest volume of materials
(or the greatest number of stacked articles) which can be located on the area of the
floor under normal operational conditions of the warehouse, allowing for the densest
stacking of materials and articles and the possible effect of the increase in density
of some materials when stored for a long time. Allow for the weight of handling
equipment, including the maximum load capable of being lifted. Ensure that the
nominal imposed floor load adopted is at least 5 kN/m2.
SABS 0160-1989
30
(As amended 1993)
5.4.2.2
Industrial OccuDancv. Determine the nominal imposed floor load in a building, or in
part of a building, of industrial occupancy, such as a workshop, taking into
consideration the weight of manufacturing plant, including
a) the weight of the plant,
b) the weight of the heaviest pieces under treatment or the weight of the maximum
volume of the product being processed,
c) the weight of gangways and working platforms,
d) the weight of handling equipment, and
e) loads resulting from necessary maintenance or replacement of stationary plant.
Ensure that the nominal floor load adopted is at least
1) 3 kN/m2 for production rooms such as workshops with lightweight equipment
(benches, machine tools weighing not more than 5 kN each), and
2) 5 kN/m2for production rooms such as workshops in works and factories.
See 5.4.3 for load reduction.
5.4.2.3
Dynamic forces. Make provision, where necessary, for the influence of dynamic
forces arising from operations with dynamically imbalanced equipment, from the
shifting of heavy loads over the floor, or from falling or suddenly displaced goods in
storage.
5.4.3
Load Reduction. The minimum uniformly distributed imposed floor load shown in
Column 3 of Table 4 or derived from 5.4.1.2 may be reduced as follows:
a) Where the tributary area of a floor, used for an assembly of persons or for storage,
manufacturing or garaging, that is supported by a column or bearing wall (the
cumulative area of all floors so supported being taken), or bya single span of a beam
or girder, or by a single panel of a slab (solid or ribbed), or flat-plate, exceeds 80 m2,
the distributed loading may, for the design of the building or of part of the building,
be multiplied by a factor equal to:
0,5
+
4’5, but with a minimum value of 0,7
@
where A = the tributary floor area that complies with the requirements of (c) below, m2
b) Where the tributary area of a floor, used for any purpose other than those in (a)
above, that is supported by a column or bearing wall (the cumulative area of all floors
so supported being taken) or a single span of a beam or girder, or a single panel of
a slab (solid or ribbed) or flat-plate, exceeds 20 m2,the distributed loading may, for
the design of the building or of part of the building, be multiplied by a factor equal to
0,3
+
g,
but with a minimum value of 0,5
@
where A = the tributary floor area that complies with the requirements of (c) below,
m2
c) Provided that (in (a) or (b) above)
1) for one-way spanning slabs, the width of the tributary area does not exceed
one-half of the span of such slab; and
2) for rectangular two-way spanning slabs, the tributary area does not exceed that of
a square of sides equal to the smaller dimension of the rectangle.
31
SABS 0160-1989
(As amended 1993)
5.4.4
Nominal Imposed Roof Loads
NOTE: In this subsection, all roof slopes are measured from the horizontal and all imposed loads
act in a vertical direction.
5.4.4.1
General. So design all roofs that they are capable of sustaining the relevant nominal
imposed loads set out in 5.4.4.2-5.4.4.6 (inclusive) in addition to the wind loads
detailed in 5.5, but:
a) for inaccessible roofs the nominal imposed roof loads and nominal wind loads
shall not be taken as acting concurrently; and
b) for accessible roofs 0,3 times the nominal imposed roof load shall be taken as
acting concurrently with the nominal wind load.
Commentary:
These are primarily maintenance or construction loads intended to
represent the effects of workmen or stacked materials, etc. Alternatively,
the distributed load will cater for limited accumulations of snow, hail or
rainwater on roofs (approximately 250 mm depth of snow, 60 mm of hail
or 50 mm of rainwater, measured vertically).
NOTE: Wind loading will usually be predominant where the roof slope is less than 30".
5.4.4.2
Accessible flat roof
a) Where access is provided to a flat roof (in addition to access necessary for
cleaning and repair), allow for a uniformly distributed imposed load of 2,O kN/m2
measured on plan, or a concentrated load of 2,O kN applied over an area of
0 , l m x 0 , l m, whichever is more severe.
b) When a roof has an intended use as a floor, design it in accordance with 5.4.1 or
5.4.2, as appropriate.
5.4.4.3
Inaccessible roof. Where no access is provided to a roof (other than that necessary
for cleaning and repair), allow for one of the following nominal loads, whichever is the
most severe:
a) A concentrated load of 0,9 kN, acting vertically downward and applied over an
area of 0 , l m x 0 , l m in any position; or
b) a uniformly distributed load, acting vertically downward, of
(0,3
+ 5-A)
60
kN/m
where A = the tributary area for the member under consideration or the area of the
roof slab confined by the perimeter of supporting members, measured on plan, m2,
as appropriate
provided that the load has a maximum intensity of 0,5 kN/m2where A is 3 m2or less
and a minimum value of 0,3 kN/m2where A is 15 m2or more; or
c) where it is known that snow of depth exceeding 250 mm could be expected to
accumulate on a roof, a distributed load corresponding to the expected depth of
snow.
Commentary:
The above loading {makes no provision for impact effects or for brittle
covering material. It is necessary that safety measures (such as gang
boarding) be introduced when work is carried out.
SABS 0160-1989
32
(As amended 1993)
5.4.4.4
Curved roof. Calculate the nominal imposed load on a curved roof by dividing the roof
into an appropriate number of segments and calculating the load on each,
appropriate to its mean slope, in accordance with 5.4.4.3.
5.4.4.5
Provision for additional loadinqs on roof trusses or other members in buildinqs
containinq industrial and storacre occupancies. Ensure that where a roof truss (or any
of its elements) or any other member is designed to sustain a specific load at a
specific location, such location is clearly identified by a suitable hook, shackle or
similar device, and that the capacity is clearly indicated.
5.4.4.6
Loads due to snow, hail and rainwater. Where the designer deems it necessary,
ensure that an allowance is made for loads (in excess of the distributed loads
prescribed in 5.4.4.2, 5.4.4.3 and 5.4.4.4) caused by snow, hail or rainwater. The
value of such loads must be based on a knowledge of the local weather conditions
and on the layout of the building concerned.
Commentary:
On flat, open surfaces, greater depths of snow or hail than those referred
to in 5.4.4 will be uncommon in most parts of the Republic of South
Africa. Local knowledge should be applied in cases where the values in
5.4.4 may be exceeded. Consideration should be given to the possibility
of greater accumulations of snow or hail at changes in slope and in
valleys and behind parapets or similar projections.
The possibility that gutters and downpipes may be blocked by hail or
snow should be borne in mind. Wire mesh hail guards can be of value for
this purpose but may not always be effective for fine hail. On flat roofs,
particularly those subject to deflection, accumulation of rainwater is
possible and the resultant ponding must be considered. Where flat roofs
are provided with parapets, scuppers should be provided through the
parapets to prevent an accumulation caused by blocked rainwater pipes.
Refer to Appendix F for information on rainfall intensity.
5.4.5
Forces on Walls, Balustrades and Glazinq
5.4.5.1
ParaDet walls. balustrades and railinqs. Take the following loads into consideration:
a) For parapet walls, balustrades and railings that guard a drop of more than
750 mm, together with members that give them immediate support, the following
nominal imposed loads (which may be assumed to be of short duration, i.e. a few
minutes):
1) The appropriate wind forces,
2) the appropriate concentrated forces set out in (b)-(f) below, or
3) the appropriate distributed forces set out in (b)-(f) below,
whichever is the most severe.
b) For walls or railings guarding stairs, landings, gangways and balconies other than
those in places of public assembly, and parapet walls or railings to all roofs to which
there is no access other than for maintenance purposes:
1) A concentrated force of 1 kN acting in any direction between vertically downward
and horizontally inward or outward, applied over a 100 mm length for beam elements
and over a 100 mm x 100 mm area for plate elements and acting at the top or any
other position of the guard, whichever is the most severe; or
33
SABS 0160-1989
(As amended 1993)
2) a distributed horizontal force of 500 N/m applied at the top of the guard and acting
outward, except that, where the guard may be exposed to crowd surge loads from
either side, the force must be taken as liable to act inward or outward.
c) For walls or railings to stairs, landings, gangways and balconies serving places of
public assembly other than grandstands, and to roofs to which the public has access:
1) A concentrated force of 1 kN applied as in (b)(l) above, or
2) a distributed force of 1 3 kN/m applied as in (b)(2) above.
d) For ramps and forwalls or railings to stairs, landings, gangways and balconies that
serve grandstands:
1) A concentrated force of 1 kN applied as in ( b ) ( l ) above, or
2)a distributed force of 3 kN/m applied as in (b)(2) above.
e) For railings to catwalks and similar access areas in industrial buildings where
crowding is unlikely: A concentrated force of 1 kN applied as in (b)(l) above.
f) For guardrails in elevated or rnultistorey parking garages for vehicles of a gross
mass not exceeding 2 500 kg: A horizontal load of 30 kN, distributed over any 1,5 m
length of barrier, acting normal to the barrier and at a height of 550 mm above floor
level.
5.4.5.2
Exterior walls, curtain walls and Dartv walls. Ensure that all external walls, curtain
walls and party walls in buildings or, in the case of sheathed and framed walls, the
framing to such walls, are capable of withstanding a nominal horizontal concentrated
force of 500 N acting normal to the wall surface over an area of 0,l m x 0,l m at any
point at a height of 1,3 m above floor level or such lesser height as may be more
critical, or a nominal horizontal distributed force of 500 N/m at a height of 1,3 m, or
the appropriate wind force, whichever is the most severe.
5.4.5.3
Boundarv. vard and aarden walls. Ensure that all concrete or masonry boundary, yard
and garden walls higher than 1,5 m are capable of withstanding a nominal horizontal
concentrated force of 1,O kN acting normal to the wall at any point at a height of 1,8 m
or at the top of the wall if it is less than 1,8 m high, or a distributed horizontal force
of 0,36 kN/m acting at a height of 1,Im, or the appropriate wind force, whichever is
the most severe.
5.4.5.4
Partition walls. Ensure that all partition walls other than those of lightweight sheeted
or boarded construction are capable of withstanding the forces (other than wind
forces) specified in 5.4.5.2. Lightweight sheeted or boarded partitions shall be
capable of withstanding a nominal horizontal distributed force of 0,5kN/m acting at
a height of 1,3 m above floor level.
5.4.5.5
ImDact forces in walls. Dartitions and alazina units. Ensure that all walls, curtain walls
and partitions, and all large glazed panels within 500 mm of the floor that may be
exposed to impacts from a person falling against or bumping into them, have a level
of impact resistance which will prevent undue risk of injury resulting from failure,
fracture or penetration of the wall, partition or glazed panel.
Commentary:
Reliable information on the calculation of resistance to human forces is
not available, particularly in the case of brittle materials such as glass.
Where it is possible to conduct impact tests, an impact of 400 J delivered
by means of a 250 rnm diameter bag filled with dry sand to a mass of
30 kg may be considered representative of the most severe conditions
likely to occur. For non-brittle materials and for masonry, the ability to
withstand the forces specified in 5.4.5.2with the normal safety factors for
the materials concerned will generally ensure adequate resistance to
human impact.
SABS 0160-1989
34
(As amended 1993)
5.4.5.6
Stackinq of materials aqainst walls. Where materials are to be stored against a wall
or partition in such a manner that a horizontal thrust is transmitted to such wall or
partition, the designer must ensure that due allowance is made for such thrust in the
design procedure. In addition, the details of such loading must be recorded.
5.5
WIND LOADS W,
5.5.1
Determination of Nominal Wind Loads. Determine the nominal wind forces on a
building or on part of a building by one of the following methods:
a) In accordance with the following formulae and the procedures given in 5.5.2, 5.5.3
and 5.5.4 for the determination of the nominal wind pressures on the relevant
surfaces :
Pe = external nominal wind pressure on surface, N/m2
Pi = internal nominal wind pressure on surface, N/m2
kp = factor for converting wind speed into velocity pressure
-
V
air density, kg/m3
2
= regional basic wind (gust) speed, according to regional location, for a 50year return period at height 10 m in Terrain Category 2, m/s
kr = factor for adjusting V to other return periods (risk factor) (see Fig. 4)
k,
= factor for converting regional wind speed into nominal wind speed
allowing for the variation of wind speed with height, according to terrain
category and class or size of building or element
Cpe= external pressure coefficient
Cp, = internal pressure coefficient
V, = nominal wind speed at height z above local ground level for given
building or element, m/s
q,
= free stream velocity pressure of wind at height z, N/m2
F
= resultant force on building or element, N
A
= area of surface concerned, m2
C, = a force coefficient
A,
= projected or effective area of building or element, m2
35
SABS 0160-1989
b) A simplified design method in accordance with 5.5.6, provided that the following
limitations on the shape and dimensions of the building are complied with:
1) The building is rectangular in plan;
2) the overall height does not exceed 20 m;
3) the ratio of overall height to least plan dimension does not exceed 4.
c) A design approach complying with the procedure set out in 3.1.2.
Commentary:
a) Section 5.5 is concerned with wind loading and the response of
buildings to such loading. However, the effects of wind on a building may
also influence non-structural aspects of its design and it is desirable that
the designer familiarize himself with these possible effects so that, where
a particular building is of such shape, size or location that special
consideration of these effects is necessary, this can be given at an early
stage of the design. For instance, the pattern of wind flow around and
over a tall building or group of tall buildings should be investigated to
ascertain its possible influence on ventilation, air conditioning and rain
penetration, and to establish whether the airflow induced at ground level
may not seriously inconvenience or endanger people at that level. Wind
tunnel or similar tests may be required to evaluate these problems. (See
also A-2(a) and (b) of Appendix A.)
b) The nature of wind flow around a building is complex and a theoretical
prediction is difficult.. Small variations in shape or in surface roughness
or in wind direction (horizontally or vertically) can cause significant
changes in the flow and hence in the magnitude and distribution of the
resulting pressures on the building. Factors such as the scale and
intensity of wind turbulence, the size of the building, the nature of the
surrounding buildings, and topographical features also have a profound
influence. A high degree of precision in the determination of pressure or
force coefficients for individual buildings is therefore not generally
possible without recourse to wind tunnel tests that model surroundings
as well as the building itself.
c) However, for the great majority of buildings with conventional shapes
conforming to those covered in the various tables in this code, it is
sufficient and more convenient to use the typical pressure or force
coefficients tabulated in this code. Outside these limitations, it will be
necessary to consult the specialist literature in this field or resort to tests,
or both. (See also A-2(c) of Appendix A.)
d) In many buildings of simple squat shape and limited height, wind
loading is not a critical parameter in the design of the structure and an
overestimate of the wind forces will not be of consequence. For these
cases, the simplified rules in 5.5.4 have been incorporated. Since they
are based on a combination of the most severe cases, they will generally
give a rather conservative estimate of the wind forces. Where a more
accurate prediction IS desired, the detailed procedure given in this code
should be used.
e) Wind is a dynamic phenomenon (i.e. it varies fairly rapidly with time)
and since buildings are deformable to a greater or lesser degree, the
fluctuations in the wind forces result in a dynamic response of the
building. The magnitude of the response will depend on factors such as
the turbulence of the wind and the shape, size, weight, stiffness and
damping characteristics of the building.
1) For the majority of buildings, the dynamic response effects are small
and a static wind loading design in which the wind forces are based on
a peak gust speed with a limited probability of occurrence during the life
of the building, as set out in the detailed procedure (and on which the
simplified procedure is also based), will suffice.
2) However, for slender or flexible structures such as towers, masts,
chimney stacks, and some tall buildings, the dynamic response effect
may be significant and more refined methods of analysis should be
employed.
36
SABS 0160-1989
(As amended 1993)
Such methods are not covered in any detail in this code, but guidance
can be found in appropriate specialist texts referred to in A-2(d)-(o),
inclusive, of Appendix A. It should also be noted that wind-induced
vibration of light, flexible roof structures or claddings can lead to
loosening of fasteners and occasionally to fatigue failure.
3) In tall, slender buildings, the dynamic oscillations not only influence
the design of the structure and the cladding but may also have a
psychological effect on the inhabitants of the building. There is no fixed
relationship between the nature of the motion and the human response
to it, but some approximate guidelines are given in the reference quoted
in A-2(i) of Appendix A.
f) The following comments are provided regarding wind tunnel testing:
1) Tests for mean and fluctuatina loads and pressures. Wind tunnel tests
used to determine mean and fluctuating loads and pressures, and similar
tests employing a fluid other than air, may be considered properly
conducted only if
i) the natural wind has been modelled to take into account the scale and
intensity of turbulence and the variation of wind speed with height, and
ii) tests on curved shapes are conducted with due regard to the effects
of Reynolds numbers.
2) Tests for dynamic response. Tests for determining the dynamic
response of a structure may be considered properlyconducted only if the
requirements of (f)(l) above are met and if, in addition, the model is
scaled with due regard to mass, length, stiffness and damping.
5.5.2
Nominal Wind Speed V,
5.5.2.1
General
a) Use the nominal wind speed V, at height z above ground level to determine the
wind forces on a building or part of it.
b) Obtain the nominal wind speed V, from the appropriate regional basic wind speed
V, determined in accordance with 5.5.2.2 and adjusted for
1) mean return period (see 5.5.2.3),
2) terrain category (see 5.5.2.4 and 5.5.2.6),
3) local effects (see 5.5.2.5),
4) height above ground (see 5.5.2.6), and
5) class of structure or element (see 5.5.2.6).
c) For buildings for which a 50-year mean return period is prescribed, the
characteristic wind speed V, must be at least 24 m/s.
5.5.2.2
Reaional basic wind speed V. Determine the regional basic wind speed V for a
building, according to its geographical location, from Fig. 3, which gives values of V
for a 50-year mean return period (see 5.5.2.3 for other return periods).
Amdt 3,
Oct. 1993
Commentary:
The background to the derivation of the wind speeds given in Fig. 3 is
discussed in Milford, RV, 'Annual maximum wind speeds for South
Africa' (The civil enaineer in South Africa, January 1987) and the values
are based on a statistical analysis of data gathered by the Weather
Bureau of the Department of Environment Affairs over many years and
at a number of stations throughout the Republic. (See also A-2(b) of
Appendix A.)
37
5.5.2.3
SABS 0 160-1989
Mean return Deriod
a) Use a regional basic wind speed V having a mean return period as set out below
or as selected by the designer for the particular nature or use of the building or
element.
Nature of buildina or element
Mean return
period, vears
All buildings other than those given below
Buildings which have special post-disaster functions, e.g. hospitals,
cornmunications buiIdings , etc.
50
100
Buildings representing a low degree of hazard to life and property in
the case of failure, e.g. isolated towers, farm buildings, etc.; side cladding to industrial buildings; and roof coverings to all buildings
25
For analysis of serviceability considerations
10
Buildings and temporary structures used only during construction
operations, e.g. formwork and falsework, site office, etc.
5
In instances where such temporary structures will remain in position for a
considerable period of time (e.g. 6 months and over), the mean return period of
5 years may need to be increased and a value of ten times the period of exposure is
suggested.
b) For mean return periods other than 50 years, determine the regional basic wind
speed Vby multiplying the value for 50 years obtained from Fig. 3 by the appropriate
correction factor k, obtained from Fig. 4.
5.5.2.4
Terrain cateaories
a) General. A terrain category defines the characteristics of those surface
irregularities of an area that arise from natural or constructed features and that create
a surface roughness affecting the degree of turbulence and the variation of speed
with height of the wind passing over the area.
In selecting a terrain category (see (b) below), take into account the permanence of
the features constituting the surface roughness and the distance (in a direction
upwind of the building under consideration) over which the terrain remains
unchanged. (See also (d) below.)
b) Cateaories. Assess the terrain in which the building stands as being of one of the
following categories:
Cateaorv 1. Exposed smooth terrain with virtually no obstructions and in which the
height of any obstruction is less than 1 3 m . This category includes open sea coasts,
lake shores and flat, treeless plains with little vegetation other than short grass.
Cateaorv 2. Open terrain with widely spaced obstructions (more than 100 m apart)
having heights and plan dimensions generally between 1,5 m and 10 m . This
category includes large airfields, open parklands or farmlands and undeveloped
outskirts of towns and suburbs, with few trees. This is the category on which the
regional basic wind speed V is based.
Cateaorv 3. Terrain having numerous closely spaced obstructions generally having
the size of domestic houses. This category includes wooded areas and suburbs,
towns and industrial areas, fully or substantially developed.
Cateqorv 4. Terrain with numerous large, tall, closely-spaced obstructions. This
category includes large city centres.
SABS 0160-1989
38
NOTE
1) It is expected that the majority of design situations will fall into Terrain Category 3 and that the
selection of a more severe (Category 1 and 2) or less severe (Category 4) terrain category will be
deliberate.
2) Owing to the large differences in wind speeds between Terrain Categories 2 and 3, and where
there is doubt whether the terrain under consideration falls into Category2 or Category 3, the design
wind speed may be obtained by interpolation between the values for these two categories.
c) Effect of wind direction. The terrain category used in the design of a building may
vary according to the direction of the wind.
However, the regional basic wind speed Vmay be varied only if for design purposes
according to specific wind directions, sufficient meteorological information is
available. (See also 5.5.2.2.)
d) Chanue in terrain cateaorv. The wind speed profile for a given terrain category
does not immediately develop to full height at the commencement of that terrain
category but is gradually established, starting nearest the ground and extending
upwards as the "fetch" (i.e. the distance the wind has blown over the new terrain)
increases.
The relationship between the fully developed height h, of the wind speed profile and
the fetch x (i.e. the distance in a direction upwind of the building under consideration
over which the terrain remains unchanged) is given in Fig. 5 for each of the four
terrain categories.
For a building of height h, or less, situated at a distance x from a change in terrain
category, design the building for wind speeds determined for the terrain category in
which the building is situated.
Fora building of height exceeding h,, situated at a distance xfrom a change in terrain
category, design the building for wind speeds determined for the less rough (more
severe) terrain category or adopt a combined wind profile determined from the
respective profiles of the terrain categories involved.
Commentary:
A procedure for the determination of a combined wind profile due to the
presence of two or more terrain categories is given in D-2 of Appendix D.
5.5.2.5
Local effects on wind w e e d
a) Shieldinq. Make no allowance for shielding from adjacent objects other than that
implied in 5.5.2.4 and 5.5.2.6.
b) ExDosure. Take account, in accordance with 5.5.2.4(d), of the effects of exposure
resulting from a fetch of open (more severe) terrain in an otherwise rougher (less
severe) terrain category.
c) Local toDouraDhy. Where the local topography is such that increases in wind speed
may occur as a result of funnelling or other effects, adjust the design wind speed
accordingly, on the basis of appropriate meteorological advice or tests.
Particular attention is drawn to the possibility that the wake flow from large buildings
can lead to increased cladding pressures on buildings downwind of such structures
and that funnelling of the wind between groups of large buildings in close proximity
can give rise to increased wind speeds which will affect both overall and local wind
pressures.
d) Sudden chanae in uround level. Take account, in accordance with 5.5.2.6(c), of
the increase in exposure due to situations on or near the edge of a cliff, bluff or
escarpment. (See also D-3 of Appendix D.)
SABS 0160-1989
39
m
aJ
U
Fig. 3 - Regional Basic Wind Speed V, m/s (Isopleths of 3 Second Gust Speeds at 10 IT 1 Height
in Terrain of Category 2, Estimated to be Exceeded on Average Only Once in 5C1 Years)
L
0
4U
0
Lc
c
.-0
L
U
aJ
L
L
0
U
0.9
O J
5
10
20
30 40 50
100
200 300 400 500
Mean r e t u r n period, years
Fig. 4 - Correction Factor K, by which Regional Basic Wind Speeds from
Fig. 3 must be Multiplied to Obtain Values for Other Mean Return
Periods (Also Applicable to Mean Wind Speeds in Fig. D - I )
SABS 0160-1989
40
180
160
E
140
120
w
60
40
20
I
I
I
I
1
0
I
2
Fetch X , krn
Fig. 5(a) - For Fetch Distances up to 2 km
500
E
x
E
c
c
'F250
f
U
-
200
0
(U
z
D
150
100
50
0
Ir
8
12
16
40
20
Fetch x, k m
Fig. 5(b) - For Fetch Distances over 2 km and up to 60 km
Fig. 5 - Fetch/Height Relationship
60
41
SABS 0160-1989
(As amended 1991)
5.5.2.6 Variations of characteristic wind speed with heiqht. class of structure and terrain
a) Wind speed multiplier. Determine the characteristic wind speed V, at a height z above
site mean ground level for the assessed terrain category and class of building or element
being designed, by multiplying the regional basic wind speed Vor k,V by the applicable
wind speed multiplier k,, given in Table 5.
b) Class of structure or element. Classify as Class A, B or C in accordance with the
following:
1) Class A: For the determination of forces on units of cladding, roofing, glazing and their
immediate fixings, including roof battens and minor purlins supporting small areas of
roofing, and on individual members of unclad frames.
2) Class B: For the determination of forces on main structural members as well as for the
overall resultant forces and for overturning moments on buildings, where neither the
height nor the width nor the depth of the building exceeds 50 m.
3) Class C: For the determination of the overall resultant forces and overturning moments
on buildings where the height or the width or the depth exceeds 50 m.
Commentary:
The free wind speed fluctuates from moment to moment as a result of
turbulence and it can be averaged over any chosen period of time; the
longer the averaging time, the lower the speed. It has been found that
the shortest duration of fluctuation (2-3 s) that the normal Weather
Bureau anemometer is capable of recording satisfactorily corresponds
to a gust whose size is insufficient to envelop obstacles of dimensions
exceeding about 20 m . The use, for design purposes, of wind speeds of
3 s duration will therefore overestimate the overall forces on most
buildings and larger structural elements, although it will be appropriate
for local forces on small elements such as cladding. For this reason,
three classes of structure, A, B and C have been adopted, corresponding
respectively to situations where a 3 s, 5 s or 10 s gust speed will be
appropriate :
3 s for cladding design
5 s for trusses, portals and other main structural elements and for overall
forces on buildings whose height or plan dimensions are not more than
50 m
10 s for overall forces on buildings wider or taller than 50 m
.
The relation between the 5 s and 10 s wind speed and the basic 3 s limit
speeds, together with their variations with height as set out in Table 5,
are based on published empirical data.
c) Measurement of heiaht. Measure the height zfrom site ground level in the immediate
vicinity of the building or, for sites on top of steeply sloping hills or cliffs, from an artificial
ground datum (see D-3 of Appendix D).
Commentary:
Where a building is situated at or near the edge of a sudden change in
ground level (e.g. a cliff), make allowance for this by the introduction of
an artificial ground datum, the determination of which is given in D-3 of
Appendix D.
5.5.3
Nominal Wind Pressures and Forces
NOTE: See Fig. D-6 of Appendix D.
Amdt 2,
Nov. 1991
SABS 0160-1989
42
5.5.3.1 Conversion of wind speed to velocity pressure. Convert the characteristic wind speed V,
to the free stream velocity pressure by means of the following equation:
q z = k,V,2
5(d)
where
q,
= free stream velocity pressure (above atmospheric pressure) at height z,
N/m2
V,
= characteristic wind speed at height z, m/s
k,
= a constant dependent on the site altitude
Values of k, for a range of site altitudes are given below:
Site altitude
above sea level, m
k
-P
0,60
0
500
1000
1500
2 000
0,56
0,53
0,50
0,47
NOTE:
a) kpis half the density of the air under the relevant conditions and therefore varies with temperature
and atmospheric pressure. A temperature of 20 " C has been selected as appropriate for South Africa
and the variation of mean atmospheric pressure with altitude is allowed for above.
b) Intermediate values of k, may be obtained by linear interpolation.
TABLE 5 -VARIATION OF CHARACTERISTIC WIND SPEED WITH
TERRAIN, HEIGHT AND CLASS OF STRUCTURE
2
1
3
4
5
6
7
8
9
10
11
12
13
Wind speed multiplier. k,
Terrain Category 1
Height z, rn
Terrain Category 2
-B
C
j
Terrain Category 3
Terrain Category 4
of building or element'
A
C
I
B
C
-
5
10
15
1,03
1,09
1,12
1,02
1,08
1,11
1,oo
1,05
1.09
0,94
1,OO
1,04
0,92
0,98
1,02
0,88
0,951
0,99
0,67
0,74
0,81
0,64
0,71
0,78
0,57
0,557
0,57
20
50
100
1,14
1,22
1,28
1,13
1,21
1,27
1,11
1,20
1,27
1,07
1,16
1.23
1,05
1,15
1,22
1,02
1,13
1,21
0,86
1,OO
1,11
0,83
0,98
1,lO
0,57
0,80
0,95
150
200
250
1,31
1,34
1.36
1,31
1,34
1,36
1,31
1,34
1,36
1,28
1,31
1,34
1,27
1,31
1,34
1,26
1,30
1,34
1,18
1,23
1,27
1,17
1,23
1,27
1,04
1.11
1.17
300
350
400
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,23
1,27
1,31
% 1,36
E:
Above 500
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1,36
1.36
1,36
1,36
1,33
1,36
1,36
Up to
I
--
1 1
-
* The wind speed multipliers for heights exceeding the height of the obstructions producing the surface rough-
ness (reference plane height), but less than the gradient height are based on the variation of gust speeds with
height, determined by the formula
SABS 0160-1989
43
(As amended 1991)
and for heights exceeding the gradient height V, = 1,36 V
Where zgis the gradient height (height above which the ground roughness no longer influences the wind speed),
z, is the height of the reference plane and a is an exponent for a short period gust, the period being
3 s for Class A
5 s for Class B
10 s for Class C.
1
2
3
Terrain
Category
ZQ
2,
(rn)
1
2
3
4
5.5.3.2
4
I
5
I
6
a
250
300
400
500
(m)
0
0
5
12
Class~
0,07
0,09
0,14
0,18
Class B
0,073
0,095
0,15
0,19
Classc
0,079
0,105
0,16
0,21
Determination of surface pressures
a) Characteristic wind pressure. Determine the characteristic wind pressure on a
surface of a building by means of the equation
Pz
= c,qz
5(e)
where
p, = pressure on the surface at height z, N/m2
C, = a pressure coefficient for the particular surface or part of the surface of
the building
q, = the velocity pressure, N/m2,from equation 5(d) in 5.5.3.1
p, and C, may be positive (pressure acting normal to and towards the surface) or
negative (pressure acting normal to and away from the surface, i.e. suction). The
pressure is taken as uniformly distributed over the designated surface or part of the
surface except that, where qz varies with height, the surface may be subdivided into
height zones and the specific pressures applied over the relevant areas. Measure the
values of z, in such cases, to the top of each height zone.
b) Pressure coefficients. Use the most adverse applicable pressure coefficients or
combinations of pressure coefficients tabulated in 5.5.4 to determine the wind forces
on a building as a whole and on its walling and roofing elements, having regard to the
effects of wind direction and the probable levels of internal pressure in the building.
SABS 0160-1989
44
c) External and internal pressure coefficients. Use the external pressure coefficients
Cp, to determine the pressure on the external surface of a space-enclosing element
such as a wall or roof and the internal pressure coefficient Cpito determine the
pressure on the internal surface of the element.
d) Resultant pressures and forces on walls and roofs. Calculate the resultant wind
force on the surfaces of a wall or roof element from the algebraic difference between
the external and internal pressures on the element.
Thus
where f, = the resultant wind force on an element of area A, at height z
e) Local pressure coefficients. Note that in addition to average external pressure
coefficients defining the pressures over a roof or wall surface as a whole, there are
local external pressure coefficients defining the higher localized negative pressures
in certain regions (generally at corners of walls and edges and ridges of roofs).
Do not apply these local pressures concurrently with the average pressures, as they
are intended only for use in the design of claddings and their immediate supporting
members and fixings in the specified regions.
Where interaction is possible, take the local external pressures as acting
simultaneously with the appropriate levels of internal pressure.
5.5.3.3
Determination of overall forces on clad buildinss
a) Determine the resultant nominal wind forces on a building as a whole by means
of the following equation:
where
f = the resultant characteristic wind force in the direction of the wind
C, = a force coefficient as given in 5.5.4
A, = the total effective frontal area of the building (projected area normal to the
wind direction), m2
Where it is necessary to allow for the variation of 9, over the height of the building,
A, may be subdivided into height zones and the appropriate value of 9, applied to
each zone. The value of C, is that for the building as a whole.
b) Alternatively, for buildings for which appropriate force coefficients are not
available, determine the overall resultant force on the building by vectorial
summation of the forces resulting from the wind pressures on the various surfaces.
Refer also to the commentary to 5.5.3.5.
5.5.3.4
Determination of frictional forces. For clad buildings of certain proportions, it is
necessary to allow for wind forces arising from frictional drag on the roof and the
walls parallel to the wind direction, in addition to the wind forces calculated in
accordance with 5.5.3.2 and 5.5.3.3. For rectangular buildings, this addition is
necessary only where the ratio d/h or d/b exceeds 4,
where h = the height of the building to eaves or parapet
b = the breadth (normal to the wind direction)
d = the depth (parallel to the wind direction)
SABS 0160-1989
45
For such buildings, determine the total frictional force Ff in the direction of the wind
by means of the following equations:
if h s b , Ff = Cf,a,b(d - 4h) + C,q,2h(d
-
4h) or
if h > b, Ff = Cf,a,b(d - 4b) + C,q,2h(d
-
4b)
5(h)
5(i)
where
Ff
= the total frictional force in the direction of the wind
C,
= a frictional drag coefficient having one of the following values:
0,Ol for smooth surfaces without corrugations or ribs across the wind
direction;
0,02for surfaces with corrugations across the wind direction;
0,04 for surfaces with ribs across the wind direction.
The first term on the right-hand side in each equation gives the frictional force on the
roof and the second term gives the frictional force on the walls.
Different values of C, and q, or both may be adopted for the roof and for the walls.
5.5.3.5
Determination of overall forces on unclad buildinas and frames. Determine the
resultant characteristic wind forces on unclad buildings, frames, lattice towers, or
individual structural members by means of the procedures and force coefficients
given in 5.5.4.
Com mentary:
Most of the force coefficients given in 5.5.4 are for regular cross-sections
with one or more axes of symmetry and for winds blowing along one of
these axes. In such cases, the resultant time averaged loading acts in
the direction of the wind. However, for asymmetrical sections and for
winds oblique to the major or minor axes of symmetrical sections, there
will be a component of force transverse to the wind direction as well as
one in the along-wind direction.
Table 22, which gives force coefficients for a variety of symmetrical and
asymmetrical structural shapes for various wind approach angles,
provides an indication of the influence of wind direction and building
shape on the normal and transverse forces. A point worth noting is that
the along-wind force on a square cross-section with the wind directed
along the diagonal is slightly greater than that with the wind normal to a
side. This is therefore likely to be a critical design condition since the
bending resistance of a square section would generally be smaller in the
diagonal plane than in the plane parallel to its sides.
It should also be noted that for buildings or structural shapes with curved
surfaces, the force coefficient is dependent on Reynolds numbers, and
separate values of C, are therefore given for subcritical and supercritical
flow conditions. In the tables, these are identified by the value of the
parameters DV, or V,b, each of which is proportional to a Reynolds
number if the kinematic viscosity of the air is assumed to be constant.
(See also D - I .2of Appendix D.)
5.5.4
Pressure and Force Coefficients
5.5.4.1
Pressure coefficients. Average and local external pressure coefficients for walls and
roofs of rectangular buildings of various types are given in Tables 6-9 (inclusive).
Table 10 gives values of internal pressure coefficients for rectangular buildings under
various conditions of roof and wall permeability.
SABS 0160-1989
46
(As amended 1993)
Arndt 3,
Oct. 1993
Tables 1I A , 11B and 11C give values of pressure coefficients for canopy roofs of
various shapes. For the purposes of these tables, a canopy roof is considered to be
one supported on a structural frame and where walls or cladding, if present, are of
minimal extent.
Table 13 gives values of pressure coefficients for grandstands with a 5 " roof slope.
Attention is drawn to the fact that no standard set of values can deal adequately with
all the variations which can occur in this type of structure. If the grandstand is of a
size and an importance that justifies an individual assessment of the pressure
distribution and loading, a wind tunnel test must be undertaken. In addition, because
of the unusual problems created by this type of structure, assessments should be
carried out by a person versed in this type of design.
Table 14 gives external pressure coefficients for the surfaces of cylindrical structures.
NOTE: The value of q, to be used with the coefficients may be varied over the height of the building
in accordance with the wind speed variations given in 5.5.2.6(a), except in the case of the average
and local coefficients for the leeward and side walls of rectangular buildings as indicated in Table 6.
In the latter cases, the value of g, applicable at the top of the walls should be used.
47
SABS 0160-1989
NOTE
a) h is the height to eaves or parapet, b is the greater horizontal dimension of a building, and w is the lesser
horizontal dimension of a building.
b) Use the following values of q,:
For windward walls: q, applicable at top of wall or as a function of height in accordance with wind speed variation
as given in 5.5.2.6(a);
for leeward and side walls: q, applicable at top of wall.
48
SABS 0160-1989
(As amended 1991)
TABLE 7 - EXTERNAL PRESSURE COEFFICIENT C,, FOR
PITCHED ROOFS OF RECTANGULAR CLAD BUILDINGS
1
2
4
3
Average C
Building
height
ratio
h/w s ?4
h/w = 1
h/w = 2
3oof
ingle,
legrees
Win
-6
6
Win1
0:
I"
FH
0
5
10
15
20
30
-0,8
-0,4
-0,4
-0,4
-0,4
-0,4
-0,4
-0,8
-0,8
-0,8
-0,8
-0,4
-0,4
-0,7
-0,6
-0.6
-0,6
40
50
60
+0,3
-0,5
-0,5
-0,6
-0,7
-0,7
-0,7
-0,6
-0,6
-0,6
-0,5
-1 ,o
-0,6
-0,6
-0,6
-1,2
-0.8
-0.5
08
+0,3
+0,7
-0,8
-0,9
-1,2
0
5
10
15
20
30
40
50
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,7
-U
-0,8
-0,9
-1,l
-0,9
-0,6
-0,6
-0,6
-0,7
-0,6
-0,6
40
0,o
+0,3
-0,5
-0,7
5
10
15
20
30
40
50
60
-0,8
-0,8
-0,9
-1 ,o
-0,5
-0,l
+0,3
+0,5
-0,5
-0,5
-0,5
-0,6
-0,6
-0,6
-0,6
-0,6
-0,5
-0,5
-0.5
-0,5
--
-0,a
-0,7
-0,8
-0,8
-0.7
-0,9
-0,7
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
- --0,9
0
5
10
15
20
30
40
50
60
-0,7
-0,7
-0,7
-0,8
-0,8
-1 ,Q
-0,2
+0.3
+0,5
-0,6
-0,6
-0,6
-0,6
-0,6
-0,5
-0,5
-0,5
-0,5
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0,8
-0.8
- --
-1 ,o
-1,2
-1,2
-1,2
-1,1
-2,o
-2,o
-2,o
-1,8
-2,o
-2,o
-2,o
-1,8
-1,5
-1,5
0
5
10
15
20
30
-U
-1.1
-0,7
+0,6
-
-2,0
-U
-2,o
-2,o
-2,o
-1,8
-0,9
60
I......
-2,o
-1,2
-2,o
-2,o
-2,o
-1,8
-0,8
-0,8
-0,8
-0,8
-0,6
-0,6
..
. ,:,'....
_.
-1,1
-1,1
-0,8
-0,8
-0,8
-0.8
-0,8
-0,8
-0,8
-0,5
-0.5
-0,5
-0,5
-0.5
10
9
-0-g
-0,9
-0,5
0
-2,o
-1,4
-1,4
-1,2
-1 ,o
-0,5
-0,5
-0,l
+0,2
+0,4
60
-0,6
-0,5
-0,9
-0,3
-0,7
8
R
I"
EG
+0.5
--
4 I h/w I 6
igle
GH
-0,9
7
Loc
EF
50
Amdt 2,
Nov. 1991 h/w =
ngle
5
for surface
-1,s
-l,o
-2,0
-13
-1,5
-1,5
-U
-U
-1 ,o
-1,2
-1,1
-1 ,o
-1 ,o
-2,0
-1,5
-1,5
-1,5
-U
-2
-1 ,o
-1,2
-1,2
-U
-0.7
-0,8
-0,8
-0,7
-2,o
-2,o
-2,o
-1,8
-1,5
-1,5
-0,7
-0,7
-0,7
-U
-0,7
-2,o
-2,o
-2,o
-1,8
-1,5
-1,5
-0.8
-0,8
-0,8
-0,8
-0,7
-0,7
-0,7
-2,o
-2,0
-2,o
-1,5
-1,5
-1,5
-2,o
-1,8
-U
-G
-2,o
-2,o
-2,o
-1,8
-2,0
-1,5
-1,5
-1,5
-U
-U
-1,5
-1,2
-1,2
-2
-1 ,o
-1,2
-1,2
-2
-U
-0,7
NOTE
a h is the height to eaves or parapet and w is the lesser horizontal dimension of a building.
b j Take the pressure coefficient on the underside of any roof overhang as that on the adjoining wall surface.
Where no local coefficients are given, the overall coefficients apply.
c) Use the value of q, applicable at ridge height.
y
h o r 0.15 w,
whichever is the
lesser
1 Ora
SABS 0160
12165-EC/00-07
TABLE 8 - EXTERNAL PRESSURE COEFFICIENT C,, FOR MONOPITCHED
ROOFS OF RECTANGULAR CLAD BUILDINGS WITH h/w e 2
Amdt 2,
Nov. 1991
Wind
__
“
1
y = h or 0,15 w , whichever
is the l e s s e r
b
7
P
NOTE: A r e a H and area L r e f e r
t o the whole quadrant
20
25
30
-0,8
-05
-0,7 -0,5
-05 -0,5
-1,0
-1 0
-1:O
-0,6
-0,6
-0,6
-0,9
-0,8
-0,8
-0,5
-0,5
-0,5
CO
-0,5
-0,3
-0,l
-0,2 -1,0 -l,8
-0,9 -061 -0,9 -1,8
-0,6
-0,6 -1,8
-1,0
-0,8
-1,4
-2,O
-0,7 -0,9 -09
-0,5 -0,5 -0:5
-210
-1,8
NOTE
a h is the hei ht to eaves at lower side, b is the greater horizontal dimension of a building, and w is the lesser horizontal dimension of a building.
b{ Use the “ a t e of g, applicable at ridge height.
-2 0
SABS 0160-1989
50
(As amended 1991)
TABLE 9 - EXTERNAL PRESSURE COEFFICIENT C,, FOR SYMMETRICAL AND
ASYMMETRICAL PITCHED ROOFS OF MULTI-SPAN BUILDINGS (ALL SPANS EQUAL)
w’
_I_
W1
W’
W1
_ I_
w’
1
y = h or 0,l w
whichever is t h e
Roof plan
t h e Lesser
h l = h, = h
Wind
___)
I
=
Section
Wind
c _ _
ff- 180°
1
SABS 0160
Drg.11903-EC/00-07
Amdt 2,
Nov. 1991
1
2
3
Wind angle 8,
degrees
Roof slope
Average C,,
0
or
180
1st windward
1st leeward
2nd windward
2nd leeward
3rd windward
3rd leeward
4th windward
4th leeward
5th windward
All succeeding
-a
) Use values from Table 7 with
) roof angle a for windward
) slope h/w = 2
-0,5
-0,5
-0,4
-b
-c
-d
-e
-f
-9
-h
-i
-j
-0,4
-0,3
-0,3
-0,3
Average C,, over distance
90
Roof angle a up to 45”
h,
-0.8
Local CO*:
-2 0
NOTE: Use the value of 9, applicable at ridge height.
h2
-0.6
h3
-0.3
-1,5
SABS 0160-1989
51
TABLE 10 - AVERAGE INTERNAL PRESSURE COEFFICIENT C,i
FOR RECTANGULAR BUILDINGS OF OPEN INTERIOR PLAN
1
Average CDi
Condition
Two opposite walls equally permeable, other walls
impermeable:
+0,2
a) Wind normal to permeable wall
b) Wind normal to impermeable wall
Four walls equally permeable
-0,3or O,O,whichever is the more severe for
combined loadings
Dominant opening on one wall, other walls of equal
permeability:
a) Dominant opening on windward wall, having a ratio
of permeability of windward wall to total permeability of
other walls and roofs subject to external suction equal
to
1 or less
+0,1
+0,3
+0,5
+0,6
+0,8
13
2
3
6 or more
b) Dominant opening on leeward wall
c) Dominant opening in side wall
d) Dominant opening in a roof segment
A building effectively sealed and having non-opening
windows
Value of C
, for leeward external wall surface in
Table 6
Value of C
, for side external wall surface in
Table 6
Value of C
, for external surface of roof segment
in Tables 7-9
-0,2or O,O,whichever is the more severe for
combined loads
NOTE
a) Internal pressures developed within an enclosed building may be positive or negative, depending on the
position and size of the openings.
b) In the context of this table, the permeability of a surface is measured by the total area of openings in the
surface under consideration.
c) As a guide, the typical permeability of an office block or house with all windows nominally closed is
between 0,Ol % and 0,05% of the wall area, depending on the degree of draughtproofing.
d) The value of Cpican be limited or controlled to advantage by deliberate distribution of permeability in the
wall and roof, or by the deliberate provision of a venting device which can serve as a dominant opening at a
position having a suitable external pressure coefficient. An example of such is a ridge ventilator on a
low-pitch roof, and this, under all directions of wind, can reduce the uplift force on the roof.
e) For buildings where internal pressurization is utilized, this additional pressure must also be considered.
f) The value of q, to be used with these coefficients is that applicable to the relevant external pressure
coefficient for the surface in which the opening is situated.
SABS 0160-1989
52
(As amended 1991)
TABLE 11 - PRESSURE COEFFICIENT C, FOR CANOPY ROOFS
NOTE: The term "canopy root" in the table refers to a free-standing structure without walls.
The tables take into account the effects of blockage caused by stacked contents.
TABLE 11A - SINGLE BAY, TWO-PITCH CANOPY ROOFS
COMPLYING WITH THE FOLLOWING LIMITATIONS
1
--<
4
h
--<
w
L
W
1 a n d 1 -< - - <
3
0
31.-
I
R o o f angle
R o o f angle
51
Negative roof angle
Amdt 2,
Nov. 1991
1
2
Positive r o o f angle
3
I
4
I
I
5
6
I
7
Pressure coefficient CL
Roof
angle,
degrees
-20
Solidity
ratio
@*
I
Maximum all @
Minimum = O
Minimum = 1
+0,7
+0,8
-0,7
-0,9
Maximum all @
Minimum = 0
Minimum = 1
+0,5
-0,9
-1,2
+0,6
$
-15
Overall
8
8
-0,6
-0,8
+0,4
-0,6
+0,6
-0,8
-0,8
-1 ,I
Maximum all @
Minimum = O
Minimum = 1
+0,3
-0,5
+0,5
+5
Maximum all @
Minimum = O
Minimum = 1
+I0
Maximum all @
Minimum = O
Minimum = 1
Maximum all @
Minimum = O
Minimum = 1
+0,3
-0,6
-0,9
+0,4
-0,7
-1 ,I
+0,4
-0,8
-1,2
+0,6
-0,9
-1,3
+0,7
-1 ,o
-1,4
+0,9
-1,o
-1,4
-10
-5
Maximum all @
Minimum = O
Minimum = 1
$
$
+I5
8
+20
Maximum all @
Minimum = O
Minimum = 1
+25
Maximum all @
Minimum = O
Minimum = 1
$
$
+30
Maximum all @
Minimum = O
Minimum = 1
$
* See footnote following Table 11C.
-0.8
al
-0,8
-1 ,I
-0,7
-1,2
+0,6
-0,6
-1,3
+0,7
-0,7
-1,4
+0,9
-0,9
-1,5
+1,1
-1,2
-1,7
+I ,2
-1,4
-1,9
+ I ,3
-1,4
-2,l
+I ,6
-1,3
-1,7
+1,5
-1,3
-1,7
+I ,4
-1,3
-1,7
+I ,5
-1,3
-1,7
+1,8
-1,4
-1,8
+ I ,8
-1,5
-2,o
+1,9
-1,7
-2,2
+ I ,9
-1,8
-2,3
+ I ,9
-1,9
-2,4
+ I ,9
-1,9
-2,6
+0,6
-1,6
-1,9
+0,7
-1,6
-1,9
+0,8
-1,5
-1,9
+0,8
-1,6
-1,9
+I ,3
-1.4
-1,8
+ I ,4
-1,4
-1,8
+I ,4
-1,4
-1,9
+ I ,5
-1,4
-1,9
+I ,6
-1,4
-2.1
+ I ,6
-1,4
-2,2
+I ,7
-0,6
-1,2
+I ,4
-0,6
-1,2
+I ,I
-0,6
-1,3
+0,8
-0,6
-1,4
+0,4
-1 ,I
-2,l
+0,4
-1,4
-2,4
+0,4
-1,8
-2,8
+0,4
-2,o
-3,O
+0,5
-2,o
-3,O
+0,7
-2,o
-3,O
SABS 0160-1989
53
TABLE 11B - MONOPITCH CANOPY ROOFS COMPLYING
WITH THE FOLLOWING LIMITATIONS
n
L
1<-<3and%<-<l
W
W
Roof angle
Section
-1
W/lO
c
K e y plan
1
t
W/lO
c
1
SABS 0160
Org.11899-EC/00-07
5
1
6
Pressure iefficient C,
Local
Roof
angle,
degrees
Solidity
ratio
(P
Overall
Maximum all @
Minimum @ = 0
Minimum ($ = 1
+0,2
-0,5
-1 ,o
+0,5
Maximum all @
Minimum @ = 0
Minimum @ = 1
+0,4
-0,7
-1,l
+O,B
10
Maximum all @
Minimum @ = 0
Minimum @ = 1
15
+I ,8
-1,3
-1 ,a
-1,9
-1 ,I
-1,6
+2,1
-1,7
-2.2
+I ,3
-1,B
-2,3
+0,5
-0,9
-1.3
+1,2
-1,5
-2,l
+2,4
-2,o
-2,6
+I ,6
-2,1
-2,7
Maximum all @
Minimum @ = 0
Minimum @ = 1
+0,7
-1,l
-1,4
+1,4
-1 ,a
-2,3
+2,7
-2,4
-2,9
+I ,a
-2,5
Maximum all @
Minimum @ = 0
Minimum @ = 1
+0,8
-1,3
-1,5
+ I ,7
-2,2
-2,6
+2,9
-2,8
-3,l
+2,1
-2,9
-3,2
25
Maximum all @
Minimum @ = 0
Minimum @ = 1
+I ,o
-1,6
-1,7
+2,0
-2,6
-2,8
+3,1
-3,2
-3,5
+2,3
-3,2
-3.5
30
Maximum all ($
Minimum @ = 0
Minimum @ = 1
+I ,2
-1 ,a
-1 ,a
+2,2
-3,O
+3,2
-3,B
-3,8
0
5
20
* See foo
-0,6
-1,2
-3,O
-3,0
SABS 0160-1989
54
(As amended 1991)
TABLE 11C - MODIFYING FACTORS FOR MULTIPLE-BAY CANOPY ROOFS
Pressures on each slope of multiple-bay canopy roofs are determined by applying
the following factors to the overall coefficients for isolated two-pitch canopies.
1
7
Bay
No.
Location
I
I
3
4
Modifying factor*
1
2
3
End bay
Second bay
Third and subsequent bays
On maximum
overall coefficient
On minimum
overall coefficient
1 ,oo
0,81
0,64
0,63
.
0,87
0,68
*The Coefficientstake account of the combined effect of the wind on both upper and lower surfaces of the canopy for all wind
directions. Where the local coefficient areas overlap, the more severe of the two given values should be taken.
For monopitch canopies, the centre of pressure should be taken to act at 0,25Wfrom the windward edge. For duopitch
canopies, the centre of pressure should be taken to act at the centre of each slope.
Each slope of a duopitch canopy should be able towithstand both the maximum and the minimum pressure, and the whole
canopy should be able to support one slope at the maximum pressure with the other slope at the minimum pressure.
The solidity ratio @ is equal to the area of obstruction under the canopy divided by the gross area under the canopy, both
areas being seen in elevation and normal to the wind direction.
@ = 0 represents a canopy with no obstructions underneath.
@ = 1 represents the canopy fully blocked to the level of the downwind eaves.
Values for C, for intermediatesolidity ratios may be interpolated linearly between these two extremes, and apply upwind of
the position of maximum blockage only. Downwind of the position of maximum blockage, the coefficientsfor @ = 0 may be
used.
In addition to the pressure forces normal to the canopy, there will be horizontal loads on the canopy owing to wind pressure
on any fascia and to friction over both upper and lower surfaces of the canopy. For any wind direction, only the more severe
of these two forces need be taken into account as the presence of a fascia tends to reduce the frictional effect. Fascia loads
should be calculated on the area of the surface on the windward side, using a force coefficient of 1,3. Frictionaldrag should
be calculated using the coefficients given in 5.5.3.4.
Amdt 3,
Oct. 1993
TABLE 12 - Deleted by Amendment No. 3.
SABS 0160-1989
55
TABLE 13 - PRESSURE COEFFICIENT C, FOR GRANDSTANDS, ROOF SLOPE 5"
Allow for local external pressure coefficient C,, of -2,Ofor the shaded area of the upper surface of the roof.
O0
K
-
t
M
The width of the shaded areas may be taken as one-tenth of the total length of the roof and one-seventh of the total width
(in the direction of the cantilever span).
3
8
9
Top and bottom surfaces of roof of stand
e,
0
45
135
180
7
6
10
11
12
13
Pressure coefficient C, for
Wind
angle
degrees
4
Front and back of wall of stand
A
B
C
D
E
F
G
H
J
K
L
-1,O
-1,O
+O,9
-1,O
-0,7
+O,9
+0,4
-0,7
-0,5
+0,9
-0,7
-0,5
+0,9
+0,9
+0,8
-1,l
-0,3
-0.5
-0,6
+0,6
+0,9
+0,9
+0,4
-0,4
-0,6
+0,7
-1,l
-0,7
-1,0
-0.3
-0,6
-0,3
-0,9
+0,8
-1,l
-0,9
+0,3
-1,0
-0,6
-0,3
-0,6
-0,3
M
-0,s
-0,4
-1,o
+0,4
-0,3
+O,g
NOTE
a) In general, the maximum load will occur when the wind is blowing into the open front of the stand.
b) The internal pressure is dependent on a number of factors (e.g. obstructions to windward, spillage through the
stand, and extent of end walls) which must be considered.
c) The majority of simple cases will need less severe loadings than those obtained from the above coefficients,
which should therefore provide a safe but excessive and uneconomic design in a number of situations.
d) For 8 = go", allow for frictional drag Ff in accordance with 5.5.3.4, and apply a force coefficient C,= + I,2 to the
area of any end screen wall.
SABS 0160-1989
56
TABLE 14 - PRESSURE DISTRIBUTION AROUND CYLINDRICAL STRUCTURES
1
Position on
periphery 8,
degrees
2
I
3
I
1
4
5
Pressure coefficient CO,for
Surface smooth
Surface rough or with projections
h*ID = 10
h*lD 1. 2,5
h*ID = 10
+I ,o
h*lD
2 2,5
+1,0
+1,0
+I ,o
+0,9
+0,7
+0,9
+0,7
+0,9
+0,7
+0,9
+0,7
30
40
50
+0,4
+0,4
+0,35
0
+0,35
-0,5
-0,4
-0,7
-0,5
60
70
80
90
100
120
-0.95
-0,8
-1,25
-1,2
-1,l
-1,05
-1,2
-1,4
-1,45
-1,05
-1,25
-1,3
-l,o
-1,4
-0,5
-0,85
-0,65
-0,35
-0,6
-0,4
-0,4
-0,4
-0,3
-0.3
-0.3
-0,35
-0,35
-0.35
-1,2
-0,85
-0,4
-0,251
-0,25
-0,25
0
10
20
140
160
180
0
-0,8
0
-1,l
0
* h is the height of a vertical cylinder or length of a horizontal cylinder. Where there is a free flow of air
around both ends of a cylinder, take h as half the length when calculating h/D.
NOTE
a) The values of C,, in the table may be used for the purpose of calculating the wind forces that act in such a way as to
deform a cylindrical structure. They apply only to supercritical flow (i.e. they should only be used where D > 0,3m).
b) The values may be used for wind blowing normal to the axes of cylinders having their axes normal to the ground plane
(i.e. chimneys, silos) and to cylinders having their axes parallel with the ground plane (i.e. horizontal tanks) provided that
the clearance between the cylinder and the ground is not less than D.
c) Use interpolation to obtain values of C, for intermediate values of h/D.
d) In the calculation of the load on the periphery of the cylinder, take the value of C,,into account.
For open-ended cylinders where h/D 1. 0,3,take C,, as -0,8.
For open-ended cylinders where h/D < 0,3,take C,,as -0,5.
e) The value of q, to be used may be varied over the height of the cylinder in accordance with the wind speed variation
as given in 5.5.2.6(a).
SABS 0160-1989
57
5.5.4.2
Force coefficients
a) Clad buildinas, free-standina walls, hoardinas and similar structures. Force coefficients for
determining the overall resultant along-wind force in accordance with 5.5.3.3are given in Fig. 6 for
rectangular clad buildings, in Table 15 for clad buildings of uniform sections as shown, and in
Table 16 for low walls or hoardings on or above the ground. In general, the value of 9,may be varied
over the height of the building.
b) Unclad buildinas, frames, screens and lattice structures
1) Sinale frames. Calculate the resultant wind force on a single frame for the case where the wind
direction is normal to the plane of the frame unless it can be shown that another wind angle is more
appropriate. Determine the force by means of equation 5(g) in 5.5.3.3but take A, as the net (i.e.
solid) projected area, excluding the openings between members.
The relevant force coefficients are given in Table 17 for a single frame consisting of
i) members of flat-sided cross-section, or
ii) members of circular cross-section,
in which all the members of the frame have DV, values less than 6 m2/sor all members have DV,
values equal to or exceeding 6 m2/s.
When single frames are composed of members of circular cross-section, it is possible that the
smaller members will be in the subcritical flow range (i.e. DV, < 6 m’/s) and the larger members will
be in the supercritical flow range (i.e. DV, 6 m2/s),and there may also be some details fabricated
from flat-sided sections.
~
In this situation, the wind force acting on the composite frame should be calculated by using an
effective force coefficient equal to:
where Z
- Area of the frame in a supercritical flow
A,
Ae
cf( SUP)
cf(Sub)
cf(Flat)
A(Circ. sub)
A (Flat)
A (Sub)
= the total effective frontal area of the frame (i.e. the net solid area)
= the force coefficient of the supercritical range for circular
sections from Table 17
= the force coefficient of the subcritical range for circular sections
from Table 17
= the force coefficient of the flat-sided sections from Table 22
= the effective area of the subcritical circular sections
= the effective area of the flat-sided sections
- A(Circ. sub) + A(Flat)
58
SABS 0160-1989
-a
-E:
\
0
.-I-
d
L
r
c
U
d
01
L
n
\
c
L:
m
._
aJ
I
0,25
0,4
0,6
0,8
1,0
2,o
Breadth/depth ratio b / d
3,O
4,O
7
1
SABS 0160
Org.10831-EC/00-07
To be used with value
o f 9, a t height h o r
with q as a function
o f height
Fig. 6 - Force Coefficients C, for Rectangular Clad Buildings with
Flat Roofs (Force Acting in the Direction of the Wind)
SABS 0160-1989
59
TABLE 15 - FORCE COEFFICIENT C,(ACTING IN THE DIRECTION OF THE WIND)
FOR CLAD BUILDINGS OF UNIFORM SECTION
3
2
1
5
4
6
7
8
9
Force coefficient C,for:
eighffbreadtt
V,b, m2/s
Plan shape
tio
I
up to
Y7
1
-~6
215
10
20
0,8
0,9
l,o
0,7
0,7
0,6
0,6
0,2
0,2
1,l
1,3
1,l
1,3
0,8
0,8
0,5
0,5
l,o
l,o
0.6
0,6
0,3
0,3
0,3
0,3
0,6
0,6
1,2
1,5
l,o
1,2
0,5
0,6
for all surfaces
0.7
6
0,7
for rough' surtaces
6
for smooth surfaces
Ellipse
-
< 10
-
Qb
b/d=1/2
10
-8
-
rj16
b/d=l
r / b =1/3
b/d=l
r / b =1/6
<4
-4
< 10
10
<3
-3
d
All values
All values
c6
0.7
6
*Rough surfaces are those with projections exceeding 1 % of the diameter.
60
SABS 0160-1989
TABLE 15 (continued)
2
1
3
4
5
6
7
8
9
Force coefficient C+for:
V,b, m2/s
Plan shape
c 10
Height
1
2
5
10
08
0,8
0,9
l,o
1,l
0,5
0,5
0,5
0,5
0,9
0,9
1,l
1,2
0,9
0,9
1,l
1,2
0,7
0,7
0,8
0,9
0,4
0,4
0,4
0,5
0,8
0,8
l,o
1,l
0,7
0,8
0,9
1.0
0,7
0,8
0,9
l,o
0,4
0,4
0,4
0,5
1,2
1,2
1.4
1,6
0,7
0,8
0,9
l,o
0,7
0,7
0,7
0,8
l,o
1,l
1,2
1,2
10
All values
-
r / a =1/48
?adth ratio
u p to %
All values
c 11
r / b =1/4
11
m
r / b =1/12
All values
r/b <I140
All values
r / b :1/4
--
8
1/40
<
r/b
< 1/12
All values
c
12
0.7
12
All values
1 ,o
NOTE
a) Where strakes are used, b may be taken as the width over the strakes. Structures that because of their size and the
design wind speed are in the supercritical flow range, may need further calculation to ensure that the greatest loads do
not occur at some wind speed below the maximum when the flow will be subcritical.
b) The coefficients are for the buildings without projections, except where otherwise shown.
c) In this table, V,b is used as an indication of the air flow regime.
d) The table may also be used for horizontally orientated members or structures, i.e. where the given shape is the end
elevation rather than the plan. In such cases, the heighvwidth ratio becomes the length/width ratio. Where there is a free
flow of air around both ends of the structure, the effective length should be taken as half the actual length, when calculating
the lenath/width ratio for use in the table. Where flow around both ends is orevented. the ratio should be taken as infinitv.
e) Theialue of q, may be varied over the height of the building in accordance with.the wind speed variation as given in
5.5.2.6(a).
61
SABS 0160-1989
TABLE 16 - FORCE COEFFICIENT C, FOR LOW WALLS
OR HOARDINGS (LESS THAN 15 rn HIGH)
b
I-
Tek.10831pAC/00-07
h'
3
0,25 h
1
I
I
2
3
Force coefficient C,
(wind normal to the face)
Width to height ratio b/h
Wall above around
Wall on around
From 0,5 to 6
10
16
20
40
60
80 or more
From 1 to 12
20
12
1.3
1.4
1.5
1.75
18
2.0
32
40
80
120
160 or more
TABLE 17 - EFFECTIVE FORCE COEFFICIENT C,
FOR SINGLE FRAMES
1
2
I
3
I
4
Force coefficient C, for:
I
* The solidity ratio I$= the effective area of a frame normal to the wind
direction divided by the area enclosed by the boundary of the frame
and normal to the wind direction.
62
SABS 0160-1989
2) Multiple frames. For structures having two or more frames in parallel where the
windward frame(s) may have a shielding effect on the leeward frame(s), calculate the
resultant wind force on the windward frame(s) and on any unsheltered parts of other
frames as in (1) above, but multiply the force on the sheltered frame(s) (calculated in the
same manner) by a factor rl, which is taken from Table 18. Where there are more than
two frames of similar geometry and spacing, take the wind force on the third and
subsequent frame(s) as being equal to that on the second frame.
Add together the loads on the various frames to obtain the total load on the structure.
TABLE 18 - SHIELDING FACTOR tl
2
1
I
3
I
4
I
I
5
I
6
Spacing ratio*
brodynan
solidity ratis
0,1
092
03
0,4
03
0,96
0,97
0,97
0,90
0,91
0,92
o,ao
3,O
1,o
1,o
1,o
o,a2
o,a4
0,6a
0,71
0,74
40
5,O
6,Oand over
1,o
1,o
1,o
o,ga
0,98
0,99
0,93
0.94
0,95
o,a6
0,77
u p to l , o
2.0
I
7
I
a
I
9
Value of shielding factor r l for:
o,aa
0,8 and
0,49
0,43
0,63
o,ao
o,a3
* The spacing ratio = the distance, centre to centre, of the frames, beams or girders divided bythe leastoveralldimension
of the frame, beam or girder measured at right angles to the direction of the wind. For triangular framed structures or
rectangularframed structures diagonal to the wind, calculate the spacing ratio from the mean distance between the
frames in the direction of the wind.
+
x a constant where the solidity ratio is as given in the footThe aerodynamic solidity ratio fi = solidity ratio
= 1,6 for flat-sided members
note to Table 17 and the constant
= 1,2 for circular members in the subcritical range and for flat-sided
members in conjunction with such circular members
= 0,5 for circular members in the supercritical range and for flat-sided
members in conjunction with such circular members.
0,90
(a)
3) Lattice towers. Lattice towers of square and equilateral triangular plan form are special
cases of multiple frame structures that are commonly encountered and for which it is
more convenient to use an overall force coefficient in calculating resultant wind forces.
Calculate the resultant wind force in the along-wind direction by means of equation 5(g)
in 5.5.3.3, using a force coefficient C, taken from Table 19 for towers composed of
flat-sided members and from Table 20 or 21 for towers composed of rounded members
and having all members in the same flow range, whether subcritical or supercritical.
NOTE
i) For convenience, the calculation is based on the wind blowing normal to a face, and the effective area A,
is therefore the net (solid) area of the front face alone. For triangular towers, the along-wind force may be
assumed to be constant for any inclination of the wind to the face. For square towers, the maximum
along-wind force occurs when the wind blows onto a corner. Tables 19 and 20 therefore give an additional
set of (larger)coefficients to cover this case; the effective area for the calculation,however, remains the same
as for the wind normal to the face, and only the direction of the resultant force and the force coefficient
change.
ii)Tables20and 21 applyonlywhenall membersforming thetowerareeitherinsubcriticalor in supercritical
flow. Where this is not the case, the wind force should be calculated as for the multiple frames with
appropriate allowance for shielding of the leeward frames as set out in (2) above.
SABS 0160-1989
63
TABLE 19 - OVERALL FORCE COEFFICIENT CfFOR LATTICE TOWERS
COMPOSED OF FLAT-SIDED MEMBERS
I
1
I
2
I
3
4
Force cof Kcient C, for:
Solidity ratio @
Equilateraltriangular towers
Square towers
All wind directions
3,1
23
23
2,9
22
2,o
2,9
2.2
13
1
1
2
3
I
I
4
5
Force coefficient C, for:
Solidity ratio of front
face @
Subcritical flow,
DV, < 6 m2/s
Supercritical flow,
DV, 1 6 m2/s
Onto face
Onto corner
Onto face
Onto corner
2,1
1,9
1,7
2,4
22
2,o
1,4
13
13
1,3
1,3
1,4
1,4
1,9
1,9
13
12
1.6
1.5
1,5
1,6
1,7
1,7
0,05
0,l
0.2
03
0,4
03
13
TABLE 21 - OVERALL FORCE COEFFICIENT CfFOR EQUILATERAL
TRIANGULAR LATTICE TOWERS COMPOSED OF ROUNDED MEMBERS
1
Solidity ratio of front
face @
I
2
I
3
I
I
4
5
Force coefficient C,for:
1
1
Subcritical flow,
DV, < 6 m2/s
Supercritical flow,
DV, 6 m2/s
All wind directions
All wind directions
13
1,1
1 ,I
1,l
1,7
13
13
13
~
1.1
1.1
NOTE: For all towers and frames, the value of qz may vary over the heights of the structure in accordance
with the wind speed variation as given in 5.5.2.6(a).
c) Individual structural members. Calculate the resultant along-wind force on individual
structural members by means of equation 5(g) in 5.5.3.3,
using the appropriate force
coefficients from Table 15.
SABS 0 160-1989
64
In the case of shapes of more complex cross-section such as angles, channels or
fabricated sections, calculate the normal and transverse components of the resultant
force on the member as follows:
Transverse force Ft = C, 9,KOj
5(1)
where C, and C, are coefficients for members of infinite length as given in Table 22
K = a reduction factor for members of finite length as given in Table 23
Q
= the length of the member
j
= the reference dimension of the member's cross-section as given in
Table 22
The coefficients apply to wind normal to the longitudinal axis of the member and the
reference plane for the normal and transverse force components is given in Table 22.
5.5.5
Dvnamic Effects. Carry out appropriate analyses or tests to ascertain the significance of
windinduced excitation or oscillation of buildings or structural elements whose shape,
mass, natural frequencies of vibration, and damping characteristics render them
susceptible to such dynamic effects. Such investigations should cover the effects of
dynamic behaviour on the strength and stability of the structure and, in addition, the
possible effects of building motion on the occupants or activities within the building.
Commentary:
a) The dynamic response of buildings to wind forces can be broadly
classified into the following two categories:
1) Effects which arise from fluctuations in wind force owing to the natural
turbulence or gustiness of the wind. These are commonly known as
buffeting and the forces and motion of the building are primarily in the
along-wind direction, although asymmetry of the structure or the fluctuation
of the wind forces can give rise to transverse or torsional motion.
2) Effects which arise from fluctuations in wind force owing to interaction
between the wind flow and the building. These are distinguished by the fact
that the forces and motion of the building are essentially transverse to the
mean wind direction. These effects include
i) vortex excitation which results from fluctuating forces owing to
unsteadiness in the wake flow of a bluff body such as a cylinder;
ii) galloping and flutter which are instability phenomena peculiar to certain
cross-sectional shapes and involve forces related to, and in phase with, the
transverse motion of the structure.
In practice, along-wind and cross-wind effects tend to occur in combination,
leading to complex response modes such as the elliptical motion traced by
the tip of a slender chimney stack. Both categories of dynamic response
may also be significantly affected by the wake flow of structures in close
proximity to one another.
b) The following is a guide to the conditions under which investigation of the
various dynamic effects is desirable (where doubt exists, specialist advice
should be sought):
SABS 0160-1989
65
TABLE 22 - NORMAL AND TRANSVERSE FORCE COEFFICIENTS Cfn
AND C, FOR INDIVIDUAL STRUCTURAL MEMBERS OF INFINITE
LENGTH AND OF FLAT-SIDED CROSS-SECTION
0
45
90
+1,4
+1,2
0
0
+1,6
+2,2
+2,05
+1,95
+0,5
+1,6
+1,5
0
0
+0,6
+0,9
0
+1,5
+1,9
+2,0
+1,8
0
0
+0,1
+0,1
+2,1
+1,4
0
0
+2.0
+1,55
0
+0,7
+0,75
0
+I,%
+2,0
NOTE: In this table the normal and transverse force coefficients C," and C,,are given in relation to the dimension j
and not, as in other cases, in relation to the effective frontal area A.
TABLE 23 - REDUCTION FACTOR K FOR STRUCTURAL
MEMBERS OF FINITE LENGTH AND SLENDERNESS
AND OF FLAT-SIDED CROSS-SECTION
1
2
3
4
5
6
7
8
5
10
20
30
50
100
00
0,6
0,70
0,80
0,85
0,90
0,95
Lengthlfrontal width
Qlis
K
1,0
SABS 0160-1989
66
(As amended 1991 and 1993)
1) Along-wind buffeting: Significant dynamic response may occur in tall
buildings, masts, towers and stacks, or other slender structures exceeding
100 m in height or with a ratio of height to minimum effective width of 5 or
more or with natural periods of vibration longer than 1 s . Some analytical
methods for predicting the response of structures to buffeting, such as the
so-called gust-energy methods, are based on the use of a maximum mean
hourly wind speed rather than a maximum 3 s gust speed. D-I of
Appendix D includes a map of mean hourly wind speeds with a 50-year
return period.
2) Vortex excitation: Lightly damped, slender structures of circular or near
circular cross-section such as unlined, welded steel chimney stacks are
particularly prone to this form of excitation but slender concrete stacks,
towers and unusually slender, tall buildings of similar cross-section may also
require investigation.
3) Galloping: This tends to be confined to extremely slender, low mass,
lightly damped structures or elements of triangular, rectangular,or D-shaped
cross-section. The classical example is that of iced powerlines or iced stay
cables, and it is seldom a problem in building structures. Wind tunnel testing
may be required to determine the critical parameters.
4) Flutter: This is typically a problem with long-span bridge decks of low
stiffness such as those in suspension bridges. Wind tunnel tests are
commonly used to investigate the problem.
Reference should be made to A-2 of Appendix A for a list of publications in
relation to the above phenomena.
5.5.6
Simplified Wind Load Desian. The simplified wind forces set out below may be adapted
for design purposes, provided that the building complies with the following requirements:
- it is rectangular in plan, and
- its overall height does not exceed 20 m, and
-the ratio of its overall height to its lesser plan dimension does not exceed 4.
The values given allow for internal positive or negative pressurization resulting from a
dominant opening in one wall. (Refer also to Subsection (a) of the Commentary to 5.5.1 .)
a) For the overall wind forces for stability analysis:
1) A horizontal force due to a pressure of 1,Iq, N/m2acting on the projected area of the
building (including its roof) normal to the wind direction;
2) an upward force due to a pressure of 1,6 q, N/m2acting on the plan area of the roof.
b) For the design of a wall as a whole and for the design of wall claddings and their
fixings in regions other than those given in (c) below, a pressure on the external surFace
of the wall of
+I
,6 q, N/m2or
-1,4 q, N/m2
Amdt 3,
Oct. 1993
c) For the design of wall claddings and their fixings in areas within a distance h from the
corners of the building, or 0,15 w (whichever is less), a pressure on the external surface
of the wall of
+I
,6q, N/m2or
-1 ,8q, N/m2
67
SABS 0160-1989
(As amended 1990,1991 and 1993)
d) For the design of roof elements and for the design of roof claddings and their fixings
in areas other than those given in (e) below, a pressure on the external surface of
+I
,3 q, N/m2or
-1,8 q, N/m2
e) For the design of roof claddings and their fixings in areas within a distance h from any
edge of the roof, or 0,15 w (whichever is less), a pressure on the external surface of
+I ,3 q, N/m2or
-2,6 q, N/m2
where
q, =
free-stream velocity pressure at the top of the building, as given in
Table 24, N/m2
w =
the width of the building, m
h
=
the height of the walls to eaves or parapet level, rn
NOTE: Positive pressure acts normal to and towards the surface. Negative pressure acts normal to and
away from the surface.
TABLE 24 - VELOCITY PRESSURE q, FOR
SIMPLIFIED PROCEDURE
4z(N/m2)
Terrain category
Height to top of building
m
5
10
15
20
1
2
3or4
1009
1 110
1 180
1230
820
930
1000
1060
390
480
590
670
5.6
EARTHQUAKE LOADS
5.6.1
Seismic Hazard Zones. Seismic zones applicableto South Africa are given in Fig. 7. Two
zones are identified, namely
Zone I : Low natural seismic activity.
Zone II: Regions of mining-induced seismic activity.
Amdt 3,
Oct. 1993
SABS 0160-1989
68
(As amended 1990 and 1993)
22'
22'
26'
26'
30'
30'
34'
34'
Fig. 7 - Seismic Hazard Zones of South Africa
Buildings and structures situated in Zone I are required to comply with the detailed
seismic design, as given in 5.6.5.
Buildings situated in Zone II need only comply with the minimum requirements for
structural and non-structural components as detailed in 5.6.7.1 and with the requirements
for ties, continuity and anchorage, as detailed in 5.6.7.2 and 5.6.7.3.
Commentary:
South Africa is characterized by low seismicity, as shown in the design
seismic hazard map of South Africa given in Fig. 8. The zones are defined
in terms of the peak ground acceleration with a 10 % probability of being
exceeded in a 50-year period, and include both natural and mining-induced
seismicity. This map is based on an assessment of the known seismic
history of the region since the beginning of the 19th century (Shapiro and
Fernandez, 1987; Fernandez and Shapiro, 1989). The estimates of seismic
hazard for the gold mining areas are gross estimates, and a more detailed
analysis would be required for specific applications, owing to the fact that
seismic activity changes substantially in time and space according to the
changes of mining activity.
NOTE: Peak ground accelerations with a 10 % probability of being exceeded in a 50-year
period are given in Table 25 for selected stations in South Africa.
Amdt 3,
Oct. 1993
SABS 0160-1989
69
(As amended 1990)
22
26
30
34
Fig. 8 - Seismic Hazard Map of South Africa
TABLE 25 - PEAK GROUND ACCELERATIONS a,, WITH A 10 %
PROBABILITY OF BEING EXCEEDED IN A 50-YEAR PERIOD
1
Station
I
2
(9)
0,070*
a10
Johannesburg
Cape Town
Maseru
0,100
0,080
Port Elizabeth
Mbabane
Bloemfontein
0,030
0,040
0,035
Pretoria
Mmabatho
Durban
0,050
0,022
0,013
‘Natural events only.
The highest natural seismic activity for which the peak ground acceleration
exceeds 0,05g occurs in the south-eastern Cape and around Lesotho.
A selected list of ground accelerationsof mining-induced seismicity recorded during 1986 is given in Table 26 (Milford, 1987). Peak ground
accelerations exceeding 0,2g are common, and the highest recorded peak
acceleration during this period was 0,45g at Carletonville. A peak ground
acceleration of 0,39g was recorded at Klerksdorp in 1977 (Fernandez and
van der Heever, 1982).
SABS 0160-1989
70
(As amended 1990 and 1993)
TABLE 26 - RECORDED PEAK GROUND ACCELERATIONS a(g)
AND VELOCITIES v DUE TO MINING-INDUCED SElSMlClTY
1
2
3
Station
4s)
v(m/s)
0,139
0,079
0,012
0,009
0,247
0,292
0,019
0,029
0,263
0,094
0,034
0,009
0,293
0,450
0,051
0,067
0,046
0,033
0,004
0,002
0,061
0,059
0,003
0,004
0,071
0,052
0,003
0.002
Carletonville
Klerksdorp
5.6.2
Desiqn Considerations for Multistorev Buildinqs in Zone I and Zone II
a) Svmmetrv in plan. Symmetry is important in both directions in plan, as lack of
symmetry produces torsional effects that are difficult to assess properly and can be very
destructive. T-shaped and L-shaped plans should not be used, and H-shaped plans
should also be avoided.
b) Continuitv of structural strenath. Astructure should be designed to have a uniform and
continuous distribution of strength and stiffness. Abrupt changes in structural strength or
stiffness from one floor level to another or from one part of a floor to another should be
avoided (see Fig. 9). The load-bearing members should be uniformly distributed.
The structure should have adequate redundancy and multiple ways of resisting lateral
forces.
Recommended
N o t recommended
a) Avoid cantilevers:
No fail-safe mechanism
b) Avoid changes of stiffness
w i t h height
Shear wall
Fig. 9 - Continuity of Structural Strength
71
SABS 0160-1989
(As amended 1990)
c) Horizontal and vertical members. Joints between beams and columns shall be as
monolithicand fully continuous as possible, using strong columns with weaker beams to
ensure that the horizontal members fail before the vertical members fail. Beams should
be free of offsets. Very slender columns should be avoided, as large second order effects
can result in high ductility.
The ability of a structure to absorb energy is dependent on the ductility of the members,
and both reinforced beams and columns require sufficient stirrups to provide
confinement.
d) Foundations. A good seismic-iresistant form of a structure is such that the vertical
loading is likely to be symmetrical.
In certain soils, liquefaction of the :jail may be possible.Where friction piles are used, the
ability of these piles to sustain repeated loads should be carefully examined.
e) Non-structural elements. lnfill panels of partial-height should be avoided as these
create short column conditions, frequently resulting in severe damage to the columns.
Full-height infill panels should be used with movement joints that can accommodate
horizontal and vertical movement in the range 20-40 mm . In the latter case, care shall
be taken to ensure adequate detailing to provide lateral stability of the elements to
out-of-plane forces.
5.6.3
Plannina Considerationsfor Low-rise Housina in Zone II
a) Svmmetrv in dan. Single-storey buildings should be so planned that there is a good
distribution of bracing walls and should preferably be of simple box plan providing
reasonably symmetrical resistance in two orthogonal directions (see Fig. 1O(a)). Slender
wings should be avoided, as well as buildings and rooms with essentially three resisting
walls (see Fig. 10(b)).
iH7R
a) Satisfactory
(b) Unsatisfactory
Fig. 10 - Plans of Shear Walls in Low-rise Housing
b) ODeninqs in walls. Openings for doors or windows require care in positioning and
detailing in order to obtain a uniform distribution of strength. The distribution of openings
in walls should be as uniform as possible, and the total area of openings should not
exceed one-third of the wall area. Large openings in masonry walls are undesirable,
particularly in external walls near corners (see Fig. 11).
( a ) Satisfactory
(b) unsatisfactory
Fig. 11 - Openings in Low-rise Masonry Construction
Org 12122-EC/00-07
72
SABS 0160-1989
(As amended 1990,1991 and 1993)
c) Roofs. Heavy roof structures such as tiled roofs are undesirable, especially on
lightweight wall construction. The roof framing must be well braced against lateral
movement.
d) Walls. Masonry walls reinforced with steel bars or wire will minimize deformation and
possibly prevent catastrophic collapse.
e) Gables and parapet walls. Gable construction should be avoided, and preference
given to hipped roofs. If masonry gables and parapet walls are used, they should be
reinforced.
f) Horizontal continuity. Horizontal continuity at roof level should be provided by special
connections or lapping reinforcement, and such continuity should go around facade
corners.
q) Chimneys and decorative panels. Elements that are stiffer and heavier than the rest
of the building, such as masonry chimneys and heavy decorative panels, should be
avoided. These elements, and the adjoining elements, are very susceptible to damage.
h) Articulation. Considerable amounts of differential horizontal and vertical movement
can be imposed on a low-rise building that has conventional foundations. Such
movements should be allowed for in the structure by providing suitable continuity or
articulation of the structure, especially at roof level. It is recommended that 40 mm wide
continuous vertical joints at intervals of 10 m be used above the base level of the
bui Iding.
5.6.4
Desian Load Effect and Load Combinations
5.6.4.1
Load factors and importance factors. The design load effect shall be obtained by
multiplying the effects of the nominal loads by the relevant partial load factors and the
relevant combination factors and, where applicable, by an importance factor as set out
in Section 4.
5.6.4.2
Orthoaonal effects. Earthquake forces act in both principal directions (in plan) of the
building simultaneously, but the earthquake effects in the two principal directions are
unlikely to reach their maximum simultaneously.
Arndt 3,
Oct. 1993
The direction of application of the seismic forces used in design shall be that which will
produce the most critical load effect combination. This condition may be assumed to be
satisfied if the following combination is used: 100 % of the forces for one direction plus
30 % of the forces for the perpendicular direction.
Commentary:
The provisions for representing the combined maximum effect have been
adopted from ATC3-06.
5.6.5
Seismic Base Shear
5.6.5.1
Seismic forces. The seismic forces are based on the equivalent static lateral force
procedure, in which the design base shear is defined in terms of the nominal base shear
coefficient C, and the factored sustained portion of the gravity load. This procedure is
only applicable to areas of natural seismicity.
The total horizontal nominal seismic force V,,on a structure shall be calculated as follows:
v,,= c,.w,,
where
C,
= nominal seismic base shear coefficient, as specified in 5.6.5.2
W,, = nominal sustained vertical load acting on the structure, as specified in
5.6.5.6
73
SABS 0160- 1989
(As amended 1990)
TABLE 27 - Deleted by Amendment No. 3.
TABLE 28 - Deleted by Amendment No. 3.
5.6.5.2
Seismic base shear coefficient. When the natural period of the building is computed, the
base shear coefficient C,shall be determined in accordance with the following formula:
where
a,
= nominal ground acceleration, normalized by the acceleration due to gra-
vity g; a, = 0,lO in Zone I
Amdt 2,
Nov. 1991
R(T) = normalized design response spectrum, as in 5.6.5.3
T
= fundamental period of vibration of the structure (in seconds), as in
5.6.5.4
K
= a behaviour factor, as in 5.6.5.5
Amdt 3,
Oct. 1993
Where the fundamental period T lis not calculated, the value of C, shall be determined
in accordance with the following formula:
a" .Rcl
c,= -
K
where
Ro is as defined in 5.6.5.3.
TABLE 29 - Deleted by Amendment No. 3.
5.6.5.3
Amdt 2,
Nov. 1991
NormalizedresDonse spectrum. The normalizedresponse spectrum R(T) corresponding
to three soil profiles is given in Fig. 12, and defined below:
R(T)=RoforO< T < To
R(V = Ro(T0mR
and R(T) > 0,3R, for T > To
where the parameters Ro,Toand 0 are as given in Table 30.
Amdt 3,
Oct. 1993
SABS 0160-1989
74
(As amended 1990 and 1993)
I
rl
0,o
s1.
s2
0,s
Drg.12127-EC/00-07
Period T s
Fig. 12 - Normalized Response Spectra R(T)
TABLE 30 - NORMALIZED RESPONSE SPECTRUM PARAMETERS
1
2
3
4
Soil
R,
To
n
s1
s2
s3
23
2,5
20
0,4
0,6
1,o
213
213
213
The three soil profiles are defined as follows:
Soil profile S1: Rock (shear wave velocity exceeding 1 000 m/s) or stable deposits or
unconsolidated minerals as for S2, with a depth of less than 50 m on a solid rock base.
Soil profile S2: Stable deposits (compact sands and gravels or stiff clays) of depth
exceeding 50 m on a solid rock base.
Soil profile S3: Soft-to-medium-stiff deposits (sands, stiff clays) having a depth of 10 m
or more.
When the site conditions are not fully known or if the site investigations do not enable any
of the profiles to be used, then the most unfavourable of the three curves shall be used.
5.6.5.4
Amdt 3 ,
Oct. 1993
Fundamental period of vibration. The fundamental period of vibration T(in seconds) may
be determined by taking into consideration the properties of the building in the direction being analysed, and assuming that the base of the building is fixed. The value of T
may not exceed 1,2T, . Alternatively, the value of T may be taken as equal to the approximate period of the building T, obtainable from the following formula:
For moment-resisting structures where the frames are not enclosed or do not adjoin more
rigid components tending to prevent the frames from deflecting when subjected to
seismic forces:
75
SABS 0160-1989
(As amended 1990)
T, = C, . h,3’4
where
C,
= 0,09for steel frames
C,
= 0,06 for concrete frames
h,
= height above the base to the highest level of the frame of the building, m
For buildings with shear walls or exterior concrete frames utilizing deep beams,
.T,
=
0,09 h + l f i
where L = overall length of the building at the base in the direction under
consideration, m
5.6.5.5
Behaviour factor
a) The behaviour factor K depends on the structural system used. In the absence of a
more detailed assessment and taking into account the required detailing requirements,
the factors given in Table 31 shall be used.
b l Structural svstems. For the purposes of Table 31 structural systems are defined as
follows:
1) Bearincl wall svstems. A system of walls or frames as vertical elements for resistance
to lateral seismic forces. Horizontal elements of the seismic-resisting system may be
diaphragms or trusses.
2) Buildina frame svstem. A system with essentially a complete space frame providing
support for vertical loads, with shear walls or vertical bracing trusses to resist the lateral
seismic force. The frame and :shear walls shall conform to the requirements of
SABS 0100 for reinforced concrete and of SABS 0162 for structural steel.
3) Moment-resistincl frame svstern. A structural system with an essentially complete
space frame providing support for vertical loads. Seismic force resistance is provided by
moment-resistingforces by flexure as well as the total prescribed forces along the axis
of the member.
i) Ordinarv reinforced concrete frame. A moment-resistingframe of ordinary reinforced
concrete without special provision for ductility in the load-carrying system and that
complies with the provisions of SHBS 0100.
ii) Ordinarv steel frame. An ordinary steel frame that complies with the provisions of
SABS 0162.
iii) Space frame. A structural system composed of interconnectingmembers, other than
bearing walls, which is capable of supporting vertical loads and may also provide
resistance to seismic forces.
SABS 0160-1989
76
(As amended 1990,1991 and 1993)
TABLE 31 - BEHAVIOUR FACTOR K
1
2
Structural system*
Behaviour factor K+
Bearing wall system:
Unreinforced masonry walls
Reinforced concrete or reinforced masonry
walls or braced frames
One-, two-, or three-storey steel frame
systems
Building frame system:
Moment-resisting frame system:
Ordinary concrete frames
Ordinary steel frames
Elevated tanks and inverted pendulum
type structures:
Structures required to remain elastic
* See the definitions applicable to structural systems given in (b) above.
+ The behaviour factors shall be reduced by a factor of 1,2 for use with
structures comprising reinforced concrete flat or waffle slabs, and by the
factor of 1,4 for use with structures comprising prestressed concrete flat or
waffle slabs
5.6.5.6
Sustained vertical load. The sustained vertical load shall be taken as the total nominal
weight of the building (including partitions and permanent equipment) and the sustained
portions of the imposed vertical loads. In the absence of other information, the sustained
portion of the imposed vertical loads W shall be taken as:
W = D, + CYL,,
I
where
D, = nominal self-weight load
Lni = imposed vertical loads
= load combination factor (see Table 2)
5.6.6
Distribution of Seismic Forces
5.6.6.1
Vertical distribution of seismic forces. The lateral seismic shear force Fx,induced at any
level shall be determined in accordance with the following formula:
where V,, = seismic base shear (see Section 5.6.5)
Amdt 3,
Oct. 1993
c,,
=
:
Wxh
Wihr
I
SABS 0160-1989
77
(As amended 1990,1991 and 1993)
where
= 1,Ofor buildings having a period of 0,5s or less
k
= 2,O for buildings having a period of 2,O s or more
= 1 + (2T- 1)/3 for a period of between 0,5s and 2,O s
5.6.6.2
W,,Wi
= portion of the vertical load at or assigned to level x or i, respectively
h,,hi
= height above the base to level x or i, respectively
Horizontal shear and torsion. The nominal seismic shear force V,,, at any level shall be
determined in accordance with the following formula:
t
V,, = ZFi,
I=x
where F,, = the lateral shear force induced at any level, determined in accordance
with 5.6.6.1
Amdt 3,
Oct. 1993
The force V,, shall be distributed to the various vertical components of the seismicresisting system in the storey below level x, with due consideration given to the relative
stiffnesses of the vertical components and the diaphragm.
For asymmetric buildings, the design shall provide for the torsion moment M,, resulting
from the location of the building masses plus the tensional moments M,,, caused by
assumed displacementof the mass each way from its actual location by a distance equal
to 5 % of the dimensions of the Ixdding perpendicular to the direction of the applied
forces.
5.6.7
Structural ComDonent Load Effects
5.6.7.1
Lateral forces on elements of structures and non-structural comDonents. Parts of
structures, non-structural components, and their anchorages to the main structural
system shall be designed to resist a lateral force equal to
where
Fpn = nominal seismic force acting on the element
a,
= nominal peak ground acceleration normalized by g, but at least 0,l
C,
= a seismic force coefficient given in Table 32
Wpn = weight of the element under consideration, plus imposed load if
applicable
The distribution of these forces shall be in accordance with the vertical loads pertaining
thereto.
Amdt 2,
Nov. 1991
SABS 0160-1989
78
(As amended 1990 and 1991)
TABLE 32 - SEISMIC FORCE COEFFICIENT C, FOR ELEMENTS OF
STRUCTURES AND NON-STRUCTURAL COMPONENTS
Amdt 2,
Nov. 1991
1
2
Structural element or non-structural component
Seismic force coefficient C,
Cantilever elements such as parapets, cantilever
walls, and chimneys on buildings
2,o
Load-bearing and non-load-bearing wall
elements, cladding elements, and partitions
1,o
Various installations in buildings such as pumps,
machines, tanks, pipes, etc
5.6.7.4
O,5to 1,O
DiaDhraams. Floor and roof diaphragms shall be designed to resist a minimum horizontal
force FDnequal to
a) 0,5a, times the weight of the diaphragm and other elements of the building attached
thereto, plus
b) the portion of V, required to be transferred to the components of the vertical seismicresisting system because of offsets or changes in stiffness of the vertical components
above and below the diaphragm,
in accordance with Section 5.6.6.2.
Commentary:
The provisions for lateral forces on elements and non-structural components have been adopted largelyfrom ANSl A58.1-1982, but categorized
to bring them more into line with the provisions in use in this code of practice. The provisions for ties and continuity, concrete and masonry wall
anchorages and diaphragms have been adopted from ATC3-06 (which is
similar to that used in ANSl A58.1-1982).
5.7
LOADS DUE TO OVERHEAD TRAVELLING CRANES
(See also E-6.4.4 of Appendix E.)
5.7.1
General. Where overhead travelling cranes are intended or likely to be installed in a
building, make provision in the design of the building or of any part of the building for the
characteristic or service loads imposed by such cranes.
5.7.2
Classification of Travellina Cranes. The design procedures described in the relevant
subsections relate to the following types of cranes:
Class 1: Liaht Dutv
Hand cranes
79
SABS 0160-1989
(As amended 1990)
Class 2: Medium Dutv
Cranes for general use in factories and workshops
Warehouse cranes - intermittent operation
Power station cranes
Machine shop cranes
Foundry cranes
Class 3: Heavv Dub
Warehouse cranes - continuous operation
Scrapyard cranes
Rolling mill cranes
Grab and magnet cranes - intermittent operation
Ladle cranes in steelworks
Class 4: Extra Heavv Duty
Grab and magnet cranes - continuous operation
Soaking pit cranes
Ingot stripping cranes
Furnace charging cranes
Forging cranes
Claw cranes
Commentary:
The types of cranes listed cover most of those likely to be encountered in
practice, but the list cannot be all-inclusive. In the case of crane types not
covered, the owner should decide the class of crane, preferably in consultation with the crane supplier.
The designer or owner may, at his discretion, allocate to any crane a higher
classification than is indicated in this subsection.
5.7.3
Vertical Wheel Loads. Take as the vertical wheel loads imposed on the gantry by a crane
the values provided by the crane manufacturer or specified by the owner. These are
referred to as the static wheel loads.
Make an allowance for impact and other dynamic effects in the vertical direction by
multiplying the static wheel load by the appropriate of the following factors:
Class 1 cranes : 1,I
0
Class 2 cranes : 1,20
Class 3 cranes : 1,251
Class 4 cranes : 1,30
Commentary:
It is important that crane loads be accurately ascertained as regards both
the wheel loads and their spacings. Where it is necessary to use a
preliminary assessmentof crane loads in the design, this should be checked
against the actual loads once these are finalized. It should never be
assumed that incorrect loading information can be compensated for by the
impact factor.
SABS 0160-1989
80
(As amended 1990)
The designer or owner may, at his discretion, specify higher wheel loads
than those given by the crane supplier to allow for the possible future
uprating of existing cranes or the installation of cranes of higher capacity.
5.7.4
Horizontal Transverse Forces
NOTE: The horizontal forces detailed in 5.7.4-5.7.6 need not be assumed to act simultaneously.
Take the horizontal forces imposed on the gantry by a crane and acting at the top of the
crane rails in a direction transverse to the direction of travel of the crane, to be the most
adverse of the following:
a) Allowance for acceleration or brakinq of the crab. Apply a force equal to the combined
weight of the crab and load lifted, multiplied by the appropriate of the following factors:
Class 1 cranes
Class 2 cranes
Class 3 cranes
Class 4 cranes
: 0,05
: 0,lO
: 0,15
: 0,20
Divide such force among all the crane wheels, taking into account the relative transverse
stiffness of the crane rail supports.
Commentary:
The above factors are based on the assumption of reasonably even
distribution of vertical load among the crab wheels. In certain types of crane
where the centre of gravity of the crab and other components rigidly
attached to it (e.g. the mast of a claw crane) is appreciably below the level
of the crab rail, the distribution of vertical load during acceleration or braking
will not be even, owing to inertia or momentum effects. In such cases, or any
other cases where appreciably uneven distribution is likely to be present, the
resultant vertical loads on the driven or braked crab wheels should be
ascertained or calculated and the relevant horizontal forces assessed,
assuming a coefficient of friction of 0,20 between wheels and rails.
b) Allowance for Dossible misaliqnment of crane wheels or qantw rails. Apply at each
wheel a force P, such that
p = -X M
'
N
where
X
= the appropriate of the following factors:
Class 1 cranes
Class 2 cranes
Class 3 cranes
Class 4 cranes
and
: 0,05
: 0,12
: 0,15
: 0,20
M = combined weight of crane bridge, crab, and load lifted
N = total number of crane travel wheels
Assume the forces P, to act in either of the direction combinations shown in Fig. 13,
whichever is the most severe.
SABS 0160-1989
81
Fig. 13 - Plan View of Crane Showing Direction of Transverse Forces P,
Commentary:
The two direction combinations of forces P, shown in Fig. 13 are intended
to allow respectively for a toe-out or toe-in misalignment of the wheels, or
a correspondingmisalignmentof the gantry rails. Note that the forces P, are
equal on both ends of the crane. The forces are specified as being applied
at both ends to enable an assessment to be made of the transfer of forces
through the roof structure of a building. This is of particular importance in
portal frame buildings and buildings having lightly constructed roof trusses,
where the presence of such forces might otherwise be overlooked.
c) Allowance for skewinq of crane in plan, caused by wheel or gantry rail misalignment
or by braking or acceleration of the crane with the crab at the extremity of its travel.
1) In the case of a crane not guided by rollers, apply at each wheel a force P2 equal to
1,5 times the force P, (see (b) above). Assume the forces P2 to act in either of the
direction combinations shown in Fig. 14, whichever is the most severe.
I
SABS 0160
Dra.ll&33-EC/00-07
Fig. 14 - Plan View of Crane Showing Direction
of Transverse Forces P2
2) In the case of a crane guided by horizontal rollers located at one end of the bridge,
apply a force P3at each pair of rollers as shown in Fig. 15 such that the couple produced
by the forces is equal to 1,3 times the couple that would have been produced by the
forces P2 at one end of a crane not guided by such rollers.
I
SABS 0160
Drg.ll433bEC/00-07
Fig. 15 - Plan View of Crane Showing Direction of Transverse Forces P3
I
SABS 0160-1989
82
(As amended 1993)
Commentary:
The forces imposed by guide rollers are difficult to determine accurately but
are known to be severe. This subsection makes provision, albeitempirically,
for the action of guide rollers and is intended to ensure that gantry rails, their
fixings, and the lateral support of the girders, are adequately catered for in
the design.
The reason for relating the forces P3to a couple and not directly to forces f 2
is that the forces P3 depend upon the spacing of the guide rollers, the
spacing of the wheels, and the number of wheels per end carriage, and
therefore a direct relationship could not have been presented in a simple
form.
5.7.5
Horizontal Lonqitudinal Force. Take the horizontal force imposed bya crane on each line
of rails, acting longitudinally in the direction of travel and caused by acceleration or
braking, to be 0,lO times the sum of the maximum static wheel loads on that line of rails.
5.7.6
Forces on End Stow. Take the horizontal force imposed on each end stop by a crane
in the direction of travel to be the lesser of the following:
a) A force equal to the combined weight of the crane bridge and crab;
b) a force calculated on the assumption that the crane strikes the end stop while
travelling at its full rated speed, taking into account the resilience of the end stops and
crane buffers.
NOTE: In (a) and (b) above, the weight of the load carried by the crane may be ignored unless it is
restrained in a horizontal direction as in a mast or claw crane.
5.7.7
Position of Crane and Crab. In determining the crane loads set out in 5.7.4-5.7.6, assume
the magnitude of the load lifted by a crane (up to its rated capacity), the position of the
crab on the crane bridge, and the position of the crane on the gantry, to be such as will
produce the most adverse effect upon the building or part of the building being designed.
5.7.8
More than One Crane in a Buildinq. Where more than one crane is to operate in a
building, regardless of the number of bays, take the total forces imposed by such cranes
to be as follows:
5.7.9
Static wheel loads
from all cranes
Allowance for impact as given in 5.7.3
from any two cranes
Horizontal forces as given in any one of
5.7.4(a), 5.7.4(b), and 5.7.5
from any two cranes
Horizontal forces as given in either of
5.7.4(c) or 5.7.6
from any one crane
Amdt 3,
Oct. 1993
Combination of Crane Lateral Forces and Wind Load. Where the effects of wind are to
be considered in combination with the horizontal forces as given in any one of 5.7.4 5.7.6, then 0,5 times the nominal crane loads shall be taken as acting concurrently with
the nominal wind load.
5.8
OTHER LOADS
5.8.1
Provision for ImDact and Vibration. Ensure that where loads (arising from machinery
runways, and other plant producing significant dynamic effects) are supported by or
communicated to the framework, allowance is made for these dynamic loadings.
83
SABS 0160-1989
5.8.2
Liftina and Handlina Eauimnent. Where lifting or handling equipment, including forklift
trucks and trolleys for heavy loads or cranes, is intended to be or is likely to be placed
on any floor of a building and would result in loads in excess of those set out in 5.4.1 or
5.4.2 being imposed on any area of slab or on any beam, make provision in the design
of the members concerned for the resultant maximum concentrated load or loads. Show
in the documentation such maximum concentrated load or loads for which the members
have been designed.
5.8.3
Lateral and UDlift Forces
a) Basement walls. etc. In the design of basement walls and other similar members
below ground level, due allowance must be made for the following forces:
1) The lateral force applied by adjacent soil;
2) fixed or moving loads on the surface of the adjacent soil; and
3) hydraulic force.
b) Basement floors, etc. In the design of basement floors and other similar members
below ground level and below the level of a free water surface, due allowance must be
made for upward hydraulic forces.
5.8.4
Inertia Swav Forces
a) Design all grandstands to resist the following inertia sway forces applied as indicated
below to each row of seats or eac:h row of standing accommodation, as applicable:
300 N/m parallel to each row, ancl
150 N/m normal to each row.
b) Where, because of the occupancy of any building other than a grandstand, the
activities within such building are liable to produce inertia effects, the designer must give
consideration to such forces in the design process.
5.8.5
Ceilinas. Skvliahts and Similar Structures. Give consideration to the loads likely to be
supported by joists and hangers for ceilings, ribs or skylights, frames, and coverings of
ceiling access hatches, and any similar structures. Such loads can be derived from
materials or workmen during construction and maintenance, and from electrical fittings,
air-conditioning ducting and other services.
6.
IN-SITU LOAD TESTING OF BUILDINGS AND BUILDING ELEMENTS
6.1
GENERAL
6.1.1
TvDes of Full Scale Load Tests. Full scale load tests fall into three main categories:
a) Tests, as provided for in 3.1.2, which are used as an aid to the design of a structure
or series of structures yet to be built.
b) Tests undertaken to monitor the quality or performance characteristics of serially
produced buildings or components.
c) In-situ tests applied to a specific building, a set of buildings, or parts of buildings,
completed or under construction, in order to assess whether they are in accordancewith
the basic standards of safety or serviceability (or both) inherent in the national building
regulations and the associated codes of practice, either because of alleged or known
inadequacies in design, construction or materials, or because of an intended extension
of or change in use, or because of possible impairment of load-bearing capacity as a
result of fire, corrosion, or similar agencies.
Commentary:
In-situ load testing is an aid to the assessment of the fitness of a building or
of part of a building to support a specified set of loads within a prescribed
SABS 0160-1989
84
set of criteria. It is an adjunct to and not a substitute for engineering analysis
or the exercise of competent professional judgement. This should be borne
in mind in the planning, execution and interpretation of the results of load
tests.
Load testing should normally not be undertaken until alternative avenues of
investigation such as calculation, measurement, non-destructive material
tests, core drilling and testing, etc., have been found insufficient. Load
testing should be preceded by a thorough analysis of the nature and extent
of the problem so that the objectives of the test or tests can be defined in
detail and testing planned accordingly.
Tests of category 6.1 .l(a) are usually applied to specially constructed
assemblies and are more in the nature of development or quasi-research
activities, and each individual case should be treated on its merits by the
designer or by the competent research or testing authority (or by both).
Tests of category 6.1 .l(b) are part of the quality control specification for a
contract and may therefore generally fall outside the scope of this code of
practice.
Tests of category 6.1. I (c) are the primary concern of this section, although
some of its principles may also apply to tests of categories (a) and (b).
Furthermore, the section is mainly concerned with tests on suspended floor
and roof constructions which are the cases most commonly encountered
and which are covered in the structural design codes for various building
materials.
Probably the most significant difference between the three categories of
load test is that, in general, the tests of categories (a) and (b) can be
deliberately continued to failure to give a direct measure of the safety
reserves of the structure, whereas in a category (c) test, the objective is to
assess whether the building will support the service loads with an adequate
margin of safety but without so overloading it as to cause serious damage
or collapse since, if the structure is found to be satisfactory, it must still be
capable of being placed in service after the test.
6.1.2
Planninq. The competent authority (see also 6.2) will plan, execute and evaluate a load
test or load tests in accordance with the principles and guidelines contained in Section 6,
where it is considered necessary to carry out such test or tests on a building or part of a
building for any of the following reasons:
a) Doubts about the adequacy of the design or construction of an existing building or one
that is under construction;
b) damage or deterioration occasioned by fire or other agencies;
c) changed loading conditions.
6.2
TESTING AUTHORITY. Ensure that the load test is designed, supervised and certified
by a competent authority acting, whenever possible, in collaboration with the designer
to ensure that the test effectively deals with those aspects of the construction that are in
doubt.
6.3
TEST PROCEDURES
NOTE: Refer also to A-2(p), (q), and (r) of Appendix A.
6.3.1
Planninq. Ensure that at the planning stage of the test, there is, as far as possible,
agreement between the parties concerned in regard to the following aspects:
a) The exact location, number and extent of the part(s) of the structure to be tested. (This
will depend on the extent of the investigation.)
85
SABS 01 60-1989
b) The test procedure to be adopted, including the following:
'I)The various stages of loading and unloading, including making up for any part of the
self-weight which may still be missing in a partially completed structure;
2) the levels of loading at each stage;
3) the allowances or procedures to be adopted to cater for lateral interaction or load
transfer between the loaded and adjacent unloaded parts of the structure or for loads
transferred to non-structural elements, or both;
4) the duration of each stage of loading and unloading, having regard to the creep
characteristics of the materials of construction involved and the short-term or long-term
nature of the service loads being simulated;
5) the method of application of the load, having regard to the nature of the service load
being simulated;
6) the response parameters to be measured, such as deflection, rotation, strain, or crack
formation, and the positions and rnethods of measurement;
7) the possible influence of, and methods of allowing for, the external environmental
factors (e.g. moisture or temperature changes) which may be in force during the test.
c) The criteria against which the results of the test and therefore the acceptability of the
structure will be judged.
6.3.2
Conductina of Tests
a) Where the elements and materials concerned are designed in accordance with a
specific code of practice and such code prescribes the load testing procedures and
interpretationsfor such elements and materials,the competentauthority must ensure that
procedures and interpretations are carried out in accordance with such prescriptions.
b) Where the elements and materials concerned are not designed as set out in (a) above,
follow the planning procedure as given in 6.3.1.
6.3.3
Test Precautions
a) Ensure that the condition of the structure and its materials (e.g. presence of floor
screeds, maturity of concrete) is similar, within practical limits, to the minimum conditions
assumed in the design.
b) Adopt a method of loading that will ensure that the error in the applied load does not
exceed 5 % of the applied load under service load conditions or 2 % of the maximum
applied load in the overload test, whichever is the greater.
c) Adopt methods of measuring the response of the structure that have an inherent
accuracy of at least k 5 % of the maximum value expected in the test.
d) Ensurethat measurementsof the deflection of members allow for settlement or elastic
deformation of the supports of the members.
e) Ensure that adequate safety precautions are taken to prevent injury to persons and
to avoid damage to property during the test, especially with regard to the possibility of
collapse of the element under test.
Commentary:
When tests are conducted, attention should be given to the following:
a) The loading should preferably be applied in a sufficient number of
increments (at least four) to enable a graph of load versus response
(generally deflection) to be plotted during the test so that discontinuities or
non-linearity in behaviour can be detected.
b) For loads other than short-term transient loads (e.g. wind), creep
behaviour should be allowed for by maintaining each incrementof load until
the response (deformation) has stabilized. The deformation may be
considered to have stabilized when the increase in deformation under
constant load during a given time interval (e.g. 5 min, or not more
than one-quarter of the total time for which the load incrementis maintained)
SABS 0160-1989
86
(As amended 1993)
does not exceed 15 % of the increase in deformation in the preceding
(equal) time increment at the same load. Generally, each increment of load
should be maintained for at least 30 min .
c) Unloading may be done in one step but more useful information can often
be obtained if unloading is done in step-wise fashion, using the same
incremental levels as for loading. Measurements of residual deformation
after unloading should continue until the response has stabilized.
d) Before the commencement of the loading test proper, a load to
compensate for the effect of that portion (if any) of the self-weight load not
already present in the assembly should be applied and maintained until all
testing has been completed. The test proper should not commence until the
deformation under the compensating load has stabilized.
e) To allow for deformations of the structure and errors in measurement
caused by temperature or other environmental changes, it is often
advantageous, especially where the test extends over one or more days, to
carry out a preliminary "dry run" during which no loads are applied but
deformations are measured over a period of time corresponding to that over
which the test will take place. If weather conditions, which should be
monitored, remain reasonably stable, then the deformations obtained in the
dry run may be used for correcting the deformations measured during the
loading test proper.
f) Lateral interaction or load sharing should be allowed for by loading a
sufficient width of slab or panel or number of interconnected beams or
trusses to ensure that all elements which are effectively interactive with the
element under test are loaded. This may be determined by analysis in some
cases; in others, the interactive width or number of elements may be
determined by a preliminary load-sharing test up to a lower level of loading
(not more than the characteristic or service load). For example, in such a
test, the selected beam or strip of a one-way slab is loaded and its
(midspan) deformation and those at the corresponding points of the
potentially inter-acting beams or strips of slab on either side are measured.
All beams or strips of slab that contribute more than 2,5% to the sum of the
deformations of the loaded and interacting elements are regarded as being
effectively interactive.
For wide one-way spanning slabs, such an analysis may be dispensed with
if a width of slab extending at least 1,5 times the span on either side of the
portion under investigation is loaded in the test. For ribbed floors and similar
constructions, it may sometimes be possible to separate a narrower test
section from the adjacent floor by cutting. For two-way spanning floor
panels, it will generally be necessary to load the whole panel. The number
of one-way or two- way spans to be loaded will depend on whether the
concern is with positive or negative moment behaviour (or both), shear
strength, etc. Where non-load-bearing elements (such as partitions) with
significant load-bearing properties are present, these may have to be
removed or cut free of slabs to ensure that they do not influence the test.
g) For checking the serviceability of the structure under working load
conditions, the applied test load(s) should normally be the nominal value(s)
of the imposed loading, i.e. the total load acting in the test is given by:
1,0 G,+ 1,0 Q,
Amdt 3,
Oct. 1993
where
G, = nominal self-weight
0,= nominal imposed load
The load should be maintained until the response has been stabilized.
At this stage it may be advantageous to unload the structure and repeat the
87
SABS 0160-1989
loading procedure to allow for "bedding in" of the structure and
instrumentationand to provide a check on observationaltechniques before
proceeding with the overload test for structural safety.
h) For assessing the safety (ultimate strength) of the structure, the load
levels should be sufficiently in excess of the nominal values to provide a
reliable indication of the overload behaviour, but not so large as to be likely
to cause failure of an acceptable structure. For example, in limit-statedesign
terms, the total load appropriate for the test might reasonably be about 0,85
times the factored loads used in design for the ultimate limit state. On this
basis, it is suggested that in the absence of other specific prescriptions, a
maximum total load of 1,2 G, + 1,4 Q, be used during the test, to ensure
safety. These values may need modification to allow for duration of load
effects with materials whose strength is highly time dependent. The values
should also be adjusted according to whether a single test is to serve as the
basis for assessing a number of nominally similar structures or only the
structure being tested. The load should be maintained until stabilization of
deformation has occurred.
i) The criteria for assessing compliance with the test for serviceability at
working loads should normally be the design limits for deflection,
deformation or cracking under service loads, reduced as may be necessary
to allow for any part of the loading effects or time effects not covered by the
test measurements. A distinction is necessary between pre-existingcracks
or deformations (which may have led to the need for a test) and those
arising or extending during the test.
j) The structure under test may be deemed to have failed the test for safety
or ultimate strength if one or more of the following conditions are attained:
1) The structure collapses or shows signs of distress or instability indicating
that collapse is imminent.
2) The maximum deflection exceeds span/50.
3) Cracking or other local damage spreads significantlyunder constant load.
4) The increase of deformation under constant load that occurs during each
of three successive equal time intervals shows no decrease. The duration
of the intervals should be sufficient to enable the increments in deformation
to be measured with sufficient accuracyfor a valid comparison to be made.
5) The recovery of deformation after removal of the test load (after allowing
for stabilization to occur) is less than about 75 ?40 of the maximum
deformation during the test. (This value may be increasedto 85 % for metal
structures, decreased to 70 % for timber structures and decreased to 60 %
for plastics structures.)
6) The residual (permanent) deformation or cracking (under dead load only)
arising from the test exceeds the values permitted in design for full service
loading.
k) When tests are performed on very stiff structures, the deformations may
be so small that they cannot be reliably determined and the criteria in (j)(4)
and (5) above cannot reasonably be applied.
I) When structures are tested that are likely to exhibit brittle failures or
instability failures, the assessment of performance becomes difficult since
the response measurements may give no indication of the imminence of
faiIure.
88
SABS 0160-1989
(As amended 1990 and 1993)
APPENDIX A. APPLICABLE PUBLICATIONS
(This appendix does not form part of the provisions of the code)
A- 1
Reference is made to the latest issues of the following standards:
ANSI A58.1 Design loads for buildings and other structures, minimum
ATC 3-06
Applied Technology Council, 1978
I S 0 2631
Evaluation of human exposure to wholebody vibration
IS04356
Bases for the design of structures. Deformations of buildings at the
serviceability limit states
I S 0 8930
General principles on reliability for structures - List of equivalent terms
SABS 0100 The structural use of concrete
SABS 0137 The installation of glazing materials in buildings
SABS 0161 The design of foundations for buildings
SABS 0162 The structural use of steel
SABS 0163 The design of timber structures
SABS 0164 Structural use of masonry
SABS 0400 The application of the National Building Regulations
A-2
The information contained in this code of practice is considered adequate for the design
of the majority of buildings. For those buildings, structures or elements that are not
adequately covered or where special conditions apply or where additional information is
desired by the designer, the following publications should be consulted:
Amdt 3,
Oct. 1993
-
Milford, RV 'Annual maximum wind speeds for South Africa', published in The civil
enaineer in South Africa, January 1987.
a) NBRl Information Sheet WBOU 2-41, 'Wind flows around and pressures on buildings',
published by the National Building Research Institute, CSIR, Pretoria, 1978.
b) Weather Bureau Report WB 38, 'Climate of South Africa, Part 12, Surface winds',
published by the Weather Bureau, Department of Environment Affairs, Pretoria, 1975.
c) NEWBERRY and EATON, Wind loadina handbook, published by the Building
Research Establishment, HMSO, London, 1974.
d) The modern desiqn of wind sensitive structures, published by the Construction
Industry Research and Information Association, London, 1971. (Wind characteristics,
along-wind response, vortex excitation, galloping, flutter.)
e) Commentaries on Part 4 of the national buildinq code of Canada 1977, published by
the National Research Council of Canada, 1977. (Along-wind response: method and
charts, vortex excitation, accelerations.)
f) DAVENPORT, AG, Gust loadinq factors, published by the American Society of Civil
Engineers, Structural Division, Journal, Vol. 93, June 1967. (Along-wind response:
method and charts.)
g) Australian Standard 1170, Part2, 1975, 'SAA loading code: "Wind forces"', published
by the Standards Association of Australia. (Along- and cross-wind response discussed
in an appendix.)
89
SABS 0160-1989
(As amended 1990)
h) VICKERY, BJ, 'On the reliability of gust factors', Civil Enaineerina Transactionsof the
Institute of Engineers, Australia, L'ol. CE 13, No. 1, April, 1971. (Along-wind response:
method and charts.)
i) SIMIU, E and SCANLEN, RH, Wind effects on structures - an introduction to wind
enqineering,publishedby John Wiley, NewYork, 1978. (Wind characteristics, along-wind
response: method and charts, vortex excitation, galloping, flutter, wind-induced
discomfort in and around buildings.)
j) SIMIU, E and LOZIER, DW, The buffetina of tall structures bv strona winds, NBS
Building Science Series 74, 1975, published by the National Bureau of Standards, US
Dept. of Commerce, Washington, 1975. (Along-wind response: method and charts,
cornputer program.)
k) PINFOLD, GM, Reinforced concrete chimnevs and towers, published by Viewpoint
Publications, London, 1975. (Dynamic wind forces on chimneys, vortex excitation.)
I) HOUGHTON, EL, and CARRUTHERS, NB, Wind forces on buildinas and structures:
an introduction, published by EdwardArnold, London, 1976. (All aspectsofwind loading.)
m) AYNSLEY RM, et al, Architectural aerodvnamics, published by Applied Science
Publishers, London, 1977. (All aspects of wind loading and environmental effects of
wind.)
n) CHASTEAU, VAL, 'Wind effects on structures', published in The civil enaineer in
South Africa, commenced in February, 1971 and concluded in March, 1971 issues.
(Analysis for thunderstorm winds.)
0)DAVENPORT, AG and NOVAK, M, Vibrations of structures induced bv wind: Shock
and vibration handbook, edited by Harris and Crede, published by McGraw-Hill, 1976.
p) 'General recommendation for loading tests of load-bearing structures in situ',
preliminaryrecommendationsof the 20-TBS Committeeof RILEM, publishedin Materials
and structures, No. 53, September - October 1976.
q) MENZIES, JB, 'Load testing of concrete building structures', published in The
structural engineer, Vol 56A, December 1978.
r) BARES, R and FITZSIMONS, N, 'Load tests of building structures', published by the
American Society of Civil Engineers, Structural Division, Journal, Vol. 101, No. ST5,
May 1975.
s ) Earthquake enaineerinq, co-ordinating editor RL WIEGEL, published by Prentice Hall,
USA.
t) Geological Survey - Seismological Series, compiled by FERNANDEZ, LM and
GUSMAN, JA: No. 9 'Seismic history of Southern Africa' No. 10 'Earthquake hazards in
Southern Africa'.
U)Weather Bureau Report WB 36, 'Climate of South Africa, Part 2, Extreme values of
rainfall, temperature and wind for selected return periods', published by the Weather
Bureau, Department of EnvironmentAffairs, Pretoria, 1974.
v) SCHWARTZ, HJ and CULLIGAN, PT, 'Roof drainage of large buildings in South
Africa'. The civil enqineer in South Africa, August 1976.
w) Hydrological Research Unit, Desian flood determination in South Africa, Report No.
1/72, University of the Witwatersrand, Johannesburg, 1972.
x) CULLIGAN, PT, Compilation of a manual for the desian of roof drainaae svstems,
M.Sc. Dissertation, University of the Witwatersrand, Johannesburg.
y) Weather Bureau Report WB 20, 'Climate of South Africa, Part 2, Rainfall statistics';
published by the Weather Bureau, Department of Transport, Pretoria.
z) DOWRICK, DJ, 'Earthquake resistant design', Wiley, 1977.
aa) DOWRICK, DJ, 'Earthquake resistantdesign. A manual for engineersand architects',
Wiley - lnterscience Publication, John Wiley & Sons, New York, 1977.
bb) FERNANDEZ, LM and SHAPIRO, A, Maps of the probabilities of earthquake
occurrence in South Africa. Geological Survey, Pretoria. (1989, In press).
cc) SHAPIRO,A and FERNANDEZ,LM, Probabilitiesof exceedance for prescribed peak
ground accelerations(PGA) at selected SouthernAfrica locations.Report No. 1987-0100,
Geological Survey, Pretoria, 1987.
SABS 0160-1989
90
APPENDIX B. NOMINAL UNIT MASSES OF MATERIALS
(This appendix does not form part of the provisions of the code)
B-1
GENERAL. This appendix sets out a schedule of nominal unit masses of some materials
used in the building process and of some liquids and semi-liquids. The values are given
either as densities or as masses per unit area for a specific thickness, as appropriate. It
is not possible to include a full range of all materials generally available or the many
different forms of composite construction now in use because of the many combinations
and variations which are possible and available.
The schedule endeavours to provide approximate information that can be used in
preliminary calculations. The degree of accuracy necessary in subsequent calculations
should be determined by the designer. The required information on the materials to be
used in the construction of the building should be calculated on values determined in
practice. Such calculations should also take into account the variations likely to be
encountered in the manufacturing process and in the climatic conditions of the particular
area where the materials are to be used.
The values given in this appendix assume the materials to be in the dry state, unless
otherwise stated and, where materials susceptible to moisture absorption are used in
positions exposed to rain or water, due allowance for increase in mass must be made.
B-2
BUILDING MATERIALS , GENERAL
B-2.1
INSULATING MATERIALS
Masshnit area
Expanded polystyrene foam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Felt, insulating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Foamed polyurethane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glassfibremat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B-2.2
0,02
02
0,1
0,04
METALS
Densitv
Aluminium alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Brass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bronze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Copper: Cast . . . . . . . .
......................
Wrought . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Iron:
Cast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..........
Wrought . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead
................................................
Stainless steel .
.............................
Steel
.................................
...........
Zinc:
Rolled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-2.3
k q h 2per mm
thickness
kn/m3
2 800
8 500
8 900
8 700
8 900
7 200
7 700
11 300
7 900
7 800
7 100
SUNDRY BUILDING MATERIALS
Density
Cork:
Granular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Compressed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Macadarn,waterbound . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tarmacadam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
U
160
350
2 700
2 600
2 300
3
91
SABS 0160-1989
Mass/unit area
Damp-proof coursing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
kn/m2
5
kdm2per mm
thickness
Asphalt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glass fibre (GRP) products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PVCproducts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Paving, stonework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-2.4
22
02
177
2.7
TIMBER
Densitv
Finishing: lroko . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mahogany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Meranti . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sapele . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Teak . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
650
520
530
570
660
South African timber:
Structural up to Grade 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
uptoGrade10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
500
700
Imported timber:
Structural pitch pine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Douglasfir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
670
550
Masslunit area
ka/m3
kdm2per mm
thickness
Timber boarding:
Blockboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chipboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fibreboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Floorboarding and blocks:
Softwood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardwood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardboard (dense) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Plywood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Woodwool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-3
CEMENT, CONCRETE AND CONCRETE PRODUCTS
8-3.1
AGGREGATES
Densitv
Cementin bulk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Coarse aggregates:
Normal weight natural aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lightweight: Clinker, foamed slag, expanded clay . . . . . . . . . . . . . .
Fine aggregates:
Normal weight: Sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lightweight: Clinker, foamed slag, expanded clay . . . . . . . . . . . . . .
kn/m3
1450
1 600
700
1 600
1000
92
SABS 0160-1989
8-3.2
CONCRETE
Density
Plain, unreinforced:
Nominal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using broken brick aggregate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lightweightaggregate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Reinforced:
Nominal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 % reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 % reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Special heavyweight concrete:
Using natural heavy aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using steel shot aggregates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-3.3
2 300
2 000
1500
2 400
2 500
2 600
3 200
5 200
FINISHES
Mass/unit area
Plaster:
Cement and sand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gypsum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lightweight vermiculite . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
kq/m2per mm
thickness
23
1,7
03
13
Granolithic, terrazzo, screeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Paving slabs, precast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-3.4
REINFORCED SLABS
Mass/unit area
Solid slabs: Thickness
B-3.5
2,3
2,4
ks/m2
75 mm
100mm
150mm
250mm
300mm
190
240
360
610
730
............................
............................
............................
............................
............................
FIBRE-CEMENT ROOF SHEETING
(Laid, including laps and fixings and at moisture content of 15 %)
Masdunit area
Corrugated roof sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Long span roofing elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
kn/m2
150
20,o
NOTE: The above are average values to cover the main types of sheeting in general use.
8-4
FLOORING
Mass/unit area
Clay floor tiles, including screed . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Granolithic, terrazzo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Floor coverings: Flexible PVC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vinyl asbestos . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
kq/m2per mm
thickness
4,4
23
1,6
1,7
22
93
B-5
WALLING
B-5.1
BRICKWORK
SABS 0160-1989
Mass/unit area
Nominal 120 mm wide clay bricks in half-brick walling
Solid bricks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Perforated bricks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-5.2
260
220
BRICKWORK AND BLOCKWORK. GENERAL
Masshnit area
Blocks. hollow clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bricks: Calcium silicate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Commonclay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Facingclay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Refractory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B-5.3
CONCRETE BLOCK WALLING
Mass/unit area
Nominal 200 mm wide blocks made from:
8-5.4
Stone aggregate: Solid blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hollow blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
440
280
Lightweight aggregate: Solid blocks . . . . . . . . . . . . . . . . . . . . . . . . .
Hollow blocks . . . . . . . . . . . . . . . . . . . . . . . .
260
210
STONEWORK
Densitv
Granite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Slate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 800
Stonerubble. packed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Quarrywaste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardcore. consolidated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B-6
STORED MATERIALS
B-6.1
LIQUIDS AND SEMI-LIQUIDS
kn/m3
2700
2500
2300
2200
1500
1900
Bulk densitv
For a liquid stored in carboys. use 0.5 of the bulk density. For a
liquid stored in drums. use 0.75 of the bulk density
ka/m3
Acids: Acetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hydrochloric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Nitric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sulphuric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Alcohol. commercial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ammonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1050
1150
1350
1850
800
900
SABS 0160-1989
Beer: Bulk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bottlesin cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Barrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 000
450
550
Benzine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bitumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Methylated spirits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Linseedoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
900
Milk
..................................................
900
1 400
850
Mineral oils: Naphtha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Paraffin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Petrol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Petroleum oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
750
800
700
900
Pulp(wood) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Tar,pitch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Turpentine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
750
1200
850
Water: Fresh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sea-water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 000
1 050
Wine:
1 000
600
Bulk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bottlesincases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1050
95
SABS 0160-1989
APPENDIX C. NOMINAL IMPOSED LOADS
(This appendix forms part of the provisions of the code)
c-1
NOMINAL IMPOSED FLOOR LOADS IN FACTORIES AND WAREHOUSES
Imposed floor loads in factories alnd warehouses consist of the following:
a) Forces, including dynamic effects if any, that are due to the following manufacturing
equipment:
1) Stationary plant and suspended manufacturing equipment, and
2) industrial pipelines.
b) Forces, including dynamic effects if any, that are due to the following handling
equipment:
1) Fixed handling equipment (conveyors, elevators, rollers, etc.), and
2) mobile handling equipment (trucks, cars, overhead cranes (see 5.7),etc.).
c) Forces due to staircases, ramps and access gangways, including movable building
parts such as partitions.
d) Forces due to service equipment (heating,ventilating, etc.) and associated equipment.
e) Forces due to materials and products, including waste products and animals, etc.,
used in production.
9 Loads due to people (operational staff, probable visitors).
g) Forces of an unusual nature (for example, forces resulting from the failure of hoppers
or mechanical equipment).
c-2
NOMINAL IMPOSED LOADS IN GENERAL
c-2.1
The characteristic value of the imposed floor load is the 95 % value of the least
favourable load which has a probability,accepted from the outset, of not being exceeded
during the service life of the building. In the absence of the necessary statistical data, the
nominal value should be chosen in accordance with the given (or expected) conditions
of normal use of the building and Ntis various floor zones. (This nominal value should be
verified from similar buildings.)
c-2.2
When structural members are being designed and calculations made, account should be
taken of possible simultaneous actions of imposed floor loads. For certain loading
conditions which are interdependent, the characteristic value should be determined
statistically for the least favourable combination of the loads. For floor loads whose floor
position may alter, account should be taken of the least favourable position relative to the
structural members being calculated for.
C-2.3
The influence of dynamic forces arising from operations with dynamically unbalanced
equipment,from the shifting of heavy loads over the floor, or from goods in storage falling
or becoming suddenly displaced, should be taken into consideration, by calculating the
structures dynamically or by using suitable dynamic coefficients.
c-3
ESTABLISHMENT OF IMPOSED FLOOR LOADS
C-3.1
Data concerning loads for calculations in respect of load-bearing structures should
include the values, directions and any application diagrams for floor loads (uniformly
distributed, concentrated, static and dynamic), determined on the basis of information
available concerning weight, overall dimensions and position of items, and the fixing of
equipment to floors, as well as the characteristics of machinery installed, etc. If erection
loads are to be taken into account,their values and their possible positions on the lifting
gear (including positions of material already lifted and of the gear and its heaviest parts)
should be determined.
SABS 0160-1989
96
The chief sources of the data referred to above are as follows:
a) Standards and catalogues of equipment;
b) data supplied by the equipment suppliers;
c) advice from experts responsible for the technicalside of the building being designed;
d) data supplied by the users of the building.
C-3.2
When the nominal load from the weight of manufacturing plant is being determined,
account should be taken of
a) the weight of the plant (including the weight of the drive, additional bearing devices,
and insulation);
b) the weight of the heaviest pieces under treatment or the weight of the products being
processed (liquids, materials in bulk);
c) the weight of gangways and working platforms;
d) loads accruing from necessary maintenance or replacement of stationary plant.
The weight of the product being processed should be determined by using its maximum
possible volume under normal operation in the plant.
c-3.3
When nominal loads due to handling equipment are being determined, the weight of the
machine should be taken as its weight under working conditions (i.e. allowance should
be made for the weight of fuel, power sources, etc.) and the load carried should be taken
as equal to the nominal load-lifting capacity of the machine.
c-3.4
Nominal loads in garages depend on the weights of vehicles, probable service
equipment, spare parts, etc., with provision for the values of possible loads on the
vehicles depending on the types of vehicles and conditions of garage use.
c-3.5
Nominal loads in warehouses should be determined with regard to the types of materials
stacked and the methods of storage. Account should be taken of the greatest volume
of materials (the greatest number of stacked articles) located on the area of the floor
under normal operational conditions of the warehouse, allowing for the densest stacking
of materials and articles and the possible effect of the increase in density of some
materials when stored for a long time (e.g. effects of the increase in moisture).
C-3.6
When loads on floor zones not occupied by stationary equipment and in warehouses are
being defined, provision should be made for loads from mobile handling equipment and
for the following loads:
a) Loads due to crowds of people possible during normal operation of the structure;
b) loads due to materials and semi-finished products temporarily stored near the
processing equipment (at intervals between machining operations or ready for transport
to the warehouse);
c) loads due to the weight of waste products, etc.
c-3.7
When stresses and deformation in buildings are being calculated, the actual floor loads
may be replaced by simplified load diagrams of equivalent effect.
97
SABS 0160-1989
APPENDIX 13. WIND FORCES
(This appendix forms part of the provisions of the code)
D-I
DYNAMIC EFFECTS
D-I .I
ALONG-WIND RESPONSE. Three basically similar methods of analysis which
nevertheless involve slightly different assumptions and simplifications are covered in
detail in A-2(e), (f) and (g), A-2(h) and A-2(i) and (j) of Appendix A. Of these, the last
appears to be based on the most realistic set of assumptions.
All three methods are based on determining the effective peak loading or response as
the sum of the (static) mean corriponent associated with the mean (e.g. hourly) wind
speed and an equivalent static cornponent due to the short-term fluctuations (gustiness)
of the wind about this mean. The latter component takes account of the distribution of
energy in the wind fluctuations in relation to the size, natural frequency and damping
characteristics of the structure.
These methods of analysis have become known as gust factor or gust energy methods.
As presently formulated, they apply only to wind originating in mature large-scale storms
(extreme pressure system winds) and not to winds in localized storms such as the
thunderstorms which are a primary source of extreme gusts on the Highveld. Such
thunderstorms are characterized by low mean speeds and high gust speeds, and the
variation of wind speed with height is known to be less than for large-scale storms.
Furthermore, the relationship between thunderstorm wind speeds and different types of
terrain has not yet been quantified.
Reference A-2(n) of Appendix A gives a method of analysing the response of a structure
to the sequence of peak gusts which characterize the initial stage of a thunderstorm. This
approach involves certain rather arbitrary assumptions and has not yet been calibrated
with the use of field observations.
Gust factor methods should not be used for buildings of height less than 75 m in areas
of Terrain Category 4 or less than 30 m in areas of Terrain Category 3.
D-I .2
VORTEX EXCITATION
a) The asymmetrical shedding of vortices into the wake of a bluff body and the resultant
variation in cross-wind force tend to be periodic with a frequency which varies with the
(mean) wind speed and is given by
where
n
= the vortex shedding frequency
S
= the Strouhal number
V,
= the mean wind speed
b
= the breadth of the structure (across wind)
Values of S are approximately
0,2 for circular cross-sections and
0,15 for rectangular cross-sections,
SABS 0160-1989
98
but the actual values are dependent on the Reynolds number and on the amplitude of
oscillation of the structure, and there is some uncertainty about the values at large
Reynolds numbers (i.e. in the region of 10').
b) If the frequency of vortex shedding at some wind speed within the expected range of
design speeds coincides with the natural frequency of vibration of a flexible, lightly
damped structure, then resonance and correspondingly large amplitudes of cross-wind
oscillation can occur. If the amplitudes of oscillation are large enough, the resulting
interactive effects may force the frequency of vortex shedding to "lock in" to the natural
frequency of the structure, even when the wind speed changes somewhat.
The critical (i.e. resonant) wind velocity is thus given by
where no = the natural frequency of the structure
The calculation should normally be based on conditions at the top of the structure ( z = h).
Where V,, lies well above the design range of wind speeds at the top of the structure,
resonance will not occur. Where Vcritis within the design wind speed range, resonance
may occur and further analysis is necessary to assess the magnitude of the response
and whether methods of reducing the response or preventing resonance are necessary.
For assessing the likelihood of occurrence of vortex shedding, a range of Strouhal
numbers should be considered, e.g. for cylindrical structures, S has a value in the range
0,15 to 0,25.
In the use of the above formulae and in the assessment of the resonant response, the
problem arises of deciding on the appropriate wind speed averaging time. Clearly, the
appropriate mean wind speed is that which persists for long enough to ensure that
appreciable oscillation amplitudes can build up. Thus the 3 s gustwill be an overestimate
while the hourly mean will be an underestimate. An averaging time corresponding to
about 30 cycles of oscillation would seem to be appropriate.
c) An estimate of the wind speed averaged over a time interval of T seconds may be
obtained by multiplying the relevant hourly mean speeds (see D-I .3) by the following
factors:
TABLE D-I -WIND SPEED MULTIPLYING FACTORS
Terrain category
Of the many methods of calculating vortex shedding response it is suggested that, for
structures of approximately uniform cross-section, the method given in A-2(0) of
Appendix A provides a simple and reasonably conservative estimate of the response,
having regard to the many uncertainties still existing in this area. According to this
approach, the dynamic effect of resonant vortex shedding may be approximated by the
influence of a static lateral force per unit height, acting in the direction of oscillation, and
varying in the same manner as the mode shape from the base to a value F, at the top
such that
SABS 0160-1989
99
0 5 C,bq,,
F, = I
n
where
D-I .3
13
= the critical damping ratio which may range from 0,001 to 0,02, depending
on whether the construction is for instance an unlined welded steel stack
or a reinforced concrete frame building with infill walls
CL
= a lift coefficient which is dependent on turbulence, surface roughness,
Reynolds number and aspect ratio or amplitude of oscillation. C,
generally lies in the range 0,15-0,25 for cylinders
qcdt
= the velocity pressure for the critical speed Vcrit.Note that the value of qcht
and hence of Fpis very sensitive to the choice of values for parameters
S and no,which may often only be known approximately
HOURLY MEAN WIND SPEEDS FOR DYNAMIC ANALYSIS. Maximum values of hourly
mean wind speeds for a 50-year return period at a height of 10 m in Terrain Category 2
for use in gust energy and vortex shedding calculations are given in Fig. D-I. The
correction factor in Fig. 4 may be used to obtain an estimate of the values for other return
periods.
NOTE: The variation with height of the hourly mean wind speed differs significantly from that for gust
speeds and the power-law exponents U in Table 5 do not apply.
The following expressions may be used to describe the variation with height of the hourly
mean wind speed:
Terrain Cateaorv 1
V, = 1,67 V (z
zg
- ZO)
-
o,ll
zg = 250 m, z, = 0
zo
Terrain Cateaorv 2
V, = 1,67 V ( z
zg
-
zo)
o,15
zg = 300 m, zo= 0
zo
Terrain Cateclorv 3
zg = 400 m, zo= 5 m
Terrain Cateaorv 4
zg = 500 m, z, = 12 m
where V is the hourly mean speed at a height of 10 m in Terrain Category 2.
As in the case of gust speeds, it is considered advisable not to allow for any decrease
in wind speed below heights of 5 m in Terrain Categories 1, 2 and 3 and 20 m in Terrain
Category 4.
D-2
CHANGES IN TERRAIN CATEGORIES
D-2.1
GENERAL. Where a change in terrain category occurs, the wind speed profile for that
particular condition does not develop to the full height h immediately but develops to a
lesser height h,, which increases with the fetch or distance upwind x.
100
SABS 0160-1989
LOW TO HIGH NUMBER. Where transition is from an area of low terrain roughness to
an area of rougher terrain (i.e. from a low category number to a high category number),
the wind speed profile over the rougher terrain is determined as follows (see Fig. D-2):
D-2.2
a) Below height h,, the speed is determined in relation to the rougher terrain.
b) Above height h,, the speed is determined in relation to the less rough (more distant)
terrain.
25
wi
rir
(U
U
al
U
7
c
c
1
30
35
15
20
25
30
Longitude, deg. E
Fig. D-I - Maximum Mean Hourly Wind Speeds (m/s)
for a 50-Year Return Period in Terrain Category 2
(NOTE: For Other Return Periods, see Fig. 3.)
D-2.3
HIGH TO LOW NUMBER. Where transition is from an area of rough terrain to an area
of less rough terrain (i.e. from a high category number to a low category number), the
wind speed profile over the less rough terrain is determined as follows (see Fig. D-3):
a) Above height h,, the speed is determined in relation to the rougher terrain.
b) Below height h,, the speed is taken as the lesser of
1) that determined in accordance with the less rough terrain, and
2) the speed at height h, as determined in relation to the rougher terrain.
SABS 0 160-1989
101
x q = fetch
h,
height for
0.000
Profile
---- Profile
Design
0
0
0
0
Category 4 (TabLe 5)
for Category 4
for Category 2
profile a t A
0
‘
4
Wind direction
’
/’
/
/
Category 2
Drg.1143O-EC/00-07
Fig. D-2 - Wind Speed Profiles - Wind Blowing from Terrain of
Lower to Higher Category Number
x 2 = fetch
hg
height for Category 2 (Table
51
I
* * * * * * Profile for Category 4
_ _ _ _ Profile for Category 2
Design profile a t A
I
I
-
1
h 2 ex2
I---
,/-
---+
JO--’
/0
Wind direction
/
**
://
/
/
Category 4
Fig. D-3 -Wind Speed Profiles - Wind Blowing from Terrain of
Higher to Lower Category Number
D-2.4
MORE THAN ONE CATEGORY. Terrain changes involving more than one category are
treated in a manner similar to those changes described in D-2.2 and D-2.3 (see example
given in Fig. D-4).
SABS 0160-1989
102
xb= fetch
h,= height f o r C a t e g o r y 4 ( T a b l e 5)
x, = f e t c h
4 = h e i g h t for C a t e g o r y 1
h 1. x
---D
Wind d i r e c t i o n
/
h
>
,
-5
,
I
/----
lb//21g7/
0
0
0
h,. x,
/'
/
Category 3
........
Profile
Profile
Profile
Design
f o r Category 4
f o r Category 3
for C a t e g o r y 1
profile
._-_____-___-
Speed
Speed
Speed
1
SABS 0160
Dra.11435-EC/00-07
-
I
I
Fig D-4 -Wind Speed Profiles where More than
One Terrain Category is involved
D-3
THE EFFECT OF A CLIFF OR AN ESCARPMENT ON THE HEIGHT z ABOVE
GROUND
D-3.1
GENERAL. The design wind speed of a building on or near the edge of an escarpment
or a relatively sudden change in ground level should be determined by using an effective
height measured from an artificial ground datum Z, as determined in 0-3.2.
D-3.2
DETERMINATION OF ARTIFICIAL GROUND DATUM
a) Where the average slope of the escarpment given by the ratio helye(see Fig. D-5) is
equal to or less than 0,3, measure the effective height from the natural ground surface
adjacent to the building.
b) Where the ratio helye exceeds 0,3, measure the effective height from the artificial
ground datum Z, obtained as in Fig. D-5, i.e. from A-D take Z,to be AB, and from D-E
obtain Z, by interpolation. Beyond E take Z, to be CDE
where AB
= the average ground level at the bottom of the escarpment
BC
= the average face of the escarpment
CDE
= the average ground level at the top of the escarpment
Z,
= the artificial ground datum
he
= the vertical height of the escarpment
ye
= the horizontal length of the escarpment
103
SABS 0160-1989
I
Fig. D-5 - Determination of Artificial Ground Datum
D-4
DETERMINATIONOF VELOCITY PRESSURE q,
D-4.1
The value of velocity pressure q, may be found from Fig. D-6.
SABS 0160-1989
104
2
s/w' A paads
0
PUIM
0
N
m
0
0
7
0
0
N
N
E
\
z
Y
N
U
(U
L
3
VI
VI
(U
L
a
+
%
-
I
-
0
0
0
0
(U
N
U
>
m
NO
-
I
0
m
c
0
t
r
0
n
"
a
T
-
o
o
M
N
Y
L
-
aJ
._
a
.-
L
2
U
(U
aJ
n
IA
U
c
._
U
G
3
3
o
-
-
~
v
O
O
S/UI
''A p a a d s
r
f
r
O
n
O
~
O
PUIM
-
O
105
SABS 0160-1989
APPENDIX E. DEFORMATION OF BUILDINGS
(This appendix does not form part of the provisions of the code)
NOTE
a) The information contained in this appendix is based on information given in IS0 4356.
b) The following definitions relate only to words or phrases appearing in this appendix:
Lonq-term temporary action. Any action that occurs either for relatively long periods of time or for short
periods of time that recur repeatedly over a long period.
Short-term temporary action. Any actiori that occurs only for short periods of time and that affects the
structure infrequently.
Temporaw action. Any action that occurs only at certain times during the construction or existence of the
structure, or whose magnitude cannot in practice be considered constant.
E-I
GENERAL
The aim of this appendix is to assist the designer to identify those aspects of deformation
that affect the suitability of a building for the purposes for which it is intended, and to
suggest criteria by which the performance of the building can be assessed. In addition,
numericalvalues for some of these criteria are suggested in order to give some guidance
where this might be desired.
The recommendationsfor criteria of deformation,and the suggestions for limiting values,
are given in Table 1 and in Tables E-I to E-5 of this appendix.
In view of the wide range of acceptable values of some of the criteria, and in view also
of the difficulties of estimating deformations, it is believed that some guidance towards
uniformity and degree of compliance would be of assistance, particularly as the
economics of modern building designs are increasingly controlled by deformation and
maintenance during use.
Some suggestions are therefore made in regard to the methods for controlling the
assessment of deformations.
E-2
AP PLCATION
E-2.1
TYPE OF BUILDING. This appendix refers to the deformations at the serviceability limit
states of buildings that are covered by this code of practice, namely
a) residential and institutional buildings;
b) offices and commercial buildings;
c) public buildings; and
d) storage and general industrial buildings.
E-2.2
ADJACENT BUILDINGS. Attention is drawn to the fact that the provision of movement
joints between adjacent buildings and the avoidance of interference with neighbouring
foundations are normal good building practice, and that it is undesirable that the
deformations of a building damage adjacent buildings or inconveniencetheir occupants
or other members of the public.
E-3
CAUSES OF DEFORMATION
E-3.1
GENERAL. Deformations are caused by major ground movements, by differential
settlements of foundations, by environmental and occupational loads, by pre-stressing
forces and by movements of building materials owing to creep and changes in
temperature, in moisture content iand in chemical composition.
SABS 0160-1989
E-3.2
106
EFFECTS AND REMEDIES. Beside possibly affecting the strength or stability of a
structure, deformations may affect serviceability by causing damage to adjacent parts of
the building, by disturbing or harming the occupants, or by preventing proper use of the
building.
In many such cases, the designer may be able to avoid troublesome effects either by
removing the original cause or by taking suitable precautions in the process of design
and construction to permit some or all of the deformation to occur freely, before or after
completion of the building, and masking the remainder by suitable constructional or
decorative treatment. This course of action has the advantage that it avoids the problem
of precisely estimating the magnitudes of causes and their effects. It can be adopted
when the deformations, and the constructional measures taken, do not conflict with other
requirements of the design. Some troubles that may often be dealt with in this way are
listed in E-8.
Camber can be used to reduce the final value of deflections. The normal use of camber
is to reduce the contribution to deformations that is made by self-weight and other
permanent or long-term temporary action. In other cases, the designer may have no
option but to provide sufficient stiffness to limit the deformations and thus reduce their
effects to acceptable levels; this will inevitably increase the first cost of the structure. The
designer may choose this course or choose to combine both approaches.
E-4
L IMlTATl0NS
E-4.1
GENERAL. Limitations may need to be applied to vertical or horizontal deflections or
deviations, to inclinations, to curvatures, to the widths of cracks or to the effects of
vibrations.
The limitation of beam or slab deformations may be basically a matter of deflection,
rotation or curvature. However, these requirements are specified throughout this
document in terms of deflection, or of deflection in relation to span, since this is the most
easily observable parameter. For simply supported spans under uniformly distributed
loading, the slope at the ends may be taken as equal to 3 times the ratio of medial
deflection to span, and the radius of curvature at the middle as equal to the span divided
by 10 times the deflection/span ratio.
E-4.2
LEVELS OF MAGNITUDE. When specifying limitations, it is necessary to consider the
levels of magnitude at which the actions that cause deformations should be assumed to
occur. A knowledge of this is essential if designers and the local authorities are to find
a common basis for assessing and controlling deformations.
Some of the factors that enter into this consideration are
a) the extent to which information is available about the actions or properties involved,
and the degree of accuracy of any estimates of the effects likely to be produced;
b) the possible response of the building or member, in view of the duration of the action
in question;
c) the probability of the simultaneous occurrence of several actions contributing to a
given kind of deformation;
d) the consequent levels of dissatisfaction.
In connection with (c) above it will be noted that both spatial and chronological variations
of disturbing actions are involved and also that, given the necessary data, an estimate
of the combined probability might be made; in the absence of sufficient data it becomes
necessary to adopt other means of expressing the reduced magnitudes of several
actions that should be assumed to be present simultaneously.
107
SABS 0160-1989
In connection with (d) above it will be noted that the sharp limit to acceptability that is
exceeded at the ultimate limit state does not, in general, exist together with serviceability
limit states and there is usually a wide range of acceptable levels of deformation,
depending on the propertiesof coritiguous materials, the reactions of individual persons,
and the possibilities and economics of repair. In this connection, it is to be noted that in
the case of widespread natural actions such as wind, snow and earthquake, whose
characteristic values are based on time-related rather than space-related probabilities,
the acceptable level of troubles due to deformation depends on the number of buildings
simultaneously at risk and on the acceptability of some of the results of a natural
calamity.
It is suggested that the limitations be based on the following:
1) The actions to be taken into account when deformations are specified or checked
should be those having a duration that is appropriate to the response of the building or
member affected;
2) for permanent actions, for long-term temporary actions and for short-term temporary
actions affecting many buildings in the course of a single year, the design levels of
magnitude of these actions should be the characteristic values;
3) a lower value than the characteristic may be specified when two or more of the above
actions occur simultaneously, or when a short-term action is not likely to affect many
buildings in the course of a single year.
E-5
STRENGTH AND STABILITY
E-5.1
GENERAL. Deformations affecting the strength and stability of a building or of its parts
are taken into account in the process of structural design for the ultimate limit state. It is,
however, necessary that designers be aware of certain cases involvingstatic or dynamic
instability where the conditions existing during normal use of the building may have a
considerable effect on the ultimate limit state.
E-5.2
ECCENTRIC LOADING OF WALLS AND COLUMNS
a) Eccentric loading of walls and columns may occur as a result of excessive
constructional deviation through inclination of these members or through deflections of
floors or roof members. In both cases, the effects may be progressive and lead to
collapse.
b) Inclination of vertical members may be due to constructional deviations or to the
effects of wind load, or of permanent and imposed loads or snow loads acting
eccentrically or causing differential settlement. The presence of properly designed
stiffening elements such as shear walls, central service cores, enclosed liftwells or
staircases may improve stability.
c) Any change of slope of floors alr roofs at junctions with supporting walls or columns,
that takes place after construction, may produce loading of the latterthat is both eccentric
and inclined. Such changes of dope may be due to the effects of permanent and
imposed and snow loads on the floors or roof members, the permanent load causing
creep deflection and the imposed and snow loads causing elasticdeflectionand possibly
creep deflection.
It is difficult for the designer to assess the problem if he is not aware of the probable
deformation of the floor or roof member, as may be the case if the member is not
designed by him.
E-5.3
RESONANCE. Near-coincidence of forced and natural vibrations may produce
resonance of any building element. The degree of resonance may be reduced by
appropriate adjustment of either of the two frequencies, or by the provision of vibration
insulation or adequate damping. The problem arises mainly where the disturbing force
is of large magnitude, i.e. in auditoria, in dance halls and in grandstands, and in buildings
having long span suspended floors with a natural frequency of about 1-5 Hz, or
containing machines with large unbalanced forces.
SABS 0160-1989
108
E-6
SERVICEABILITY
E-6.1
GENERAL. Deformations, although possibly not affecting the strength or stability of a
building, may cause damage to members (load-bearing or otherwise) and to finishes and
claddings.
They may produce unpleasant psychological effects, even to the extent of causing alarm.
Finally, they may be physically such as to effectively prevent the use of the building for
its intended purpose or to impair the health of the occupants. Some deformations may
produce more than one kind of effect.
E-6.2
DEFORMATIONS CAUSING DAMAGE TO THE BUILDING
E-6.2.1
Crackina and SDallina of Walls. Change of slope of floors and roofs at junctions with
supporting walls or columns and lifting of the insufficiently restrained corners of
torsionally stiff floor slabs may cause horizontal cracking (particularly undesirable where
floors are carried through to the face of the external wall) and also spalling of internal or
external finishes. The actions involved are permanent load causing creep deflection and
the imposed floor load and any roof load (including snow) causing elastic deflection and
creep deflection.
Differential settlement and wind forces may also cause such cracking and spalling.
Thermal and moisture movements in finishes are also involved. More severe limitation
may be necessary if deep edge stiffening beams are incorporated into the walls.
E-6.2.2
Crackina and SDallina of Ceilinas. Curvature of the floor or roof may cause cracking in
decoration on the underside of concrete slabs. Curvature subsequent to plastering may
cause cracking of the plaster in the span and spalling in regions of negative curvature.
The actions involved are the permanent loading of the floors or roofs causing creep
deflection and the imposed loading causing elastic deflection and possibly creep
deflection. Repeated thermal and moisture movements in the plaster may also be
involved. Good extensibilityof the plaster and good distribution of concentrated loads are
ameliorating factors as is also the fact that cracks may be covered by redecoration. The
permissible degree of cracking is largely subjective but depends on the use of the
building.
E-6.2.3
Crackina and Spallina of Brittle Partitions and Non-loadbearinq Walls
a) Apart from cracking, spalling and local bulging due to thermal and moisture
movements in the partitions themselves, or in the supporting structure, damage to brittle
partitions may arise as a result of the differential settlement of foundations, deflection of
floors or roofs, or lateral movements of the building.
Estimation of this damage depends on a determination of the total tensile or compressive
effects arising from all causes, together with information about the limiting tensile and
compressive properties of the partitions, the effects on the number and width of cracks
of any restraints to movement, and the degree of cracking that can be tolerated for the
given type of surface finish and the given use of the building. Such procedure is not yet
sufficiently developed and it is meanwhile recommended that the deformation arising
from various causes be dealt with separately. The suggested limiting values may permit
a certain amount of cracking. Where this cannot be accepted, a more severe limitation,
or more tolerant partitions, may be called for.
b) Differential settlement of foundations subsequent to the erection of partitions may
produce diagonal cracking across the body of the latter. The actions involved are the
self-weight load, including that of the partitions, and all long-term temporary actions
capable of influencing settlement.
109
SABS 0160-1989
c) Deflectionsof floors or roofs may damage partitions in a number of ways. In all cases
the effects involved are those occurring after the erection of partitions, i.e. the self-weight
load of the floor or roof, and in some cases that of the partitions, together with any
pre-stress, causes creep deflections; the imposed floor or roof load (including snow load
and any self-weight loads such as screeds and floor finishes applied after erection of
partitions) causes elastic deflection and creep deflection; also, curvature and other
movements of the floor may be caused by possible unrestrained moisture movements.
In general, the greater the rigidity of the floor transverse to the span, the worse are the
effects of its deformations. Three main types of behaviour are known:
1) With the first type of behaviour,i3 partition parallel to the span deforms in its own plane
to follow the deformations of the floor below it, possibly producing vertical cracks in the
bending tension zone, diagonal shear cracks, or a gap above the partition. This type of
behaviour is most likely to occur where the partition is of relatively long span
(length/height exceeding 3,5 approximately for non-cantilevered spans); or is not
longitudinally restrained by the structure or by contiguous partitions; or contains many
openings; or is of low rigidity. In this case, apart from the weight of the partition
concerned, one of the actions involved is the contributionfrom the weight of partitionson
the floor or floors above, assuming that this can be transmitted to the partition in
question.
In the case of a cantilevered span, there is a greater possibility of cracking in the upper
part of the partition and damage to fascias owing to non-uniform deflection of supporting
cantilevers.
2) With the second type of behaviour, a partition parallel (or in some cases transverse)
to the span tends to support itself by arching horizontallyor diagonally. This is most likely
to occur where the partition has a high compressive modulus and limit of deformability;
where the ratio of length to height lies in the range 1 , 5 3 5 approximately; where the
partition is longitudinally restrained by the structure or by contiguous walls or partitions;
and where there are few openings or continuous vertical slidingjoints to interfere with the
arching.
If, in such case, the floor below the partition deflects more than the partition (possibly
owing to the absence of a partition, a stiffening beam, or other support underneath), a
horizontal crack may be formed along the base of the partition, or a horizontal or
arc-shaped crack may be formed in the lower portion of the partition, together with
diagonal cracks across the upper corners owing to extension of the undersurface of the
floor above. (If such horizontal cracks are likely to occur, their formation may be limited
to the floor level where they can Subsequently be masked by the provision of a chase or
a separation layer. The cracks can then be masked by a skirting board fixed to the floor.)
If, on the other hand, the floor or roof above the partition deflects more than does the
partition and there is no compressible packing at the head of the partition, the partition
tends to be crushed and there may be vertical cracks in the lower part and diagonal
cracks across the upper corners.
3) With the third type of behaviour, the partition is loaded by the upper floor and carries
these loads by strut-action to the ends of the span of the lower floor. This is most likely
to happen when the ratio of length to height of the partition is less than 1 3 approximately.
The type of damage is the same as in (2) above.
When the partitions have openings, a combination of some of the above phenomena is
likely to occur or there may be simple rotation of the parts of the partition. Diagonal
cracks radiating from the corners of the openings may also be produced. Some
horizontal or inclined reinforcementat such places is therefore advisable where it is not
possible to break the continuity of the partition above or below the opening.
d) Lateral deflection of a building as a result of wind forces may cause diagonal cracking
across the body of a partition. The action involved is that of the wind gust in having a
duration of sufficient length to produce the necessary deflection. Low-cycle fatigue
damage may occur. Strong shear walls, central core zones or enclosed staircases have
an ameliorating effect.
SABS 0160-1989
E-6.2.4
110
Damaae to Roof Coverinas. Claddinq and Glazinq. Deflections of roofs may cause
damage to roof coverings of felt or metal, to roof sheeting or to roof glazing or tiling. The
actions involved are the production of creep deflections by the permanent load and the
production of elastic deflections by any imposed load, snow or hail loading, and/or wind
gusts of appropriate duration.
The limitation of deflection may need to be more restrictive for roofs covered with sheet
materials which become brittle with age. The cladding fixing should be so designed that
structural loads are not transferred to cladding panels when the structural frame deforms.
E-6.3
DEFORMATIONS AFFECTING APPEARANCE
E-6.3.1
Visible Saa of Floors and Ceilinas. Visible deviations of floors and ceilings from the
straight line or plane (unless obviously intentional) cause subjective feelings that are
unpleasant and possiblyalarming. The actions involved are those of the permanent load
and the imposed loads in producing elastic deflections and possibly creep deflections,
and also constructional deviations and thermal and moisture movements and, in the case
of cantilevers, differential settlement. The provision of a camber or of a false ceiling can
improve matters.
Subjective appraisal depends on the type of roof or floor (whether flat soffit, beam and
slab, trough or ribbed construction), the area of it that is visible, its height and its
relationship to other elements of the construction (particularly elements that are
horizontal or in a horizontal plane), and the lighting conditions.
E-6.3.2
Visible Lean of Walls and Columns. Visible deviation of vertical members from the
vertical (unless obviously intentional) is also a source of subjective unrest. The actions
involved are those of the dead (self-weight) loads and imposed loads causing differential
settlements, but constructional deviations and the overturning effects of eccentric and
inclined loads on walls and columns may be contributing factors. Persons vary in their
appraisal of lean but are often guided by neighbouring vertical elements.
E-6.4
DEFORMATIONS AFFECTING USE
E-6.4.1
Curvature of Floors. Curvature of floors and the inclinations that it produces may cause
people to stumble or slip, trolleys to move, furniture and equipment to tilt or rock, and spilt
liquids to spread. Curvature may be due to constructional deviations and to elastic
deflections and creep deflections (possibly upward) under permanent load alone or under
permanent load and imposed floor loads, or to thermal or moisture movements. The
provision of screeds or a camber may be appropriate.
E-6.4.2
Non-horizontalitv of Floor S U R R O ~Unintentional
~S.
lack of horizontality of floor supports
causes a number of the effects referred to in E-6.4.1. It may be due to constructional
deviations or to differential settlement under dead (self-weight) loads and imposed floor
loads, or to rotation of the point of support in the case of cantilevers.
E-6.4.3
Oscillations Generated Within the Buildinq or bv Wind Forces. Apart from man-made
external sources of vibration, such as nearby industrial and transport activities, whose
effects are not a matter for this appendix, the main sources of oscillations of buildings are
foot traffic and machinery within the building, together with wind gusts. (Earthquakes are
dealt with in E-6.5.2.) The acceptable magnitudes of such oscillations, which may cause
unpleasant sensations, including alarm, or prevent the carrying on of required activities,
depend on human sensitivity, on the activity to be pursued, on the degree of damping
present, and on the duration of the impulses and the interval between them.
Recommendations for the limitation of oscillations of frequency exceeding 1 Hz are given
in IS0 2631.
111
SABS 0160-1989
E-6.4.4
Deformations Affectina Special Reauirements in Use
E-6.4.4.1
General. E-6.4.1 to E-6.4.3 refer to deformations affecting the use of common types of
buildings within the scope of this code of practice. However, in certain types of buildings
there may be special requirements in connection with, for example, particular activities
of occupants or the use of machinery or precision apparatus. Examples of such
requirements are as follows:
a) Deflections of overhead travellins crane airders. Travelling cranes produce
1) vertical deflections of the runway girders (and of supporting brackets in some cases)
owing to their self-weight and that of the load carried, and
2) horizontal lateral and longitudinal deflections of the supporting columns owing to the
forces of acceleration and braking.
(It is assumed here that the effects of constructional deviations and any subsequent
movements of supports have been negated by the levelling and lining up of the crane
rails. Any upward deflection due to pre-stress may be taken into account.)
In the case of vertical deflection:; of the runway girders, there may be a problem of
clearances. The principal problems, however, are the overloading of the means of
propulsion owing to the slope of the runway girders when under load and the
maintenance of steady motion over the points of support.
In the case of horizontal deflections of the columns, it is necessary to limit the transverse
deflection to prevent the crane gantry itself from rotating excessively about the vertical
(slewing), or becoming dislodged, and also to limit both transverse and longitudinal
deflections to prevent excessive deformations of the supporting columns from leading
to damage to cladding and fixings (or to instability; see E-6.2).
b) Other special requirements. These requirements should be agreed upon in
consultation with the owner and the suppliers of any equipment involved, before design
and construction commences. Examples of problems that may arise are
1) vibration of weighing and measuring apparatus;
2) damage to impermeable membranes used for isolation or protection of liquids and
gases;
3) twist of floors carrying machines operating on sheet materials;
4) inclinations affecting co-linearity of apparatus or levels of liquids;
5) interference with fine manual movements.
E-6.5
DEFORMATIONS REQUIRING GENERAL OVERALL CONTROL
E-6.5.1
General. Cracks in building elernents may damage coverings, permit corrosion of
reinforcing elements or allow penetrationof liquids, gases or radiation(thus, for example,
reducing thermal or airborne sound insulation, or admitting rain, dust or light). Cracks
may also constitute disfigurement or cause alarm. (They are unlikely to cause structural
collapse unless extremely wide and extensive, but they are early evidence of excessive
action.)
In many cases, cracks may be avoided, may be located in one or more convenient places
or may be hidden, by means of appropriate initial design and construction measures. In
other cases, the requirements of standards for other types of deformation may prevent
the formation of cracks.
However, it must be borne in mind that design and construction measures may be only
partially successful in controlling cracking, and that, in any event, cracks may occur in
circumstances other than those provided for in standards; it is necessary to impose a
general overall limitation on the width of cracks.
SABS 0160-1989
112
In laying down limitations, consideration must be given to the building materials involved,
whether the cracks are through-cracks or surface cracks, whether they are likely to open
further or close, whether they are repairable or capable of being covered by decoration,
whether penetration of liquids, etc., is a factor, and the probable attitude of persons
affected, in view of the intended use of the building.
In the case of possible corrosion of reinforcement, the permissible width of cracks should
be laid down in consultation with specialist organizations. Where corrosion of
reinforcement is not in question,
1) through-cracks should not be permitted at positions where the transfer of water (e.g.
by gravity, wind pressure or capillary actions) to the inside surfaces of rooms could occur;
2) cracks should individually not exceed an average width of 0,2 mm if it is intended that
they be coverable by redecoration;
3) if cracks are likely to be permanent, neither through-cracks nor surface cracks should
individually exceed an average width of 2 mm, or such lower figure as may be required
in particular circumstances (for example, in the presence of corrosive or humid
atmospheres).
The widths of cracks and any resulting out-of-plane dislocations may be controlled by
prestressed (or other) reinforcement.
E-6.5.2
Deformations Due to Earthauakes. Apart from the hammering of adjacent buildings
owing to insufficient clearance as referred to in E-8(d), oscillations during an earthquake
may cause considerable damage. Methods of predicting and assessing the damage are
still the subject of disagreement between experts, and research continues.
It is therefore not possible at present to make any recommendation regarding limitation
of deformation during an earthquake.
E-7
METHODS OF ASSESSING PROBABLE DEFORMATIONS
The method used to assess or control the probable deformation is a matter for the
structural designer. For example, he may determine deformations by calculation or by
model or prototype testing; he may control them by the adoption of limiting span/depth
ratios or other measures. Whatever the method used, it should be such that it gives an
acceptable probability of meeting the requirements given in this appendix. A probability
of not exceeding limits of 97 % is suggested as a desirable minimum.
When deformations are determined by calculation, such calculation should be based on
the characteristic values of actions (loads, moisture movements, thermal movements)
and of properties of members (elastic properties, creep and thermal coefficients of
materials, and dimensions), due allowance being made (as provided for in E-4.2(c)) for
any appropriate combinations of other parameters.
The calculations should take into account constructional deviations, thermal movements,
moisture movements, cracking of reinforced materials, and creep of materials under
permanent and long-term temporary loads. In addition, the assistance received from
various sources (for example, partial fixity at ends of beams and slabs, partial support
from partitions), that cannot be sufficiently relied upon when strength properties are
assessed, may be taken into account.
In calculating any required camber, it is suggested that the magnitude of the action
involved be the mean value.
The deformation limitation to be met should be the most severe of any values suggested
for any particular criterion.
113
E-8
SABS 0160-1989
COMMON CAUSES OF DEFLECTION AND DEFORMATION
The following is a summary of the more common actions that are responsible for
deflection and deformation in buildings:
a) Major ground movementsor movementsof moisture-reactivesoils (where movements
are usually so great that special constructional measures are required);
b) relative movement between contiguous buildings, or at the point of entry or exit of
services, due to differential settlement;
c) differential settlement causing nipping of walls, partitions and services on a
ground-bearing floor slab;
d) hammering of inadequately spaced buildings during an earthquake;
e) ponding on roofs;
f) vibrations of cladding, and noises due to oscillations produced by wind;
g) differential settlement causing nipping of windows and doors and jamming or
demounting of sliding doors;
h) thermal expansion, particularly of roofs and exposed columns, and differential thermal
expansion of different building materials or of thin exposed members such as cladding;
i) differential shrinkage of different building materials or of different qualities of the same
material, possibly at different stages in their moisture movement;
j) long-term expansion of clay products, particularly in parapets, fascias, and floor
coverings;
k) chemical deterioration, e.g. forrriation of sulpho-aluminatesor of rust or other corrosion
products;
I) upward creep deflection of unrestrained prestressed roof members.
E-9
Tables E-I to E-5 (inclusive) give information on damage caused by various forms of
deformation. The references giver1 in the tables are to the relevant subsections in the text
of this appendix.
TABLE E-1 - DEFORMATIONS AFFECTING STRENGTH AND STABILITY (SEE E-5)
1
7
Defect
Cause
E-5.2 Damage due to
eccentric loading of
walls and columns
E-5.3 Damage due to
resonance
I
I
3
Actions involved
E-5.2(b) Inclination of
walls and columns
(Constructional deviations)
Differential settlement
Wind load
Eccentric vertical loads
E-5.2(c) Rotation of
floors and roofs
Permanent load
Imposed load
Snow load
Differential settlement
Near-coincidence of
forced and natural
oscillations
Unbalanced machinery
(starting, running, stopping)
Foot traffic
Synchronous crowd movements
I
I
4
I
5
Possible ameliorating
I
Recommended criterion
fartnrc
Shear walls
Central core zones
Enclosed staircases
Adjustment of frequencies
Vibration insulation
Damping
7
Suggested limiting value
Comments
Terminal deviation of
vertical members
None suggested in view
of various remedies
available
A matter for the
designer
Medial deflection of floor
or roof member, as a
measure of rotation
About span/300
Differential settlement a matter for
the designer
No simple criterion
Dynamic analysis
required
None suggested
Machinery, auditoria, dance halls,
grandstands, long
span floors
TABLE E-2 - DEFORMATIONS AFFECTING SERVICEABILITY (SEE E-6)
1
2
3
Defect
Cause
Actions involved
E-6.2.1 Cracking and
a) Deflection of floors
spalling of walls at points b) Movement of vertical
of support of floors and
members
roofs
Permanent load
Imposed load
Snow load
Wind load
Differential settlement
Thermal and moisture
movements
E-6.2.2 Cracking and
spalling of ceiling
Permanent load
Imposed load
Snow load
Thermal and moisture
movements
Curvature of floors or roofs
4
Possible ameliorating factors
Sood extensibility of finishes
Sood distribution of
:oncentrated loads
Redecoration
I
5
Recommended criterion
6
Suggested limiting value
a) Medial deflection of
floor, as a measure of
rotation under floor loads
b) Terminal deflection of
horizontal or vertical
members
About span/300
I) About span/100 or storey
ieightllO0
Medial deflection of floor,
as a measure of curvature
(Terminal deflection for
cantilevers)
Vone suggested
See text
Terminal deflection of
horizontal members
About span1500
Comments
I)
Iepends on personal
'actors and type of
luilding
E-6.2.3(a) Cracking and spalling of brittle partitions
Diagonal cracking
across body
E-6.2.3(b) Differential
settlement (see also
E-6.2.3fd)l
I
Self-weight and other
long-term gravity effects
E-6.2.3(c) Deflection of fli 3rs or roofs
Tensile deformability
involved
Bending-typecracking
Gap at top
Partition follows movement
of floor beneath
Permanent load
Imposed load
Thermal and moisture
movements
Horizontal cracking in
lower part
Gap at bottom
Excessive deflection of floor
below
Permanent load
Imposed load
Thermal and moisture
movements
See text
Medial deflection of floor,
as a measure of arching
tendency in partition
About 10 mm
Crushing of upper part
Excessive deflection of floor
above, or of roof
Permanent load
Imposed load
Snow load
Thermal and moisture
movements
See text
Medial deflection of floor,
as a measure of tendency
to crush partition
From about 10 mm to about Compressive
deformability involved
15 mm as limit of
deformability increases
Diagonal cracking
across body
E-6.2.3(d) Lateral
movements of building (see
Wind load
Shear walls
Central core zones
Enclosed staircases
Terminal deflection of
vertical members
About storey heighV500
Low-cycle fatigue damage
may be involved
Medial deflection of
supporting element, as a
measure of curvature
(Terminal deflection for
cantilevers)
About span1125 for tiles
and ductile sheetings
About span1250 for brittle
sheetings
Measured normal to the
roof
as a measure of curvature
in plane of partition
(Terminal deflection for
cantilevers)
From about span1500 to
about span/300 according
to limit of deformability
~~
coverings, cladding and
glazing
Permanent load
Imposed load
Snow load
Wind load
Q)
?
cn
D
m
cn
TABLE E-3 - DEFORMATIONS AFFECTING APPEARANCE (SEE E-6.3)
0
3
m
1
2
3
4
5
6
Defect
Actions involved
Possible ameliorating
factors
Recommended criterion
Suggested limiting value
Comments
E-6.3.1 Visible sag of
floors and ceilings
(Constructional deviations)
Permanent load
Imposed load
Thermal and moisture movements
E-6.3.2 Visible lean
of walls and columns
(Constructional deviations)
Differential settlement
Eccentric or inclined forces from
self-weight and imposed loads
Camber
False ceiling
Medial deviation of
member (or of its visible
Parts)
(Terminal deviation for
cantilevers)
Approximate visible
length/250 or 30 mm,
whichever is less (For
cantilevers, visible
length/250 or 15 mm)
Terminal deviation of
vertical members
Approximate storey
heighU250
Assumed slab, or simple
beam and slab, type
construction
I
2
to
CO
a
TABLE E-4 - DEFORMATIONS AFFECTING USE (SEE E-6.4)
1
2
Defect
I
Cause or actions involved
E-6.4.1 Curvature
of floors
(Constructional deviations)
Permanent load
Imposed load
E-6.4.2 Non-horizontality of floor
supports
(Constructional deviations)
Differential settlement
3
4
Possible amelioratina factors
Recommended criterion
6
Suggested limiting value
Camber
Screed or floor finishes
Medial deviation of floor
surface with and without
imposed load
(Terminal deviation for
cantilevers)
About span/300 (About
span/125 for cantilevers)
Screed in certain cases
Terminal deviation of
horizontal members
About span/lOO
No recommendation
No recommendation
a) Medial vertical deflection of girder, as a measure of slope
b) Horizontal deflection of
supports (see also E-6.2.2)
a) About span1500
b) About height of
support1200
I
Comments
I
I
E-6.4.2 not applicable
where slope is intentional
E-6.4.3 Oscillations generated within the building or by wind forces
I
Oscillations of
members
Unbalanced machinery
Foot traffic
Crowd movements
Oscillations of the
building as a whole
Wind gusts
I
Vibration insulation
Adjustment of machine frequencies
DamDina
Damping
E-6.4.4 Deformation affecting special requirement? in use
E-6.4.4(a) Deflection of overhead
crane runways
a) vertically
b) horizontallv
E-6.4.4(b) Other
special requirements
a) Permanent load
Imposed load
b) Longitudinal and transverse forces
I
Assumes support
maintained level and
in line
To be agreed upon
before design and
construction commences
TABLE E-5 - DEFORMATIONS REQUIRING GENERAL OVERALL CONTROL (SEE E-6.5)
1
Defect
L
3
4
5
6
7
Cause
Recommended criterion
Suggested limiting value
Comments
Actions involved
Possible ameliorating factors
E-6.5.1 Cracking
Multiple causes
All actions in appropriate
circumstances
Good building practice (see E-8)
Provision of crack-control
reinforcement
Average width of widest
individual crack
E-6.5.2 Deformations
due to earthquakes
Earthquake
All actions in appropriate
circumstances
See E-8
No recommendation yet
possible
See E-6.5
Not necessarily adequate where corrosion
of reinforcement may
occur
119
SABS 0160-1989
APPENDIX F. RAINFALL INTENSITY
(This appendix does not form part of the provisions of the code)
F-I
GENERAL
While the code of practice covers loads and loadings that, in relation to rainfall, relate to
horizontal areas and associated tributary areas, it is considered desirable to include in
this appendix a brief guide to rainfall intensity as related to horizontal surfaces and to
rainwater disposal from roofs.
Large variations in rainfall are encountered throughout the Republic of South Africa (see
Fig. F-I), storms of high intensity and short duration being encountered in a number of
localities. The increase in recent years in the number of reports of water damage to the
contents of buildings has been, in the majority of cases, the direct result of an inadequate
capacity of the drainage facilities for these high intensity, short duration storms. Such a
lack of capacity can be due either to an underestimation in the design criteria or to lack
of maintenance and repair on the part of the owner.
On sloping roofs, the overflow from eaves gutters that falls free of the building will not
affect the building or its contents. On the other hand, with valley gutters and box gutters,
any overflow can result in serious damage to the contents of the building and involve the
owner in heavy compensation, repair and redecoration costs. In the case of flat roofs,
ponding is responsible for water penetration into the building where waterproofing
membranes or flashings (or both) are either ruptured or inadequate.
The concept of peak flow reduction of stormwater by "storage ponding" (or detention) is
employed by a number of overseas countries to reduce the high initial flows experienced
during high intensity, short duration rainstorms. If such an approach is consideredwithin
the Republic of South Africa for flat roofs (in the context of this code of practice), it will
be necessary to give special attention to the waterproofing and design of such roofs.
F-2
DESIGN APPROACH
The general approach to the design of rainwater discharge has been to use charts
prepared (generally) by the manufacturers of the various materials used. These charts
are related to roof area when the size of gutters and discharge pipes is determined. The
data are based usually on a rainfall intensity which is not necessarily related to the actual
rainfall intensity of the area under consideration. A value of about 200 mm/h is
sometimes used by some authorities.
The application of a general design value relieves the designer of the responsibility of
establishing the design intensity criteria. The authority concerned has either established
that such a value is adequate for design purposes, or is possibly prepared to admit
responsibility for any excess volurne.
It is necessary for the designer to select a design intensity that is realistic for the area
under consideration.This is particularlynecessarywhenstormwater drainage is designed
for buildings that house machinery, stock or materials whose replacement cost is high.
F-3
RA1NFALL INTENSITY
F-3.1
ROOF FLOODING. Where a flat roof is provided with rainwater outlets built into the
construction of the roof, it is essential that these outlets always be kept free of
obstructions. This is particularly necessary for any roof where the construction is subject
to increasing deflection with increasing load or where such a roof is surrounded by
parapet walls or other upstands.
N
0
10
'
12'
14'
16'
180
20'
22'
24"
26'
Fig F-I -Annual Rainfall
28'
30°
32O
34'
36O
SABS 0160-1989
121
It is suggested that the design load for rain on such a flat roof be based on the 24 h
rainfall intensity for the area and tributary area of the roof. The value of this intensity must
take into consideration the type of building and its occupancy, and the designer must
establish the appropriate return period. The 24 h rainfall intensity for return periods of 25,
50,and 100 years can be obtained from A-2(u) of Appendix A, which covers 62 stations
in Namibia.
F-3.2
GUTTERS. From the meteorological point of view, the rainfall in the Republic of South
Africa can be divided into three basic zones, namely the winter rainfall, summer rainfall,
and year-round rainfall zones (see Fig. F-2).
I
I
Windhoek
0
I
3
I Piet!rsburg
I
I
I
I
I
I
Fig. F-2 Rainfall Zones
For a conventional building, the critical period or critical duration for a storm is very short.
The shortest duration given in A-2(u) of Appendix A for a storm is 15 min . This is
generally felt to be too long and a period of 5 min has been suggested as being more
realistic (see A-2(v) of Appendix A).
Work carried out by the Hydrological Research Unit of the University of the
Witwatersrand (see A-2(w) of Appendix A) and by PT Culligan (see A-2(x) of Appendix A) has produced, for various return periods, 5-min duration intensities for the three
rainfall zones (see Fig. F-2), based on the mean annual precipitation. These values are
reproduced in Fig. F-3, F-4 and F-5. The annual precipitation may be obtained from
Fig. F-I , which gives four categories of values. If a more accurate value of annual rainfall
for a particular locality is desired, reference should be made to Table II in the Weather
Bureau Report referred to in A-2(y) of Appendix A, which gives the average annual
rainfall and the period over which this value has been calculated. Alternatively, the
designer may use a value from a reliable station in the area concerned, in which case a
time base of at least 15 years is the desired minimum.
The return period to be used for 21 particular design will depend on the type of building
and the occupancy, the commodity being considered (e.g. gutters, discharge pipes) and
the degree of damage to which such commodity is liable. An external eaves gutter with
an overhang of, say, 450 mm will cause less damage internally than will a box gutter or
valley gutter if overflow should occur. It is suggested that an overhanging eaves gutter
be designed on, say, a 5-year return period but that internal box gutters be designed on
a greater return period depending on the type of damage likely to be suffered.
The designer must decide on the suitable return period after having considered all the
relevant facts.
SABS 0160-1989
122
Return
period,
years
400
100
350
50
300
20
250
10
r
\
E
E
h
L
.In
c
200
0.l
c
c
.-
150
(U
c
3
.-c
E
100
I
(U
w
._
LL
50
100 200
500
750
1 000
1 500
2 000
2 200
Mean annual rainfall, rnm
Fig. F-3- Summer Rainfall Zone Design Curve
I I
I
Return
period,
years
I
200
150
100
50
-
100
=
50
-
1
20
10
-
5
:
2
L
:
-
100
200
500
750
1 000
1 500
Mean annual rainfall, rnrn
Fig. F-4 -Winter Rainfall Zone Design Curve
2 000
2 200
SABS 0160-1989
123
Return
period,
years
100
400
350
50
300
250
20
200
10
150
5
100
2
50
100 200
500
750
1 000
1 500
2 000 2 200
Mean annual rainfall, mm
Fig F-5 - Year-round Rainfall Zone Design Curve
sabs pta
(Pdf)