AMERICAN FOREST & PAPER ASSOCIATION
American Wood Council
Engineered and Traditional Wood Products
American Wood Council
Engineered and Traditional Wood Products
BCD201:
Fire Design Methodologies
for Code Acceptance
A F & P A®
®
Copyright © 2004 American Forest & Paper Association, Inc. All rights reserved.
Welcome to eCourse BCD 201 titled Fire Design Methodologies for Code Acceptance.
Copyright © 2004, 2007 American Forest & Paper Association, Inc.
All rights reserved.
1
Copyright of Materials
This presentation is protected by US and International copyright
laws. Reproduction, distribution, display and use of the
presentation without written permission of the American Forest &
Paper Association / American Wood Council is prohibited.
Copyright © 2004 American Forest & Paper Association, Inc.
All rights reserved.
3
BCD201: Learning Outcomes
• By the end of this eCourse, you will be:
1.
2.
3.
4.
Able to apply provisions for designing wood
members for fire safety, including the
Component Additive Method
Able to design heavy timber for fire resistance
Able to determine flame spread ratings
Familiar with fire-rated assemblies
In this eCourse, you will learn to apply provisions for designing wood members for fire
safety, including: using the component additive method, designing heavy timber for fire
resistance, flame spread ratings, and fire-rated assemblies.
4
Design for Code Acceptance Pubs
AWC publishes 4 Design for Code Acceptance (DCA) publications and one Technical
Report that deal with fire.
5
Outline
• DCA1: Fire Spread Performance of Wood Products
• DCA3: Fire Rated Wood Wall Assemblies
• DCA4: Component Additive Method (CAM) for
Calculating and Demonstrating Assembly
Fire Endurance
• DCA2: Design of Fire-Resistive Exposed Wood
Members
• TR10: Calculating the Fire Resistance of Exposed
Wood Members
• Detailing for Fire Control
This presentation will highlight all 5 documents and show by example how to use the
information contained in them. Also, information on detailing for the prevention of fire spread
will be covered.
6
Design for Code Acceptance 1
DCA 1
Fire Spread Performance
of Wood Products
Design for Code Acceptance 1 (DCA 1): Flame Spread Performance of Wood Products.
7
Design for Code Acceptance 1
E 84 Tunnel
Apparatus
The Steiner Tunnel Test is used to determine flame spread rating. It is calibrated with Red
Oak flooring and measures the relative spread of fire over time. The measure is expressed
as an index where the Red Oak standard is given the value of 100, and cementitious board
is given a value of zero.
8
DCA 1: Flame Spread Ratings for
Various Wood Products
Class I or A
0 - 25
fire retardant treated wood
Class II or B
26 - 75
redwood
cedar
Class III or C
76 - 200
most other wood species
softwood plywood
hardwood plywood
particleboard
based on Red Oak = 100
Typical flame spread ratings for various woods are grouped for acceptance in the building
code provisions. The lower the rating number, the lower the ability of flame to spread. Some
examples of flame spread rating numbers are:
•FRTW: 0-25
•Redwood & Cedar: 26-75
•Other woods: 76-200
DCA 1 now lists flame spread ratings for a variety of domestic wood species and materials
and is updated frequently on the web as new material ratings become available.
9
Design for Code Acceptance 3
DCA 3
Fire Rated Wood Wall
Assemblies
revised with new title
and contents 2001
DCA 3: One-hour Fire Rated Exterior Walls.
10
DCA 3: Designing for Fire
Endurance
Tools for designing wood frame construction to provide
fire endurance:
• traditional ASTM E-119 Assemblies
• Component Additive Method (DCA 4)
• Beam/Column Calculation Method (TR10)
There are several code accepted methods for designing to provide fire endurance. ASTM
E119 assemblies; component additive method (CAM); beam/column calculation method.
The latter two methods will be discussed later in order of complexity.
DCA 3 lists and describes complete assemblies that have been approved to meet a specific
time rating for fire endurance. This is the simplest approach to designing to meet a given fire
endurance requirement in the building code - simply pick an approved assembly that meets
the time required, i.e. a one-hour fire assembly. Each assembly has been furnace-tested to
the standard ASTM E119.
11
ASTM E-119 Joist Assembly
Typical 1 hour rated assembly:
19/32" plywood
15/32" plywood
2" x 10" joists @ 16" o/c
1/2" type X gypsum wallboard
The figure above shows a 1-hr E119 joist assembly (UL512). It uses ½" type X gypsum
board on 2x10 floor joists with 2 layers of plywood: 19/32" flooring over 15/32" subfloor.
12
ASTM E-119 Truss Assembly
Typical 1 hour rated assembly:
3/4" plywood
parallel chord truss
steel furring channel
5/8" proprietary type X wallboard
The above figure is a typical 1-hr E119 truss assembly (UL528). It uses 5/8" type C gypsum
board on furring channels (note the channels are doubled at board edges). This is on
parallel chord trusses with 1 layer of 3/4" plywood. Note that each assembly is generic in
description, and that each assembly description is cataloged by Underwriters Laboratories in
terms of a catalog number.
13
ASTM E-119 Truss Assembly
As constructed:
The figure above shows what that assembly looks like as constructed prior to testing in an E119 furnace.
14
DCA 3: Designing for Fire
Endurance
DCA 3 lists and describes
many of the common fire
rated wood assemblies for
wood construction by
duration
list and descriptions are
updated frequently as test
results become available
The figure above shows the form of a DCA 3 rated assembly description sheet.
15
Design for Code Acceptance 4
DCA 4
Component Additive
Method (CAM) for
Calculating and
Demonstrating Assembly
Fire Endurance
DCA 4: Component Additive Method (CAM) for Calculating and Demonstrating Assembly
Fire Endurance. Should a tested assembly, not be available, or applicable, one can “create”
a conforming assembly using the Component Additive Method. This is most frequently
utilitarian when designing in existing structures where the existing assemblies may not be
easily altered.
16
DCA 4: CAM Background
Component Additive Method (CAM)
• developed by NRC using NBS tests
• recognized by SBCCI and ICBO
• published by BOCA
• for new and existing assemblies
CAM was developed by the National Research Center of Canada using National Building
Science data, based upon Harmathy's 10 rules of fire endurance. Recognized by ICBO and
SBCCI and published by BOCA, the CAM applies to both new and existing assemblies. The
complete background to CAM is described in DCA 4, along with the required tables and
examples for design. CAM is implemented by adding time contributions from each materials
layer through the thickness of the entire assembly.
17
DCA 4: CAM Membrane Table
Time Assigned to Protective Membranes
Description of Finish
3/8" Douglas-fir plywood, phenolic bonded
1/2" Douglas-fir plywood, phenolic bonded
5/8" Douglas-fir plywood, phenolic bonded
3/8" gypsum board
1/2" gypsum board
5/8" gypsum board
1/2" Type X gypsum board
5/8" Type X gypsum board
Double 3/8" gypsum board
1/2" + 3/8" gypsum board
Double 1/2" gypsum board
Time
(minutes)
5
10
15
10
15
20
25
40
25
35
40
Here is an example of the table from DCA 4 of times assigned to protective membrane
materials, i.e. ½" gypsum board: 15 minutes; 5/8" doug-fir plywood: 15 min.
18
DCA 4: Wall Membranes
Membranes on Exterior Face of Walls
Sheathing
5/8" T&G lumber
5/16" exterior grade plywood
1/2" gypsum board
None
Paper
Exterior Finish
Sheathing Lumber siding: or
paper
Wood shakes & shingles
1/4" external grade plywood
1/4" hardboard
Metal siding
Stucco on metal lath
Masonry veneer
None
3/8" external grade plywood
The table lists the minimum membrane protection required when the assembly is
asymmetrical. Membrane protection on each side is required if exposure to fire may occur
from either side.
19
DCA 4: CAM Wood Component
Table
Assigned Times for Wood Components
Description of Frames
Time
(minutes)
Wood studs, 16 inches on center
20
Wood joists, 16 inches on center
10
Wood roof and floor truss assemblies
24 inches on center
5
Here is another table from DCA 4 listing assigned times for various wood components, for
example:
studs 16” o.c. - 20 min.
joists 16” o.c. - 10 min.
trusses 24” o.c. - 5 min.
20
DCA 4: CAM Cavity Insulation
Table
Assigned Times for Insulation of Cavity
Insulation Type
Time
(minutes)
Mineral wool batts
15
Glass fiber batts, non-loadbearing walls
5
Here is another example of a table from DCA 4 listing assigned times for cavity insulation,
i.e. mineral wool batts assigned a time of 15 minutes.
21
DCA 4: CAM Example 1
Component Additive Method (CAM) - Interior Wall
2" X 4" Wood Stud
5/8" Type X Gypsum Board
2" X 4" Wood Stud
20 minutes
5/8 " Type X Gypsum Board
40 minutes
Total
60 minutes
To apply Component Additive Method, take each material layer in the assembly, find its
respective assigned time from the DCA table, and sum the materials times together. The
summed time yields the time rating for the assembly.
Example: 2x4 studs@16"o.c. = 20 min.; 2 layers 5/8" type X gypsum board = 40 min.; total =
60 min.
This interior wall assembly would satisfy a 1 hour requirement.
22
DCA 4: CAM Example 2a
Component Additive Method (CAM) - Exterior Wall
2" X 4" Wood Stud
Glass Fiber Insulation
1/2" Gypsum Board
2" X 4" Wood Stud
20 minutes
1/2 " Gypsum Board
15 minutes
Total
35 minutes
Consider this exterior wall for a 1 hour time requirement. From the DCA 4 tables, the
materials times are as follows: 2x4 studs@16"o.c. = 20 min.; 1 layer ½" gypsum board = 15
min.; total = 35 min. That’s less than the 1 hour required.
23
DCA 4: CAM Example 2b
Component Additive Method (CAM) - Exterior Wall
2" X 4" Wood Stud
Glass Fiber Insulation
1/2" Gypsum Board & 1/2" Type X Gypsum Board
2" X 4" Wood Stud
1/2 " Gypsum Board
Total
1/2" Type X Gypsum Board
Total
20 minutes
15 minutes
35 minutes
25 minutes
60 minutes
To meet the minimum 1 hour requirement, add an additional layer of ½" type X gypsum = 25
min., for a total of 60 min. Now the assembly is OK.
24
Design for Code Acceptance 2
DCA 2
Design of Fire-Resistive
Exposed Wood Members
Design for Code Acceptance 2 (DCA 2): Design of Fire Resistive Exposed Wood Members.
Should you have exposed structural wood material, you can provide meaningful fire
protection by design. DCA 2 provides the necessary guidance and formulae based on
extensive fire testing and char rate modeling.
25
DCA 2: E-119 Fire Test
Beam Fire Test
The figure above shows a glulam beam being tested in an ASTM E119 furnace.
26
DCA 2: Charred Cross-section
Beam Fire Design
Heated
zone
D
Charred
wood
W
Analysis of wood members subjected to fire yields the following characteristics about their
cross section. Wood is a natural insulator that chars from the outside-in at a measurable,
predictable rate when exposed to fire. The outer layer is a char layer (sacrificial wood). The
heated zone is where some strength reduction in the wood occurs due to elevated
temperature. The inner zone is unaffected during the fire. This affords good residual loadcarrying ability for the wood member based on the size or cross section of the inner zone.
27
DCA 2: Section Terminology
Design Methodology for Beams and Columns
b
d
z
r
t
is the width (inches) of beam or larger column face
is the depth (inches) of beam or narrower column face
is the load factor
is the load ratio
is the fire endurance time (minutes)
The following terminology is used in this calculation method (see slide).
28
DCA 2: Beams
Fire Endurance Time for Beams
(1) fire exposure on four sides
t = 2.54 z b [4-2(b/d)]
(2) fire exposure on three sides
t = 2.54 z b [4-(b/d)]
The beam fire endurance calculation formulae is: (see slide). Note the distinction for 3-sided
vs. 4-sided exposure.
29
DCA 2: Columns
Fire Endurance Time for Columns
(1) fire exposure on four sides
t = 2.54 z b [3-2(d/b)]
(2) fire exposure on three sides
t = 2.54 z b [3-(d/2b)]
The fire endurance time equation for columns is: (see slide). Again, note the distinction
between 3-sided and 4-sided fire exposure.
30
DCA 2: Columns
Column Stability - Fixity Factors
Buckling Modes
Recommended Ke Values 0.5 0.7 1.0 1.0 2.0 2.0
Ke is normally assigned to be 1.0 for pin/pin end fixity conditions. The table, shown above,
recommends Ke values based upon the buckling modes expected in the condition of the
design.
31
DCA 2: Load Factor
Load Factor z
For columns with Ke /d <11:
z = 1.5
for r ≤ 50
z = 0.9 + 30/r
for r > 50
Load factors are shown graphically in DCA 2. Load factor, z, for columns with slenderness
ratio Kel/d < 11 (see slide).
32
DCA 2: Load Factor
Load Factor z
For columns with Ke /d >11, and all beams:
z = 1.3
for r ≤ 50
z = 0.7 + 30/r
for r > 50
Again note, load factors are shown graphically in DCA 2. Note the distinction for slender
columns with Ke l/d > 11 and for all beams (see slide).
33
DCA 2: Load Ratio
Load Ratio r
r=
Loadmax allowable
loadactual
can be expressed as geometry or other ratio forms since load is
a linear variable
“r” is the Load Ratio and can be expressed in geometry or in other ratio forms since load is a
linear variable (see slide).
34
DCA 2: Exposed Beam Example
Given: 8.75”x24” Glulam beam exposed to fire
on 3 sides; Sreq’d = 753 in3
Need:
1 hour rating
Consider this example: Design an 8.75” x 24” glulam beam for 1-hr fire endurance rating
assuming 3 sides exposed to fire. Assume a required section modulus (Sreq'd) of 753 in3
based on actual loads.
35
DCA 2: Exposed Beam Example
• Calculate the Load Ratio, r
r = Sreq’d / Ssupplied = 753 in3 / 840 in3
= 90%
• Calculate the Load Factor, z
z = 0.7 + 30/r = 0.7 + 30 / 90
= 1.035
The Load Ratio is the applied load on a member as a percentage of the allowable load. The
Load Factor, z, is determined from this load ratio (see slide).
36
DCA 2: Exposed Beam Example
• Calculate the Fire Endurance Time, t
t = 2.54 z b [4-b/d]
= 2.54 (1.035)(8.75) [4-(8.75/24)]
= 83 minutes
Calculate the fire endurance time in minutes using the time formula for a 3-sided exposed
beam (see slide). This is equal to 83 minutes. This beam exceeds the one-hour (60 minutes)
requirement in this design. If the time, t, calculated is less than 60 minutes, then to get the
one-hour requirement for this exposed beam, the section size would need to be increased
slightly.
37
Technical Report 10
TR10
Calculating the Fire
Resistance of Exposed
Wood Members
Technical Report 10 (TR 10): Design of Fire Resistive Exposed Wood Members, forms the
technical basis for DCA 2. It is also complete with detailed explanation, test results, and
comprehensive calculation examples.
38
Technical Report 10
• Superior fire performance of heavy timbers
– attributed to the charring effect of wood
• Benefits of charring
– an insulating char layer is formed
– protects the core of the section
The physical basis for the DCA 2 and TR 10 documents is the charring characteristic of
wood when subjected to fire. Charring of wood occurs at a measurable, predictable rate, and
because of wood’s insulation properties, the cross-section interior remains capable of
sustaining and carrying the load.
39
Technical Report 10
• Experimental charring rates measured in various parts
of the world appear to be consistent
– North America - Standard fire endurance test ASTM E-119
– many other countries - comparable fire exposure in ISO 834
• Effects of fire on adhesives
– synthetic glues used in the manufacture of glulam do not
adversely affect performance
Charring rates of wood under standard fire exposure conditions were measured in studies
world-wide. Glued products did not perform any differently than their solid counterparts.
40
Analog for Cross-Sectional Dimensions
A standard terminology was established for describing the charred and uncharred section
dimensions for two common fire exposures.
41
Estimating Cross-sectional
Dimensions due to Charring
• 4-Sided Exposure (i.e. columns) b = B - 2βt
d = D - 2βt
• 3-Sided Exposure (i.e. beams)
b = B - 2βt
d = D - βt
• 2-Sided Exposure (i.e. decking)
b = B - βt
d = D - βt
where:
β
t
is the char rate of the material
is the fire exposure time
…which resulted in these relations for charred width and depth as shown in the table above.
42
ASCE 29 Method for Beams
(Lie Empirical Method)
2.54 Z B (4 - 2B/D)
4-sided exposure
2.54 Z B (4 - B/D)
3-sided exposure
1.3
0.7 + 0.3 / R
R < 0.5
R > 0.5
tf =
where:
Z=
and, where:
R is the ratio of applied to allowable load (load ratio)
tf is the fire endurance time (minutes)
Here is the ASCE 29 Method for beams of 3- and 4-sided exposure. Note that the the failure
time is expressed in minutes (see slide).
43
ASCE 29 Method for Columns
(Lie Empirical Method)
2.54 Z D (3 - D / B)
4-sided exposure
2.54 Z B (3 - D / (2B))
3-sided exposure
tf =
For short columns (Ke / D < 11):
1.5
0.9 + 0.3 / R
For long columns (Ke / D > 11):
Z=
Z=
1.3
0.7 + 0.3 / R
R < 0.5
R > 0.5
R < 0.5
R > 0.5
And, where:
R is the ratio of applied to allowable load (load ratio)
tf is the failure time (minutes)
Likewise, here is the ASCE 29 Method for columns of 3- and 4-sided exposure, and varying
slenderness to allow for the buckling effect as charred section increases with exposure time.
Note that the the failure time is expressed in minutes (see slide).
44
New Mechanics-Based Design
Method
• expands the use of large exposed wood members:
– loading conditions
– fire exposures
– mechanical properties
– stress interactions
– expanded range of wood products
This design method is a rational approach that allows for exposed structural wood members
to be used in structures that could be exposed to fire.
45
Design Considerations
• predicts reduced cross-sectional dimensions
• adjusts for charring at the corners
• accounts for the loss of strength and stiffness in the
heated zone
The equations used in this method account for all the charring characteristics of a wood
cross-section exposed to fire.
46
Model for Charring of Wood
• Nonlinear char model used - nominal linear char rate input.
• To account for rounding at corners and reduction of strength and
stiffness of the heated zone, the nominal char rate values, β n, are
increased 20%.
βeff = 1.2 β n
t 0.187
where:
β eff is the effective char rate (in/hr), adjusted for exposure time, t
β n is the nominal linear char rate (in/hr), based on 1-hr exposure
t
is the exposure time (hrs)
In terms of the charring characteristics of wood, this is the char model used.
47
Effective Char Rates and Char Layer Thickness
(for βn = 1.5 inches/hour)
Required Fire
Endurance
(hr)
1-Hour
1½-Hour
2-Hour
Effective Char
Rate, βeff
(in/hr)
1.80
1.67
1.58
Effective Char Layer
Thickness, αchar
(in)
1.8
2.5
3.2
…and these are the charring results based on a typical char rate of 1.5 inches per hour.
48
Design for Member Capacity
Dead Load + Live Load ≤ K * Allowable Design Capacity
Where:
K
is a factor to adjust from allowable design capacity to
average ultimate capacity
The factor, K, adjusts from allowable design capacity of the member to average ultimate
capacity - the maximum capacity the member can physically sustain (no safety factors).
49
Allowable Design Stress to Average
Ultimate Strength Adjustment Factor
Member Capacity
K
Bending Moment Capacity, in-lb.
Tensile Capacity, lb.
Compression Capacity, lb.
Beam Buckling Capacity, lb.
Column Buckling Capacity, lb.
2.85
2.85
2.58
2.03
2.03
This table lists the values of K for various mode capacities to adjust to an ultimate strength
basis.
50
General Comparison
• Given the theoretical derivation of the new mechanics-based design
method, existing test results from fire tests of exposed, large wood
members were compared against the model predictions.
• International and North American test data were reviewed.
The theoretical model was checked against full scale tests from all over the world.
51
Predicted Time vs. Fire Test Observed Time
(Wood Beams Exposed on 3-Sides)
Predicted Time to Failure (minutes)
Mechanics-Based Model Prediction
160
140
120
100
80
60
40
20
0
0
20
40
60
80
100
120
140
160
Observed Time to Failure (minutes)
Model and test agreement were good for wood beams exposed on 3 sides.
52
Predicted Time vs. Fire Test Observed Time
(Wood Columns Exposed on 4-Sides)
Predicted Time to Failure (minutes)
Mechanics-Based Model Prediction
140
120
100
80
60
40
20
0
0
20
40
60
80
100
120
140
Observed Time to Failure (minutes)
….also for wood columns exposed on 4 sides.
53
Predicted Time vs. Fire Test Observed Time
(Wood Tension Members Exposed on 4-Sides)
Predicted Time to Failure (minutes)
Mechanics-Based Model Prediction
160
140
120
100
80
60
40
20
0
0
20
40
60
80
100
120
140
160
Observed Time to Failure (minutes)
…and for wood in tension exposed on 4 sides.
54
Predicted Time vs. Fire Test Observed Time
(Decking Exposed on Bottom Side)
Mechanics-Based Model Prediction
Predicted Time to Failure (minutes)
100
80
60
40
20
0
0
20
40
60
80
100
Observed Time to Failure (minutes)
…as well as for decking exposed on the bottom side.
55
Technical Report 10
– Expands the uses for large,
exposed wood members (tension,
bending/compression,
bending/tension members,
decking)
– Expands applicability of current
methods to other EWP’s (SCL)
– Expands use of large, exposed
wood members to 2 hour fire
endurance applications.
The model and methodology described in TR 10 holds several advantages for structural
wood applications.
56
TR 10: Design Example
• Douglas fir glulam beams
– Span
– Spaced at
L = 18 feet
s = 6 feet
• Design Load
– qlive = 100 psf
– qdead = 15 psf
• Timber decking nailed to the compression edge of beams provides
lateral bracing
Size the beam for required bending strength for 1 hour fire duration
Here is a detailed example, worked from start to finish - with more depth than that presented
previously in DCA 2.
Consider Douglas fir beams spanning 18 feet and spaced 6 feet apart. The beams support
100 psf live load and 15 psf dead load. Timber decking laterally braces the compression
flange of the beams.
Size the beam for a 1 hour rating.
57
TR 10: Design Example
For the structural design of the beam, calculate the induced moment:
• Beam load:
wtotal = s (qdead + qlive) = (6’)(15+100)
= 690 plf
• Induced demand moment:
Mmax = wtotal L2 / 8 = (690)(18)2 / 8
= 27,945 ft-lb
Solution:
First, calculate the induced demand moment based on the tributary width of 6 feet (beam
spacing).
58
TR 10: Design Example
Select a 6-3/4” x 12” 24F-V4 Douglas-fir glulam beam
Tabulated bending stress, Fb, equal to 2400 psi
Calculate the beam section modulus:
Ss = BD2/6 = (6.75)(12)2 / 6
= 162.0 in3
Calculate the adjusted allowable bending stress:
Assuming: CD = 1.0, CM = 1.0, Ct = 1.0, CL = 1.0, CV = 0.99
F’b = Fb(CD)(CM)(Ct)(lesser of CL or CV)
= 2400(1.0)(1.0)(1.0)(0.99)
= 2371 psi
Pick a beam, calculate its section modulus from actual dimensions, and the adjusted
allowable bearing stress of the material.
59
TR 10: Design Example
Calculate the design resisting moment:
M’ = F’b Ss = (2371)(162) / 12
Structural Capacity Check:
= 32,009 ft-lb
M’ > Mmax
32,009 ft-lb > 27,945 ft-lb
Multiply the adjusted allowable bending stress by the section modulus to get the maximum
resisting moment offered by your chosen beam. Check for adequacy, and in this case, OK.
60
TR 10: Design Example
For the fire design of the wood beam:
• the loading is unchanged,
• therefore, the maximum moment is unchanged,
• the fire resistance must be calculated
From TR 10 table, find charring depth αchar for 1 hour duration:
Required Fire
Endurance
(hr)
1-Hour
1½-Hour
2-Hour
Effective Char
Rate, βeff
(in/hr)
1.80
1.67
1.58
Effective Char Layer
Thickness, αchar
(in)
1.8
2.5
3.2
Now, design the cross-section for fire endurance. A certain amount of the cross-section will
char during the duration of the rating time, reducing the cross-section size required to
sustain load.
From the table in TR 10, find the char depth for the duration you are seeking, in this case, 1
hour.
61
TR 10: Design Example
Substitute in residual cross-section dimensions for 3-sided beam into
the section modulus relation, i.e.:
• 3-Sided Exposure (i.e. beams) b = B - 2βt
= B - 2αchar
d = D - βt
= D - αchar
Calculate charred beam section modulus exposed on 3-sides:
Sf = (B-2αchar)(D- αchar)2 / 6 = (6.75 - 2(1.8))(12-1.8)2 / 6
= 54.6 in3
Determine the charred section dimensions and calculate a new charred section modulus for
the residual section.
62
TR 10: Design Example
Calculate the adjusted allowable bending stress (some adjustment
factors don’t apply and may have been other than 1.0 before):
F’b = Fb(lesser of CL or CV) = 2400(0.99)
= 2371 psi
Calculate strength resisting moment using charred cross-section:
M’ = K F’b Sf = (2.85)(2371)(54.6)/12
Fire Capacity Check:
= 30,758 ft-lb
M’ > Mmax
30,758 ft-lb > 27,945 ft-lb
Recalculate the adjusted allowable bending stress, since not all of the adjustment factors
apply here and may have been other than 1.0 before.
Determine the strength resisting moment based on the charred cross-section, and in this
case is good for a 1 hour fire duration.
63
TR 10 Conclusions
• Full-scale test results indicate that the mechanics-based method
will conservatively estimate the fire endurance time of large,
exposed wood members.
• Given the theoretical derivation of the new mechanics-based design
method, it can be easily incorporated in current wood structural
design provisions.
• Incorporation of new mechanics-based method in the NDS will
assist in the proper design of large, exposed wood members for
standard fire exposures.
TR 10 concludes that the modeled behavior is conservatively accurate, that it can be easily
implemented as a design process, and that will permit designers to use exposed large
section wood members in structural applications that could be subject to fire exposure.
64
Standardization of New Method
New Design Method has been
approved for inclusion in:
2001 National Design
Specification® for Wood
Construction.
This design approach has been approved for inclusion in the 2001 NDS.
65
Detailing for Fire Control
To reduce the spread of fire, use:
• fire blocking
– prevents movement of flame and gases to other areas of
the building through small concealed spaces in framing
and building components
• draft stopping
– prevents movement of air, smoke, flame, and gases to
other areas of the building through large concealed
spaces such as attics and floor assemblies with
suspended ceilings or open-web trusses
Apart from designing cross-sections to withstand fire endurance, there are other design
provisions that can be implemented to reduce the spread of fire in wood frame buildings.
Two compartmentalization techniques have been shown to be effective to this end: fire
blocking, and draft stopping. The difference between the two is scale - fire blocking for small
openings, and draft stopping for separating large assemblies.
66
Detailing for Fire Control
Fire Blocking: Walls
Balloon Framing
2x plates act as
fireblock between
wall and attic
Continuous studs
2 or more stories
2x to fireblock
stud space
2x fireblock between
walls and floors
Lack of fire blocking in balloon framing can quickly lead to catastrophic results, since flame
can quickly climb through wall and floor cavities through chimney effect. Here are key
locations to limit the spread of fire through the cavities of a balloon frame.
67
Detailing for Fire Control
Fire Blocking: Walls
Platform Framing
2x plates act as
fireblock between
wall and attic
2x plates act as
fireblock between
walls and floor
2x plates act as
fireblock between
wall and floor
Platform framing offers a little more flame spread protection because of the platform nature
of the framing. Here, continuity of the fire blocks is important.
68
Detailing for Fire Control
Fire Blocking: Walls
Subfloor or underlayment
at Soffits
2x top plates
Soffit
2x fireblock
Fire blocks at soffit locations offer protection from flame spread into the soffit cavity.
69
Detailing for Fire Control
Fire Blocking: Walls
at Drop Ceiling
Subfloor or underlayment
2x top plates
Dropped ceiling
2x fireblock
Similarly, fire blocks at the dropped ceiling level also serve the same protection.
70
Detailing for Fire Control
Fire Blocking Walls:
at Cove Ceiling
Subfloor or underlayment
2x top plates
Cove ceiling
2x fireblock
…as well as at ceiling coves.
71
Detailing for Fire Control
Fire Blocking: Stairs
2x Fireblock at top
and bottom between
stringers
To prevent fire from migrating into the joist spaces of floors, fire blocks should be located at
the top and bottom of stair runs. Often framing headers serve this function.
72
Detailing for Fire Control
Fire Blocking: Pipes
Approved
noncombustible
firestop
2x Scab to
reduce
opening
Plate
Crevices around piping offer a sneaky way for fire to slip into a cavity. A fire block is needed
here.
73
Detailing for Fire Control
Fire Blocking: Chimneys
Approved
noncombustible
fireblock
Floor level
A non-combustible fire block is to provided at all chimney openings to limit fire migration
upward beside the chimney.
74
Detailing for Fire Control
Draft Stopping: Single Family Dwellings
Floor / Ceiling
Floor Joists
Draftstop
Drop Ceiling
Area on either side
of draftstop is limited
To prevent the spread of flame through assemblies, draft stopping is used. One application
is compartmentalization of false or dropped ceilings into void volumes that are smaller so
that fire is confined.
75
Detailing for Fire Control
Draft Stopping: Single Family Dwellings
Floor / Ceiling
Draftstop
Drop Ceiling
Open-Web trusses
Area on either side of
draftstop is limited
For trussed floors or ceilings, sheathing the truss will compartmentalize the void space into
smaller volumes.
76
Detailing for Fire Control
Draft Stopping: Multi-Family (2 or more) Dwellings
Floor / Ceiling
Ceiling joist
Drop Ceiling
Tenant separation wall
Draftstop in
line with tenant
separation wall
Draft stopping between dwelling units in the void space over tenant separation walls will also
help to confine fire.
77
Detailing for Fire Control
Draft Stopping: Multi-Family (2 or more) Dwellings
In attic in line
Floor / Ceiling
with separation wall
Tenant
separation wall
In mansard
or overhang
Also draft stopping the attic space in line over tenant separation walls will also
compartmentalize the attic space into smaller volumes.
78
…available from www.awc.org
These documents are available free in HTML or PDF form from www.awc.org.
Thank you!
79
Appendix - Test Data
Appendix - Test Data
80
Beams Tested
Designation
Breadth Depth
(in)
(in)
Specific
Gravity
(psi)
E
x10 6
(psi)
Resisting
Moment
(ft-lbs)
Induced
Moment
(ft-lbs)
Fb-ult
TRADA
5.5
9.0
0.49
7,530
2.0
45,528
9,832
NFoPA
8.75
16.5
0.47
6,840
1.6
222,356
55,855
AF&PA-27
8.75
16.5
0.47
6,840
1.6
222,762
18,937
AF&PA-44
8.75
16.5
0.47
6,840
1.6
222,762
30,707
AF&PA-91
8.75
16.5
0.47
6,840
1.6
222,762
65,075
FCNSW1
5.9
16.5
0.82
28,485
2.7
621,507
74,789
FCNSW2
5.9
16.5
0.52
14,500
1.7
318,918
20,504
81
Columns tested in France
Designation
Depth Breadth Specific
(in)
(in)
Gravity
(lb/ft3)
Fc-ult
(psi)
E
x106
(psi)
Resisting
Capacity
(lbs)
Induced
Load
(lbs)
CSTB44
7
7.875
0.56
2,565
1.6
132,365
39,790
CSTB45
7
7.875
0.56
2,565
1.6
132,365
39,790
82
Columns tested in Germany
by Stanke et al.
Designation
Depth Breadth Specific
(in)
(in)
Gravity
Fc-ult
(psi)
E
x106
(psi)
Resisting
Capacity
(lbs)
Induced
Load
(lbs)
R14A
5.5
5.5
0.44
7,368
2.5
84,644
19,026
R14B
5.5
5.5
0.45
7,929
2.3
80,310
19,026
R14C
5.5
5.5
0.45
8,131
2.4
82,217
9,524
R14D
5.5
5.5
0.43
7,447
2.2
75,740
14,264
H14A
5.5
5.5
0.44
8,050
2.0
70,825
19,026
H14B
5.5
5.5
0.48
7,652
2.4
82,598
19,026
H14C
5.5
5.5
0.45
8,131
2.4
82,217
9,524
H14D
5.5
5.5
0.43
7,447
2.2
75,740
14,264
H14/24A
5.5
9.5
0.41
6,243
1.7
99,126
32,628
H14/24B
5.5
9.5
0.41
6,169
1.6
98,033
32,628
H14/30A
5.5
11.75
0.45
6,914
1.7
130,414
40,786
H14/30B
5.5
11.75
0.47
8,690
2.7
198,238
20,393
H14/30C
5.5
11.75
0.46
7,165
1.8
134,828
20,393
83
Columns tested in Germany
by Stanke et al.
(psi)
E
x106
(psi)
5.5
15.75
0.45
6,675
1.6
158,898
54,234
R15A
5.875
5.875
0.38
5,995
1.8
78,944
24,030
R15B
5.875
5.875
0.38
5,970
1.8
78,629
24,030
H15A
5.875
5.875
0.40
6,515
1.9
85,341
24,030
H15B
5.875
5.875
0.37
5,868
1.7
77,371
24,030
R16
5.875
5.875
0.31
4,302
1.3
72,417
29,432
H16A
6.25
6.25
0.37
5,723
1.7
94,688
29,432
H16B
6.25
6.25
0.40
6,595
1.9
108,172
29,432
R16/30
6.25
11.75
0.41
5,944
1.5
163,784
27,558
H16/30A
6.25
11.75
0.42
6,229
1.6
171,131
55,116
H16/30B
6.25
11.75
0.44
6,666
1.7
182,354
55,116
H16/30C
6.25
11.75
0.43
6,470
1.6
177,337
55,116
H16/30D
6.25
11.75
0.40
5,710
1.5
157,743
27,558
Designation
H14/40
Depth Breadth Specific
(in)
(in)
Gravity
Fc-ult
Resisting
Capacity
(lbs)
Induced
Load
(lbs)
84
Columns tested in Germany
by Stanke et al.
Designation
Depth Breadth Specific
(in)
(in)
Gravity
Fc-ult
(psi)
R20A
7.875
7.875
0.40
5,931
E
x106
(psi)
Resisting
Capacity
(lbs)
Induced
Load
(lbs)
1.6
199,681
56,438
R20B
7.875
7.875
0.39
6,657
1.7
219,632
56,438
R20C
7.875
7.875
0.46
9,003
2.2
288,658
28,219
R20D
7.875
7.875
0.43
5,685
1.6
198,702
28,219
H20A
7.875
7.875
0.38
5,903
1.7
209,239
56,438
H20B
7.875
7.875
0.39
6,031
1.8
218,955
56,438
H20C
7.875
7.875
0.45
8,676
2.1
270,840
28,219
H20D
7.875
7.875
0.45
7,370
2.0
254,219
28,219
H20/40A
7.875
15.75
0.44
6,651
1.6
413,483
112,877
H20/40B
7.875
15.75
0.45
5,415
1.3
340,466
112,877
H24A
9.5
9.5
0.40
5,639
1.5
344,680
89,949
H24B
9.5
9.5
0.38
6,616
1.8
401,964
89,949
85
Columns tested in Germany
by Stanke et al.
Designation
Depth Breadth Specific
(in)
(in)
Gravity
Fc-ult
(psi)
E
x106
(psi)
Resisting
Capacity
(lbs)
Induced
Load
(lbs)
H26A
10.25
10.25
0.42
6,346
1.7
485,005
110,672
H26B
10.25
10.25
0.42
5,579
1.5
428,165
110,672
R27A
10.625 10.625
0.38
5,220
1.3
428,663
121,034
R27B
10.625 10.625
0.40
5,504
1.6
483,442
121,034
R27C
10.625 10.625
0.41
6,229
1.6
528,292
121,034
H27A
10.625 10.625
0.42
6,216
1.9
555,826
121,034
H27B
10.625 10.625
0.40
5,448
1.4
463,536
121,034
H27C
10.625 10.625
0.41
6,181
1.6
524,303
121,034
H28A
11.00
0.40
5,806
1.5
543,889
132,939
H28B
11.00
11.00
0.42
6,260
1.6
585,187
132,939
H40
15.75
15.75
0.41
5,659
1.4
1,257,232
308,647
11.00
86
Columns tested in England
by Malhotra et al.
Designation
Depth Breadth Specific
(in)
(in)
Gravity
Fc-ult
(psi)
E
x106
(psi)
Resisting
Capacity
(lbs)
Induced
Load
(lbs)
FR3
5.6
15.0
0.59
5,197
1.7
327,980
35,990
FP4
9.0
9.0
0.59
5,197
1.7
397,461
143,962
HR7
6.9
12.0
0.54
4,454
1.5
319,043
62,060
HP8
9.0
9.0
0.54
4,454
1.5
340,497
62,060
RR11
9.0
9.0
0.54
3,961
1.2
300,777
110,452
RP12
6.9
12.0
0.54
3,961
1.2
279,505
27,613
CR15
9.0
9.0
0.38
3,218
1.0
244,966
44,754
CP16
5.6
15.0
0.38
3,218
1.0
199,062
44,754
87
Tension Members Tested
Designation
Breadth Depth Specific 1
(in)
(in)
Gravity
(psi)
E
x10 6
(psi)
F t-ult
Resisting
Capacity
(lbs)
Tension
Load
(lbs)
4x6 Timber
3.38
5.31
0.49
2,132
1.4
38,223
3,194
5x9 Glulam
5.06
8.81
0.50
4,560
1.6
203,437
35,167
9x9 Glulam
8.56
8.75
0.50
4,560
1.6
341,644
19,580
1
Specific gravity estimated for grade and species
88
Measured and Calculated
Decking Fire Resistance Times
Designation
Species
Breadth
(in)
Depth
(in)
UL #2
Douglas fir
5.5
1.5
UL #4
Douglas fir
5.5
HT1
Subalpine fir
HT2
Minduced
Mult
Measured tf
(min)
Calculated tf
(min)
0.16
24+
25
1.5
0.21
18+
23
1.625
3.625
0.07
62
58
Subalpine fir
1.625
3.625
0.07
56
58
HT3
Southern pine
5.625
2.625
0.15
54
53
HT4
Southern pine
5.625
2.625
0.15
NR
53
HT5
Southern pine
5.625
2.625
0.18
NR
49
HT6
Southern pine
5.625
2.625
0.18
45
49
NR = Not Reported
89
Questions?
• www.awc.org
– Online eCourses
– FAQ’s
• HelpDesk
– AWCinfo@afandpa.org
– (202) 463-4713 or (800) 292-2372
• Comments
– AWC_education@afandpa.org
This concludes this approved
continuing education program.
90