ASTM D6305-98e1

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e1
Designation: D 6305 – 98
Standard Practice for
Calculating Bending Strength Design Adjustment Factors
for Fire-Retardant-Treated Plywood Roof Sheathing
This standard is issued under the fixed designation D 6305; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Eq 18 was corrected in April 2000.
1. Scope 2. Referenced Documents
1.1 This practice covers procedures for calculating bending 2.1 ASTM Standards:
strength design adjustment factors for fire-retardant-treated D 9 Terminology Relating to Wood
plywood roof sheathing. The methods utilize the results of D 5516 Test Method for Evaluating the Mechanical Prop-
strength testing after exposure at elevated temperatures and erties of Fire-Retardant Treated Softwood Plywood Ex-
computer generated thermal load profiles reflective of expo- posed to Elevated Temperatures
sures encountered in normal service conditions in a wide
3. Terminology
variety of climates.
1.2 Necessarily, common laboratory practices were used to 3.1 Definitions:
3.1.1 Definitions used in this practice are in accordance with
develop the methods herein. It is assumed that the procedures
will be used for fire-retardant-treated plywood installed using Terminology D 9.
3.2 Definitions of Terms Specific to This Standard:
appropriate construction practices recommended by the fire
retardant chemical manufacturers which include avoiding ex- 3.2.1 bin mean temperature—10°F (5.5°C) temperature
ranges having mean temperatures of 105 (41), 115 (46), 125
posure to precipitation, direct wetting, or regular condensation.
1.3 The heat gains, solar loads, roof slopes, ventilation rates (52), 135 (57), 145 (63), 155 (68), 165 (74), and 175°F (79°C).
and other parameters used in this practice were chosen to
4. Summary of Practice
reflect common sloped roof designs. This practice is applicable
4.1 The test data determined by Test Method D 5516 are
to roofs of 3 in 12 or steeper slopes, to roofs designed with vent
used to develop adjustment factors for fire-retardant treatments
areas and vent locations conforming to national standards of
to apply to untreated plywood design values. The test data are
practice and to designs in which the bottom side of the
used in conjunction with climate models and other factors and
sheathing is exposed to ventilation air. These conditions may
the practice thus extends laboratory strength data measured
not apply to significantly different designs and therefore this
after accelerated aging to design value recommendations.
practice may not apply to such designs.
1.4 Information and a brief discussion supporting the pro-
5. Significance and Use
visions of this practice are in the Commentary in the appendix.
5.1 This practice develops treatment factors that shall be
A large, more detailed, separate Commentary is also available
used by fire retardant chemical manufacturers to adjust bending
from ASTM.
strength design values for untreated plywood to account for the
1.5 The methodology in this practice is not meant to account
fire-retardant treatment effects. This practice uses data from
for all reported instances of fire retardant plywood undergoing
reference thermal load cycles designed to simulate tempera-
premature heat degradation.
tures in sloped roofs of common design to evaluate products
1.6 This practice is written in inch-pound units with SI units
fore 50 iterations.
provided in parentheses for information only.
5.2 This practice applies to material installed using con-
1.7 This standard does not purport to address all of the
struction practices recommended by the fire retardant chemical
safety concerns, if any, associated with its use. It is the
manufacturers that include avoiding exposure to precipitation,
responsibility of the user of this standard to establish appro-
direct wetting, or regular condensation. This practice is not
priate safety and health practices and determine the applica-
meant to apply to buildings with significantly different designs
bility of regulatory limitations prior to use.
than those described in 1.3.
5.3 Test Method D 5516 caused thermally induced strength
This practice is under the jurisdiction of ASTM Committee D-7 on Wood and
losses in laboratory simulations within a reasonably short
is the direct responsibility of Subcommittee D07.07 on Fire Performance of Wood.
Current edition approved July 10, 1998. Published March 1999.
Commentary on this practice is available from ASTM Headquarters. Request
File No. D07–1004. Annual Book of ASTM Standards, Vol 04.10.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 6305
period. The environmental conditions used in the laboratory plywood panel providing test material, the analysis shall be as
activated chemical reactions that are considered to be similar to in the following sections.
those occurring in the field. This assumption is the fundamental
6.2.1 The average maximum moment ( M) of the treated and
basis of this practice.
untreated specimens from each panel conditioned at the same
temperature for the same period of time shall be computed and
6. Procedure to Calculate Strength Loss Rate
the ratio of these moments determined. The average of these
6.1 Use the load-carrying capacity in bending, referred to as
panel ratios shall be designated the test treatment ratio, R :
t
maximum moment (M), as the controlling property for pur-
R 5 M /M (4)
t TRT,EX UNTRT,EX
poses of determining allowable spans.
6.2.2 The slope and intercept of the linear relationship
6.1.1 Test Results Based on Randomized Block Sampling—
between the mean average maximum moment for untreated
Analyze average maximum moment ( M) data for treated and
specimens and days of exposure for all elevated temperatures
untreated plywood developed in accordance with Test Method
evaluated using the specimens from the same panels shall be
D 5516 using randomized block sampling as in the following
determined in accordance with 6.1.1.2. Averages for untreated
sections:
specimens conditioned at room temperature but not exposed to
6.1.1.1 Linear regressions of the form:
elevated temperature prior to testing shall be included as zero
M 5 a~D! 1 b (1)
day data in the regression analysis. If the slope of this
relationship is negative and is significant at the 95 % confi-
where:
dence level, the test treatment ratio determined in 6.2.1 shall be
M = average maximum moment,
D = number of days of elevated temperature exposure, and
adjusted by the ratio of the average untreated test maximum
a,b = constants.
moment for all specimens at the same temperature and expo-
shall be fitted to the maximum moment and exposure time
sure period and the intercept or zero day average maximum
data for each elevated temperature exposure for both treated
moment for untreated specimens.
and untreated specimens. Average moments for specimens
6.2.3 For each temperature exposure, linear regressions of
conditioned at room temperature but not exposed to elevated
the form:
temperature prior to testing shall be included as zero day data
R 5 a~D! 1 b (5)
t
in the regression analysis.
6.1.1.2 The intercept, or estimated maximum moment at
where:
zero days, of the regression for the treated specimens shall be
D,a,b = as previously defined.
taken as the unexposed average for treated specimens. For the
shall be fitted to the test treatment ratio, or adjusted test
untreated specimens, if a significant negative slope term (a)at
treatment ratio, and number of days of elevated temperature
the 95 % confidence level is obtained, the intercept of the
exposure. The intercept or zero day ratio estimated from this
untreated regression shall be designated the unexposed aver-
regression shall be designated the immediate treatment effect,
age. If a negative slope of the untreated specimen regression is
R , associated with the room temperature conditioning expo-
o
not significant at the 95 % level or if the slope is positive, the
sure of T . The treatment ratio estimated from the regression
o
average of the mean maximum moments at each exposure
for 60 day exposure shall be designated the 60 day treatment
period, including zero, shall be considered the unexposed
ratio, R , at exposure temperature T :
ti i
average moment for untreated specimens.
R 5 b at Temperature, T (6)
o TRT,UNEX o
6.1.1.3 The ratio of the unexposed average maximum mo-
ment (M) for treated specimens to the unexposed average
R 5 R at Temperature, T (7)
ti TRT,60 i
moment for untreated specimens shall be designated the
immediate treatment effect, R associated with the room tem-
6.3 The ratio R from 6.1.1.3 or 6.2.3 shall be adjusted to a
o ti
perature conditioning exposure of T . The ratio of the maxi-
50 % relative humidity (RH) basis by the following equation:
o
mum moments estimated from the regression for treated
R 5 R – R 2R 50/RH (8)
@ #@ #
i o o ti i
specimens at 60 days to the unexposed average for untreated
specimens shall be designated the 60 day treatment ratio R at where:
ti
R = 60 day treatment ratio at 50 % RH,
exposure temperature T :
i
i
RH = elevated temperature test RH, and
i
R 5 M /M at Temperature, T (2)
o TRT,UNEX UNTRT,UNEX o
R ,R = as previously defined.
o ti
6.4 If Test Method D 5516 protocol testing was only done at
R 5 M /M at Temperature, T (3)
ti TRT,60 UNTRT,UNEX i
one elevated temperature, rates at other temperatures shall be
6.2 Test Results Using End-Matched Treated and Untreated
estimated by the use of an Arrhenius equation that states that
Samples—When end-matching of treated and untreated speci-
the rate of a chemical reaction is approximately halved for each
mens is employed to reduce variability in accordance with Test
18°F (10°C) the temperature is reduced. (Conversely, the rate
Method D 5516 and each conditioning temperature used is
approximately doubles for each 18°F (10°C) that the tempera-
represented by at least one paired specimen set from each
ture is increased.)
6.4.1 To accomplish this, the rate constant, k , for the loss of
4 maximum moment (M) at the temperature, T , shall be first
The 60 day period was selected as a reference level for calculation purposes. 1
See Test Method D 5516. determined as:
D 6305
Rate 5 D~maximum moment ~M!! 5 k * D (9)
mation for various locations, an indexed attic temperature and
moisture content model developed by the Forest Products
Laboratory and a south facing roof system ventilated as
D~Maximum moment ~M!!
k 5 (10)
D required by the applicable code having dark-colored shingle
roofing, shall be considered the standard thermal environments
where:
fire-retardant-treated plywood roof sheathing is exposed to in
D = days, as previously defined.
different snow load zones (3). The specific model inputs used
Then, from the Arrhenius equation, the rate constant, k ,at
were 0.65 shingle absorptivity and a ventilation rate of 8 ach .
temperature, T , is related by:
See Table 1.
k E ~T – T !
6.9 Annual Capacity Loss—Total annual capacity loss
1 a 1 2
ln 5 (11)
k RT T
2 1 2 (CLT) due to elevated temperature exposure shall be deter-
mined for locations within each zone as the summation of the
5,6
where: (1)
product of the capacity loss per day (CL) rate from 6.5 and the
E = 21 810 cal/mole (91 253 J/mole),
a
cumulative average days per year from 6.8 for each mean bin
R = 1.987 cal./mole-°K = (8.314 J/mole-°K) = gas con-
temperature.
stant, and T and T are in °K.
1 2
The rate constants, k , shall be used to calculate estimated
7. Treatment Factor
maximum moments at 60 days by:
7.1 For each zone, a treatment factor (TF) shall be calcu-
M 5 k ~60! (12)
est,T 2
lated as:
The estimated maximum moments at the different tempera-
TF 5 @12IT2n~CF!~CLT!# (14)
tures shall be reduced by 10 % to allow for the uncertainty in
where:
only one measurement of the ratio and then used to calculate R
t
TF = treatment factor #1.00 - IT,
in accordance with 6.1.1.3 or 6.2.3.
IT = initial treatment effect = 1-R ,
6.5 Compute estimated treatment ratios, R , for T and for e0
ei o
n = number of iterations = 50,
bin mean temperatures of 105 (41), 115 (46), 125 (52), 135
CF = Cyclic factor = 0.6, and
(57), 145 (63), 155 (68), 165 (74) and 175°F (79°C). Deter-
CLT = total annual capacity loss.
mine capacity loss per day rates associated with each bin mean
temperature as:
8. Allowable Roof Sheathing Loads
CL 5 ~R – R !/60 (13)
e0 ei
8.1 Maximum allowable roof live plus dead uniform loads
for a particular plywood thickness and roof sheathing span
where:
shall be determined as:
CL = capacity loss per day, dimensionless,
R = estimated treatment ratio at T , and 2
e0 o
w 5 TF! C! F KS! DOL!/L (15)
~ ~ ~ ~
b
R = estimated treatment ratio at bin mean temperature T
ei i
6.6 If Test Method D 5516 testing was done at two elevated
temperature exposures, the rate constants shall be calculated
Based on reported data given in Ref (4).
using the procedures of 6.4 for each temperature. The resulting
This factor was derived by comparing the mechanical property data obtained
moments are reduced by 5 % and the average of the reduced
from plywood exposed to continuous elevated temperatures to data obtained from
moments used in further calculations in accordance with
cyclic exposures that peaked at the same elevated temperature as the continuous
exposure. The respective publications are given in Ref (5).
6.1.1.3 or 6.2.3.
6.7 If Test Method D 5516 testing was done at three or more
TABLE 1 Reference Thermal Load Profiles
elevated temperature exposures, capacity losses shall be estab-
lished by fitting a linear regression to ln (R -R ) and 1/T , Sheathing Mean Cumulative Days/Year
o i i
A A A
Bin Temperature, °F(°C) Zone 1A Zone 1B Zone 2
where: T is in °K.
i
105(41) 10.960 34.281 10.970
NOTE 1—This constructs an Arrhenius plot using classical chemical
115(46) 8.053 24.911 8.308
kinetics techniques. Other modeling techniques are available but require a 125(52) 8.597 13.529 5.041
135(57) 7.885 6.856 1.532
different procedure for calculating strength loss rates.
145(63) 6.798 0.960 0.283
6.8 Reference Thermal Load Profiles—The cumulative days
155(68) 5.083 . .
165(74) 0.586 . .
per year the average sheathing temperature falls within
175(79) . . .
10°F(5.6°C) bins having mean temperatures of 105(41),
185(85) 0.021 . .
115(46), 125(52), 135(57), 145(63), 155(68), 165(74) and
195(91) 0.021 . .
$ 200(93) 0.021 . .
175°F(79°C) represent a thermal load profile. The profiles
A
tabulated below, based on reference year weather tape in
...