1、Designation: D 6305 02e1Standard Practice forCalculating Bending Strength Design Adjustment Factorsfor Fire-Retardant-Treated Plywood Roof Sheathing1This standard is issued under the fixed designation D 6305; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEThe title for Table 6 was corrected from “One” to “Three Exposure Temperatures” in Oc
3、tober 2002.1. Scope1.1 This practice covers procedures for calculating bendingstrength design adjustment factors for fire-retardant-treatedplywood roof sheathing. The methods utilize the results ofstrength testing after exposure at elevated temperatures andcomputer-generated thermal load profiles re
4、flective of expo-sures encountered in normal service conditions in a widevariety of climates.1.2 Necessarily, common laboratory practices were used todevelop the methods herein. It is assumed that the procedureswill be used for fire-retardant-treated plywood installed usingappropriate construction p
5、ractices recommended by the fireretardant chemical manufacturers, which include avoidingexposure to precipitation, direct wetting, or regular condensa-tion.1.3 The heat gains, solar loads, roof slopes, ventilation rates,and other parameters used in this practice were chosen toreflect common sloped r
6、oof designs. This practice is applicableto roofs of 3 in 12 or steeper slopes, to roofs designed with ventareas and vent locations conforming to national standards ofpractice and to designs in which the bottom side of thesheathing is exposed to ventilation air. These conditions maynot apply to signi
7、ficantly different designs and therefore thispractice may not apply to such designs.1.4 Information and a brief discussion supporting the pro-visions of this practice are in the Commentary in the appendix.A large, more detailed, separate Commentary is also availablefrom ASTM.21.5 The methodology in
8、this practice is not meant to accountfor all reported instances of fire-retardant plywood undergoingpremature heat degradation.1.6 This practice is written in inch-pound units with SI unitsprovided in parentheses for information only.1.7 This standard does not purport to address all of thesafety con
9、cerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 9 Terminology Relating to Wood3D 5516
10、 Test Method for Evaluating the Flexural Propertiesof Fire-Retardant Treated Softwood Plywood Exposed toElevated Temperatures33. Terminology3.1 Definitions:3.1.1 Definitions used in this practice are in accordance withTerminology D 9.3.2 Definitions of Terms Specific to This Standard:3.2.1 bin mean
11、temperature10F (5.5C) temperatureranges having mean temperatures of 105 (41), 115 (46), 125(52), 135 (57), 145 (63), 155 (68), 165 (74), and 175F (79C).4. Summary of Practice4.1 The test data determined by Test Method D 5516 areused to develop adjustment factors for fire-retardant treatmentsto apply
12、 to untreated-plywood design values. The test data areused in conjunction with climate models and other factors andthe practice thus extends laboratory strength data measuredafter accelerated aging to design value recommendations.5. Significance and Use5.1 This practice develops treatment factors th
13、at shall beused by fire retardant chemical manufacturers to adjust bendingstrength design values for untreated plywood to account for thefire-retardant treatment effects. This practice uses data fromreference thermal-load cycles designed to simulate tempera-tures in sloped roofs of common design to
14、evaluate productsfor 50 iterations.5.2 This practice applies to material installed using con-struction practices recommended by the fire retardant chemicalmanufacturers that include avoiding exposure to precipitation,1This practice is under the jurisdiction of ASTM Committee D07 on Wood andis the di
15、rect responsibility of Subcommittee D07.07 on Fire Performance of Wood.Current edition approved April 10, 2002. Published June 2002. Originallypublished as D 6305-98. Last previous edition D 6305-98e1.2Commentary on this practice is available from ASTM Headquarters. RequestFile No. D071004.3Annual B
16、ook of ASTM Standards, Vol 04.10.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.direct wetting, or regular condensation. This practice is notmeant to apply to buildings with significantly different designsthan those described in 1.3
17、.5.3 Test Method D 5516 caused thermally induced strengthlosses in laboratory simulations within a reasonably shortperiod. The environmental conditions used in the laboratory-activated chemical reactions that are considered to be similar tothose occurring in the field. This assumption is the fundame
18、ntalbasis of this practice.6. Procedure to Calculate Strength Loss RateThe procedure is a multistep calculation where first an initialstrength loss is determined, then the rates of strength loss atvarious temperatures are calculated, and finally the initial lossand rates are combined into the overal
19、l treatment adjustmentfactor.6.1 Use the load-carrying capacity in bending, referred to asmaximum moment (M), as the controlling property for pur-poses of determining allowable spans.6.1.1 The ratio of the average maximum moment (M) forunexposed treated specimens to the average moment forunexposed u
20、ntreated specimens shall be designated the Initialtreatment effect, Ro, associated with the room temperatureconditioning exposure of To.Ro5 MTRT, UNEX/MUNTRT,UNEX(1)6.1.2 If testing is done at more than one temperature, Roishall be determined at each temperature and used in subsequentrate calculatio
21、ns for that specific temperature. The average ofthese values, Ro,avgshall be used in initial treatment effectcalculations (see 7.1).6.2 The average maximum moment (M) of the treatedspecimens conditioned at the same temperature for the sameperiod of time shall be computed. The ratio of these momentst
22、o the moment of the untreated, unexposed specimens asobtained in 6.2.1 and 6.2.2 shall be designated the testtreatment ratio, Rt. Include the ratio for specimens conditionedat room temperature but not exposed to elevated temperatureprior to testing.Rt5 Rtest5 MTRT,UNEX, EX!/MUNTRT,UNEX per 6.2.2!(2)
23、NOTE 1When end matching of treated and untreated specimens isemployed to reduce variability in accordance with Test Method D 5516,use the ratio of the matched pairs from each panel to calculate the panelmean. The average of the panel means shall be used to calculate Rt.6.2.1 For untreated specimens,
24、 linear regressions of theform:M 5 aD! 1 b (3)where:M = average maximum moment,D = number of days of elevated temperature exposure,a = constant, andb = intercept.shall be fitted to the maximum moment and exposure time datafor each elevated temperature exposure. Average moments foruntreated specimens
25、 conditioned at room temperature but notexposed to elevated temperature prior to testing shall beincluded as zero day data in the regression analysis.6.2.2 The intercept of the regression obtained in 6.2.1 forthe untreated specimens shall be designated the unexposedaverage. If a negative slope of th
26、e untreated specimen regres-sion is not obtained, the average of the mean maximummoments at each exposure period, including zero, shall beconsidered the unexposed average moment for untreated speci-mens.NOTE 2The intercept value obtained in 6.2.2 may be different fromthe unexposed, untreated value u
27、sed in 6.1.1 for determining Ro.6.3 The slope and intercept of the linear relationship be-tween the ratios and days of exposure for all elevated tempera-tures shall be determined by linear regressions of the form:Rt,i5 ktD! 1 c (4)where:Rt,i= test ratios of average maximum moments,D = number of days
28、 of elevated temperature exposure,kt= slope, andc = intercept.Include the ratio for treated specimens conditioned at roomtemperature but not exposed to elevated temperature prior totesting as zero day data in the regression analysis.6.3.1 If a negative slope is not obtained in 6.3, there was noappar
29、ent strength loss at the exposure temperature and alternateprocedures described in 7.2 are required.6.3.2 The slope ktfrom 6.3 shall be adjusted to a 50 %relative humidity (RH) basis by the following equation:k50,i5 kt50/RHi! (5)where:k50,i= slope at 50 % RH at temperature i, andRHi= elevated temper
30、ature test RH.6.4 If Test Method D 5516 protocol testing was only done atone elevated temperature, rates at other temperatures shall beestimated by the use of Arrhenius equation, which states thatthe rate of a chemical reaction is approximately halved for each10C the temperature is reduced. (Convers
31、ely, the rate approxi-mately doubles for each 10C that the temperature is in-creased.)6.4.1 If testing was done at only one temperature, then toallow for the uncertainty in only one measurement of the ratio,the rate k50,ishall be increased by 10 % prior to the Arrheniuscalculations. If testing was d
32、one at two temperatures, then therate at each temperature shall be increased by 5 % prior to theArrhenius calculations.NOTE 3Increasing the rate of k50,ihas the effect of increasing theapparent strength loss.6.4.2 The Arrhenius equation is used to estimate rates atother temperatures. The rate consta
33、nt, k2,at temperature, T2,isrelated byInk50,ik25Ea T12 T2!RT1T2(6)where:Ea = 21 810 cal/mole (91 253 J/mole) (1)4,5,D630502e12R = 1.987 cal./mole-K = (8.314 J/mole-K) = gas con-stant, andT1and T2are in K.6.5 Compute capacity loss as the negative value of the rates(k2) for bin mean temperatures of 10
34、5 (41), 115 (46), 125 (52),135 (57), 145 (63), 155 (68), 165 (74), and 175F (79C).NOTE 4Use the negative values of the rates (k2) for CLT since CLT isexpressed as a loss.6.6 If Test Method D 5516 testing was done at three or moreelevated temperature exposures, capacity losses shall be estab-lished b
35、y fitting a linear regression to the natural logarithm ofthe negative of the slopes of the regressions obtained in 6.3 ateach exposure temperature and 1/Tiwhere Tiis in K.NOTE 5This constructs an Arrhenius plot using classical chemicalkinetics techniques, which is the simplest modeling approach. Oth
36、er moresophisticated modeling techniques are available but require a differentprocedure for calculating strength loss rates6.6.6.1 If Test Method D 5516 testing was done at twotemperatures, the two rate constants (k2) calculated from Eq 6shall be averaged for each bin mean temperature.6.7 Reference
37、Thermal Load Profiles:6.7.1 The cumulative days per year the average sheathingtemperature falls within 10F (5.6C) bins having meantemperatures of 105 (41), 115 (46), 125 (52), 135 (57), 145(63), 155 (68), 165 (74), and 175F (79C) represent a thermalload profile. The profiles tabulated below, based o
38、n referenceyear weather tape information for various locations, an indexedattic temperature and moisture model developed by the ForestProducts Laboratory, and a south-facing roof system ventilatedas required by the applicable code having dark-colored shingleroofing, shall be considered the standard
39、thermal environmentsfire-retardant-treated plywood roof sheathing is exposed to indifferent snow load zones (4). The specific model inputs usedwere 0.65 shingle absorptivity and a ventilation rate of 8 ach7.See Table 1.6.8 Annual Capacity LossTotal annual capacity loss(CLT) due to elevated temperatu
40、re exposure shall be deter-mined for locations within each zone as the summation of theproduct of the capacity loss per day (CL) rate from 6.5 and thecumulative average days per year from 6.8 for each mean bintemperature.7. Treatment Factor7.1 For each zone, a treatment adjustment factor (TF) shallb
41、e calculated as:TF 5 12IT2nCF!CLT!# (7)where:TF = treatment adjustment factor #1.00 - IT,IT = initial treatment effect = 1-R0,n = number of iterations = 50,CF = Cyclic factor8= 0.6, andCLT = total annual capacity loss.7.2 If testing was only done at one exposure temperaturethat was 168F (76C) or gre
42、ater and a negative slope was notobtained in 6.3, there was no apparent strength loss and henceno annual capacity loss can be calculated. In this case, thetreatment adjustment factor will be the lesser of the initialtreatment effect (1-Ro) or 0.90, which reflects the 10 %allowance for uncertainty in
43、 only measuring at one tempera-ture.TF 5 lesser of 12Ro! or 0.90 (8)7.2.1 If the exposure temperature was less than 168F(76C) and a negative slope was not obtained in 6.3, then theexposure testing must be repeated at a higher temperature thateither exceeds 168F (76C) or causes a negative slope in 6.
44、3.8. Allowable Roof Sheathing Loads8.1 Maximum allowable roof live plus dead uniform loadsfor a particular plywood thickness and roof sheathing spanshall be determined as:w 5 TF!C!FbKS!DOL!/L2(9)where:w = allowable total uniform load based on bendingstrength, (lb/ft2(Pa),TF = zone treatment factor #
45、 (100 - IT),C = 120 in./ft (10 m/m) for panels continuous overthree or more spans, and,4Pasek and McIntyre (1) have shown that the Arrhenius parameter, Ea, forphosphate-based fire retardants for wood averages 21 810 cal/mole (91 253 J/mole).Other values are appropriate for fire retardants that are n
46、ot phosphate based.5The boldface numbers in parentheses refer to a list of references at the end ofthe text.6A description of other models is available in Refs (2) and (3).7Based on reported data given in Ref (5).8This factor was derived by comparing the mechanical property data obtainedfrom plywood
47、 exposed to continuous elevated temperatures to data obtained fromcyclic exposures that peaked at the same elevated temperature as the continuousexposure. The respective publications are Ref (6) and (7).TABLE 1 Reference Thermal Load ProfilesSheathing Mean Cumulative Average Days/YearBin Temperature
48、, F(C) Zone 1AAZone 1BAZone 2A105(41) 10.960 34.281 10.970115(46) 8.053 24.911 8.308125(52) 8.597 13.529 5.041135(57) 7.865 6.856 1.532145(63) 6.798 0.960 0.283155(68) 5.083 . .165(74) 0.586 . .175(79) . . .185(85) 0.021 . .195(91) 0.021 . .$ 200(93) 0.021 . .AZone Definition:(1) Minimum roof live l
49、oad or maximum ground snow load #20 psf (# 958 Pa)A. Southwest Arizona, southeast Nevada (Las Ve-gas, Yuma, Phoenix, Tucson triangle)B. All other qualifying areas(2) Maximum ground snow load 20 psf ( 958 Pa)D630502e13= 96 in./ft (8 m/m) for panels on single span orcontinuous over two spans,FbKS = published design maximum moment or bendingstrength for untreated plywood of the grade andthickness being used (in-lb/ft (kNm/m),NOTE 6Such design values for FbKS are published by panel agenciesand associations.DOL = duration of load adjustment= 1
