1、Designation: D 6305 08Standard 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, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers procedures for calculating bendingstrength design adjustment
3、factors for fire-retardant-treatedplywood roof sheathing. The methods utilize the results ofstrength testing after exposure at elevated temperatures andcomputer-generated thermal load profiles reflective of expo-sures encountered in normal service conditions in a widevariety of continental United St
4、ates 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 practices recommended by the fireretardant chemical manufacturers, which include
5、 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 roof designs. This practice is applicableto roofs of 3 in 12 or steeper slopes,
6、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 significantly different designs and therefore thispractice may not apply to such de
7、signs.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 this practice is not meant to accountfor all reported instances of fire-retard
8、ant plywood undergoingpremature heat degradation.1.6 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.7 This standard does not purport t
9、o address all of thesafety concerns, 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:3D9 Termi
10、nology Relating to Wood and Wood-Based Prod-uctsD 5516 Test Method for Evaluating the Flexural Propertiesof Fire-Retardant Treated Softwood Plywood Exposed toElevated Temperatures3. Terminology3.1 Definitions:3.1.1 Definitions used in this practice are in accordance withTerminology D9.3.2 Definition
11、s of Terms Specific to This Standard:3.2.1 bin mean temperature10F (5.5C) temperatureranges having mean temperatures of 105 (41), 115 (46), 125(52), 135 (57), 145 (63), 155 (68), 165 (74), 175 (79), 185 (85),195 (91), and 200F (93C).4. Summary of Practice4.1 The test data determined by Test Method D
12、 5516 areused to develop adjustment factors for fire-retardant treatmentsto apply 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 recom
13、mendations.5. Significance and Use5.1 This practice develops treatment factors that 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-lo
14、ad cycles designed to simulate tempera-tures in sloped roofs of common design to evaluate productsfor 50 iterations.1This practice is under the jurisdiction of ASTM Committee D07 on Wood andis the direct responsibility of Subcommittee D07.07 on Fire Performance of Wood.Current edition approved Aug.
15、1, 2008. Published September 2008. Originallyapproved in 1998. Last previous edition approved in 2002 as D 6305 021.2Commentary on this practice is available from ASTM Headquarters. RequestFile No. D071004.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer
16、Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 This practice applies to material in
17、stalled using con-struction practices recommended by the fire retardant chemicalmanufacturers that include avoiding exposure to precipitation,direct wetting, or regular condensation. This practice is notmeant to apply to buildings with significantly different designsthan those described in 1.3.5.3 T
18、est 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 fundamentalbas
19、is 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 overall treat
20、ment 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 untreate
21、d 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 calculations for
22、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 momentsto the m
23、oment 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)NOTE 1W
24、hen 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, linear
25、 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 condit
26、ioned 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 the untre
27、ated 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 used in
28、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 of ele
29、vated 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 noapparent str
30、ength 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 temperature t
31、est 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. (Conversely, th
32、e 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 done at
33、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 constant, k2,
34、at temperature, T2,isrelated byInk50,ik25Ea T12 T2!RT1T2(6)D6305082where:Ea = 21 810 cal/mol (91 253 J/mol) (1),4,5R = 1.987 cal/mol-K = (8.314 J/mol-K) = gas constant,andT1and T2are in K.6.5 Compute capacity loss as the negative value of the rates(k2) for bin mean temperatures of 105 (41), 115 (46)
35、, 125 (52),135 (57), 145 (63), 155 (68), 165 (74), 175 (79), 185 (85), 195(91), and 200F (93C).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 e
36、stab-lished by 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
37、approach. Other moresophisticated modeling techniques are available but require a differentprocedure for calculating strength loss rates.66.6.1 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
38、.7 Reference 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), 175 (79), 185 (85), 195 (91), and200F (93C) represent a thermal load pro
39、file. The profilestabulated below, based on reference year weather tape infor-mation for various locations, an indexed attic temperature andmoisture model developed by the Forest Products Laboratory,and a south-facing roof system ventilated as required by theapplicable code having dark-colored shing
40、le roofing, shall beconsidered the standard thermal environments fire-retardant-treated plywood roof sheathing is exposed to in different snowload zones (4). The specific model inputs used were 0.65shingle absorptivity and a ventilation rate of 8 air changes perhour (ach).7See Table 1.6.8 Annual Cap
41、acity LossTotal annual capacity loss(CLT) due to elevated temperature 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
42、 Factor7.1 For each zone, a treatment adjustment factor (TF) shallbe 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
43、was only done at one exposure temperaturethat was 168F (76C) or greater 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
44、(1-Ro) or 0.90, which reflects the 10 %allowance for uncertainty in 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 tempera
45、ture thateither exceeds 168F (76C) or causes a negative slope in 6.3.8. 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
46、 based on bendingstrength, (lb/ft2(Pa),TF = zone treatment factor # (100 - IT),C = 120 in./ft (3.05 m/m) for panels continuous overthree or more spans,4The boldface numbers in parentheses refer to a list of references at the end ofthe text.5Pasek and McIntyre (1) have shown that the Arrhenius parame
47、ter, Ea, forphosphate-based fire retardants for wood averages 21 810 cal/mol (91 253 J/mol).Other values are appropriate for fire retardants that are not phosphate based.6A description of other models is available in Refs (2) and (3).7Based on reported data given in Ref (5).8This factor was derived
48、by comparing the mechanical property data obtainedfrom plywood exposed to continuous elevated temperatures to data obtained fromcyclic exposures that peaked at the same elevated temperature as the continuousexposure. The respective publications are Refs (6) and (7).TABLE 1 Reference Thermal Load Pro
49、filesSheathing Mean Cumulative Average Days/YearBin Temperature, 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 load or maximum ground snow load #20psf (#958 Pa)A. Southwest Arizona and Southeast Nevada(Area bound by Las Vegas, Yuma, Phoenix,Tucson)B. All other qualifying areas(2) Maximum gro
