Designation:D2555−15StandardPracticeforEstablishingClearWoodStrengthValues1ThisstandardisissuedunderthefixeddesignationD2555;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.INTRODUCTIONThedevelopmentofsafeandefficientworkingstressesforlumber,laminatedtimber,plywood,roundtimbers,andothersolidwoodproducts,eachwithitsownspecialrequirementshas,asacommonstartingpoint,theneedforanauthoritativecompilationofclearwoodstrengthvaluesforthecommerciallyimportantspecies.Alsorequiredareproceduresforestablishing,fromthesedata,valuesapplicabletogroupsofspeciesortoregionalgroupingswithinaspecieswherenecessitatedbymarketingconditions.Thisstandardhasbeendevelopedtomeettheseneedsandtoprovide,inaddition,informationonfactorsforconsiderationintheadjustmentoftheclearwoodstrengthvaluestothelevelofworkingstressesfordesign.Sincefactorssuchasspeciespreference,speciesgroupings,marketingpractices,designtechniques,andsafetyfactorsvarywitheachtypeofproductandenduse,itiscontemplatedthatthisstandardwillbesupplementedwherenecessarybyotherappropriatestandardsrelatingtospecificworkstressesforeachsuchproduct.PracticeD245isanexampleofsuchastandardapplicabletotheinterpretationoftheclearwoodstrengthvaluesintermsofworkingstressesforstructurallumber.Aprimaryfeatureofthispracticeistheestablishmentoftablespresentingthemostreliablebasicinformationdevelopedonthestrengthofclearwoodanditsvariabilitythroughmanyyearsoftestingandexperience.ThetestingtechniquesemployedarethosepresentedinTestMethodsD143.Amongtherecognizedlimitationsofsuchstrengthdataarethoseresultingfromtheproblemsofsamplingmaterialfromforestsextendingoverlargeregions,andtheuneconomicalfeasibilityofcompletelytestinganintensivesample.Apracticalapproachtotheimprovementofstrengthdataisthroughtheapplicationoftheresultsofdensitysurveysinwhichthespec...
