Designation:D2555−17aStandardPracticeforEstablishingClearWoodStrengthValues1ThisstandardisissuedunderthefixeddesignationD2555;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.INTRODUCTIONThedevelopmentofsafeandefficientdesignvaluesforlumber,laminatedtimber,plywood,roundtimbers,andothersolidwoodproducts,eachwithitsownspecialrequirementshas,asacommonstartingpoint,theneedforanauthoritativecompilationofclearwoodstrengthvaluesforthecommerciallyimportantspecies.Alsorequiredareproceduresforestablishing,fromthesedata,valuesapplicabletogroupsofspeciesortoregionalgroupingswithinaspecieswherenecessitatedbymarketingconditions.Thispracticehasbeendevelopedtomeettheseneedsandtoprovide,inaddition,informationonfactorsforconsiderationintheadjustmentoftheclearwoodstrengthvaluestodesignvaluesforengineering.Sincefactorssuchasspeciespreference,speciesgroupings,marketingpractices,designtechniques,andsafetyfactorsvarywitheachtypeofproductandenduse,itiscontemplatedthatthispracticewillbesupplementedwherenecessarybyotherappropriatestandardsrelatingtospecificdesignvaluesforeachsuchproduct.PracticeD245isanexampleofsuchastandardapplicabletotheinterpretationoftheclearwoodstrengthvaluesintermsofallowablepropertiesforvisuallygradedlumber.Aprimaryfeatureofthispracticeistheestablishmentoftablespresentingthemostreliablebasicinformationdevelopedonthestrengthofclearwoodanditsvariabilitythroughmanyyearsoftestingandexperience.ThetestingtechniquesemployedarethosepresentedinTestMethodsD143.Amongtherecognizedlimitationsofsuchstrengthdataarethoseresultingfromtheproblemsofsamplingmaterialfromforestsextendingoverlargeregions,andtheuneconomicalfeasibilityofcompletelytestinganintensivesample.Apracticalapproachtotheimprovementofstrengthdataisthroughtheapplicationoftheresultsofdensitysurveysinwhichthespecif...
