ASTM_D_6555_-_17.pdf

Designation:D655517Standard Guide forEvaluating System Effects in Repetitive-Member WoodAssemblies1This standard is issued under the fixed designation D6555;the number immediately following the designation indicates the year oforiginal adoption or,in 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.INTRODUCTIONThe apparent stiffness and strength of repetitive-member wood assemblies is generally greater thanthe stiffness and strength of the members in the assembly acting alone.The enhanced performance isa result of load sharing,partial composite action,and residual capacity obtained through the joiningof members with sheathing or cladding,or by connections directly.The contributions of these effectsare quantified by comparing the response of a particular assembly under an applied load to theresponse of the members of the assembly under the same load.This guide defines the individual effectsresponsible for enhanced repetitive-member performance and provides general information on thevariables that should be considered in the evaluation of the magnitude of such performance.The influence of load sharing,composite action,and residual capacity on assembly performancevaries with assembly configuration and individual member properties,as well as other variables.Therelationship between such variables and the effects of load sharing and composite action is discussedin engineering literature.Consensus committees have recognized design stress increases forassemblies based on the contribution of these effects individually or on their combined effect.The development of a standardized approach to recognize“system effects”in the design ofrepetitive-member assemblies requires standardized analyses of the effects of assembly constructionand performance.Users are cautioned to understand that the performance improvements that might beobserved in system testing are often related to load paths or boundary conditions in the assembly thatdiffer from those of individual members.This is especially true for relatively complex assemblies.Forsuch assemblies,users are encouraged to design the test protocols such that internal load paths,as wellas summations of“loads in”versus“loads out”are measured(see X3.11.7.1).Data from testing,preferably coupled with analytical predictions,provide the most effective means by which systemfactors can be developed.When system factors are intended to apply to strength(rather than beinglimited to stiffness),loads must be applied to produce failures so that the effects of nonlinearities orchanges in failure modes can be quantified.1.Scope1.1 This guide identifies variables to consider when evalu-ating repetitive-member assembly performance for parallelframing systems.1.2 This guide defines terms commonly used to describeinteraction mechanisms.1.3 This guide discusses general approaches to quantifyingan assembly adjustment including limitations of methods andmaterials when evaluating repetitive-member assembly perfor-mance.1.4 This guide does not detail the techniques for modelingor testing repetitive-member assembly performance.1.5 The analysis and discussion presented in this guidelineare based on the assumption that a means exists for distributingapplied loads among adjacent,parallel supporting members ofthe system.1.6 Evaluation of creep effects is beyond the scope of thisguide.1.7 This guide does not purport to suggest or establishappropriate safety levels for assemblies,but cautions users thatdesigners often interpret that safety levels for assemblies andfull structures should be higher than safety levels for individualstructural members.NOTE1Methods other than traditional safety factor approaches,such1This guide is under the jurisdiction of ASTM Committee D07 on Wood and isthe direct responsibility of Subcommittee D07.05 on Wood Assemblies.Current edition approved Nov.1,2017.Published November 2017.Originallyapproved in 2000.Last previous edition approved in 2014 as D6555 03(2014).DOI:10.1520/D6555-17.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1 as reliability methods,are increasingly used to estimate the probability offailure of structural elements.However,the extension of these methods toassemblies or to complete structures is still evolving.For example,complete structures will likely exhibit less variability than individualstructural elements.Additionally,there is a potential for beneficial changesin failure modes(i.e.,more ductile failure modes in systems).Theseconsiderations