1、Designation: D6555 17Standard 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 revisi
2、on. 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 t
3、he 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 t
4、he 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 t
5、he 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
6、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 effe
7、cts” 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
8、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
9、.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 effect
10、s 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 dis
11、cusses 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 discus
12、sion 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 s
13、afety 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.NOTE 1Methods other than traditional safety factor approaches, such1This guide is under the jurisdic
14、tion 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 Inter
15、national, 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,
16、Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1as 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
17、 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 are beyond the scope of this guide.1.8
18、 The values stated in inch-pound units are to be regardedas the standard. The SI equivalents are approximate in manycases.1.9 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-
19、priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.10 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of Inte
20、rnational Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D245 Practice for Establishing Structural Grades and Re-lated Allowable Properties for Visually Graded LumberD1990 Practice fo
21、r Establishing Allowable Properties forVisually-Graded Dimension Lumber from In-Grade Testsof Full-Size SpecimensD2915 Practice for Sampling and Data-Analysis for Struc-tural Wood and Wood-Based ProductsD5055 Specification for Establishing and Monitoring Struc-tural Capacities of Prefabricated Wood
22、I-Joists2.2 Other Documents:ANSI/ASAE EP559.1-2010 Design Requirements andBending Properties for Mechanically-Laminated WoodAssemblies3ASCE/SEI 7-10 Minimum Design Loads for Buildings andOther Structures4ANSI/AWC SPDWS-2015 Special Design Provisions forWinds and Seismic5ANSI/AWC NDS-2015 National De
23、sign Specification(NDS) for Wood Construction5ANSI/TPI 1-2014 National Design Standard for Metal PlateConnected Wood Truss Construction63. Terminology3.1 Definitions:3.1.1 composite action, ninteraction of two or more con-nected wood members that increases the effective sectionproperties over that d
24、etermined for the individual members.3.1.2 element, na discrete physical piece of a membersuch as a truss chord.3.1.3 global correlation, ncorrelation of member proper-ties based on analysis of property data representative of thespecies or species group for a large defined area or regionrather than
25、mill-by-mill or lot-by-lot data. The area representedmay be defined by political, ecological, or other boundaries.3.1.4 load sharing, ndistribution of load among adjacent,parallel members in proportion to relative member stiffness.3.1.5 member, na structural wood element or elementssuch as studs, jo
26、ists, rafters, trusses, that carry load directly toassembly supports. A member may consist of one element ormultiple elements.3.1.6 parallel framing system, na system of parallel fram-ing members.3.1.7 repetitive-member wood assembly, na system inwhich three or more members are joined using a transv
27、erseload-distributing element.3.1.7.1 DiscussionException: Two-ply assemblies can beconsidered repetitive-member assemblies when the membersare in direct side-by-side contact and are joined together bymechanical connections or adhesives, or both, to distributeload.3.1.8 residual capacity, nratio of
28、the maximum assemblycapacity to the assembly capacity at first failure of an indi-vidual member or connection.3.1.9 sheathing gaps, ninterruptions in the continuity of aload-distributing element such as joints in sheathing or deck-ing.3.1.10 transverse load-distributing elements, nstructuralcomponen
29、ts such as sheathing, siding and decking that supportand distribute load to members. Other components such ascross bridging, solid blocking, distributed ceiling strapping,strongbacks, and connection systems may also distribute loadamong members.4. Significance and Use4.1 This guide covers variables
30、to be considered in theevaluation of the performance of repetitive-member woodassemblies. System performance is attributable to one or moreof the following effects:4.1.1 Load sharing,4.1.2 Composite action, or4.1.3 Residual capacity.4.2 This guide is intended for use where design stressadjustments f
31、or repetitive-member assemblies are being devel-oped.4.3 This guide serves as a basis to evaluate design stressadjustments developed using a combination of analysis andtesting.NOTE 2Enhanced assembly performance due to intentional overde-sign or the contribution of elements not considered in the des
32、ign are2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Society of Agricultural and B
33、iological Engineers(ASABE), 2950 Niles Road, St. Joseph, MI 49085, http:/www.asabe.org.4Available from American Society of Civil Engineers (ASCE), 1801 AlexanderBell Dr., Reston, VA 20191, http:/www.asce.org.5Available from American Wood Council, 222 Catoctin Circle SE, Suite 201,Leesburg, VA 20175.
34、6Available from Truss Plate Institute, 218 N. Lee Street, Ste. 312, Alexandria,VA 22314.D6555 172beyond the scope of this guide.5. Load Sharing5.1 Explanation of Load Sharing:5.1.1 Load sharing reduces apparent stiffness variability ofmembers within a given assembly. In general, member stiffnessvari
35、ability results in a distribution of load that increases load onstiffer members and reduces load on more flexible members.5.1.2 A positive strength-stiffness correlation for membersresults in load sharing increases, which give the appearance ofhigher strength for minimum strength members in an assem
36、blyunder uniform loads.NOTE 3Positive correlations between modulus of elasticity andstrength are generally observed in samples of “mill run” dimensionlumber; however, no process is currently in place to ensure or improve thecorrelation of these relationships on a grade-by-grade or lot-by-lot basis.W
37、here design values for a member grade are based on global values,global correlations may be used with that grade when variability in thestiffness of production lots is taken into account. Users are cautioned tonot extrapolate bending strength and stiffness correlations to otherproperties. As discuss
38、ed in the appendices, early implementation ofrepetitive-member factors focused on sawn lumber flexural members. Thebeneficial load sharing in these systems was often characterized as beingrelated to the positive correlation between flexural strength and stiffness inthese elements. For other systems
39、where stresses are primarily axial(compression or tension), the appropriate property correlation (if used inthe analysis) should relate axial strength and stiffness rather than flexuralcorrelations.5.1.3 Load sharing tends to increase as member stiffnessvariability increases and as transverse load-d
40、istributing ele-ment stiffness increases. Assembly capacity at first memberfailure is increased as member strength-stiffness correlationincreases.NOTE 4From a practical standpoint, the system performance due toload sharing is bounded by the minimum performance when the minimummember in the assembly
41、acts alone and by the maximum performancewhen all members in the assembly achieve average performance.5.2 Variables affecting Load Sharing Effects on Stiffnessinclude:5.2.1 Loading conditions;5.2.2 Member span, end conditions, and support conditions;5.2.3 Member spacing;5.2.4 Variability of member s
42、tiffness;5.2.5 Ratio of average transverse load-distributing elementstiffness to average member stiffness;5.2.6 Sheathing gaps;5.2.7 Number of members;5.2.8 Load-distributing element end conditions;5.2.9 Lateral bracing; and5.2.10 Attachment between members.5.3 Variables affecting Load Sharing Effec
43、ts on Strengthinclude:5.3.1 Load sharing for stiffness (5.2), and5.3.2 Level of member strength-stiffness correlation.6. Composite Action6.1 Explanation of Composite Action:6.1.1 For bending members, composite action results inincreased flexural rigidity by increasing the effective momentof inertia
44、of the combined cross-section. The increased flexuralrigidity results in a redistribution of stresses which usuallyresults in increased strength.6.1.2 Partial composite action is the result of a non-rigidconnection between elements which allows interlayer slipunder load.6.1.3 Composite action decrea
45、ses as the rigidity of theconnection between the transverse load-distributing elementand the member decreases.6.2 Variables affecting Composite Action Effects on Stiff-ness include:6.2.1 Loading conditions,6.2.2 Load magnitude,6.2.3 Member span,6.2.4 Member spacing,6.2.5 Connection type and stiffnes
46、s,6.2.6 Sheathing gap stiffness and location in transverseload-distributing elements, and6.2.7 Stiffness of members and transverse load-distributingelements (see 3.1.5).6.3 Variables affecting Composite Action Effects onStrength include:6.3.1 Composite action for stiffness (6.2), and6.3.2 Location o
47、f sheathing gaps along members.7. Residual Capacity of the Assembly7.1 Explanation of Residual Capacity:7.1.1 Residual capacity is a function of load sharing andcomposite action which occur after first member failure. As aresult, actual capacity of an assembly can be higher thancapacity at first mem
48、ber failure.NOTE 5Residual capacity theoretically reduces the probability that a“weak-link” failure will propagate into progressive collapse of theassembly. However, an initial failure under a gravity or similar typeloading may precipitate dynamic effects resulting in instantaneous col-lapse.7.1.2 R
49、esidual capacity does not reduce the probability offailure of a single member. In fact, the increased number ofmembers in an assembly reduces the expected load at whichfirst member failure (FMF) will occur (see Note 6). For somespecific assemblies, residual capacity from load sharing afterFMF may reduce the probability of progressive collapse orcatastrophic failure of the assembly.NOTE 6Conventional engineering design criteria do not includefactors for residual capacity after FMF in the design of single structuralmembers. The increased probability of FMF
