1、Designation: D 6555 03 (Reapproved 2008)Standard Guide forEvaluating System Effects in Repetitive-Member WoodAssemblies1This standard is issued under the fixed designation D 6555; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 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 stiffne
3、ss 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 quant
4、ified 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 shou
5、ld 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 variable
6、s 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 r
7、ecognize “system effects” in the design ofrepetitive-member assemblies requires standardized analyses of the effects of assembly constructionand performance.1. Scope1.1 This guide identifies variables to consider when evalu-ating repetitive-member assembly performance for parallelframing systems.1.2
8、 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 techniqu
9、es 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
10、 the scope of thisguide.1.7 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-priate safety and health practices and determine the applica-bility of regulatory limitations prio
11、r to use.2. Referenced Documents2.1 ASTM Standards:2D 245 Practice for Establishing Structural Grades and Re-lated Allowable Properties for Visually Graded LumberD 1990 Practice for Establishing Allowable Properties forVisually-Graded Dimension Lumber from In-Grade Testsof Full-Size SpecimensD 2915
12、Practice for Evaluating Allowable Properties forGrades of Structural Lumber1This 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 Aug. 1, 2008. Published August 2008. Originallyapproved in
13、 2000. Last previous edition approved in 2003 as D 6555 03.2For 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.1C
14、opyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.D 5055 Specification for Establishing and MonitoringStructural Capacities of Prefabricated Wood I-Joists3. Terminology3.1 Definitions:3.1.1 composite action, ninteraction of two or moreco
15、nnected wood members that increases the effective sectionproperties over that determined 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 representativ
16、e of thespecies or species group for a large defined area or regionrather than 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
17、stiffness.3.1.5 member, na structural wood element or elementssuch as studs, joists, rafters, tresses, that carry load directly toassembly supports. A member may consist of one element ormultiple elements.3.1.6 parallel framing system, na system of parallelframing members.3.1.7 repetitive-member woo
18、d assembly, na system inwhich three or more members are joined using a transverseload-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
19、 or adhesives, or both, to distributeload.3.1.8 residual capacity, nratio of 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
20、or deck-ing.3.1.10 transverse load-distributing elements, nstructuralcomponents 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 distrib
21、ute loadamong members.4. Significance and Use4.1 This guide covers variables 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
22、 capacity.4.2 This guide is intended for use where design stressadjustments for repetitive-member assemblies are being devel-oped.4.3 This guide serves as a basis to evaluate design stressadjustments developed using analytical or empirical proce-dures.NOTE 1Enhanced assembly performance due to inten
23、tional overde-sign or the contribution of elements not considered in the design arebeyond 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 stiffnessvariability result
24、s 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 assemblyunder unifo
25、rm loads.NOTE 2Positive 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.Where design va
26、lues 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.5.1.3 Load sharing tends to increase as member stiffnessvariability increases and as transverse load-distributing ele-ment stif
27、fness increases. Assembly capacity at first memberfailure is increased as member strength-stiffness correlationincreases.NOTE 3From a practical standpoint, the system performance due toload sharing is bounded by the minimum performance when the minimummember in the assembly acts alone and by the max
28、imum 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 stiffness;5.2.5 Ratio of a
29、verage 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 Effects on Strengthinclude:5.3
30、.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 of the combined cross-sec
31、tion. 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.D 6555 03 (2008)26.1.3 Composite action decreases as t
32、he 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 stiffness,6.2.6
33、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 of sheath
34、ing 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 member fail
35、ure.NOTE 4Residual 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 Residual
36、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 5). For somespecific assemblies, residual capacity from load sharing afterFMF may reduce the
37、 probability of progressive collapse orcatastrophic failure of the assembly.NOTE 5Conventional engineering design criteria do not includefactors for residual capacity after FMF in the design of single structuralmembers. The increased probability of FMF with increased number ofmembers can be derived
38、using probability theory and is not unique towood. The contribution of residual capacity should not be included in thedevelopment of system factors unless it can be combined with loadsharing beyond FMF and assembly performance criteria which take intoaccount general structural integrity requirements
39、 such as avoidance ofprogressive collapse (that is, increased safety factor, load factor, orreliability index). Development of acceptable assembly criteria shouldconsider the desired reliability of the assembly.7.2 Variables affecting Residual Capacity Effects onStrength include:7.2.1 Loading condit
40、ions,7.2.2 Load sharing,7.2.3 Composite action,7.2.4 Number and type of members,7.2.5 Member ductility (brittle versus ductile),7.2.6 Connection system,7.2.7 Contribution from structural or nonstructural elementsnot considered in design, and7.2.8 Contribution from structural redundancy.8. Quantifyin
41、g Repetitive-Member Effects8.1 GeneralThis section describes procedures for evalu-ating the system effects in repetitive-member wood assembliesusing either analytical or empirical methods. Analysis of theresults for either method shall follow the requirements of 8.4.8.2 Analytical Method:8.2.1 Syste
42、m effects in repetitive-member wood assembliesshall be quantified using methods of mechanics and statistics.8.2.2 Each component of the system factor shall be consid-ered.8.2.3 Confirmation tests shall be conducted to verify ad-equacy of the derivation in 8.2.1 to compute force distribu-tions. Tests
43、 shall cover the range of conditions (that is,variables listed in 5.2, 5.3, 6.2, 6.3, and 7.2) anticipated in use.If it is not possible to test the full range of conditionsanticipated in use, the results of limited confirmation tests shallbe so reported and the application of such test results clear
44、lylimited to the range of conditions represented by the tests.Confirmation tests shall reflect the statistical assumptions of8.2.1.NOTE 6When analyzing the results of confirmation tests, the user iscautioned to differentiate between system effects in repetitive-memberwood assemblies that occur prior
45、 to first member failure and systemeffects which occur after first member failure as a result of residualcapacity in the test assembly (see Section 7).8.2.4 If increased performance is to be based on materialproperty variability, the effects of the property variability shallbe included in the analys
46、is.8.2.4.1 For material properties which are assigned usingglobal ingrade test data, the effects of the property variability,including lot-by-lot variation, shall be accounted for throughMonte Carlo simulation using validated property distributionsbased on global ingrade test data (Practice D 1990).
47、8.2.4.2 For material properties that are assigned using millspecific data, the effects of the property variability shall beaccounted for using criteria upon which ongoing evaluation ofthe material properties under consideration are based.8.2.5 Extrapolation of results beyond the limitations as-signe
48、d to the analysis of 8.2.1 is not permitted.8.3 Empirical Method:8.3.1 System effects in repetitive-member wood assembliesquantified using empirical test results shall be subject to thefollowing limitations:8.3.1.1 For qualification, a minimum of 28 assembly speci-mens shall be tested for a referenc
49、e condition. Additionalsamples containing 28 assembly specimens shall be tested foradditional loading and test conditions.Exception: When system factors are limited to serviceability,the number of assembly tests need not exceed that required toestimate the mean within 65 % with 75 % confidence.NOTE 7The minimum sample size of 28 was selected from Table 2 ofPractice D 2915.8.3.1.2 Extrapolation of results to other loading and testconditions is not permitted.8.3.1.3 Interpolation of results between test conditions islimited to one variable.D 6555 03 (2008)38.3.1.4
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