1、Designation: D 6555 03Standard 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 year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 o
3、f 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 comparin
4、g 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
5、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
6、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 e
7、ffects” 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 This guide define
8、s 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
9、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 this
10、guide.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 prior to use.2. Refere
11、nced 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 Practice for Evalu
12、ating 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 Oct. 1, 2003. Published November 2003. Originallyapproved in 2000. Last prev
13、ious edition approved in 2000 as D 6555 00a.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.1Copyright ASTM I
14、nternational, 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 moreconnected wood me
15、mbers 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 representative of thespecies
16、 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 stiffness.3.1.5
17、 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 wood assembly, na
18、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 or adhesives,
19、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 or deck-ing.3.1
20、.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 distribute loadamong m
21、embers.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 capacity.4.2 T
22、his 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 intentional overde-s
23、ign 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 results in a distribu
24、tion 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 uniform loads.NOTE 2
25、Positive 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 values for a memb
26、er 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 stiffness increases
27、. 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 maximum performanc
28、ewhen 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 average transvers
29、e 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:5.3.1 Load sharing
30、for stiffness (5.2),5.3.2 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-section. The increased
31、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.D65550326.1.3 Composite action decreases as the rigidity of theconnection
32、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 Sheathing gap stiffness and l
33、ocation 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),6.3.2 Location of sheathing gaps along members.7. Residua
34、l Capacity of the Assembly7.1 Explanation of Residual Capacity7.1.1 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 failure.NOTE 4Residual capacity theore
35、tically 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 capacity does not reduce the proba
36、bility 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 probability of progressive collap
37、se 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 using probability theory and is no
38、t 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 such as avoidance ofprogressive c
39、ollapse (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 conditions,7.2.2 Load sharing,7.2.3 Comp
40、osite 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. Quantifying Repetitive-Member Effects8.1 Gen
41、eralThis 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 System effects in repetitive-member woo
42、d 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 shall cover the range of conditio
43、ns (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 clearlylimited to the range of condition
44、s 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 to first member failure and system
45、effects 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 analysis.8.2.4.1 For material properties
46、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).8.2.4.2 For material properties tha
47、t 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-signed to the analysis of 8.2.1 is not p
48、ermitted.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 reference condition. Additionalsamples cont
49、aining 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.D65550338.3.1.4 Additional sampling for each of the elements i
