1、Designation: D6555 03 (Reapproved 2014)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 revisio
2、n, 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 s
3、tiffness 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
4、 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
5、 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 var
6、iables 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
7、 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 pat
8、hs 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”
9、 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 f
10、ailures so that the effects of nonlinearities orchanges in failure modes can be quantified.1. Scope1.1 This guide identifies variables to consider when evaluating repetitive-member assembly performance for parallel framingsystems.1.2 This guide defines terms commonly used to describe interaction mec
11、hanisms.1.3 This guide discusses general approaches to quantifying an assembly adjustment including limitations of methods andmaterials when evaluating repetitive-member assembly performance.1.4 This guide does not detail the techniques for modeling or testing repetitive-member assembly performance.
12、1.5 The analysis and discussion presented in this guideline are based on the assumption that a means exists for distributingapplied loads among adjacent, parallel supporting members of the system.1.6 Evaluation of creep effects is beyond the scope of this guide.1 This guide is under the jurisdiction
13、 of ASTM Committee D07 on Wood and is the direct responsibility of Subcommittee D07.05 on Wood Assemblies.Current edition approved Aug. 1, 2014Nov. 1, 2017. Published August 2014November 2017. Originally approved in 2000. Last previous edition approved in 20082014as D6555 03 (2008).(2014). DOI: 10.1
14、520/D6555-03R14.10.1520/D6555-17.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recomm
15、ends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.7 This guide
16、does not purport to suggest or establish appropriate safety levels for assemblies, but cautions users that designersoften interpret that safety levels for assemblies and full structures should be higher than safety levels for individual structuralmembers.NOTE 1Methods other than traditional safety f
17、actor approaches, such as reliability methods, are increasingly used to estimate the probability of failureof structural elements. However, the extension of these methods to assemblies or to complete structures is still evolving. For example, complete structureswill likely exhibit less variability t
18、han individual structural elements. Additionally, there is a potential for beneficial changes in failure modes (i.e., moreductile failure modes in systems). These considerations are beyond the scope of this guide.1.8 The values stated in inch-pound units are to be regarded as the standard. The SI eq
19、uivalents are approximate in many cases.1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatoryli
20、mitations prior to use.1.10 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization
21、Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D245 Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded LumberD1990 Practice for EstablishingAllowable Properties for Visually-Graded Dimension Lumber from In-Grade Te
22、sts of Full-SizeSpecimensD2915 Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based ProductsD5055 Specification for Establishing and Monitoring Structural Capacities of Prefabricated Wood I-Joists2.2 Other Documents:ANSI/ASAE EP559.1-2010 Design Requirements and Bending Propert
23、ies for Mechanically-Laminated Wood Assemblies3ASCE/SEI 7-10 Minimum Design Loads for Buildings and Other Structures4ANSI/AWC SPDWS-2015 Special Design Provisions for Winds and Seismic5ANSI/AWC NDS-2015 National Design Specification (NDS) for Wood Construction5ANSI/TPI 1-2014 National Design Standar
24、d for Metal Plate Connected Wood Truss Construction63. Terminology3.1 Definitions:3.1.1 composite action, ninteraction of two or more connected wood members that increases the effective section propertiesover that determined for the individual members.3.1.2 element, na discrete physical piece of a m
25、ember such as a truss chord.3.1.3 global correlation, ncorrelation of member properties based on analysis of property data representative of the speciesor species group for a large defined area or region rather than mill-by-mill or lot-by-lot data. The area represented may be definedby political, ec
26、ological, 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 elements such as studs, joists, rafters, tresses,trusses, that carry load directly toassembly supports. A me
27、mber may consist of one element or multiple elements.3.1.6 parallel framing system, na system of parallel framing members.3.1.7 repetitive-member wood assembly, na system in which three or more members are joined using a transverseload-distributing element.3.1.7.1 DiscussionException: Two-ply assemb
28、lies can be considered repetitive-member assemblies when the members are in direct side-by-sidecontact and are joined together by mechanical connections or adhesives, or both, to distribute load.3.1.8 residual capacity, nratio of the maximum assembly capacity to the assembly capacity at first failur
29、e of an individualmember or connection.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from Ameri
30、can Society of Agricultural and Biological Engineers (ASABE), 2950 Niles Road, St. Joseph, MI 49085, http:/www.asabe.org.4 Available from American Society of Civil Engineers (ASCE), 1801 Alexander Bell Dr., Reston, VA 20191, http:/www.asce.org.5 Available from American Wood Council, 222 Catoctin Cir
31、cle SE, Suite 201, Leesburg, VA 20175.6 Available from Truss Plate Institute, 218 N. Lee Street, Ste. 312, Alexandria, VA 22314.D6555 1723.1.9 sheathing gaps, ninterruptions in the continuity of a load-distributing element such as joints in sheathing or decking.3.1.10 transverse load-distributing el
32、ements, nstructural components such as sheathing, siding and decking that support anddistribute load to members. Other components such as cross bridging, solid blocking, distributed ceiling strapping, strongbacks,and connection systems may also distribute load among members.4. Significance and Use4.
33、1 This guide covers variables to be considered in the evaluation of the performance of repetitive-member wood assemblies.System performance is attributable to one or more of 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
34、where design stress adjustments for repetitive-member assemblies are being developed.4.3 This guide serves as a basis to evaluate design stress adjustments developed using analytical or empirical procedures.acombination of analysis and testing.NOTE 2Enhanced assembly performance due to intentional o
35、verdesign or the contribution of elements not considered in the design are beyond thescope of this guide.5. Load Sharing5.1 Explanation of Load Sharing:5.1.1 Load sharing reduces apparent stiffness variability of members within a given assembly. In general, member stiffnessvariability results in a d
36、istribution of load that increases load on stiffer members and reduces load on more flexible members.5.1.2 Apositive strength-stiffness correlation for members results in load sharing increases, which give the appearance of higherstrength for minimum strength members in an assembly under uniform loa
37、ds.NOTE 3Positive correlations between modulus of elasticity and strength are generally observed in samples of “mill run” dimension lumber; however,no process is currently in place to ensure or improve the correlation of these relationships on a grade-by-grade or lot-by-lot basis. Where design value
38、sfor a member grade are based on global values, global correlations may be used with that grade when variability in the stiffness of production lots is takeninto account. Users are cautioned to not extrapolate bending strength and stiffness correlations to other properties. As discussed in the appen
39、dices, earlyimplementation of repetitive-member factors focused on sawn lumber flexural members. The beneficial load sharing in these systems was oftencharacterized as being related to the positive correlation between flexural strength and stiffness in these elements. For other systems where stresse
40、s areprimarily axial (compression or tension), the appropriate property correlation (if used in the analysis) should relate axial strength and stiffness rather thanflexural correlations.5.1.3 Load sharing tends to increase as member stiffness variability increases and as transverse load-distributing
41、 elementstiffness increases. Assembly capacity at first member failure is increased as member strength-stiffness correlation increases.NOTE 4From a practical standpoint, the system performance due to load sharing is bounded by the minimum performance when the minimummember in the assembly acts alone
42、 and by the maximum performance when all members in the assembly achieve average performance.5.2 Variables affecting Load Sharing Effects on Stiffness include: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
43、;5.2.5 Ratio of average transverse load-distributing element stiffness 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 S
44、trength include: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 in increased flexural rigidity by increasing the effective moment of inertiaof th
45、e combined cross-section. The increased flexural rigidity results in a redistribution of stresses which usually results inincreased strength.6.1.2 Partial composite action is the result of a non-rigid connection between elements which allows interlayer slip under load.D6555 1736.1.3 Composite action
46、 decreases as the rigidity of the connection between the transverse load-distributing element and themember decreases.6.2 Variables affecting Composite Action Effects on Stiffness 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 s
47、tiffness,6.2.6 Sheathing gap stiffness and location in transverse load-distributing elements, and6.2.7 Stiffness of members and transverse load-distributing elements (see 3.1.5).6.3 Variables affecting Composite Action Effects on Strength include:6.3.1 Composite action for stiffness (6.2), and6.3.2
48、Location of 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 and composite action which occur after first member failure. As a result,actual capacity of an assembly can be higher than capacity
49、at first member failure.NOTE 5Residual capacity theoretically reduces the probability that a “weak-link” failure will propagate into progressive collapse of the assembly.However, an initial failure under a gravity or similar type loading may precipitate dynamic effects resulting in instantaneous collapse.7.1.2 Residual capacity does not reduce the probability of failure of a single member. In fact, the increased number of membersin an assembly reduces the expected load at which first member failure (FMF) will occur (see Note 56). For some specificassemblies, re
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