ASTM_D_3957_-_09_2020.pdf

Designation:D395709(Reapproved 2020)Standard Practices forEstablishing Stress Grades for Structural Members Used inLog Buildings1This standard is issued under the fixed designation D3957;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.INTRODUCTIONThese practices are based on the assumption that structural members in log buildings can bestress-graded by methods that derive from accepted standards for conventional solid sawn lumber andround timbers.It is assumed that the material to be graded bears enough similarity to either sawnlumber or round timber,both in dimensional properties and in use,to warrant application ofstress-grading standards written for sawn-lumber or round-timber,or both.These practices,such asPractices D245 and D2899,cannot be applied directly because the structural members used in logbuildings are generally neither perfectly rectangular nor perfectly round in section.These practices usecertain conventions regarding cross-sectional dimensions that make it possible to extend establishedstress-grading methodologies to cover the members used in log buildings.Where log member characteristics deviate from sawn lumber or round timber standards,there maybe uncertainty as to the exact effect of the deviation on strength properties.To compensate for thisuncertainty,some design stress values are herein derived with practices that are,by engineeringjudgment,conservative.The philosophy guiding this approach is that while the absence ofexperimental data may make a measure of conservatism unavoidable,the reliability of design stressvalues must not be achieved through wood quality or size requirements that are an unnecessary burdenon the wood resource.In general,the sawing,cutting,and shaving required to bring a piece to its final shape must becompleted before it can be visually graded using the principles in these practices.Small cuts may beallowed after grading if it can be shown that either(1)the cuts do not affect the grade,or(2)the gradetakes the additional cuts into consideration.Both sawn lumber standards and round timber standards are herein referenced,because these twostress-grading methodologies can be assumed to apply to two different types of structural membersused in log buildings:wall-logs and round timber beams.Since wall-logs must be provided with ameans of joining together(for example,tongue-and-groove joints),they resemble sawn lumber and aretreated as such in the standard.Rafters,purlins,and beams,on the other hand,are sometimes left asround logs,except for a small amount of sawing to provide a flat nailing surface.These practices thusdeal with stress-grading of wall-logs and round-timber beams separately.1.Scope1.1 These practices cover the visual stress-grading prin-ciples applicable to structural wood members of nonrectangu-lar shape,as typically used in log buildings.These practices aremeant to supplement the ASTM standards listed in Section 2,which cover stress-grading of sawn lumber and round timbers.Pieces covered by these practices may also be used in buildingtypes other than log buildings.1.2 The grading provisions used as illustrations herein arenot intended to establish grades for purchase,but rather toshow how stress-grading principles are applied to membersused in log buildings.Detailed grading rules for commercialstress grades which serve as purchase specifications are estab-lished and published by agencies that formulate and maintainsuch rules and operate inspection facilities covering the variousspecies.1.3 The values stated in inch-pound units are to be regardedas standard.The values given in parentheses are mathematical1These practices are under the jurisdiction of ASTM Committee D07 on Woodand are the direct responsibility of Subcommittee D07.02 on Lumber and Engi-neered Wood Products.Current edition approved April 1,2020.Published April 2020.Originallyapproved in 1980.Last previous edition approved in 2015 as D3957 09(2015).DOI:10.1520/D3957-09R20.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.conversions to SI units that are provided for information onlyand are not considered standard.1.4 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,health,and environmental practices and deter-mine the applicability of regulatory limita