1、Designation:D24506(Reapproved 2011)Standard Practice forEstablishing Structural Grades and Related AllowableProperties for Visually Graded Lumber1This standard is issued under the fixed designation D245;the number immediately following the designation indicates the year oforiginal adoption or,in the
2、 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.This standard has been approved for use by agencies of the U.S.Department of Defense.1.Scope1.1 This pra
3、ctice(1,2)2covers the basic principles forestablishing related unit stresses and stiffness values for designwith visually-graded solid sawn structural lumber.This prac-tice starts with property values from clear wood specimens andincludes necessary procedures for the formulation of structuralgrades
4、of any desired strength ratio.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.Detailed grad-ing rules for commercial stress grades which serve as purchasespecifications are establishe
5、d and published by agencies whichformulate and maintain such rules and operate inspectionfacilities covering the various species.1.3 The material covered in this practice appears in thefollowing order:SectionScope1Significance and Use3Basic Principles of Strength Ratios4Estimation and Limitation of
6、Growth Characteristics5Allowable Properties for Timber Design6Modification of Allowable Properties for Design Use7Example of Stress-Grade Development81.4 The values given in parentheses are provided for infor-mation purposes only.1.5 This standard does not purport to address all of thesafety concern
7、s,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.Referenced Documents2.1 ASTM Standards:3D9 Terminology Relating to Wood and Wood-Based
8、 Prod-uctsD143 Test Methods for Small Clear Specimens of TimberD2555 Practice for Establishing Clear Wood Strength ValuesE105 Practice for Probability Sampling of MaterialsIEEE/ASTM SI-10 Practice for Use of the InternationalSystem of Units(SI)(the Modernized Metric System)3.Significance and Use3.1
9、Need for Lumber Grading:3.1.1 Individual pieces of lumber,as they come from thesaw,represent a wide range in quality and appearance withrespect to freedom from knots,cross grain,shakes,and othercharacteristics.Such random pieces likewise represent a widerange in strength,utility,serviceability,and v
10、alue.One of theobvious requirements for the orderly marketing of lumber isthe establishment of grades that permit the procurement of anyrequired quality of lumber in any desired quantity.Maximumeconomy of material is obtained when the range of quality-determining characteristics in a grade is limite
11、d and all piecesare utilized to their full potential.Many of the grades areestablished on the basis of appearance and physical character-istics of the piece,but without regard for mechanical proper-ties.Other grades,called structural or stress grades,areestablished on the basis of features that rela
12、te to mechanicalproperties.The latter designate near-minimum strength andnear-average stiffness properties on which to base structuraldesign.3.1.2 The development of this practice is based on extensiveresearch covering tests of small clear specimens and offull-sized structural members.Detailed studi
13、es have includedthe strength and variability of clear wood,and the effect on1This practice is under the jurisdiction of ASTM Committee D07 on Wood andis the direct responsibility of Subcommittee D07.02 on Lumber and EngineeredWood Products.Current edition approved Oct.1,2011.Published October 2011.O
14、riginallyapproved in 1926.Last previous edition approved in 2006 as D245 06.DOI:10.1520/D0245-06R11.2The boldface numbers in parentheses refer to references at the end of thispractice.3For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.or
15、g.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 strength from various factors such as density,knots(SeeTerminology D9),a
16、nd other defects,seasoning,duration ofstress,and temperature.3.2 How Visual Grading is Accomplished Visual gradingis accomplished from an examination of all four faces and theends of the piece,in which the location as well as the size andnature of the knots and other features appearing on the surfacesare evaluated over the entire length.Basic principles ofstructural grading have been established that permit the evalu-ation of any piece of stress-graded lumber in terms of astrength ratio for each