ASTM D2555-17a Standard Practice for Establishing Clear Wood Strength Values.pdf

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1、Designation: D2555 17aStandard Practice forEstablishing Clear Wood Strength Values1This standard is issued under the fixed designation D2555; 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 pa

2、rentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe development of safe and efficient design values for lumber, laminated timber, plywood, roundtimbers, and other solid wood products, each with i

3、ts own special requirements has, as a commonstarting point, the need for an authoritative compilation of clear wood strength values for thecommercially important species.Also required are procedures for establishing, from these data, valuesapplicable to groups of species or to regional groupings wit

4、hin a species where necessitated bymarketing conditions. This practice has been developed to meet these needs and to provide, inaddition, information on factors for consideration in the adjustment of the clear wood strength valuesto design values for engineering. Since factors such as species prefer

5、ence, species groupings,marketing practices, design techniques, and safety factors vary with each type of product and end use,it is contemplated that this practice will be supplemented where necessary by other appropriatestandards relating to specific design values for each such product. Practice D2

6、45 is an example of sucha standard applicable to the interpretation of the clear wood strength values in terms of allowableproperties for visually graded lumber.A primary feature of this practice is the establishment of tables presenting the most reliable basicinformation developed on the strength o

7、f clear wood and its variability through many years of testingand experience. The testing techniques employed are those presented in Test Methods D143. Amongthe recognized limitations of such strength data are those resulting from the problems of samplingmaterial from forests extending over large re

8、gions, and the uneconomical feasibility of completelytesting an intensive sample. A practical approach to the improvement of strength data is through theapplication of the results of density surveys in which the specific gravity of the entire forest stand foreach species is determined on a sound sta

9、tistical basis. Through regression equations derived frompresently available strength data, revised strength values are established from the specific gravity-strength relationship for clear wood. This procedure greatly extends current capabilities to developnew estimates of strength and to improve o

10、r verify estimates made in the past.1. Scope1.1 This practice covers the determination of strength valuesfor clear wood of different species in the unseasoned condition,unadjusted for end use, applicable to the establishment ofdesign values for different solid wood products such as lumber,laminated

11、wood, plywood, and round timbers. Presented are:1.1.1 Procedures by which test values obtained on smallclear specimens may be combined with density data fromextensive forest surveys to make them more representative,1.1.2 Guidelines for the interpretation of the data in terms ofassigned values for co

12、mbinations of species or regional divi-sions within a species to meet special marketing needs, and1.1.3 Information basic to the translation of the clear woodvalues into design values for different solid wood products fordifferent end uses.1.1.4 For species where density survey data are not as yetav

13、ailable for the re-evaluation of average strength properties,the presently available data from tests made under the samplingmethods and procedures of Test Methods D143 or PracticeE105 are provided with appropriate provision for their appli-cation and use. Because of the comprehensive manner in which

14、the density survey is undertaken, it follows that the re-evaluated strength data are intended to be representative of theforest stand, or rather large forest subdivisions.1.1.5 Some useful mechanical properties (tensile strengthsparallel and perpendicular to grain, modulus of rigidity for a1This pra

15、ctice is under the jurisdiction of ASTM Committee D07 on Wood andare the direct responsibility of Subcommittee D07.02 on Lumber and EngineeredWood Products.Current edition approved Aug. 1, 2017. Published October 2017. Originallyapproved in 1966. Last previous edition approved in 2017 as D2555 17. D

16、OI:10.1520/D2555-17A.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 th

17、eDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1longitudinal-transverse plane, and transverse modulus of elas-ticity) have not been extensively evaluated. Methods aredescribed for estimating these

18、 properties by their relation toother properties.1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport t

19、o 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 limitations prior to use.1.4 This international standard was

20、 developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Reference

21、d Documents2.1 ASTM Standards:2D143 Test Methods for Small Clear Specimens of TimberD245 Practice for Establishing Structural Grades and Re-lated Allowable Properties for Visually Graded LumberD2915 Practice for Sampling and Data-Analysis for Struc-tural Wood and Wood-Based ProductsE105 Practice for

22、 Probability Sampling of Materials3. Summary of Methods3.1 Two methods are presented for establishing tables ofclear wood strength properties for different species and re-gional subdivisions thereof in the unseasoned condition andunadjusted for end use. These are designated Method A andMethod B.3.1.

23、1 MethodAprovides for the use of the results of surveysof wood density involving extensive sampling of forest trees,in combination with the data obtained from standard strengthtests made in accordance with Test Methods D143. Theaverage strength properties are obtained from wood densitysurvey data th

24、rough linear regression equations establishing therelation of specific gravity to the several strength properties.NOTE 1Density surveys have been completed for only a limitednumber of species. Data are thus not currently available for the use ofMethod A on all commercial species. As such data become

25、 available theywill be incorporated in revisions of this practice.3.1.2 Method B provides for the establishment of tables ofstrength values based on standard tests of small clear speci-mens in the unseasoned condition for use when data fromdensity surveys are not available. Separate tables are emplo

26、yedto present the data on woods grown in the United States and onwoods grown in Canada.4. Procedure for Establishing Clear Wood StrengthValues4.1 Method ASix steps are involved in establishingstrength values by the wood density survey procedure. Theseare: conducting the wood density survey, developm

27、ent of unitareas, determination of average specific gravity for a unit area,determination of strength-specific gravity relations, estimationof average strength properties for a unit area, and combiningvalues for unit areas into basic groups and establishing averagestrength properties and estimates o

28、f variance for the groups. Inthese methods a basic group is a combination of unit areasrepresenting a species or a regional division thereof.4.1.1 Conducting Wood Density SurveyA well-designedand thorough wood density survey is required to provideneeded data on specific gravity for the reevaluation

29、of strengthproperties. Such a survey requires consideration of the geo-graphic range to be covered, the representativeness of thesample, the techniques of density evaluation, and adequate dataanalysis.NOTE 2Detailed information on an acceptable method of conductingwood density surveys, together with

30、 survey data, are presented in the U.S.Forest Service Research Paper FPL 27 (1).34.1.2 Development of Unit AreasSubdivide the geographi-cal growth range of each species into unit areas that contain1 % or more of the estimated cubic foot volume of standingtimber of the species and are represented by

31、reliable estimatesof specific gravity of at least 20 trees. Make up unit areas ofU.S. Forest Service Survey Units, or similar units or subdivi-sions of units, for which reliable estimates of timber volumeare available. Develop unit areas objectively by means of thefollowing steps:4.1.2.1 Select a ba

32、se survey unit or subdivision of a surveyunit to be grouped with others,4.1.2.2 Group with similar adjacent areas to make up a unitarea on the basis of a timber volume, and4.1.2.3 Determine the number of tree specific gravitysamples available in the proposed unit area.NOTE 3The rules for developing

33、unit areas should represent an effortto subdivide objectively and uniquely the range of a species into smallgeographic areas, which are assumed to be considerably more homoge-neous with respect to the mechanical properties of the species than is theentire range itself. The number of unit areas assoc

34、iated with a species isa function of the volume of timber on the smallest usable areas and thenumber of tree specific gravity samples taken. In general, the larger therange and the greater the commercial importance of the species, thegreater are the number of unfit areas. One acceptable procedure fo

35、restablishing unit areas is presented in Appendix C of U.S. Forest ServiceResearch Paper FPL 27 (1).4.1.3 Determination of Average Specific Gravity for a UnitAreaCalculate the average specific gravity of trees in eachunit area as the simple average of individual estimates ofspecific gravity of trees

36、 within the unit area.4.1.4 Determination of Strength-Specific GravityRelationsFrom matched specific gravity and strength data onsmall clear specimens of wood, establish relationships of theform:2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

37、serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.D2555 17a2y 5 a1bx (1)where:y = estimated strength value,a, b = constant

38、s for the species, andx = specific gravity of the species.for each species, using standard statistical methods ofregression analysis. Equations for modulus of rupture, modulusof elasticity, maximum crushing strength, and maximum shear-ing strength are established in this manner. The distribution ofs

39、pecific gravity in the samples used to compute regressionsshould be representative of the species and, in particular, shallrepresent the full specific gravity range. The nature of the truedistribution of specific gravity can be obtained from results ofwood density surveys. Obtain the data from speci

40、mens testedin accordance with Test Methods D143.4.1.4.1 Several methods are available for securing suitablesamples for obtaining data to compute strength-specific gravityrelationships, as follows: strength and specific gravity valuesfrom samples obtained in conformance with Test MethodsD143 may be e

41、mployed solely or in combination with datasecured by sampling techniques described below or testsamples may be obtained from the forest resource in the formof trees, logs, or lumber. Select samples that are representativeof all growing stock from each of at least five differentlocations within the g

42、rowth range of a species that include thescope of environmental conditions of the range. This impliesthat the sample from a single location must be such that all ofthe growing stock from that location is represented.4.1.4.2 Where relationships between strength and specificgravity are shown to have a

43、 statistically significant difference atthe 5 % level within a species growth range, subdivide therange to permit the development of more accurate estimatingequations for each subdivision. Develop equations for subdi-visions of a species growth range only if specimens from atleast five distinctly di

44、fferent places in the proposed subdivisionare available and if the correlation coefficients from thestrength-specific gravity regressions are 0.50 or greater.4.1.5 Estimation of the Average Strength Properties for aUnit AreaGiven a set of strength-specific gravity estimatingequations for each specie

45、s or subdivision thereof, computeaverage strength properties for each unit area using theseequations and the average specific gravity for the unit area.4.1.6 Combining Unit Areas into Basic Groups and Devel-opment of Average Strength Properties and Estimates ofVariance for the GroupsCombine all unit

46、 areas containingtimber whose properties are described by the same strength-specific gravity relationships to produce a basic group of unitareas. Develop the following information for these basicgroups:4.1.6.1 For each unit area, obtain, from reliable volumedata, the volume of the species being cons

47、idered and estimatestrength properties from appropriate equations. Determineaverage strength properties for a group of unit areas for aspecies or a subdivision thereof by the following equation:Y%5(iYiVi/V! (2)where:Y5= weighted average strength property for the group ofunit areas,Yi= average streng

48、th property for the ith unit area,VI= percentage of standing timber volume of the species forthe ith unit area, andV = total percentage of standing timber volume of thespecies in the group of unit areas being combined.4.1.6.2 Compute the variability index, which is a measure ofthe homogeneity among

49、average values for unit areas within agroup, by dividing the group average by the lowest unit areaaverage included in the group.4.1.6.3 Estimate a standard deviation, providing a measureof the dispersion of individual strength values about the groupaverage, for each basic group of unit areas using informationon variance obtained from density survey and standard strengthdata. Compute estimates of standard deviation for each prop-erty as:s 5 =b2sw21sa2!1RMS (3)where:s = standard deviationb = slope of the strength-specific gravity relation,sw2= within-tree variance in spe