ASTM D2555-2015 Standard Practice for Establishing Clear Wood Strength Values《用于确定清晰的木材强度值的标准实施规程》.pdf

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1、Designation: D2555 06 (Reapproved 2011)D2555 15Standard 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

2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe development of safe and efficient working stresses for lumber, laminated timber, plywood,round timbers, and other soli

3、d wood products, each with its own special requirements has, as acommon starting 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

4、or to regional groupings within a species where necessitated bymarketing conditions. This standard 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 the level of working stresses for desig

5、n. Since factors such as species preference, species groupings,marketing practices, design techniques, and safety factors vary with each type of product and end use,it is contemplated that this standard will be supplemented where necessary by other appropriatestandards relating to specific work stre

6、sses for each such product. Practice D245 is an example of sucha standard applicable to the interpretation of the clear wood strength values in terms of workingstresses for structural lumber.A primary feature of this practice is the establishment of tables presenting the most reliable basicinformati

7、on developed on the strength of 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 f

8、orests extending over large regions, 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 specie

9、s is determined on a sound statistical 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 estimate

10、s of strength and to improve or verify estimates made in the past.1. Scope1.1 This practice covers the determination of strength values for clear wood of different species in the unseasoned condition,unadjusted for end use, applicable to the establishment of working stresses for different solid wood

11、 products such as lumber,laminated wood, plywood, and round timbers. Presented are:1.1.1 Procedures by which test values obtained on small clear specimens may be combined with density data from extensiveforest surveys to make them more representative,1.1.2 Guidelines for the interpretation of the da

12、ta in terms of assigned values for combinations of species or regional divisionswithin a species to meet special marketing needs, and1.1.3 Information basic to the translation of the clear wood values into working stresses for different solid wood products fordifferent end uses.1.1.4 For species whe

13、re density survey data are not as yet available for the re-evaluation of average strength properties, thepresently available data from tests made under the sampling methods and procedures of Test Methods D143 or Practice E105 are1 This practice is under the jurisdiction of ASTM Committee D07 on Wood

14、 and are the direct responsibility of Subcommittee D07.01 on Fundamental Test Methods andProperties.Current edition approved Oct. 1, 2011Sept. 1, 2015. Published October 2011December 2015. Originally approved in 1966. Last previous edition approved in 20062011as D2555 06.D2555 06(2011). DOI: 10.1520

15、/D2555-06R11.10.1520/D2555-15.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 recommend

16、s 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 States1provided with appr

17、opriate provision for their application and use. Because of the comprehensive manner in which the densitysurvey is undertaken, it follows that the re-evaluated strength data are intended to be representative of the forest stand, or ratherlarge forest subdivisions.1.1.5 Some useful mechanical propert

18、ies (tensile strengths parallel and perpendicular to grain and grain, modulus of rigidity fora longitudinal-transverse plane) plane, and transverse modulus of elasticity) have not been extensively evaluated. Methods aredescribed for estimating these properties by their relation to other properties.1

19、.2 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 regulatorylimitations prior to use.2. Referenced Docu

20、ments2.1 ASTM Standards:2D143 Test Methods for Small Clear Specimens of TimberD245 Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded LumberD2915 Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based ProductsE105 Practice for Probabi

21、lity Sampling of Materials3. Summary of Methods3.1 Two methods are presented for establishing tables of clear wood strength properties for different species and regionalsubdivisions thereof in the unseasoned condition and unadjusted for end use. These are designated Method A and Method B.3.1.1 Metho

22、d A provides for the use of the results of surveys of wood density involving extensive sampling of forest trees, incombination with the data obtained from standard strength tests made in accordance withTest Methods D143.The average strengthproperties are obtained from wood density survey data throug

23、h linear regression equations establishing the relation of specificgravity to the several strength properties.NOTE 1Density surveys have been completed for only a limited number of species. Data are thus not currently available for the use of Method Aon all commercial species. As such data become av

24、ailable they will be incorporated in revisions of this practice.3.1.2 Method B provides for the establishment of tables of strength values based on standard tests of small clear specimens inthe unseasoned condition for use when data from density surveys are not available. Separate tables are employe

25、d to present thedata on woods grown in the United States and on woods grown in Canada.4. Procedure for Establishing Clear Wood Strength Values4.1 Method ASix steps are involved in establishing strength values by the wood density survey procedure. These are:conducting the wood density survey, develop

26、ment of unit areas, determination of average specific gravity for a unit area,determination of strength-specific gravity relations, estimation of average strength properties for a unit area, and combining valuesfor unit areas into basic groups and establishing average strength properties and estimat

27、es of variance for the groups. In thesemethods a basic group is a combination of unit areas representing a species or a regional division thereof.4.1.1 Conducting Wood Density SurveyAwell-designed and thorough wood density survey is required to provide needed dataon specific gravity for the reevalua

28、tion of strength properties. Such a survey requires consideration of the geographic range to becovered, the representativeness of the sample, the techniques of density evaluation, and adequate data analysis.NOTE 2Detailed information on an acceptable method of conducting wood density surveys, togeth

29、er with survey data, are presented in the U.S. ForestService Research Paper FPL 27, “Western Wood Density Survey Report No. 1.”4.1.2 Development of Unit AreasSubdivide the geographical growth range of each species into unit areas that contain 1 % ormore of the estimated cubic foot volume of standing

30、 timber of the species and are represented by reliable estimates of specificgravity of at least 20 trees. Make up unit areas of U.S. Forest Service Survey Units, or similar units or subdivisions of units, forwhich reliable estimates of timber volume are available. Develop unit areas objectively by m

31、eans of the following steps:4.1.2.1 Select a base survey unit or subdivision of a survey unit to be grouped with others,4.1.2.2 Group with similar adjacent areas to make up a unit area on the basis of a timber volume, and4.1.2.3 Determine the number of tree specific gravity samples available in the

32、proposed unit area.NOTE 3The rules for developing unit areas should represent an effort to subdivide objectively and uniquely the range of a species into smallgeographic areas, which are assumed to be considerably more homogeneous with respect to the mechanical properties of the species than is the

33、entirerange itself. The number of unit areas associated with a species is a function of the volume of timber on the smallest usable areas and the number of treespecific gravity samples taken. In general, the larger the range and the greater the commercial importance of the species, the greater are t

34、he number ofunfit areas. One acceptable procedure for establishing unit areas is presented in U.S. Forest Service Research Paper FPL 27, “Western Wood DensitySurvey Report No. 1,” Appendix C.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at servi

35、ceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.D2555 1524.1.3 Determination of Average Specific Gravity for a Unit AreaCalculate the average specific gravity of trees in each unitarea as the simple average of individu

36、al estimates of specific gravity of trees within the unit area.4.1.4 Determination of Strength-Specific Gravity RelationsFrom matched specific gravity and strength data on small clearspecimens of wood, establish relationships of the form:y 5a1bx (1)where:y = estimated strength value,a, b = constants

37、 for the species, andx = specific gravity of the species.for each species, using standard statistical methods of regression analysis. Equations for modulus of rupture, modulus ofelasticity, maximum crushing strength, and maximum shearing strength are established in this manner. The distribution of s

38、pecificgravity in the samples used to compute regressions should be representative of the species and, in particular, shall represent thefull specific gravity range. The nature of the true distribution of specific gravity can be obtained from results of wood densitysurveys. Obtain the data from spec

39、imens tested in accordance with Test Methods D143.4.1.4.1 Several methods are available for securing suitable samples for obtaining data to compute strength-specific gravityrelationships, as follows: strength and specific gravity values from samples obtained in conformance with Test Methods D143 may

40、be employed solely or in combination with data secured by sampling techniques described below or test samples may be obtainedfrom the forest resource in the form of trees, logs, or lumber. Select samples that are representative of all growing stock from eachof at least five different locations withi

41、n the growth range of a species that include the scope of environmental conditions of therange. This implies that the sample from a single location must be such that all of the growing stock from that location isrepresented.4.1.4.2 Where relationships between strength and specific gravity are shown

42、to have a statistically significant difference at the5 % level within a species growth range, subdivide the range to permit the development of more accurate estimating equations foreach subdivision. Develop equations for subdivisions of a species growth range only if specimens from at least five dis

43、tinctlydifferent places in the proposed subdivision are available and if the correlation coefficients from the strength-specific gravityregressions are 0.50 or greater.4.1.5 Estimation of the Average Strength Properties for a Unit AreaGiven a set of strength-specific gravity estimatingequations for

44、each species or subdivision thereof, compute average strength properties for each unit area using these equations andthe average specific gravity for the unit area.4.1.6 Combining Unit Areas into Basic Groups and Development of Average Strength Properties and Estimates of Variance forthe GroupsCombi

45、ne all unit areas containing timber whose properties are described by the same strength-specific gravityrelationships to produce a basic group of unit areas. Develop the following information for these basic groups:4.1.6.1 For each unit area, obtain, from reliable volume data, the volume of the spec

46、ies being considered and estimate strengthproperties from appropriate equations. Determine average strength properties for a group of unit areas for a species or a subdivisionthereof by the following equation:Y% 5(i Y iVi/V! (2)where:Y5 = weighted average strength property for the group of unit area

47、s,Yi = average strength property for the ith unit area,VI = percentage of standing timber volume of the species for the ith unit area, andV = total percentage of standing timber volume of the species in the group of unit areas being combined.4.1.6.2 Compute the variability index, which is a measure

48、of the homogeneity among average values for unit areas within agroup, by dividing the group average by the lowest unit area average included in the group.4.1.6.3 Estimate a standard deviation, providing a measure of the dispersion of individual strength values about the groupaverage, for each basic

49、group of unit areas using information on variance obtained from density survey and standard strength data.Compute estimates of standard deviation for each property as:s 5=b2sw21sa2!1RMS (3)where:s = standard deviationb = slope of the strength-specific gravity relation,sw2 = within-tree variance in specific gravity estimated from data used to obtain strength-specific gravity relations,sa 2 = among-tree variance in specific gravity obtained from density survey data,(sw2 + s a2) = estimate of total variance in specific gravity, andRMS = residual mean square from the s