ASTM D2555-06(2011)
(Test Method)Standard Practice for Establishing Clear Wood Strength Values
Standard Practice for Establishing Clear Wood Strength Values
ABSTRACT
This practice presents the two standard methods for determining the strength values of clear wood of different species in the unseasoned condition, unadjusted for end use, applicable to the establishment of working stresses for different solid wood products such as lumber, laminated wood, plywood, and round timbers. Method A provides for the use of the results of surveys of wood density involving extensive sampling of forest trees, in combination with the data obtained from standard strength tests. The average strength properties are obtained from wood density survey data through linear regression equations establishing the relation of specific gravity to the several strength properties. Method B, on the other hand, provides for the establishment of tables of strength values based on standard tests of small clear specimens in the unseasoned condition for use when data from density surveys are not available. Separate tables are employed to present the data on woods grown in the United States and on woods grown in Canada. Guidelines for the interpretation of the data in terms of assigned values, information basic to the translation of the clear wood values into working stresses, presently available data with appropriate provisions for their application and use, and methods for estimating some useful mechanical properties by relating them to other properties are presented herein as well.
SCOPE
1.1 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 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 extensive forest surveys to make them more representative,
1.1.2 Guidelines for the interpretation of the data in terms of assigned values for combinations of species or regional divisions within a species to meet special marketing needs, and
1.1.3 Information basic to the translation of the clear wood values into working stresses for different solid wood products for different end uses.
1.1.4 For species where density survey data are not as yet available for the re-evaluation of average strength properties, the presently available data from tests made under the sampling methods and procedures of Test Methods D143 or Practice E105 are provided with appropriate provision for their application and use. Because of the comprehensive manner in which the density survey is undertaken, it follows that the re-evaluated strength data are intended to be representative of the forest stand, or rather large forest subdivisions.
1.1.5 Some useful mechanical properties (tensile strengths parallel and perpendicular to grain and modulus of rigidity for a longitudinal-transverse plane) have not been extensively evaluated. Methods are described for estimating these properties by their relation to other properties.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D2555 − 06(Reapproved 2011)
Standard Practice for
Establishing Clear Wood Strength Values
This standard is issued under the fixed designation D2555; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The development of safe and efficient working stresses for lumber, laminated timber, plywood,
round timbers, and other solid wood products, each with its own special requirements has, as a
common starting point, the need for an authoritative compilation of clear wood strength values for the
commerciallyimportantspecies.Alsorequiredareproceduresforestablishing,fromthesedata,values
applicable to groups of species or to regional groupings within a species where necessitated by
marketing conditions. This standard has been developed to meet these needs and to provide, in
addition, information on factors for consideration in the adjustment of the clear wood strength values
tothelevelofworkingstressesfordesign.Sincefactorssuchasspeciespreference,speciesgroupings,
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 appropriate
standardsrelatingtospecificworkstressesforeachsuchproduct.PracticeD245isanexampleofsuch
a standard applicable to the interpretation of the clear wood strength values in terms of working
stresses for structural lumber.
A primary feature of this practice is the establishment of tables presenting the most reliable basic
information developed on the strength of clear wood and its variability through many years of testing
and experience. The testing techniques employed are those presented in Test Methods D143. Among
the recognized limitations of such strength data are those resulting from the problems of sampling
material from forests extending over large regions, and the uneconomical feasibility of completely
testing an intensive sample. A practical approach to the improvement of strength data is through the
application of the results of density surveys in which the specific gravity of the entire forest stand for
each species is determined on a sound statistical basis. Through regression equations derived from
presently available strength data, revised strength values are established from the specific gravity-
strength relationship for clear wood. This procedure greatly extends current capabilities to develop
new estimates of strength and to improve or verify estimates made in the past.
1. Scope 1.1.2 Guidelinesfortheinterpretationofthedataintermsof
assigned values for combinations of species or regional divi-
1.1 Thispracticecoversthedeterminationofstrengthvalues
sions within a species to meet special marketing needs, and
forclearwoodofdifferentspeciesintheunseasonedcondition,
1.1.3 Information basic to the translation of the clear wood
unadjusted for end use, applicable to the establishment of
values into working stresses for different solid wood products
working stresses for different solid wood products such as
for different end uses.
lumber, laminated wood, plywood, and round timbers. Pre-
1.1.4 For species where density survey data are not as yet
sented are:
available for the re-evaluation of average strength properties,
1.1.1 Procedures by which test values obtained on small
thepresentlyavailabledatafromtestsmadeunderthesampling
clear specimens may be combined with density data from
methods and procedures of Test Methods D143 or Practice
extensive forest surveys to make them more representative,
E105 are provided with appropriate provision for their appli-
cationanduse.Becauseofthecomprehensivemannerinwhich
1 the density survey is undertaken, it follows that the re-
This practice is under the jurisdiction of ASTM Committee D07 on Wood and
are the direct responsibility of Subcommittee D07.01 on FundamentalTest Methods evaluated strength data are intended to be representative of the
and Properties.
forest stand, or rather large forest subdivisions.
Current edition approved Oct. 1, 2011. Published October 2011. Originally
1.1.5 Some useful mechanical properties (tensile strengths
approved in 1966. Last previous edition approved in 2006 as D2555 – 06. DOI:
10.1520/D2555-06R11. parallel and perpendicular to grain and modulus of rigidity for
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2555 − 06 (2011)
a longitudinal-transverse plane) have not been extensively these methods a basic group is a combination of unit areas
evaluated. Methods are described for estimating these proper- representing a species or a regional division thereof.
ties by their relation to other properties.
4.1.1 Conducting Wood Density Survey—A well-designed
and thorough wood density survey is required to provide
1.2 This standard does not purport to address all of the
needed data on specific gravity for the reevaluation of strength
safety concerns, if any, associated with its use. It is the
properties. Such a survey requires consideration of the geo-
responsibility of the user of this standard to establish appro-
graphic range to be covered, the representativeness of the
priate safety and health practices and determine the applica-
sample,thetechniquesofdensityevaluation,andadequatedata
bility of regulatory limitations prior to use.
analysis.
2. Referenced Documents
NOTE 2—Detailed information on an acceptable method of conducting
wood density surveys, together with survey data, are presented in the U.S.
2.1 ASTM Standards:
Forest Service Research Paper FPL 27, “Western Wood Density Survey
D143 Test Methods for Small Clear Specimens of Timber
Report No. 1.”
D245 Practice for Establishing Structural Grades and Re-
4.1.2 Development of Unit Areas—Subdividethegeographi-
lated Allowable Properties for Visually Graded Lumber
cal growth range of each species into unit areas that contain
D2915 Practice for Sampling and Data-Analysis for Struc-
1 % or more of the estimated cubic foot volume of standing
tural Wood and Wood-Based Products
timber of the species and are represented by reliable estimates
E105 Practice for Probability Sampling of Materials
of specific gravity of at least 20 trees. Make up unit areas of
U.S. Forest Service Survey Units, or similar units or subdivi-
3. Summary of Methods
sions of units, for which reliable estimates of timber volume
3.1 Two methods are presented for establishing tables of
are available. Develop unit areas objectively by means of the
clear wood strength properties for different species and re-
following steps:
gional subdivisions thereof in the unseasoned condition and
4.1.2.1 Select a base survey unit or subdivision of a survey
unadjusted for end use. These are designated Method A and
unit to be grouped with others,
Method B.
4.1.2.2 Group with similar adjacent areas to make up a unit
3.1.1 MethodAprovidesfortheuseoftheresultsofsurveys
area on the basis of a timber volume, and
of wood density involving extensive sampling of forest trees,
4.1.2.3 Determine the number of tree specific gravity
in combination with the data obtained from standard strength
samples available in the proposed unit area.
tests made in accordance with Test Methods D143. The
average strength properties are obtained from wood density
NOTE 3—The rules for developing unit areas should represent an effort
surveydatathroughlinearregressionequationsestablishingthe to subdivide objectively and uniquely the range of a species into small
geographic areas, which are assumed to be considerably more homoge-
relation of specific gravity to the several strength properties.
neous with respect to the mechanical properties of the species than is the
NOTE 1—Density surveys have been completed for only a limited entire range itself. The number of unit areas associated with a species is
number of species. Data are thus not currently available for the use of
a function of the volume of timber on the smallest usable areas and the
MethodAon all commercial species.As such data become available they number of tree specific gravity samples taken. In general, the larger the
will be incorporated in revisions of this practice.
range and the greater the commercial importance of the species, the
greater are the number of unfit areas. One acceptable procedure for
3.1.2 Method B provides for the establishment of tables of
establishing unit areas is presented in U.S. Forest Service Research Paper
strength values based on standard tests of small clear speci-
FPL 27, “Western Wood Density Survey Report No. 1,” Appendix C.
mens in the unseasoned condition for use when data from
4.1.3 Determination of Average Specific Gravity for a Unit
density surveys are not available. Separate tables are employed
Area—Calculate the average specific gravity of trees in each
to present the data on woods grown in the United States and on
unit area as the simple average of individual estimates of
woods grown in Canada.
specific gravity of trees within the unit area.
4.1.4 Determination of Strength-Specific Gravity
4. Procedure for Establishing Clear Wood Strength
Relations—From matched specific gravity and strength data on
Values
small clear specimens of wood, establish relationships of the
4.1 Method A—Six steps are involved in establishing
form:
strength values by the wood density survey procedure. These
y 5 a1bx (1)
are: conducting the wood density survey, development of unit
areas, determination of average specific gravity for a unit area,
where:
determination of strength-specific gravity relations, estimation
y = estimated strength value,
of average strength properties for a unit area, and combining
a, b = constants for the species, and
values for unit areas into basic groups and establishing average
x = specific gravity of the species.
strength properties and estimates of variance for the groups. In
for each species, using standard statistical methods of
regressionanalysis.Equationsformodulusofrupture,modulus
of elasticity, maximum crushing strength, and maximum shear-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ing strength are established in this manner. The distribution of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
specific gravity in the samples used to compute regressions
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. should be representative of the species and, in particular, shall
D2555 − 06 (2011)
represent the full specific gravity range. The nature of the true 4.1.6.2 Computethevariabilityindex,whichisameasureof
distribution of specific gravity can be obtained from results of the homogeneity among average values for unit areas within a
wood density surveys. Obtain the data from specimens tested group, by dividing the group average by the lowest unit area
in accordance with Test Methods D143. average included in the group.
4.1.6.3 Estimate a standard deviation, providing a measure
4.1.4.1 Several methods are available for securing suitable
of the dispersion of individual strength values about the group
samples for obtaining data to compute strength-specific gravity
average, for each basic group of unit areas using information
relationships, as follows: strength and specific gravity values
onvarianceobtainedfromdensitysurveyandstandardstrength
from samples obtained in conformance with Test Methods
data. Compute estimates of standard deviation for each prop-
D143 may be employed solely or in combination with data
erty as:
secured by sampling techniques described below or test
samples may be obtained from the forest resource in the form
2 2 2
s 5 =b s 1s 1RMS (3)
~ !
w a
of trees, logs, or lumber. Select samples that are representative
where:
of all growing stock from each of at least five different
locations within the growth range of a species that include the
s = standard deviation
scope of environmental conditions of the range. This implies b = slope of the strength-specific gravity relation,
that the sample from a single location must be such that all of s = within-tree variance in specific gravity esti-
w
the growing stock from that location is represented. mated from data used to obtain strength-
specific gravity relations,
4.1.4.2 Where relationships between strength and specific
s = among-tree variance in specific gravity ob-
gravityareshowntohaveastatisticallysignificantdifferenceat a
tained from density survey data,
the 5 % level within a species growth range, subdivide the
2 2
(s +s ) = estimate of total variance in specific gravity,
w a
range to permit the development of more accurate estimating
and
equations for each subdivision. Develop equations for subdi-
RMS = residual mean square from the strength-
visions of a species growth range only if specimens from at
specific gravity relation.
least five distinctly different places in the proposed subdivision
NOTE 4—When a sampling technique is used that ensures only one
are available and if the correlation coefficients from the
specimen will be taken per tree (such as a suitably designed mill sample),
2 2
strength-specific gravity regressions are 0.50 or greater.
the quantity (s + s ) is automatically obtained as a total variance of
w a
specific gravity.
4.1.5 Estimation of the Average Strength Properties for a
NOTE 5—An alternative procedure for developing average strength
Unit Area—Given a set of strength-specific gravity estimating
values where all unit areas are contained within a single species or
equations for each species or subdivision thereof, compute
regional subdivision thereof consists of combining the volume weighted
average strength properties for each unit area using these
unit area specific gravities to establish a species or regional subdivision
equations and the average specific gravity for the unit area. specific gravity and then computing the average strength properties by
substituting the average specific gravity in the strength-specific gravity
4.1.6 Combining Unit Areas into Basic Groups and Devel-
regression equations.
opment of Average Strength Properties and Estimates of
4.1.6.4 Average compression perpendicular to the grain
Variance for the Groups—Combine all unit areas containing
values have not been developed by the procedures described in
timber whose properties are described by the same strength-
the preceding paragraphs but are based on available standard
specific gravity relationships to produce a basic group of unit
strength data alone as in Method
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.