ASTM D2555-17a(2024)e1
(Practice)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 design values 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 design values 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, modulus of rigidity for a longitudinal-transverse plane, and transverse modulus of elasticity) have not been extensively evaluated. Methods are described for estimating these properties by their relation to other properties.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.3 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation: D2555 − 17a (Reapproved 2024)
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.
ε NOTE—Reference 4 was corrected editorially in February 2024.
INTRODUCTION
The development of safe and efficient design values 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
commercially important species. Also required are procedures for establishing, from these data, values
applicable to groups of species or to regional groupings within a species where necessitated by
marketing conditions. This practice 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
to design values for engineering. 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 practice will be supplemented where necessary by other appropriate
standards relating to specific design values for each such product. Practice D245 is an example of such
a standard applicable to the interpretation of the clear wood strength values in terms of allowable
properties for visually graded 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 Guidelines for the interpretation of the data in terms of
assigned values for combinations of species or regional divi-
1.1 This practice covers the determination of strength values
sions within a species to meet special marketing needs, and
for clear wood of different species in the unseasoned condition,
unadjusted for end use, applicable to the establishment of 1.1.3 Information basic to the translation of the clear wood
design values for different solid wood products such as lumber, values into design values for different solid wood products for
laminated wood, plywood, and round timbers. Presented are:
different end uses.
1.1.1 Procedures by which test values obtained on small
1.1.4 For species where density survey data are not as yet
clear specimens may be combined with density data from
available for the re-evaluation of average strength properties,
extensive forest surveys to make them more representative,
the presently available data from tests made under the sampling
methods and procedures of Test Methods D143 or Practice
1 E105 are provided with appropriate provision for their appli-
This practice is under the jurisdiction of ASTM Committee D07 on Wood and
are the direct responsibility of Subcommittee D07.02 on Lumber and Engineered
cation and use. Because of the comprehensive manner in which
Wood Products.
the density survey is undertaken, it follows that the re-
Current edition approved Feb. 1, 2024. Published February 2024. Originally
evaluated strength data are intended to be representative of the
approved in 1966. Last previous edition approved in 2017 as D2555 – 17a. DOI:
10.1520/D2555-17AR24E01. forest stand, or rather large forest subdivisions.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D2555 − 17a (2024)
1.1.5 Some useful mechanical properties (tensile strengths to present the data on woods grown in the United States and on
parallel and perpendicular to grain, modulus of rigidity for a woods grown in Canada.
longitudinal-transverse plane, and transverse modulus of elas-
ticity) have not been extensively evaluated. Methods are 4. Procedure for Establishing Clear Wood Strength
described for estimating these properties by their relation to
Values
other properties.
4.1 Method A—Six steps are involved in establishing
1.2 The values stated in inch-pound units are to be regarded
strength values by the wood density survey procedure. These
as standard. The values given in parentheses are mathematical are: conducting the wood density survey, development of unit
conversions to SI units that are provided for information only
areas, determination of average specific gravity for a unit area,
and are not considered standard. determination of strength-specific gravity relations, estimation
of average strength properties for a unit area, and combining
1.3 This standard does not purport to address all of the
values for unit areas into basic groups and establishing average
safety concerns, if any, associated with its use. It is the
strength properties and estimates of variance for the groups. In
responsibility of the user of this standard to establish appro-
these methods a basic group is a combination of unit areas
priate safety, health, and environmental practices and deter-
representing a species or a regional division thereof.
mine the applicability of regulatory limitations prior to use.
4.1.1 Conducting Wood Density Survey—A well-designed
1.4 This international standard was developed in accor-
and thorough wood density survey is required to provide
dance with internationally recognized principles on standard-
needed data on specific gravity for the reevaluation of strength
ization established in the Decision on Principles for the
properties. Such a survey requires consideration of the geo-
Development of International Standards, Guides and Recom-
graphic range to be covered, the representativeness of the
mendations issued by the World Trade Organization Technical
sample, the techniques of density evaluation, and adequate data
Barriers to Trade (TBT) Committee.
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 (1).
D143 Test Methods for Small Clear Specimens of Timber
4.1.2 Development of Unit Areas—Subdivide the geographi-
D245 Practice for Establishing Structural Grades and Re-
cal growth range of each species into unit areas that contain
lated Allowable Properties for Visually Graded Lumber
1 % or more of the estimated cubic foot volume of standing
D2915 Practice for Sampling and Data-Analysis for Struc-
timber of the species and are represented by reliable estimates
tural Wood and Wood-Based Products
of specific gravity of at least 20 trees. Make up unit areas of
E105 Guide for Probability Sampling of Materials
U.S. Forest Service Survey Units, or similar units or subdivi-
sions of units, for which reliable estimates of timber volume
3. Summary of Methods
are available. Develop unit areas objectively by means of the
3.1 Two methods are presented for establishing tables of
following steps:
clear wood strength properties for different species and re-
4.1.2.1 Select a base survey unit or subdivision of a survey
gional subdivisions thereof in the unseasoned condition and
unit to be grouped with others,
unadjusted for end use. These are designated Method A and
4.1.2.2 Group with similar adjacent areas to make up a unit
Method B.
area on the basis of a timber volume, and
3.1.1 Method A provides for the use of the results of surveys
4.1.2.3 Determine the number of tree specific gravity
of wood density involving extensive sampling of forest trees,
samples available in the proposed unit area.
in combination with the data obtained from standard strength
tests made in accordance with Test Methods D143. The NOTE 3—The rules for developing unit areas should represent an effort
to subdivide objectively and uniquely the range of a species into small
average strength properties are obtained from wood density
geographic areas, which are assumed to be considerably more homoge-
survey data through linear regression equations establishing the
neous with respect to the mechanical properties of the species than is the
relation of specific gravity to the several strength properties.
entire range 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
NOTE 1—Density surveys have been completed for only a limited
number of tree specific gravity samples taken. In general, the larger the
number of species. Data are thus not currently available for the use of
range and the greater the commercial importance of the species, the
Method A on all commercial species. As such data become available they
greater are the number of unfit areas. One acceptable procedure for
will be incorporated in revisions of this practice.
establishing unit areas is presented in Appendix C of U.S. Forest Service
3.1.2 Method B provides for the establishment of tables of Research Paper FPL 27 (1).
strength values based on standard tests of small clear speci-
4.1.3 Determination of Average Specific Gravity for a Unit
mens in the unseasoned condition for use when data from
Area—Calculate the average specific gravity of trees in each
density surveys are not available. Separate tables are employed
unit area as the simple average of individual estimates of
specific gravity of trees within the unit area.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to a list of references at the end of
the ASTM website. this standard.
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D2555 − 17a (2024)
4.1.4 Determination of Strength-Specific Gravity average strength properties for a group of unit areas for a
Relations—From matched specific gravity and strength data on species or a subdivision thereof by the following equation:
small clear specimens of wood, establish relationships of the
% ¯
Y 5 ~Y V /V! (2)
(i i i
form:
where:
y 5 a1bx (1)
= weighted average strength property for the group of
Y
where:
unit areas,
y = estimated strength value,
¯
Y = average strength property for the ith unit area,
i
a, b = constants for the species, and
V = percentage of standing timber volume of the species for
I
x = specific gravity of the species.
the ith unit area, and
V = total percentage of standing timber volume of the
for each species, using standard statistical methods of
species in the group of unit areas being combined.
regression analysis. Equations for modulus of rupture, modulus
of elasticity, maximum crushing strength, and maximum shear-
4.1.6.2 Compute the variability index, which is a measure of
ing strength are established in this manner. The distribution of the homogeneity among average values for unit areas within a
specific gravity in the samples used to compute regressions
group, by dividing the group average by the lowest unit area
should be representative of the species and, in particular, shall average included in the group.
represent the full specific gravity range. The nature of the true 4.1.6.3 Estimate a standard deviation, providing a measure
distribution of specific gravity can be obtained from results of of the dispersion of individual strength values about the group
average, for each basic group of unit areas using information
wood density surveys. Obtain the data from specimens tested
on variance obtained from density survey and standard strength
in accordance with Test Methods D143.
data. Compute estimates of standard deviation for each prop-
4.1.4.1 Several methods are available for securing suitable
erty as:
samples for obtaining data to compute strength-specific gravity
relationships, as follows: strength and specific gravity values 2 2 2
s 5 =b s 1s 1RMS (3)
~ !
w a
from samples obtained in conformance with Test Methods
where:
D143 may be employed solely or in combination with data
s = standard deviation
secured by sampling techniques described below or test
b = slope of the strength-specific gravity relation,
samples may be obtained from the forest resource in the form
s = within-tree variance in specific gravity esti-
of trees, logs, or lumber. Select samples that are representative w
mated from data used to obtain strength-
of all growing stock from each of at least five different
specific gravity relations,
locations within the growth range of a species that include the
s = among-tree variance in specific gravity ob-
a
scope of environmental conditions of the range. This implies
tained from density survey data,
that the sample from a single location must be such that all of
2 2
(s + s ) = estimate of total variance in specific gravity,
w a
the growing stock from that location is represented.
and
4.1.4.2 Where relationships between strength and specific
RMS = residual mean square from the strength-specific
gravity are shown to have a statistically significant difference at
gravity relation.
the 5 % level within a species growth range, subdivide the
NOTE 4—When a sampling technique is used that ensures only one
range to permit the development of more accurate estimating specimen will be taken per tree (such as a suitably designed mill sample),
2 2
the quantity (s + s ) is automatically obtained as a total variance of
equations for each subdivision. Develop equations for subdi-
w a
specific gravity.
visions of a species grow
...
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