ASTM D2555-98

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: D 2555 – 98
Standard Test Methods for
Establishing Clear Wood Strength Values
This standard is issued under the fixed designation D 2555; 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 (e) 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
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 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
to the level of working stresses for design. 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 appropriate
standards relating to specific work stresses for each such product. ASTM Practice D 245 is an example
of such 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 standard 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 Methods D 143. 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 sions within a species to meet special marketing needs, and
1.1.3 Information basic to the translation of the clear wood
1.1 These test methods cover the determination of strength
values into working stresses for different solid wood products
values for clear wood of different species in the unseasoned
for different end uses.
condition, unadjusted for end use, applicable to the establish-
1.1.4 For species where density survey data are not as yet
ment of working stresses for different solid wood products such
available for the reevaluation of average strength properties,
as lumber, laminated wood, plywood, and round timbers.
the presently available data from tests made under the sampling
Presented are:
methods and procedures of Methods D 143, or Practice E 105,
1.1.1 Procedures by which test values obtained on small
are provided with appropriate provision for their application
clear specimens may be combined with density data from
and use. Because of the comprehensive manner in which the
extensive forest surveys to make them more representative,
density survey is undertaken, it follows that the reevaluated
1.1.2 Guidelines for the interpretation of the data in terms of
strength data are intended to be representative of the forest
assigned values for combinations of species or regional divi-
stand, or rather large forest subdivisions.
1.1.5 Some useful mechanical properties (tensile strengths
These test methods are under the jurisdiction of ASTM Committee D-7 on
parallel and perpendicular to grain and modulus of rigidity for
Wood and are the direct responsibility of Subcommittee D07.01 on Fundamental
a longitudinal-transverse plane) have not been extensively
Test Methods and Properties.
evaluated. Methods are described for estimating these proper-
Current edition approved July 10, 1998. Published March 1999. Originally
e1
published as D 2555 – 66 T. Last previous edition D 2555 – 96 . ties by their relation to other properties.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2555
1.2 This standard does not purport to address all of the properties. Such a survey requires consideration of the geo-
safety concerns, if any, associated with its use. It is the graphic range to be covered, the representativeness of the
responsibility of the user of this standard to establish appro- sample, the techniques of density evaluation, and adequate data
priate safety and health practices and determine the applica- analysis.
bility of regulatory limitations prior to use.
NOTE 2—Detailed information on an acceptable method of conducting
wood density surveys, together with survey data, are presented in the U.S.
2. Referenced Documents
Forest Service Research Paper FPL 27, “Western Wood Density Survey
2.1 ASTM Standards:
Report No. 1.”
D 143 Methods of Testing Small Clear Specimens of Tim-
4.1.2 Development of Unit Areas—Subdivide the geo-
ber
graphical growth range of each species into unit areas that
D 245 Practice for Establishing Structural Grades and Re-
contain 1 % or more of the estimated cubic foot volume of
lated Allowable Properties for Visually Graded Lumber
standing timber of the species and are represented by reliable
D 2915 Practice for Evaluating Allowable Properties for
estimates of specific gravity of at least 20 trees. Make up unit
Grades of Structural Lumber
areas of U.S. Forest Service Survey Units, or similar units or
E 105 Practice for Probability Sampling of Materials
subdivisions of units, for which reliable estimates of timber
volume are available. Develop unit areas objectively by means
3. Summary of Test Methods
of the following steps:
3.1 Two methods are presented for establishing tables of
4.1.2.1 Select a base survey unit or subdivision of a survey
clear wood strength properties for different species and re-
unit to be grouped with others,
gional subdivisions thereof in the unseasoned condition and
4.1.2.2 Group with similar adjacent areas to make up a unit
unadjusted for end use. These are designated Method A and
area on the basis of a timber volume, and
Method B.
4.1.2.3 Determine the number of tree specific gravity
3.1.1 Method A provides for the use of the results of surveys
samples available in the proposed unit area.
of wood density involving extensive sampling of forest trees,
in combination with the data obtained from standard strength NOTE 3—The rules for developing unit areas should represent an effort
to subdivide objectively and uniquely the range of a species into small
tests made in accordance with Methods D 143. The average
geographic areas which are assumed to be considerably more homoge-
strength properties are obtained from wood density survey data
neous with respect to the mechanical properties of the species than is the
through linear regression equations establishing the relation of
entire range itself. The number of unit areas associated with a species is
specific gravity to the several strength properties.
a function of the volume of timber on the smallest usable areas and the
number of tree specific gravity samples taken. In general, the larger the
NOTE 1—Density surveys have been completed for only a limited
range and the greater the commercial importance of the species, the
number of species. Data are thus not currently available for the use of
greater are the number of unfit areas. One acceptable procedure for
Method A on all commercial species. As such data become available they
establishing unit areas is presented in U.S. Forest Service Research Paper
will be incorporated in revisions of this standard.
FPL 27, “Western Wood Density Survey Report No. 1,” Appendix C.
3.1.2 Method B provides for the establishment of tables of
4.1.3 Determination of Average Specific Gravity for a Unit
strength values based on standard tests of small clear speci-
Area—Calculate the average specific gravity of trees in each
mens in the unseasoned condition for use when data from
unit area as the simple average of individual estimates of
density surveys are not available. Separate tables are employed
specific gravity of trees within the unit area.
to present the data on woods grown in the United States and on
4.1.4 Determination of Strength-Specific Gravity
woods grown in Canada.
Relations—From matched specific gravity and strength data on
4. Procedure for Establishing Clear Wood Strength
small clear specimens of wood, establish relationships of the
Values
form:
4.1 Method A—Six steps are involved in establishing
y 5 a 1 bx (1)
strength values by the wood density survey procedure. These
where:
are: conducting the wood density survey, development of unit
y = estimated strength value,
areas, determination of average specific gravity for a unit area,
a = constant for the species,
determination of strength-specific gravity relations, estimation
b = a constant for the species, and
of average strength properties for a unit area, and combining
x = specific gravity of the species
values for unit areas into basic groups and establishing average
for each species, using standard statistical methods of
strength properties and estimates of variance for the groups. In
regression analysis. Equations for modulus of rupture, modulus
these methods a basic group is a combination of unit areas
of elasticity, maximum crushing strength, and maximum shear-
representing a species or a regional division thereof.
ing strength are established in this manner. The distribution of
4.1.1 Conducting Wood Density Survey—A well-designed
specific gravity in the samples used to compute regressions
and thorough wood density survey is required to provide
should be representative of the species and, in particular, shall
needed data on specific gravity for the reevaluation of strength
represent the full specific gravity range. The nature of the true
distribution of specific gravity can be obtained from results of
2 wood density surveys. Obtain the data from specimens tested
Annual Book of ASTM Standards, Vol 04.10.
Annual Book of ASTM Standards, Vol 14.02. in accordance with Methods D 143.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2555
4.1.4.1 Several methods are available for securing suitable 4.1.6.3 Estimate a standard deviation, providing a measure
samples for obtaining data to compute strength-specific gravity
of the dispersion of individual strength values about the group
relationships, as follows: strength and specific gravity values average, for each basic group of unit areas using information
from samples obtained in conformance with Methods D 143
on variance obtained from density survey and standard strength
may be employed solely or in combination with data secured
data. Compute estimates of standard deviation for each prop-
by sampling techniques described below or testsamples may be
erty as:
obtained from the forest resource in the form of trees, logs, or
2 2 2
s 5 b ~s 1 s ! 1 RMS (3)
=
w a
lumber. Select samples that are representative of all growing
stock from each of at least five different locations within the
where:
growth range of a species that include the scope of environ-
s = standard deviation
mental conditions of the range. This implies that the sample
b = slope of the strength-specific gravity rela-
from a single location must be such that all of the growing
tion,
stock from that location is represented.
s = within-tree variance in specific gravity esti-
w
4.1.4.2 Where relationships between strength and specific mated from data used to obtain strength-
gravity are shown to have a statistically significant difference at specific gravity relations,
the 5 % level within a species growth range, subdivide the s = among-tree variance in specific gravity ob-
a
range to permit the development of more accurate estimating tained from density survey data,
2 2
(s +s ) = estimate of total variance in specific gravity,
equations for each subdivision. Develop equations for subdi-
w a
and
visions of a species growth range only if specimens from at
RMS = residual mean square from the strength-
least five distinctly different places in the proposed subdivision
specific gravity relation.
are available and if the correlation coefficients from the
strength-specific gravity regressions are 0.50 or greater.
NOTE 4—When a sampling technique is used that ensures only one
4.1.5 Estimation of the Average Strength Properties for a
specimen will be taken per tree (such as a suitably designed mill sample),
2 2
Unit Area—Given a set of strength-specific gravity estimating
the quantity (s + s ) is automatically obtained as a total variance of
w a
equations for each species or subdivision thereof, compute
specific gravity.
average strength properties for each unit area using these
NOTE 5—An alternative procedure for developing average strength
equations and the average specific gravity for the unit area. values, where all unit areas are contained within a single species or
regional subdivision thereof consists of combining the volume weighted
4.1.6 Combining Unit Areas into Basic Groups and Devel-
unit area specific gravities to establish a species or regional subdivision
opment of Average Strength Properties and Estimates of
specific gravity and then computing the average strength properties by
Variance for the Groups—Combine all unit areas containing
substituting the average specific gravity in the strength-specific gravity
timber whose properties are described by the same strength-
regression equations.
specific gravity relationships to produce a basic group of unit
4.1.6.4 Average compression perpendicular to the grain
areas. Develop the following information for these basic
values h
...