ASTM D245-00
(Practice)Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber
Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber
SCOPE
1.1 This practice (1,2) covers the basic principles for establishing related unit stresses and stiffness values for design with visually-graded solid sawn structural lumber. This practice starts with property values from clear wood specimens and includes necessary procedures for the formulation of structural grades of any desired strength ratio.
1.2 The grading provisions used as illustrations herein are not intended to establish grades for purchase, but rather to show how stress-grading principles are applied. Detailed grading rules for commercial stress grades which serve as purchase specifications are established and published by agencies which formulate and maintain such rules and operate inspection facilities covering the various species.
1.3 The material covered in this practice appears in the following order: SectionScope 1Significance and Use3Basic Principles of Strength Ratios4Estimation and Limitation of Growth Characteristics5Allowable Properties for Timber Design6Modification of Allowable Properties for Design Use7Example of Stress-Grade Development8
1.4 The values given in parentheses are provided for information purposes only.
1.5 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.
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Designation: D 245 – 00
Standard Practice for
Establishing Structural Grades and Related Allowable
Properties for Visually Graded Lumber
This standard is issued under the fixed designation D 245; 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.
1. Scope D 2555 Test Methods for Establishing Clear-Wood Strength
Values
1.1 This practice (1,2) covers the basic principles for
E 105 Practice for Probability Sampling of Materials
establishing related unit stresses and stiffness values for design
E 380 Practice for Use of the International System of Units
with visually-graded solid sawn structural lumber. This prac-
(SI) (the Modernized Metric System)
tice starts with property values from clear wood specimens and
includes necessary procedures for the formulation of structural
3. Significance and Use
grades of any desired strength ratio.
3.1 Need for Lumber Grading:
1.2 The grading provisions used as illustrations herein are
3.1.1 Individual pieces of lumber, as they come from the
not intended to establish grades for purchase, but rather to
saw, represent a wide range in quality and appearance with
show how stress-grading principles are applied. Detailed grad-
respect to freedom from knots, cross grain, shakes, and other
ing rules for commercial stress grades which serve as purchase
characteristics. Such random pieces likewise represent a wide
specifications are established and published by agencies which
range in strength, utility, serviceability, and value. One of the
formulate and maintain such rules and operate inspection
obvious requirements for the orderly marketing of lumber is
facilities covering the various species.
the establishment of grades that permit the procurement of any
1.3 The material covered in this practice appears in the
required quality of lumber in any desired quantity. Maximum
following order:
economy of material is obtained when the range of quality-
Section
determining characteristics in a grade is limited and all pieces
Scope 1
Significance and Use 3
are utilized to their full potential. Many of the grades are
Basic Principles of Strength Ratios 4
established on the basis of appearance and physical character-
Estimation and Limitation of Growth Characteristics 5
istics of the piece, but without regard for mechanical proper-
Allowable Properties for Timber Design 6
Modification of Allowable Properties for Design Use 7
ties. Other grades, called structural or stress grades, are
Example of Stress-Grade Development 8
established on the basis of features that relate to mechanical
1.4 The values given in parentheses are provided for infor-
properties. The latter designate near-minimum strength and
mation purposes only. near-average stiffness properties on which to base structural
1.5 This standard does not purport to address all of the
design.
safety concerns, if any, associated with its use. It is the 3.1.2 The development of this practice is based on extensive
responsibility of the user of this standard to establish appro-
research covering tests of small clear specimens and of
priate safety and health practices and determine the applica- full-sized structural members. Detailed studies have included
bility of regulatory limitations prior to use. the strength and variability of clear wood, and the effect on
strength from various factors such as density, knots (See
2. Referenced Documents
Terminology D 9), and other defects, seasoning, duration of
2.1 ASTM Standards:
stress, and temperature.
D 9 Terminology Relating to Wood 3.2 How Visual Grading is Accomplished— Visual grading
D 143 Methods of Testing Small Clear Specimens of Tim-
is accomplished from an examination of all four faces and the
ber ends of the piece, in which the location as well as the size and
nature of the knots and other features appearing on the surfaces
are evaluated over the entire length. Basic principles of
structural grading have been established that permit the evalu-
This practice is under the jurisdiction of ASTM Committee D-7 on Wood and
is the direct responsibility of Subcommittee D07.02 on Lumber and Engineered
ation of any piece of stress-graded lumber in terms of a
Wood Products.
strength ratio for each property being evaluated. The strength
Current edition approved April 10, 1999. Published June 1999. Originally
published as D 245 – 26. Last previous edition D 245 – 99.
The boldface numbers in parentheses refer to references at the end of this
practice. Annual Book of ASTM Standards, Vol 14.02.
3 5
Annual Book of ASTM Standards, Vol 04.10. Annual Book of ASTM Standards, Vol 14.02 (excerpts in Vol 04.10).
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 245
ratio of stress-graded lumber is the hypothetical ratio of the 4. Basic Principles of Strength Ratios
strength property being considered compared to that for the
4.1 General Considerations:
material with no strength-reducing characteristic. Thus a piece
4.1.1 Strength ratios associated with knots in bending mem-
of stress-graded lumber with a strength ratio of 75 % in
bers have been derived as the ratio of moment-carrying
bending would be expected to have 75 % of the bending
capacity of a member with cross section reduced by the largest
strength of the clear piece. In effect, the strength ratio system
knot to the moment-carrying capacity of the member without
of visual structural grading is thus designed to permit practi-
defect. This gives the anticipated reduction in bending strength
cally unlimited choice in establishing grades of any desired
due to the knot. For simplicity, all knots on the wide face are
quality to best meet production and utilization requirements.
treated as being either knots along the edge of the piece (edge
3.3 Classification of Stress-Graded Lumber:
knots) or knots along the centerline of the piece (centerline
3.3.1 The various factors affecting strength, such as knots,
knots).
deviations of grain, shakes, and checks, differ in their effect,
4.1.2 Strength ratios associated with slope of grain in
depending on the kind of loading and stress to which the piece
bending members, and in members subjected to compression
is subjected. Stress-graded lumber is often classified according
parallel to grain, were obtained, experimentally (3).
to its size and use. Four classes are widely used, as follows:
4.1.3 Strength ratios associated with shakes, checks, and
3.3.1.1 Dimension Lumber—Pieces of rectangular cross
splits are assumed to affect only horizontal shear in bending
section, from nominal 2 to 4 in. thick and 2 or more in. wide,
members. These strength ratios were derived, as for knots, by
graded primarily for strength in bending edgewise or flatwise,
assuming that a critical cross section is reduced by the amount
but also frequently used where tensile or compressive strength
of the shake, or by an equivalent split or check.
is important. Dimension lumber covers many sizes and end
4.1.4 Strength ratios associated with knots in compression
uses. Lumber graded for specific end uses may dictate a special
members have been derived as the ratio of load-carrying
emphasis in grading and require an identifying grade name.
capacity of a member with cross section reduced by the largest
knot to the load-carrying capacity of the member without
NOTE 1—For example, in North American grading under the American
Lumber Standards Committee, stress graded dimension lumber categories
defect. No assumption of combined compression and bending
that reflect end use include Light Framing, Structural Light Framing,
is made.
Structural Joists and Planks, and Studs.
4.1.5 Tensile strength of lumber has been related to bending
strength and bending strength ratio from experimental results
3.3.1.2 Beams and Stringers—Pieces of rectangular cross
(4).
section, 5 in. nominal and thicker, nominal width more than 2
in. greater than nominal thickness, graded for strength in 4.1.6 Strength in compression perpendicular to grain is little
affected in lumber by strength-reducing characteristics, and
bending when loaded on the narrow face.
strength ratios of 100 % are assumed for all grades.
3.3.1.3 Posts and Timbers—Pieces of square or nearly
square cross section, 5 by 5 in., nominal dimensions and larger, 4.1.7 Modulus of elasticity of a piece of lumber is known to
be only approximately related to bending strength ratio. In this
nominal width not more than 2 in. greater than nominal
thickness, graded primarily for use as posts or columns. standard, the relationship between full-span, edgewise bending
modulus of elasticity and strength ratio was obtained experi-
3.3.1.4 Stress-Rated Boards—Lumber less than 2 in. nomi-
nal in thickness and 2 in. or wider nominal width, graded mentally.
primarily for mechanical properties. 4.1.8 In developing a stress-grade rule, economy may be
served by specifying strength ratios such that the allowable
3.3.2 The assignment of names indicating the uses for the
various classes of stress-graded lumber does not preclude their stresses for shear and for extreme fiber in bending will be in
balance, under the loading for which the members are de-
use for other purposes. For example, posts and timbers may
give service as beams. The principles of stress grading permit signed.
the assignment of any kind of allowable properties to any of the 4.1.9 A strength ratio can also be associated with specific
classes of stress-graded lumber, whether graded primarily for gravity. Three selection classes called dense, close grain, and
that property or not. Recommendations for allowable proper- medium grain are described herein, based on experimental
ties may include all properties for all grades or use classes. findings (5).
While such universal application may result in loss of effi-
4.2 Strength Ratios:
ciency in some particulars, it offers the advantage of a more
4.2.1 Table 1 gives strength ratios, corresponding to various
simple system of grades of stress-graded lumber.
slopes of grain for stress in bending and compression parallel
3.4 Essential Elements in a Stress-Grade Description:
to grain.
3.4.1 A stress grade formulated by this practice contains the
4.2.2 Strength ratios for various combinations of size and
following essential elements: location of knot and width of face are given in Table 2, Table
3.4.2 A grade name that identifies the use-class as described 3, and Table 4. Since interpolation is often required in the
in 3.3. development of grading rules, the use of formulas in Table 2,
3.4.3 A description of permissible growth characteristics Table 3 and Table 4 is acceptable. These formulas are found in
that affect mechanical properties. Characteristics that do not the Appendix.
affect mechanical properties may also be included. 4.2.2.1 Use of the tables is illustrated by the following
1 1
3.4.4 One or more allowable properties for the grade related example: The sizes of knots permitted in a 7 ⁄2 by 15 ⁄2-in. (190
to its strength ratio. by 394-mm) (actual) beam in a grade having a strength ratio of
D 245
TABLE 1 Strength Ratios Corresponding to Various Slopes of
angle between the direction of the fibers and the edge of the
Grain
piece. The angle is expressed as a slope. For instance, a slope
Maximum Strength Ratio, %
of grain of 1 in 15 means that the grain deviates 1 in. (2.5 mm)
Bending or Compression
from the edge in 15 in. (381 mm) of length.
Slope of Grain
Tension Parallel Parallel
5.2.2 When both diagonal and spiral grain are present, the
to Grain to Grain
combined slope of grain is taken as the effective slope.
1in6 40 56
5.2.3 Slope of grain is measured and limited at the zone in
1in8 53 66
1in10 61 74 the length of a structural timber that shows the greatest slope.
1in12 69 82
It shall be measured over a distance sufficiently great to define
1in14 74 87
the general slope, disregarding such short local deviations as
1in15 76 100
1in16 80 .
those around knots except as indicated in 5.2.5.
1in18 85 .
5.2.4 In 1-in. nominal boards (See Terminology D 9), or
1 in 20 100 .
similar small sizes of lumber, a general slope of grain any-
where in the length shall not pass completely through the
thickness of the piece in a longitudinal distance in inches less
70 % in bending are desired. The smallest ratio in the column
than the number expressing the specified permissible slope.
fora7 ⁄2-in. (190-mm) face in Table 2 that equals or exceeds
Where such a slope varies across the width of the board, its
70 % is opposite 2 ⁄8 in. (54 mm) in the size-of-knot column. A
average may be taken.
similar ratio in the column for 15 ⁄2-in. (394-mm) face in Table
5.2.5 Local deviations must be considered in small sizes,
3 is opposite 4 ⁄4in. (108 mm). Hence, the permissible sizes are
and if a local deviation occurs in a piece less than 4 in. nominal
1 1
2 ⁄8 in. (54 mm) on the 7 ⁄2-in. (190-mm) face and at the edge
in width or on the narrow face of a piece less than 2 in. nominal
of the wide face (see 5.3.5.2) and 4 ⁄4 in. (108 mm) on the
in thickness, and is not associated with a permissible knot in
centerline of the 15 ⁄2-in. (394-mm) face.
the piece, the measurement of slope shall include the local
4.2.3 For all lumber thicknesses, a strength ratio of 50 %
deviation.
shall be used for all sizes of shakes, checks and splits. A 50 %
5.3 Knots:
strength ratio is the maximum effect a shake, check or split can
5.3.1 A knot cluster is treated as an individual knot. Two or
have on the load-carrying capacity of a bending member.
more knots closely spaced, with the fibers deflected around
Limitations in grading rules placed on the characteristics at
each knot individually, are not a cluster.
time of manufacture are for appearance and general utility
5.3.2 Holes associated with knots are measured and limited
purposes, and these characteristics shall not be used as a basis
in the same way as knots.
for increasing lumber shear design values.
5.3.3 A knot on the wide face of a bending or tension
NOTE 2—The factor of 0.5 (50 %) is not strictly a “strength ratio” for
member is considered to be at the edge of the wide face if the
horizontal shear, since the factor represents more than just the effects of
center of the knot lies within two thirds of the knot diameter
shakes, checks and splits. The factor also includes differences between test
from the edge.
values obtained in Methods D 143 shear block tests and full-size
5.3.4 Knots in Dimension Lumber:
solid-sawn beam shear tests. The strength ratio
...
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