ASTM D245-06(2019)

Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber

SIGNIFICANCE AND USE
3.1 Need for Lumber Grading:  
3.1.1 Individual pieces of lumber, as they come from the saw, represent a wide range in quality and appearance with respect to freedom from knots, cross grain, shakes, and other characteristics. Such random pieces likewise represent a wide range in strength, utility, serviceability, and value. One of the obvious requirements for the orderly marketing of lumber is the establishment of grades that permit the procurement of any required quality of lumber in any desired quantity. Maximum economy of material is obtained when the range of quality-determining characteristics in a grade is limited and all pieces are utilized to their full potential. Many of the grades are established on the basis of appearance and physical characteristics of the piece, but without regard for mechanical properties. Other grades, called structural or stress grades, are established on the basis of features that relate to mechanical properties. The latter designate near-minimum strength and near-average stiffness properties on which to base structural design.  
3.1.2 The development of this practice is based on extensive research covering tests of small clear specimens and of full-sized structural members. Detailed studies have included the strength and variability of clear wood, and the effect on strength from various factors such as density, knots (See Terminology D9), and other defects, seasoning, duration of stress, and temperature.  
3.2 How Visual Grading is Accomplished—Visual grading is accomplished from an examination of all four faces and the 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 evaluation of any piece of stress-graded lumber in terms of a strength ratio for each property being evaluated. The strength ratio of stress-graded lumber is the hypothet...
SCOPE
1.1 This practice (1,2)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:    
Section  
Scope  
1  
Significance and Use  
3  
Basic Principles of Strength Ratios  
4  
Estimation and Limitation of Growth Characteristics  
5  
Allowable Properties for Timber Design  
6  
Modification of Allowable Properties for Design Use  
7  
Example of Stress-Grade Development  
8  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 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

• Status: Historical
• Publication Date: 30-Sep-2019
• ICS: 79.040 - Wood, sawlogs and sawn timber
• Technical Committee: D07 - Wood
• Drafting Committee: D07.02 - Lumber and Engineered Wood Products

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: D245 − 06 (Reapproved 2019)
Standard Practice for
Establishing Structural Grades and Related Allowable
Properties for Visually Graded Lumber
This standard is issued under the fixed designation D245; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope ization established in the Decision on Principles for the
2 Development of International Standards, Guides and Recom-
1.1 This practice (1,2) covers the basic principles for
mendations issued by the World Trade Organization Technical
establishing related unit stresses and stiffness values for design
Barriers to Trade (TBT) Committee.
with visually-graded solid sawn structural lumber. This prac-
tice starts with property values from clear wood specimens and
2. Referenced Documents
includes necessary procedures for the formulation of structural
2.1 ASTM Standards:
grades of any desired strength ratio.
D9 Terminology Relating to Wood and Wood-Based Prod-
1.2 The grading provisions used as illustrations herein are
ucts
not intended to establish grades for purchase, but rather to
D143 Test Methods for Small Clear Specimens of Timber
show how stress-grading principles are applied. Detailed grad-
D2555 PracticeforEstablishingClearWoodStrengthValues
ing rules for commercial stress grades which serve as purchase
E105 Practice for Probability Sampling of Materials
specifications are established and published by agencies which
IEEE/ASTM SI-10 Practice for Use of the International
formulate and maintain such rules and operate inspection
System of Units (SI) (the Modernized Metric System)
facilities covering the various species.
3. Significance and Use
1.3 The material covered in this practice appears in the
following order: 3.1 Need for Lumber Grading:
3.1.1 Individual pieces of lumber, as they come from the
Section
Scope 1
saw, represent a wide range in quality and appearance with
Significance and Use 3
respect to freedom from knots, cross grain, shakes, and other
Basic Principles of Strength Ratios 4
characteristics. Such random pieces likewise represent a wide
Estimation and Limitation of Growth Characteristics 5
Allowable Properties for Timber Design 6
range in strength, utility, serviceability, and value. One of the
Modification of Allowable Properties for Design Use 7
obvious requirements for the orderly marketing of lumber is
Example of Stress-Grade Development 8
the establishment of grades that permit the procurement of any
1.4 The values given in parentheses are provided for infor-
required quality of lumber in any desired quantity. Maximum
mation purposes only.
economy of material is obtained when the range of quality-
1.5 This standard does not purport to address all of the
determining characteristics in a grade is limited and all pieces
safety concerns, if any, associated with its use. It is the
are utilized to their full potential. Many of the grades are
responsibility of the user of this standard to establish appro-
established on the basis of appearance and physical character-
priate safety, health, and environmental practices and deter-
istics of the piece, but without regard for mechanical proper-
mine the applicability of regulatory limitations prior to use.
ties. Other grades, called structural or stress grades, are
1.6 This international standard was developed in accor-
established on the basis of features that relate to mechanical
dance with internationally recognized principles on standard-
properties. The latter designate near-minimum strength and
near-average stiffness properties on which to base structural
design.
3.1.2 Thedevelopmentofthispracticeisbasedonextensive
This practice is under the jurisdiction of ASTM Committee D07 on Wood and
is the direct responsibility of Subcommittee D07.02 on Lumber and Engineered
research covering tests of small clear specimens and of
Wood Products.
Current edition approved Oct. 1, 2019. Published November 2019. Originally
approved in 1926. Last previous edition approved in 2011 as D245–06(2011). DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D0245-06R19. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
The boldface numbers in parentheses refer to references at the end of this Standards volume information, refer to the standard’s Document Summary page on
practice. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D245 − 06 (2019)
full-sized structural members. Detailed studies have included ties may include all properties for all grades or use classes.
the strength and variability of clear wood, and the effect on While such universal application may result in loss of effi-
strength from various factors such as density, knots (See ciency in some particulars, it offers the advantage of a more
Terminology D9), and other defects, seasoning, duration of simple system of grades of stress-graded lumber.
stress, and temperature.
3.4 Essential Elements in a Stress-Grade Description:
3.2 How Visual Grading is Accomplished— Visual grading
3.4.1 Astress grade formulated by this practice contains the
is accomplished from an examination of all four faces and the
following essential elements:
ends of the piece, in which the location as well as the size and
3.4.2 Agrade name that identifies the use-class as described
natureoftheknotsandotherfeaturesappearingonthesurfaces
in 3.3.
are evaluated over the entire length. Basic principles of
3.4.3 A description of permissible growth characteristics
structural grading have been established that permit the evalu-
that affect mechanical properties. Characteristics that do not
ation of any piece of stress-graded lumber in terms of a
affect mechanical properties may also be included.
strength ratio for each property being evaluated. The strength
3.4.4 One or more allowable properties for the grade related
ratio of stress-graded lumber is the hypothetical ratio of the
to its strength ratio.
strength property being considered compared to that for the
material with no strength-reducing characteristic. Thus a piece
4. Basic Principles of Strength Ratios
of stress-graded lumber with a strength ratio of 75 % in
bending would be expected to have 75 % of the bending
4.1 General Considerations:
strength of the clear piece. In effect, the strength ratio system
4.1.1 Strength ratios associated with knots in bending mem-
of visual structural grading is thus designed to permit practi-
bers have been derived as the ratio of moment-carrying
cally unlimited choice in establishing grades of any desired
capacity of a member with cross section reduced by the largest
quality to best meet production and utilization requirements.
knot to the moment-carrying capacity of the member without
defect.This gives the anticipated reduction in bending strength
3.3 Classification of Stress-Graded Lumber:
due to the knot. For simplicity, all knots on the wide face are
3.3.1 The various factors affecting strength, such as knots,
treated as being either knots along the edge of the piece (edge
deviations of grain, shakes, and checks, differ in their effect,
knots) or knots along the centerline of the piece (centerline
depending on the kind of loading and stress to which the piece
knots).
is subjected. Stress-graded lumber is often classified according
4.1.2 Strength ratios associated with slope of grain in
to its size and use. Four classes are widely used, as follows:
bending members, and in members subjected to compression
3.3.1.1 Dimension Lumber—Pieces of rectangular cross
parallel to grain, were obtained, experimentally (3).
section, from nominal 2 to 4 in. thick and 2 or more in. wide,
graded primarily for strength in bending edgewise or flatwise, 4.1.3 Strength ratios associated with shakes, checks, and
splits are assumed to affect only horizontal shear in bending
but also frequently used where tensile or compressive strength
is important. Dimension lumber covers many sizes and end members. These strength ratios were derived, as for knots, by
assuming that a critical cross section is reduced by the amount
uses.Lumbergradedforspecificendusesmaydictateaspecial
emphasis in grading and require an identifying grade name. of the shake, or by an equivalent split or check.
4.1.4 Strength ratios associated with knots in compression
NOTE 1—For example, in NorthAmerican grading under theAmerican
members have been derived as the ratio of load-carrying
Lumber Standards Committee, stress graded dimension lumber categories
capacity of a member with cross section reduced by the largest
that reflect end use include Light Framing, Structural Light Framing,
Structural Joists and Planks, and Studs.
knot to the load-carrying capacity of the member without
defect. No assumption of combined compression and bending
3.3.1.2 Beams and Stringers—Pieces of rectangular cross
is made.
section, 5 in. nominal and thicker, nominal width more than 2
4.1.5 Tensile strength of lumber has been related to bending
in. greater than nominal thickness, graded for strength in
strength and bending strength ratio from experimental results
bending when loaded on the narrow face.
(4).
3.3.1.3 Posts and Timbers—Pieces of square or nearly
4.1.6 Strength in compression perpendicular to grain is little
squarecrosssection,5by5in.,nominaldimensionsandlarger,
affected in lumber by strength-reducing characteristics, and
nominal width not more than 2 in. greater than nominal
strength ratios of 100 % are assumed for all grades.
thickness, graded primarily for use as posts or columns.
4.1.7 Modulus of elasticity of a piece of lumber is known to
3.3.1.4 Stress-Rated Boards—Lumber less than 2 in. nomi-
nal in thickness and 2 in. or wider nominal width, graded be only approximately related to bending strength ratio. In this
primarily for mechanical properties. standard, the relationship between full-span, edgewise bending
modulus of elasticity and strength ratio was obtained experi-
3.3.2 The assignment of names indicating the uses for the
mentally.
various classes of stress-graded lumber does not preclude their
use for other purposes. For example, posts and timbers may 4.1.8 In developing a stress-grade rule, economy may be
give service as beams. The principles of stress grading permit served by specifying strength ratios such that the allowable
theassignmentofanykindofallowablepropertiestoanyofthe stresses for shear and for extreme fiber in bending will be in
classes of stress-graded lumber, whether graded primarily for balance, under the loading for which the members are de-
that property or not. Recommendations for allowable proper- signed.
D245 − 06 (2019)
4.1.9 A strength ratio can also be associated with specific 4.2.5 Strength ratios in tension parallel to grain are 55 % of
gravity. Three selection classes called dense, close grain, and the corresponding bending strength ratios.
medium grain are described herein, based on experimental 4.2.6 Table 6 gives strength ratios and quality factors for the
findings (5). special specific gravity classes described in 4.1.9.
4.2 Strength Ratios:
5. Estimation and Limitation of Growth Characteristics
4.2.1 Table 1 gives strength ratios, corresponding to various
5.1 General Quality of Lumber:
slopes of grain for stress in bending and compression parallel
5.1.1 All lumber should be well manufactured.
to grain.
5.1.2 Only sound wood, free from any form of decay, shall
4.2.2 Strength ratios for various combinations of size and
be permitted, unless otherwise specified. Unsound knots and
location of knot and width of face are given in Table 2, Table
limited amounts of decay in its early stages are permitted in
3, and Table 4. Since interpolation is often required in the
some of the lower stress-rated grades of lumber intended for
development of grading rules, the use of formulas in Table 2,
light frame construction.
Table 3 and Table 4 is acceptable. These formulas are found in
5.1.3 In stress-grading, all four faces and the ends shall be
the Appendix.
considered.
4.2.2.1 Use of the tables is illustrated by the following
1 1
example:Thesizesofknotspermittedina7 ⁄2by15 ⁄2-in.(190
5.2 Slope of Grain:
by 394-mm) (actual) beam in a grade having a strength ratio of
5.2.1 Slope of grain resulting from either diagonal sawing
70 % in bending are desired. The smallest ratio in the column
or from spiral or twisted grain in the tree is measured by the
fora7 ⁄2-in. (190-mm) face in Table 2 that equals or exceeds
angle between the direction of the fibers and the edge of the
70 % is opposite 2 ⁄8 in. (54 mm) in the size-of-knot column.A
piece. The angle is expressed as a slope. For instance, a slope
similar ratio in the column for 15 ⁄2-in. (394-mm) face in Table
of grain of 1 in 15 means that the grain deviates 1 in. (2.5 mm)
3isopposite4 ⁄4in.(108mm).Hence,thepermissiblesizesare
from the edge in 15 in. (381 mm) of length.
1 1
2 ⁄8 in. (54 mm) on the 7 ⁄2-in. (190-mm) face and at the edge
5.2.2 When both diagonal and spiral grain are present, the
of the wide face (see 5.3.5.2) and 4 ⁄4 in. (108 mm) on the
combined slope of grain is taken as the effective slope.
centerline of the 15 ⁄2-in. (394-mm) face.
5.2.3 Slope of grain is measured and limited at the zone in
4.2.3 For all lumber thicknesses, a strength ratio of 50 %
the length of a structural timber that shows the greatest slope.
shall be used for all sizes of shakes, checks and splits. A50 %
It shall be measured over a distance sufficiently great to define
strength ratio is the maximum effect a shake, check or split can
the general slope, disregarding such short local deviations as
have on the load-carrying capacity of a bending member.
those around knots except as indicated in 5.2.5.
Limitations in grading rules placed on the characteristics at
5.2.4 In 1-in. nominal boards (See Terminology D9), or
time of manufacture are for appearance and general utility
similar small sizes of lumber, a general slope of grain any-
purposes, and these characteristics shall not be used as a basis
where in the length shall not pass completely through the
for increasing lumber shear design values.
thickness of the piece in a longitudinal distance in inches less
than the number expressing the specified permissible slope.
NOTE 2—The factor of 0.5 (50 %) is not strictly a “strength ratio” for
Where such a slope varies across the width of the boa
...

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. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D245 − 06 (Reapproved 2011) D245 − 06 (Reapproved 2019)
Standard Practice for
Establishing Structural Grades and Related Allowable
Properties for Visually Graded Lumber
This standard is issued under the fixed designation D245; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. 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:
Section
Scope 1
Significance and Use 3
Basic Principles of Strength Ratios 4
Estimation and Limitation of Growth Characteristics 5
Allowable Properties for Timber Design 6
Modification of Allowable Properties for Design Use 7
Example of Stress-Grade Development 8
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
D9 Terminology Relating to Wood and Wood-Based Products
D143 Test Methods for Small Clear Specimens of Timber
D2555 Practice for Establishing Clear Wood Strength Values
E105 Practice for Probability Sampling of Materials
IEEE/ASTM SI-10 Practice for Use of the International System of Units (SI) (the Modernized Metric System)
3. Significance and Use
3.1 Need for Lumber Grading:
This practice is under the jurisdiction of ASTM Committee D07 on Wood and is the direct responsibility of Subcommittee D07.02 on Lumber and Engineered Wood
Products.
Current edition approved Oct. 1, 2011Oct. 1, 2019. Published October 2011November 2019. Originally approved in 1926. Last previous edition approved in 20062011
as D245 – 06.D245–06(2011). DOI: 10.1520/D0245-06R11.10.1520/D0245-06R19.
The boldface numbers in parentheses refer to references at the end of this practice.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D245 − 06 (2019)
3.1.1 Individual pieces of lumber, as they come from the saw, represent a wide range in quality and appearance with respect
to freedom from knots, cross grain, shakes, and other characteristics. Such random pieces likewise represent a wide range in
strength, utility, serviceability, and value. One of the obvious requirements for the orderly marketing of lumber is the establishment
of grades that permit the procurement of any required quality of lumber in any desired quantity. Maximum economy of material
is obtained when the range of quality-determining characteristics in a grade is limited and all pieces are utilized to their full
potential. Many of the grades are established on the basis of appearance and physical characteristics of the piece, but without regard
for mechanical properties. Other grades, called structural or stress grades, are established on the basis of features that relate to
mechanical properties. The latter designate near-minimum strength and near-average stiffness properties on which to base
structural design.
3.1.2 The development of this practice is based on extensive research covering tests of small clear specimens and of full-sized
structural members. Detailed studies have included the strength and variability of clear wood, and the effect on strength from
various factors such as density, knots (See Terminology D9), and other defects, seasoning, duration of stress, and temperature.
3.2 How Visual Grading is Accomplished— Visual grading is accomplished from an examination of all four faces and the 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 evaluation of any piece
of stress-graded lumber in terms of a strength ratio for each property being evaluated. The strength ratio of stress-graded lumber
is the hypothetical ratio of the strength property being considered compared to that for the material with no strength-reducing
characteristic. Thus a piece of stress-graded lumber with a strength ratio of 75 % in bending would be expected to have 75 % of
the bending strength of the clear piece. In effect, the strength ratio system of visual structural grading is thus designed to permit
practically unlimited choice in establishing grades of any desired quality to best meet production and utilization requirements.
3.3 Classification of Stress-Graded Lumber:
3.3.1 The various factors affecting strength, such as knots, deviations of grain, shakes, and checks, differ in their effect,
depending on the kind of loading and stress to which the piece is subjected. Stress-graded lumber is often classified according to
its size and use. Four classes are widely used, as follows:
3.3.1.1 Dimension Lumber—Pieces of rectangular cross section, from nominal 2 to 4 in. thick and 2 or more in. wide, graded
primarily for strength in bending edgewise or flatwise, but also frequently used where tensile or compressive strength is important.
Dimension lumber covers many sizes and end uses. Lumber graded for specific end uses may dictate a special emphasis in grading
and require an identifying grade name.
NOTE 1—For example, in North American grading under the American Lumber Standards Committee, stress graded dimension lumber categories that
reflect end use include Light Framing, Structural Light Framing, Structural Joists and Planks, and Studs.
3.3.1.2 Beams and Stringers—Pieces of rectangular cross section, 5 in. nominal and thicker, nominal width more than 2 in.
greater than nominal thickness, graded for strength in bending when loaded on the narrow face.
3.3.1.3 Posts and Timbers—Pieces of square or nearly square cross section, 5 by 5 in., nominal dimensions and larger, nominal
width not more than 2 in. greater than nominal thickness, graded primarily for use as posts or columns.
3.3.1.4 Stress-Rated Boards—Lumber less than 2 in. nominal in thickness and 2 in. or wider nominal width, graded primarily
for mechanical properties.
3.3.2 The assignment of names indicating the uses for the various classes of stress-graded lumber does not preclude their use
for other purposes. For example, posts and timbers may give service as beams. The principles of stress grading permit the
assignment of any kind of allowable properties to any of the classes of stress-graded lumber, whether graded primarily for that
property or not. Recommendations for allowable properties may include all properties for all grades or use classes. While such
universal application may result in loss of efficiency in some particulars, it offers the advantage of a more simple system of grades
of stress-graded lumber.
3.4 Essential Elements in a Stress-Grade Description:
3.4.1 A stress grade formulated by this practice contains the following essential elements:
3.4.2 A grade name that identifies the use-class as described in 3.3.
3.4.3 A description of permissible growth characteristics that affect mechanical properties. Characteristics that do not affect
mechanical properties may also be included.
3.4.4 One or more allowable properties for the grade related to its strength ratio.
4. Basic Principles of Strength Ratios
4.1 General Considerations:
4.1.1 Strength ratios associated with knots in bending members have been derived as the ratio of moment-carrying capacity of
a member with cross section reduced by the largest knot to the moment-carrying capacity of the member without defect. This gives
the anticipated reduction in bending strength due to the knot. For simplicity, all knots on the wide face are treated as being either
knots along the edge of the piece (edge knots) or knots along the centerline of the piece (centerline knots).
4.1.2 Strength ratios associated with slope of grain in bending members, and in members subjected to compression parallel to
grain, were obtained, experimentally (3).
D245 − 06 (2019)
4.1.3 Strength ratios associated with shakes, checks, and splits are assumed to affect only horizontal shear in bending members.
These strength ratios were derived, as for knots, by assuming that a critical cross section is reduced by the amount of the shake,
or by an equivalent split or check.
4.1.4 Strength ratios associated with knots in compression members have been derived as the ratio of load-carrying capacity of
a member with cross section reduced by the largest knot to the load-carrying capacity of the member without defect. No assumption
of combined compression and bending is made.
4.1.5 Tensile strength of lumber has been related to bending strength and bending strength ratio from experimental results (4).
4.1.6 Strength in compression perpendicular to grain is little affected in lumber by strength-reducing characteristics, and
strength ratios of 100 % are assumed for all grades.
4.1.7 Modulus of elasticity of a piece of lumber is known to be only approximately related to bending strength ratio. In this
standard, the relationship between full-span, edgewise bending modulus of elasticity and strength ratio was obtained
experimentally.
4.1.8 In developing a stress-grade rule, economy may be served by specifying strength ratios such that the allowable stresses
for shear and for extreme fiber in bending will be in balance, under the loading for which the members are designed.
4.1.9 A strength ratio can also be associated with specific gravity. Three selection classes called dense, close grain, and medium
grain are described herein, based on experimental findings (5).
4.2 Strength Ratios:
4.2.1 Table 1 gives strength ratios, corresponding to various slopes of grain for stress in bending and compression parallel to
grain.
4.2.2 Strength ratios for various combinations of size and location of knot and width of face are given in Table 2, Table 3, and
Table 4. Since interpolation is often required in the development of grading rules, the use of formulas in Table 2, Table 3 and Table
4 is acceptable. These formulas are found in the Appendix.
1 1
4.2.2.1 Use of the tables is illustrated by the following example: The sizes of knots permitted in a 7 ⁄2 by 15 ⁄2-in. (190 by
394-mm) (actual) beam in a grade having a strength ratio of 70 % in bending are desired. The smallest ratio in the column for a
1 1
7 ⁄2-in. (190-mm) face in Table 2 that equals or exceeds 70 % is opposite 2 ⁄8 in. (54 mm) in the size-of-knot column. A similar
1 1 1
ratio in the column for 15 ⁄2-in. (394-mm) face in Table 3 is opposite 4 ⁄4 in. (108 mm). Hence, the permissible sizes are 2 ⁄8 in.
1 1
(54 mm) on the 7 ⁄2-in. (190-mm) face and at the edge of the wide face (see 5.3.5.2) and 4 ⁄4 in. (108 mm) on the centerline of
the 15 ⁄2-in. (394-mm) face.
4.2.3 For all lumber thicknesses, a strength ratio of 50 % shall be used for all sizes of shakes, checks and splits. A50 % strength
ratio is the maximum effect a shake, check or split can have on the load-carrying capacity of a bending member. Limitations in
grading rules placed on the characteristics at time of manufacture are for appearance and general utility purposes, and these
characteristics shall not be used as a basis for increasing lumber shear design values.
NOTE 2—The factor of 0.5 (50 %) is not strictly a “strength ratio” for horizontal shear, since the factor represents more than just the effects of shakes,
checks and splits. The factor also includes differences between test values obtained in Methods D143 shear block tests and full-size solid-sawn beam shear
tests. The strength ratio terminology is retained for compatibility with prior versions of Practice D143, but prior provisions permitting design increases
for members with lesser-size cracks have been deleted since the factor is related to more than shakes, checks and splits.
4.2.4 Modulus of elasticity is modified by a quality factor that is related to bending strength ratio, as given in Table 5.
4.2.5 Strength ratios in tension parallel to grain are 55 % of the corresponding bending strength ratios.
4.2.6 Table 6 gives strength ratios and quality factors for the special specific gravity classes described in 4.1.9.
5. Estimation and Limitation of Growth Characteristics
5.1 General Quality of Lumber:
5.1.1 All lumber should be well manufactured.
TABLE 1 Strength Ratios Corresponding to Various Slopes of
Grain
Maximum Strength Ratio, %
Bending or Compression
Slope of Grain
Tension Parallel Parallel
to Grain to Grain
1 in 6 40 56
1 in 8 53 66
1 in 10 61 74
1 in 12 69 82
1 in 14 74 87
1 in 15 76 100
1 in 16 80 .
1 in 18 85 .
1 in 20 100 .
D245 − 06 (2019)
TABLE 2 Strength Ratios Corresponding to
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