ASTM D1990-19

Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens

SIGNIFICANCE AND USE
4.1 The procedures described in this practice are intended to be used to establish allowable stress and modulus of elasticity values for solid sawn, visually graded dimension lumber from In-Grade type test data. These procedures apply to the tested and untested sizes and grades when an adequate data matrix of sizes and grades exists. In addition, the methodology for establishing allowable stress and modulus of elasticity values for combinations of species and species groups is covered. Allowable stress and modulus of elasticity values may also be developed for a single size or a single grade of lumber from test data.  
4.2 Methods for establishing allowable stress and modulus of elasticity values for a single size/grade test cell are covered in Practice D2915. The appropriateness of these methods to establish allowable stress and modulus of elasticity values is directly dependent upon the quality and representativeness of the input test data.  
4.3 A monitoring program shall be established to periodically review the continued applicability of allowable properties derived by this practice. A monitoring program will establish data sets that are either the same as, above, or below the data that was used to develop the current allowable properties. Upon detection of a statistically significant downward shift, evaluation of the data and confirmation of remedial actions shall be undertaken. When evaluation is not undertaken or the results of the evaluation indicate an adjustment to allowable properties is appropriate, a reassessment shall be conducted to re-establish allowable properties.  
Note 5: It is recognized that over time there is the potential for changes in the raw material or product mix. In response to this a monitoring program must be conducted to ensure design values derived by this practice are not invalidated by such changes. If the data collected with a monitoring provides evidence of an statistically significant downward shift in lumber properties an ...
SCOPE
1.1 This practice covers the principles and procedures for establishing allowable stress values for bending, tension parallel to grain, compression parallel to grain and modulus of elasticity values for structural design from “In-Grade” tests of full-size visually graded solid sawn dimension lumber. This practice also covers procedures for periodic monitoring, and additional procedures, if needed, for evaluation and possible reassessment of assigned design values. This practice is focused on, but is not limited to, grades which used the concepts incorporated in Practice D245 and were developed and interpreted under American Softwood Lumber PS 20.  
1.2 A basic assumption of the procedures used in this practice is that the samples selected and tested are representative of the entire global population being evaluated. This approach is consistent with the historical clear wood methodology of assigning an allowable property to visually-graded lumber which was representative of the entire growth range of a species or species group. Every effort shall be made to ensure the test sample is representative of population by grade and size (see 7.1.1 and 7.1.2).  
1.3 Due to the number of specimens involved and the number of mechanical properties to be evaluated, a methodology for evaluating the data and assigning allowable properties to both tested and untested grade/size cells is necessary. Sampling and analysis of tested cells are covered in Practice D2915. The mechanical test methods are covered in Test Methods D198 and D4761. This practice covers the necessary procedures for assigning allowable stress and modulus of elasticity values to dimension lumber from In-Grade tests. The practice includes methods to permit assignment of allowable stress and modulus of elasticity values to untested sizes and grades, as well as some untested properties. The practice includes procedures for periodic monitoring of the species or species gr...

General Information

• Status: Published
• 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

Relations

• Replaces: ASTM D1990-16 - Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens
• Effective Date: 01-Oct-2019
• Refers: ASTM D2555-17a(2024) - Standard Practice for Establishing Clear Wood Strength Values
• Effective Date: 01-Feb-2024
• Refers: ASTM D2555-17a(2024)e1 - Standard Practice for Establishing Clear Wood Strength Values
• Effective Date: 01-Feb-2024
• Refers: ASTM D4442-20 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• Effective Date: 01-Mar-2020
• Refers: ASTM D4761-19 - Standard Test Methods for Mechanical Properties of Lumber and Wood-Based Structural Materials
• Effective Date: 01-Apr-2019
• Refers: ASTM D4761-18 - Standard Test Methods for Mechanical Properties of Lumber and Wood-Based Structural Materials
• Effective Date: 01-Nov-2018
• Refers: ASTM D4444-13(2018) - Standard Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
• Effective Date: 01-Jul-2018
• Refers: ASTM D2555-17a - Standard Practice for Establishing Clear Wood Strength Values
• Effective Date: 01-Aug-2017
• Refers: ASTM D2555-17 - Standard Practice for Establishing Clear Wood Strength Values
• Effective Date: 15-Apr-2017
• Refers: ASTM D4442-16 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• Effective Date: 15-Nov-2016
• Refers: ASTM D2555-16 - Standard Practice for Establishing Clear Wood Strength Values
• Effective Date: 01-Aug-2016
• Refers: ASTM D2555-15 - Standard Practice for Establishing Clear Wood Strength Values
• Effective Date: 01-Sep-2015
• Refers: ASTM D4442-15 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• Effective Date: 01-Jun-2015
• Refers: ASTM D198-14 - Standard Test Methods of Static Tests of Lumber in Structural Sizes
• Effective Date: 01-Feb-2014
• Refers: ASTM D198-14e1 - Standard Test Methods of Static Tests of Lumber in Structural Sizes
• Effective Date: 01-Feb-2014

Overview

ASTM D1990-19: Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens guides the process for determining structural design values for dimension lumber. This ASTM standard outlines the methodology for using in-grade tests on full-size, visually graded, solid sawn lumber to establish allowable stress values in bending, tension parallel to grain, compression parallel to grain, as well as modulus of elasticity (MOE) values. ASTM D1990-19 addresses both tested and untested grades and sizes, ensures periodic monitoring of these values, and provides guidance on the reassessment of design values if statistical changes in lumber properties are detected over time.

Key Topics

• Establishing Allowable Properties: The standard details procedures to calculate permissible stresses and MOE based on full-size specimen testing, ensuring values reflect representative lumber qualities for practical structural application.
• Representativeness: Emphasizes sampling techniques that ensure test specimens accurately reflect the grade and size mix of lumber across regions and species.
• Data Analysis and Adjustment: Covers the use of statistical methods and adjustment procedures to account for variables like size, moisture content, temperature, and the grade quality index (GQI).
• Monitoring and Reassessment: Requires ongoing monitoring programs to verify the continued suitability of established design values and mandates evaluation and adjustment if statistically significant shifts in lumber properties occur.
• Groupings of Species: Provides methodology for establishing combined property values for groups of species or species combinations, enhancing applicability to market realities.
• Documentation: Demands rigorous reporting and archival of test data and adjustment methods to support validation and regulatory compliance.

Applications

ASTM D1990-19 is essential for:

• Lumber Producers and Grading Agencies: Ensuring grading systems used in production are consistent and that their products meet industry expectations and regulatory standards.
• Structural Engineers and Designers: Providing a basis for calculating safe load-carrying capacities in wood-framed structures, ensuring the integrity of building designs.
• Building Code Officials and Inspectors: Supporting the validation of lumber used in code-compliant construction through standardized design values and documented procedures.
• Product Certification and Regulatory Compliance: Supporting third-party verification and documentation required for demonstrating compliance with industry and international standards.
• Research and Development: Offering foundational methodology for developing new grading approaches and for research in structural wood properties across species and production regions.
• Market Grouping: Allowing the establishment of joint design values for combined species, enabling efficient marketing and specification of lumber products.

Related Standards

The following standards are frequently referenced alongside or in support of ASTM D1990-19:

• ASTM D245 - Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber
• ASTM D2915 - Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
• ASTM D198 - Test Methods of Static Tests of Lumber in Structural Sizes
• ASTM D4761 - Test Methods for Mechanical Properties of Lumber and Wood-Based Structural Materials
• ASTM D2555 - Practice for Establishing Clear Wood Strength Values
• ASTM D4442 / D4444 - Test Methods for Moisture Content Measurement
• National Institute of Standards and Technology PS 20 - American Softwood Lumber Standard

Practical Value

By systematically establishing and periodically validating allowable mechanical properties, ASTM D1990-19 protects the built environment and supports the reliable use of visually graded dimension lumber. It is a foundational document for anyone involved in the grading, specification, engineering, manufacturing, and compliance assessment of wood structural materials, ensuring that design values for lumber remain scientifically credible, industry-accepted, and code-compliant.

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.
Designation: D1990 − 19
Standard Practice for
Establishing Allowable Properties for Visually-Graded
Dimension Lumber from In-Grade Tests of Full-Size
Specimens
This standard is issued under the fixed designation D1990; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Visual stress-grades of lumber manufactured in North America have evolved from the procedures
of Practice D245.Allowable stress and modulus of elasticity values were determined for these grades
using the procedures of Practice D245 and the appropriate clear wood values of Practice D2555. The
clear wood values of Practice D2555 were developed from tests of small clear specimens.
Development of allowable stress and modulus of elasticity values from tests of full-size structural
lumberascommerciallyproducedandmarketedhasbecomepossiblewiththedevelopmentofsuitable
test equipment that permits rapid rates of loading to test large numbers of pieces from commercial
lumber production. These tests can be carried out at the production sites or in a laboratory.
1. Scope ogy for evaluating the data and assigning allowable properties
to both tested and untested grade/size cells is necessary.
1.1 This practice covers the principles and procedures for
Sampling and analysis of tested cells are covered in Practice
establishing allowable stress values for bending, tension par-
D2915. The mechanical test methods are covered in Test
allel to grain, compression parallel to grain and modulus of
Methods D198 and D4761. This practice covers the necessary
elasticity values for structural design from “In-Grade” tests of
procedures for assigning allowable stress and modulus of
full-size visually graded solid sawn dimension lumber. This
elasticity values to dimension lumber from In-Grade tests.The
practice also covers procedures for periodic monitoring, and
practice includes methods to permit assignment of allowable
additional procedures, if needed, for evaluation and possible
stress and modulus of elasticity values to untested sizes and
reassessment of assigned design values. This practice is fo-
grades, as well as some untested properties. The practice
cused on, but is not limited to, grades which used the concepts
includes procedures for periodic monitoring of the species or
incorporated in Practice D245 and were developed and inter-
species group to quantify potential changes in the product and
preted under American Softwood Lumber PS 20.
verification of the assigned design values through, evaluation,
1.2 A basic assumption of the procedures used in this
and reassessment.
practice is that the samples selected and tested are representa-
NOTE 1—In the implementation of the North American In-Grade test
tive of the entire global population being evaluated. This
program, allowable stress values for compression perpendicular to grain
approach is consistent with the historical clear wood method-
and shear parallel to grain for structural design were calculated using the
ology of assigning an allowable property to visually-graded
procedures of Practice D245.
lumber which was representative of the entire growth range of
1.4 This practice only covers dimension lumber.
aspeciesorspeciesgroup.Everyeffortshallbemadetoensure
1.5 This standard does not purport to address all of the
the test sample is representative of population by grade and
safety concerns, if any, associated with its use. It is the
size (see 7.1.1 and 7.1.2).
responsibility of the user of this standard to establish appro-
1.3 Due to the number of specimens involved and the
priate safety, health, and environmental practices and deter-
number of mechanical properties to be evaluated, a methodol-
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
This practice is under the jurisdiction ofASTM Committee D07 on Wood and
is the direct responsibility of Subcommittee D07.02 on Lumber and Engineered
ization established in the Decision on Principles for the
Wood Products.
Development of International Standards, Guides and Recom-
Current edition approved Oct. 1, 2019. Published November 2019. Originally
mendations issued by the World Trade Organization Technical
approved in 1991. Last previous edition approved in 2016 as D1990–16. DOI:
10.1520/D1990-19. Barriers to Trade (TBT) Committee.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1990 − 19
2. Referenced Documents appropriatenessshallbedemonstrated.(SeePracticeD2915for
2 guidance on selection of distribution.)
2.1 ASTM Standards:
D9Terminology Relating to Wood and Wood-Based Prod-
NOTE 3—The described adjustment factors and allowable stress and
modulus of elasticity value assignment procedures were developed based
ucts
on test data of visual grades of major volume, commercially available
D198Test Methods of Static Tests of Lumber in Structural
NorthAmerican softwood species groups. For other species (see Nomen-
Sizes
clature D1165) and for other grading methods, it may be necessary to
D245Practice for Establishing Structural Grades and Re-
verify that the listed adjustments are applicable. The commercial species
lated Allowable Properties for Visually Graded Lumber groups and grading criteria used in the development of these procedures
wereasdescribedinthegradingrulesforDouglasFir-Larch,Hem-Firand
D1165Nomenclature of Commercial Hardwoods and Soft-
Southern Pine from the United States, and Spruce-Pine-Fir, Douglas
woods
fir(N),andHem-Fir(N)fromCanada (1, 2, 3,and 4) .Thespecificspecies
D2555PracticeforEstablishingClearWoodStrengthValues
groupings, together with botanical names are given in Nomenclature
D2915Practice for Sampling and Data-Analysis for Struc-
D1165.
tural Wood and Wood-Based Products
3.2.3 grade quality index (GQI)—A numerical assessment
D4442Test Methods for Direct Moisture Content Measure-
of the characteristics found in the sample specimens which are
ment of Wood and Wood-Based Materials
considered to be related to strength and are limited as part of
D4444Test Method for Laboratory Standardization and
the grade description. The grade quality index is a scaling
Calibration of Hand-Held Moisture Meters
parameter which allows modeling of strength and modulus of
D4761Test Methods for Mechanical Properties of Lumber
elasticity with respect to grade (Note 4).
and Wood-Based Structural Materials
NOTE 4—In the North American In-Grade test program, lumber
E380Practice for Use of the International System of Units
produced in accordance with visual stress grading rules (1, 2, 3, 4, 5, and
(SI) (the Modernized Metric System) (Withdrawn 1997)
6)developedfromtheproceduresofPracticeD245wassampled.Foreach
IEEE/ASTMSI10Standard for Use of the International
test specimen a strength ratio was calculated for the particular type of
System of Units (SI): The Modern Metric System
failure indicated by the failure code (see Test Methods D4761). Strength
ratios were calculated according to the formulas given in the appendix of
2.2 American Softwood Lumber Standard:
Practice D245 for bending test specimens. Strength ratios for lumber
National Institute of Standards and Technology Voluntary
tested in tension and compression parallel to grain were calculated as for
Product Standard PS 20-94
bending. The sample grade quality index for each sample was calculated
as the nonparametric five percentile point estimate of the distribution of
strengthratios.Specimenswhichfailedinclearwoodwereexcludedfrom
3. Terminology
the sample for determining the sample GQI.
3.1 Definitions:
3.2.4 In-Grade—samples collected from lumber grades as
3.1.1 For definitions of terms related to wood, refer to
commercially produced.
Terminology D9.
3.2.4.1 Discussion—Samples collected in this manner are
3.2 Definitions of Terms Specific to This Standard:
intended to represent the full range of strength and modulus of
3.2.1 characteristic size—the standard dimensions of the
elasticity values normally found within a grade.
piece at which the characteristic value is calculated (Note 2).
3.2.5 monitoring, n—a periodic review of a subset of
NOTE 2—In the North American In-Grade program, the characteristic
structuralpropertiesofalumbercelltodetermineifapotential
size used was 1.5 in. (38 mm) thick by 7.25 in. (184 mm) wide by 144 in.
downward shift from the assigned values indicates a need for
(3.658 m) in length at 15% moisture content.
an evaluation or reassessment, or both, of allowable properties
3.2.2 characteristic value—the population mean, median or
developed with this practice (Stage 1).
tolerance limit value estimated from the test data after it has
3.2.6 evaluation, n—Theprocessofexaminingdata,includ-
been adjusted to standardized conditions of temperature, mois-
ing that collected over the course of a monitoring program that
ture content and characteristic size.
has detected a shift in cell properties, to determine the likely
3.2.2.1 Discussion—The characteristic value is an interme-
cause for the detected shift in cell properties, developing the
diatevalueinthedevelopmentofallowablestressandmodulus
best response to the data, and establishing that the actions are
of elasticity values. Typically for structural visual grades,
sufficient (Stage 2).
standardized conditions are 73°F (23°C), and 15% moisture
content(Note3).Anonparametricestimateofthecharacteristic
3.2.6.1 Discussion—The response to the evaluation can
value is the preferred estimate. If a distributional form is used
include altering the grade description, or the input resource, or
to characterize the data at the standardized conditions, its
changing the method of processing. Testing is conducted to
confirm that the action taken corrected the affected properties.
3.2.7 reassessment, n—Therecalculationofallowableprop-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
erties derived by this practice because of a change in product
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
properties (Stage 3).
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 3.2.8 statistically significant downward shift, n—A statisti-
The last approved version of this historical standard is referenced on
cally significant downward change in the monitored size grade
www.astm.org.
AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http:// The boldface numbers in parentheses refer to the references listed at the end of
www.access.gpo.gov. this practice.
D1990 − 19
cellpropertyinrelationtoasinglecellfromthematrixusedto Upon detection of a statistically significant downward shift,
derive the current allowable property for which further action evaluation of the data and confirmation of remedial actions
is required in this Practice. shall be undertaken. When evaluation is not undertaken or the
results of the evaluation indicate an adjustment to allowable
3.2.8.1 Discussion—TheWilcoxonnonparametricstatistical
properties is appropriate, a reassessment shall be conducted to
test showing a change that is significant at the 0.05 level has
re-establish allowable properties.
been selected as the consensus statistical method for determin-
NOTE 5—It is recognized that over time there is the potential for
ing when further action is required in this Standard.
changes in the raw material or product mix. In response to this a
3.2.9 action level—Thelowerpropertyboundary,represent-
monitoringprogrammustbeconductedtoensuredesignvaluesderivedby
ing a statistically significant downward shift, used in monitor-
thispracticearenotinvalidatedbysuchchanges.Ifthedatacollectedwith
ing to define the property level at which additional confirma-
a monitoring provides evidence of an statistically significant downward
tion testing during monitoring, or further action beyond
shift in lumber properties an evaluation program in accordance with the
procedures of this practice is needed to detect and confirm that responses
monitoring is necessary.
to such changes are appropriate. Evaluation, if undertaken, provides a
3.2.10 sampling matrix—the collective designation used to
means for responding to the data and assessing if the actions taken are
describe all of the individual test cells. The sampling matrix is
sufficient. Following the confirmation of a statistically significant down-
ward shift, reassessment of values shall be conducted if evaluation is
intended to characterize the property trends for a range of
either not undertaken or does not adequately address the downward shift.
grades for a single size or a range of sizes for a single grade or
a combination of both sizes and grades for a species or species
5. Documentation of Results, Adjustments, and
group.
Development of Allowable Properties
3.2.10.1 Discussion—The sampling matrix is intended to 5.1 Reporting Test Data:
characterize the property trends for a range of grades for a
5.1.1 Summarizing Statistics:
single size or a range of sizes for a single grade or a 5.1.1.1 Provide a set of summarizing statistics that includes
combination of both sizes and grades for a species or species
sample size, mean, median, standard deviation, confidence
group. intervals, and nonparametric point estimates and tolerance
3.2.11 test cell—the combined test data for a single size/
limits. If parametric methods are used to characterize the data,
grade/species/property which is intended to characterize that provide a description of selection procedures and a tabulation
sampling unit. of distribution parameters. Document any “best fit” judgments
made in the selection of a distribution.
3.2.12 thickness—the lesser dimension perpendicular to the
5.1.1.2 Provide a description of all statistical methods used
long axis of lumber.
with the summarizing statistics.
3.2.13 tolerance limit (TL)—refers to the tolerance limit
5.1.2 Unadjusted Test Results—To permit verification of
with 95% content and 75% confidence.
property calculations by regulatory and third party reviewers,
3.2.14 width—the greater dimension perpendicular to the
unadjustedindividualspecimentestresultsshallbemaintained
long axis of lumber.
insuitableachivalform.Thearchivedrecordsshallberetained
as long as the derived property values are applicable.Archived
4. Significance and Use
records shall be retained by the user of this practice and an
4.1 Theproceduresdescribedinthispracticeareintendedto
independent public institution.
be used to establish allowable stress and modulus of elasticity
NOTE 6—In the United States, the USDA Forest Products Laboratory,
values for solid sawn, visually graded dimension lumber from
theAmericanLumberStandardsCommittee,andcollegesanduniversities
In-Grade type test data. These procedures apply to the tested
areconsideredsuitableindependentpublicinstitutions.Itmaybedesirable
and untested sizes and grades when an adequate data matrix of
for historical or other purposes to continue to archive the records after the
sizes and grades exists. In addition, the methodology for derived values are no longer applicable. In such cases, the records should
be maintained by a public institution.
establishing allowable stress and modulus of elasticity values
for combinations of species and species groups is covered.
5.1.3 Significant Digits—With example calculations, illus-
Allowable stress and modulus of elasticity values may also be trate that adequate significant digits were maintained in inter-
developedforasinglesizeorasinglegradeoflumberfromtest
mediate calculations to avoid round-off errors. Table3 and
data. Section 4 of Practice E380 provide guidance.
4.2 Methods for establishing allowable stress and modulus 5.2 Graphical Presentation—Graphical presentations are
of elasticity values for a single size/grade test cell are covered recommended to illustrate typical data sets. If parametric
in Practice D2915. The appropriateness of these methods to methods are used, histograms or cumulative distribution func-
establish allowable stress and modulus of elasticity values is tionsshallbeshownsuperimposedontheparametricfunctions.
directly dependent upon the quality and representativeness of Class widths shall meet the requirements of Practice D2915,
the input test data. Table7.
4.3 A monitoring program shall be established to periodi- 5.3 Preparation of Characteristic Values
callyreviewthecontinuedapplicabilityofallowableproperties 5.3.1 Adjustments to Test Data:
derived by this practice. A monitoring program will establish 5.3.1.1 Document each of the adjustments to the test data.
data sets that are either the same as, above, or below the data 5.3.1.2 If the adjustments to the test data follow procedures
that was used to develop the current allowable properties. found in other ASTM standards or are documented in other
D1990 − 19
samples with sample sizes of 200 or more. The use of large sample sizes
sources, reference these sources in a manner permitting the
is not sufficient by itself to assure that the sample is representative of the
reader to recreate the use of these sources in the same
population. It is often necessary to sample sub-regions (or locations) to
application. Indicate the limitations of application.
represent variability due to geography, production and growing condi-
5.3.1.3 In the presentation, explain adjustments made to the
tions; in the North American In-Grade Program, this was typically a
data which cannot be referenced to acknowledged sources.
minimum of three sub-regions, but more for the major volume species
groups. If this is not possible justification needs to be provided to
5.3.1.4 Provide examples of all adjustment procedures.
demonstrate that an alternate sampling plan adequately represents these
5.4 Development of Allowable Properties:
sources of variability.
5.4.1 Explain each step of the development of allowable
7.1.2 Grade Representativeness—The sampling shall be
properties with reference to the appropriate paragraph of this
collected in a random sampling design intended to represent
practice.
the range of strength reducing characteristics allowed by the
5.4.2 Grouping—Summarize all grouping calculations in
grade.
tabularformandexamplespresentedtoillustrateapplicationof
7.2 Grade—To adequately model grade performance, it is
limiting criteria.
necessarytosampleaminimumoftwogradesrepresentativeof
5.4.3 Allowable Property Adjustments—Illustrate each of
the range of grade quality (Note 4). Grades sampled to model
the adjustments for allowable properties for at least one of the
grade relationships shall be separated by no more than one
size/grade combinations presented. Present all adjustments in
intermediary grade and no more than one quarter of the total
tabular form. Examples may be presented.
possible range (Note 9) in assumed bending GQI.
5.5 Summary/Index—Prepare a brief summary of the pre-
NOTE 9—For the grading system sampled in the North American
sentation that highlights each of the major steps. An index or
In-Grade test program, the total possible range in strength ratio (GQI) is
tableofcontentsshallaccompanythedocumentthatreferences
0 to 100%. The strength ratio concept is described in greater detail in
the content and the corresponding paragraphs of this practice.
Practice D245.
7.3 Width—In order to adequately develop the data for
6. Development of Stress Grades
width, at least three widths per grade shall be tested, and the
6.1 Stress grades for lumber are designed to separate the
maximum difference in width between two adjacent widths
raw material source into marketable groups of specific quality
shall be 4 in. (10 cm).
levels to which allowable stress and modulus of elasticity
7.4 Minimum Full Matrix—Afullmatrixofgradesandsizes
values can be assigned. Stress grading systems used with this
shall contain a minimum of six test cells composed of at least
practice shall be internally consistent and continuous (Note 7).
twogradesandthreewidthsforeachofthegrades,meetingthe
NOTE 7—To be considered internally consistent, a grading system
restrictions of 7.2 and 7.3, to be considered adequate for the
should not be based on two or more methods of determining an allowable
developmentofafullmatrixofvalues,includinguntestedcells
property.Acontinuous system should not skip levels of material strength.
(Note 10).
For example, the North American In-Grade test program sampled grades
which were developed using the stress ratio system of Practice D245 (see
NOTE 10—The sampling matrix judged to be acceptable for the North
Refs 1, 2, 3, and 4).
American In-Grade test program for the major species groups (Note 2)
with large geographic range, consisted of six test cells with large samples
7. Minimum Sampling Matrix
(at least 360 pieces per cell). The test cells were nominal 2 by 4, 1.5 in.
by 3.5 in. (38 mm by 89 mm); nominal 2 by 8, 1.5 in. by 7.25 in. (38 mm
7.1 General Considerations—Development of allowable
by184mm);andnominal2by10,1.5in.by9.25in.(38mmby235mm)
stress and modulus of elasticity values under this practice may
dimension lumber of select structural grade (65% minimum bending
be for either a single size (7.3) or a single grade (7.2) or a full
strength ratio) and No. 2 grade (45% minimum bending strength ratio).
matrix of sizes and grades (7.4).The required sampling matrix
Samples were selected for tests of four properties (modulus of elasticity,
is determined by the desired end result. The intent of a sample
modulus of rupture, ultimate tensile stress parallel to grain, and ultimate
compressive stress parallel to grain). For complete grade descriptions, see
matrixistoprovidesufficientdataacrossthesizesorgrades,or
Refs. 1, 2, 3,or 4).Sampleswereselectedproportionaltoproductionfrom
both,topermitinterpolationbetweendatapoints.Extrapolation
the entire geographic growth and production range of each species group.
beyond the sample matrix may be misleading and therefore is
not recommended. Assignment of allowable stress values
8. Input Test Data and Adjustments to Input Test Data
beyondthesamplematrixispermittedwhenthereisadditional
8.1 Methods for sampling and analysis of matrix input test
supporting information to indicate that the assigned values are
dataarefoundinPracticeD2915.Fortesting,useTestMethods
conservative estimates.
D198 or Test Method D4761. Other standards may be em-
7.1.1 Population Representativeness—The sampling plan
ployed if demonstrated to be applicable.
shall be designed to represent the region to be sampled (see
Note 8).
8.2 Because the range of quality within any one specific
grademaybelarge,itisnecessarytoassesstheobservedgrade
NOTE 8—Consideration should be given to potential sources of vari-
qualityofthesampledmaterialinrelationtotheassignedgrade
ability in the allocation of the random sample and the design of the
sampling plan. The North American In-grade test program samples were
quality used to establish the matrix (7.2). The following
considered representative because the design of the sampling plan
procedures provide one way to make this assessment.
required sampling proportional to production in at least 3 sub regions of
8.2.1 TheobservedGQIdeterminedfromfailurecodeddata
the growing range for each of the species groups with substantial
can be used to assess whether the test cells are representative
production; this resulted in a minimum cell size of 360 pieces. Smaller
geographic regions equivalent to several U.S. states had representative of the visual grade that is the target by comparing the 5th
D1990 − 19
percentile point estimate (5th %tle PE) GQI of the test cells exceedsthegradeGQIbymorethan7pointsusingtheformula
with the assigned GQI for the target grade (Note 4). The in8.3.1.2.IftheaverageofallindividualcellGQIsinthegrade
observed GQI shall be calculated for all pieces associated with exceeds the grade GQI by more than 5 points, reduce the
knots, slope of grain, and distorted grain, or other strength property value for all specimens in each cell that exceeds the
reducing characteristics at point of failure. The calculation grade GQI by more than 5 points using the formula in 8.3.1.2.
methodology shall be documented (see X12.6) Cells adjusted, using this procedure, are assumed to be
compliant and no further grade quality adjustment is required
8.2.2 Whencalculatingstrengthratiosusingtheappendixof
Practice D245, two strength ratios shall be calculated for for the grade in question.
(2)Adjust the grade definition to support a higher grade
combination knot failures: (1) using the total combined knot
cross section in the equation for center of wide face knots, and GQI so that it is within 5 points of the observed GQI.
(2) using the largest single edge knot from the cross{section in
NOTE 12—Failure of the sample to meet these criteria could be a result
the equation for narrow face knots. The smaller of these two
of several causes, some of which may be acceptable or correctable by
calculated strength ratios shall be permitted to be used in the usinganothermethod.Itcouldbedesirabletoreassesstheappropriateness
of the GQI scale used. A proposal for replacement or augmentation of
calculation of fifth percentile point estimate of the distribution
existing data should include adequate statistical analyses and information
of strength ratios.
to determine if the new data substantiates retaining existing data,
8.2.3 Fifth percentile point estimates of the distribution of
augments existing data, or replaces existing data.
strength ratios shall be presented to decimal place, using the
8.3.1.2 Wherestructuralpropertydataofacellisrequiredto
rounding procedures of Section 6.4 in Practice E29.
be modified to adjust to standardized conditions of assigned
8.2.4 To comply with the requirements of 7.2 and 8.2 both
GQI, the data for all specimens in the cell shall be multiplied
of the following conditions (Note 11) shall be met:
by the following factor (Note 13):
(1)The average of all individual cell GQIs in one grade
Factor 5 ~assigned GQI15% points!/~observed GQI! (1)
shall not exceed the assigned grade GQI by more than 5
percentage points, and
An alternative relationship shall be permitted to be used to
(2)Each individual cell GQI shall not exceed the assigned
modify the modulus of elasticity to standardized GQI
grade GQI by more than 7 percentage points.
conditions, provided this relationship is based on documented
If both conditions are not met one of the options in 8.3 shall
evidence.An example equation for the adjustment of modulus
be followed.
of elasticity can be found in X12.5.6.
NOTE 11—GQI evaluation and adjustment is an additional procedure
NOTE 13—The GQI evaluation and adjustment is an additional proce-
overlaid on the representative sampling requirement to assure final
dure applied to the final strength property assignments to account for the
strength property assignments account for the full range of grade
maximumsizeofgradecharacteristicspermittedineachvisualgrade.The
characteristics permitted in each visual grade. The basis for these
adjustment factor is an override that can be applied without further
procedures were developed using distribution data of GQI measurements
sampling. It has been shown that application of GQI adjustment factors
ofthemajorNorthAmericanspeciesgroupsaspartoftheNorthAmerican
ranging from 0.95 to 0.89 can leave the final design values unchanged or
In-Grade Lumber Testing program. A modification of the GQI scale or
can change the final design values by 1 rounding rule.
calculation methodology may be appropriate. The GQI for a sample is
8.3.2 Temperature—Test samples at 736 5°F (23 6 3°C).
determined from defects associated with the failure of the pieces in the
sample after test loading. The determination of a GQI value depends on
When this is not possible, adjust individual test data to 73°F
the assessment and measurement of knot types, sizes, and their locations
(23°C) by an adjustment model demonstrated to be appropri-
as well as the maximum slope of grain of the piece. Sample size,
ate.
measurement variation, species variability, and methods of analysis can
8.3.3 Moisture:
significantly impact the final GQI value (See X12).
8.3.3.1 Where possible, test the samples at the moisture
8.3 Standardized Conditions:
content (15%) at which the characteristic value is to be
8.3.1 Grade Quality
determined. When this is not possible, adjust the data to 15%
8.3.1.1 If the average of all individual cell GQIs in one
moisturecontentbytheadjustmentproceduresinAnnexA1or
grade for a sample is no more than 5 percentage points above
byproceduresdocumentedasadequateforthemethodadopted
thegradeGQI,andeachindividualcellGQIforasampleisno
prior to developing the characteristic values.
morethan7percentagepointsabovethegradeGQIthatsample
8.3.3.2 Determinationofspecimenmoisturecontentshallbe
shallbeconsideredtosupporttheintentof7.2.Otherwise,itis
made in accordance with Test Methods D4442 and D4444.
permissible to re-sample or collect more samples to address
8.4 Size:
non-compliance and re-evaluate the new or augmented sample
8.4.1 Adjustspecimendimensionsto15%moisturecontent
for grade representativeness using GQI procedures (Note 11).
using the adjustment procedure given inAppendix XI or other
Sampling used for augmentation or re-sampling shall follow
demonstrably appropriate adjustment model.
the same sampling protocol applied to the original sample and
be representative of population and grade as specified in 7.1.1 8.4.2 For the purposes of the equation in 8.4.3, the standard
dressed size may be used in place of actual specimen dimen-
and 7.1.2. If the requirements of this clause are not met or if
re-sampling is not possible, then the following are possible sionswhenthemoisturecontentadjustedspecimendimensions
1 1
are within 6 ⁄16 in. (2 mm) in thickness and 6 ⁄4 in. (6 mm) in
actions to address non-compliance:
(1)If the average of all cell GQIs in one grade does not width of the standard dressed size.
exceed the grade GQI by more than 5 points, reduce the 8.4.3 Thepropertyvaluesofalltestdatashallbeadjustedto
property value for all specimens in any cell whose GQI the characteristic size (for example, 1.5 by 7.25 by 144 in. [38
D1990 − 19
by 184 by 3658 mm] at 15% MC) using the following 9.3.3 All individual data values shall be converted to the
equation(Note14)orotherappropriatesizeadjustmentpriorto characteristicsizebytheproceduresof8.4.3,andthetolerance
developing the characteristic value: limit shall be determined for the combined data set.
w l t
9.3.4 Thecalculatedtolerancelimitfrom9.3.3shallbeused
W L T
1 1 1
F 5 F (2)
S D S D S D
2 1
with the procedures of 8.4.3 to generate a size-adjusted
W L T
2 2 2
estimate for each cell in the test matrix.
where:
9.3.5 Thesize-adjustedestimatefrom9.3.4foreachtestcell
F = property value at Volume 1, psi,
shall be compared to the upper limit of the 75% confidence
F = property value at Volume 2, psi,
interval on the nonparametric fifth percentile estimate for the
W = width at F , in.,
1 1
testdatainthatcell.Ifthesize-adjustedestimatefrom9.3.4for
W = width at F , in.,
2 2
any cell does not exceed the confidence interval limit, the
L = length at F , in.,
1 1
characteristic value shall be the tolerance limit as calculated in
L = length at F , in.,
2 2
9.3.3.
T = thickness at F , in.,
1 1
9.3.6 If the size-adjusted estimate from 9.3.4 does exceed
T = thickness at F , in.,
2 2
w = 0.29 for modulus of rupture (MOR) and ultimate
the upper limit of the 75% confidence interval from 9.3.5 for
tensilestressparalleltograin(UTS);0.13forultimate anycell,reducethetolerancelimitcalculatedin9.3.3untilthis
compressive stress parallel to grain (UCS); 0 for
condition does not exist. The reduced tolerance limit estimate
modulus of elasticity (MOE), shall be the characteristic value for that grade.
l = 0.14formodulusofruptureandUTSparalleltograin:
9.4 For modulus of elasticity, the characteristic values for
0 for UCS parallel to grain and modulus of elasticity,
each grade are the mean, median, and the lower tolerance limit
and
(or other measure of dispersion).
t = 0 for modulus of rupture, UTS parallel to grain, UCS
9.4.1 Whenmorethanonewidthistested,thecharacteristic
parallel to grain, and modulus of elasticity.
value shall be based on the combined data of all widths
NOTE14—Theadjustmentstomechanicalpropertiesforpiecegeometry
given in 8.4.2 were developed from test data (adjusted to 15% MC and
adjusted by the procedures of Section 8 to the standardized
73°F) of visual grades of lumber (1, 2, 3, 4) using Test Methods D4761.
conditions.
Thelengthadjustmentsgivenabovearebasedontheactualtestclearspan
betweenreactionsorgrips.Thebendingtestsusedthirdpointloadingwith
9.5 Estimates of Characteristic Values for Untested Proper-
aconstantspantodepthratioof17to1.Thetensiontestswereconducted
ties:
with an 8 ft (2.4 m) clear span for 2 by 4 (Southern Pine was tested on a
9.5.1 These formulas were developed from large data bases
12 ft (3.7 m) span) and a 12 ft (3.7 m) clear clear span for 2 by 6 ft and
wider. The adjustment equation of 8.4.2 has not been verified for widths ofseveralNorthAmericancommercialspeciesgroups,andare
less than 3.5 in. (89 mm) nor greater than 9.25 in. (286 mm). Additional
intendedtoproduceconservativepropertyestimateswhenonly
information regarding the basis for and recommended limitations to Eq 2
one property was tested. The derivation of these formulas is
is given in Appendix X2.
discussed in detail in Appendix X4.
9. Establishment of Characteristic Values
9.5.2 Estimates Based on Modulus of Rupture:
9.1 For strength values, the characteristic value (see 3.2.2)
9.5.2.1 An estimate of the ultimate tensile stress character-
for each grade (GQI class) tested shall be the tolerance limit
istic value (T), in psi, may be calculated from the modulus of
(see3.2.13)fromthedataadjustedbytheproceduresinSection rupture characteristic value (R), in psi, with the following
8 to standardized conditions of temperature, moisture content
formula:
and size.
T 50.45 3R (3)
9.2 When more than one width is tested, the characteristic
9.5.2.2 An estimate of the ultimate compressive stress
value shall be developed using the combined data of all widths
characteristic value (C), in psi, may be calculated from the
adjusted to standardized conditions modified as necessary by
modulus of rupture characteristic value (R), in psi, with the
the test data check given in 9.3.
following formula:
9.3 Test Cell Data Check:
For R #7200psi (4)
9.3.1 The purpose of the test cell data check is to minimize
the probability of developing nonconservative property esti-
C 5 @1.55 2 ~0.32 3R/1000! 1 ~0.022 3~R/1000! !# 3R
mates by comparing the model generated property values
against the confidence interval for each cell in the test matrix.
For R.7200psi
This test ensures that the individual matrix cell estimates
C 50.39 3R
generated with the volume adjustment procedures of 8.4.3 and
the tolerance limit of the combined data do not lay above the
9.5.3 Estimates Based on Ultimate Tensile Stress:
upper limit of the confidence interval for the fifth percentile of
9.5.3.1 An estimate of the modulus of rupture characteristic
any tested cell.
value (R), in psi, may be calculated from the ultimate tensile
9.3.2 When species are grouped (Section 10), the test cell
stress characteristic value (T), in psi, with the following
data check shall be performed after grouping using the com-
formula:
bined data of the controlling species in each test cell. An
example is given in Appendix X3. R 51.2 3T (5)
D1990 − 19
9.5.3.2 An estimate of the ultimate compressive stress The median or mean characteristic value for the group shall be
characteristic value (C), in psi, may be calculated from the determined from the combined data of all the species in this
ultimate tensile stress characteristic value (T), in psi, with the subgroup.
following formula:
10.2.2 Adding New Species to Existing Group:
10.2.2.1 Anew species may be added to an existing species
For T #5400psi (6)
grouping without modification of the group median or mean
C 5 @2.40 2 ~0.70 3T/1000!1~0.065 3~T/1000! !# 3T
characteristic value if the median value of the new species is
greater than or equal to the existing group median character-
For T.5400psi
istic value.
10.2.2.2 If the requirements of 10.2.2.1 are not met, deter-
C 50.52 3T
mine the combined group median or mean characteristic value
9.5.4 When both bending and tension parallel to grain data
inaccordancewith10.2.1.Ifthedatawillnotpermittheuseof
are available, use the lower of the two estimates for the
10.2.1, then the group median or mean characteristic value
compression parallel to grain value.
shall be the median or mean of the newly included species.
9.5.5 Compressionparalleltograintestsshallnotbeusedto
10.3 Grouping for Tolerance Limit Properties:
estimate either the modulus of rupture (R) characteristic value
10.3.1 New Species Grouping:
or the ultimate tensile stress (T) characteristic value.
10.3.1.1 To assign a tolerance limit characteristic value to a
new grouping, determine the tolerance limit value for the
10. Adjustments to Characteristic Values
combinedgrouping(Note16).Determinethenumberofpieces
10.1 Grouping of Data to Form a New Species Grouping—
in each species group below the group tolerance limit value.
Frequently, because of species similarities or marketing
Conduct a Chi Square test (Appendix X7) to determine if the
convenience, it is desirable to combine two or more species
percent of pieces below the group value is statistically signifi-
into a single marketing group (Note 15). When this is done, it
cant for each species in the group.
is necessary to determine the characteristic values for the
combined group of species. There are no limitations as to how NOTE 16—To determine a group tolerance limit value, each species to
be included in the group should have a minimum sample size of at least
manyorwhichspeciescanbecombinedtoformanewspecies
100perpropertyinorderfortheChiSquaretesttobesufficientlysensitive
grouping, but the group characteristic values shall be deter-
(8) .
mined from the procedures of 10.2 for each median or mean
10.3.1.2 If the test is not significant at the 0.01 level, the
property to be established, and the procedures of 10.3 for each
group characteristic value shall be determined from the
tolerance limit property to be established. When a mean value
grouped data of all the species in the new grouping.
istobedetermined,thegroupshallbeformedusingthemedian
10.3.1.3 Ifthetestissignificantatthe0.01level,beginwith
values. Sections 10.2 and 10.3 cover procedures for establish-
a subgroup consisting of the two species with the highest
ing entirely new species groups, as well as adding a new
percent of pieces below the group value. Use the Chi Square
species to an existing species grouping. All grouping is done
testtodetermineifthepercentofpiecesbelowthegroupvalue
after the data have been adjusted to standardized conditions of
are comparable. Repeat this process, adding the species with
temperature, moisture content and characteristic size in accor-
the next highest percent of pieces below the group value to the
dance with 8.3 and 8.4 (see Appendix X3 for example).
previous group. Continue adding species until the test is
NOTE 15—For grouping by other appropriate technical criteria, see
significant at the 0.01 level. The group tolerance limit is
Appendix X9.
determined from the combined data of the last subgroup of
10.2 Grouping for Median Properties
species for which the Chi Square test was not significant at the
10.2.1 New Species Grouping:
0.01 level.
10.2.1.1 To assign a median or mean characteristic value to
10.3.2 Adding New Species to Existing Group:
a new grouping of species, begin by conducting a nonparamet-
10.3.2.1 A new species may be included with an existing
ric analysis of variance (Appendix X5) to test for equality of
species grouping if the tolerance limit of the new species is
median values of the separate species. This can be done for
equal to or greater than the current characteristic value for the
eitherasinglegradeoramatrixofgrades.Wherethegoalisto
group.
assign values to a matrix of grades, this grouping procedure
10.3.2.2 If the requirements of 10.3.2.1 are not met, deter-
shall be conducted on each grade. Perform grouping tests on
mine the combined species group value in accordance with
thedataonlyafterithasbeenadjustedtothecharacteristicsize
10.3.1. If the data will not permit the use of 10.3.1, the group
by the procedures in 8.4.3.
characteristic value shall be the tolerance limit value of the
10.2.1.2 If the test is not significant at the 0.01 level, the
newly included species.
median or mean characteristic value for the group shall be the
median or mean of the combined group data.
11. Establishing Grade Relationships for Stress and
10.2.1.3 If the test is significant at the 0.01 level, determine
Modulus of Elasticity
the subgroup of species in the grouping which are indistin-
guishable from the species with the lowest median character- 11.1 The adjustment model for grade shall be based on
istic value using a Tukey multiple comparison test (Appendix relating the characteristic values determined in Section 9
X4 and Ref (7)) on the medians at a 0.01 significance level. modified for species grouping (Section 10), if appropriate, to
D1990 − 19
the corresponding assumed minimum GQI values (see Appen- dimension lumber manufactured at 19% or less moisture
dix X8). The grade model constructed from the data may content when used in dry use conditions, where the moisture
consist of either a linear relationship connecting the adjacent content of the wood is not expected to exceed 19%.
points or a mathematically fitted curve. The selected relation- 12.5.2 For lumber used where end-use conditions are ex-
ship shall be demonstrated to be appropriate (Note 17). pected to produce moisture contents in the wood in excess of
19%, multiply the allowable property values at 15% moisture
NOTE 17—The structural visual grade No. 1 (1, 2, 3, 4) has a highly
content by the factors in Table 1 (Note 18).
restrictedgradedescription.IntheNorthAmericanIn-Gradetestprogram,
itwasdeemedappropriateforbendingandtensiontouseonly85%ofthe
NOTE 18—The allowable properties derived from the characteristic
No. 1 value that linear interpolation between select structural and No. 2
valuesat15%moisturecontentandtheadjustmentsinTable1accountfor
permitted. For compression, 95% of the permitted No. 1 value was used
the normal shrinking and swelling of lumber with changes in moisture
(see Appendix X8). Alternatively, the No. 1 values could have been set
content, as well as the changes in mechanical property values with
equal to the No. 2 values.
moisture content. The basis of the adjustment factors in Table 1 are
discussed in Appendix X10.
11.2 Estimate the characteristic values for untested grades
from the model selected in 11.1. Use the assumed minimum
12.5.3 The adjustment factors in Table 1 assume the stan-
GQI for the grade determined from the minimum grade
dard dressed size at the dry use moisture content. Lumber
requirements (see Appendix X8).
surfaced unseasoned shall take this into account when estab-
11.2.1 If the grade adjustment model is used to extrapolate
lishing characteristic values either by surfacing sufficiently
beyondthesamplematrix,provideadditionalsupportingdocu-
oversizetoaccountforthesedimensionalchanges,oradjusting
mentation to demonstrate that the procedure is conservative.
the allowable property values accordingly. The effects of
changesinmoisturecontentondimensionsisdiscussedfurther
12. Establishing Allowable Properties
in Appendix X1, and adjustment factors in Table 1 are
discussed in Appendix X10.
12.1 The characteristic values established in Section 9 and
modified in Sections 10 and 11, and the estimated values for
12.6 Strength property values derived from 9.3 shall not
untested grades are based on short term tests adjusted to e
...

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: D1990 − 16 D1990 − 19
Standard Practice for
Establishing Allowable Properties for Visually-Graded
Dimension Lumber from In-Grade Tests of Full-Size
Specimens
This standard is issued under the fixed designation D1990; 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
Visual stress-grades of lumber manufactured in North America have evolved from the procedures
of Practice D245. Allowable stress and modulus of elasticity values were determined for these grades
using the procedures of Practice D245 and the appropriate clear wood values of Practice D2555. The
clear wood values of Practice D2555 were developed from tests of small clear specimens.
Development of allowable stress and modulus of elasticity values from tests of full-size structural
lumber as commercially produced and marketed has become possible with the development of suitable
test equipment that permits rapid rates of loading to test large numbers of pieces from commercial
lumber production. These tests can be carried out at the production sites or in a laboratory.
1. Scope
1.1 This practice covers the principles and procedures for establishing allowable stress values for bending, tension parallel to
grain, compression parallel to grain and modulus of elasticity values for structural design from “In-Grade” tests of full-size visually
graded solid sawn dimension lumber. This practice also covers procedures for periodic monitoring, and additional procedures, if
needed, for evaluation and possible reassessment of assigned design values. This practice is focused on, but is not limited to, grades
which used the concepts incorporated in Practice D245 and were developed and interpreted under American Softwood Lumber PS
20.
1.2 A basic assumption of the procedures used in this practice is that the samples selected and tested are representative of the
entire global population being evaluated. This approach is consistent with the historical clear wood methodology of assigning an
allowable property to visually-graded lumber which was representative of the entire growth range of a species or species group.
Every effort shall be made to ensure the test sample is representative of population by grade and size (see 7.1.1 and 7.1.2).
1.3 Due to the number of specimens involved and the number of mechanical properties to be evaluated, a methodology for
evaluating the data and assigning allowable properties to both tested and untested grade/size cells is necessary. Sampling and
analysis of tested cells are covered in Practice D2915. The mechanical test methods are covered in Test Methods D198 and D4761.
This practice covers the necessary procedures for assigning allowable stress and modulus of elasticity values to dimension lumber
from In-Grade tests. The practice includes methods to permit assignment of allowable stress and modulus of elasticity values to
untested sizes and grades, as well as some untested properties. The practice includes procedures for periodic monitoring of the
species or species group to quantify potential changes in the product and verification of the assigned design values through,
evaluation, and reassessment.
NOTE 1—In the implementation of the North American In-Grade test program, allowable stress values for compression perpendicular to grain and shear
parallel to grain for structural design were calculated using the procedures of Practice D245.
1.4 This practice only covers dimension lumber.
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.
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 May 1, 2016Oct. 1, 2019. Published June 2016November 2019. Originally approved in 1991. Last previous edition approved in 20142016 as
D1990 – 14.D1990–16. DOI: 10.1520/D1990-16.10.1520/D1990-19.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1990 − 19
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
D198 Test Methods of Static Tests of Lumber in Structural Sizes
D245 Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber
D1165 Nomenclature of Commercial Hardwoods and Softwoods
D2555 Practice for Establishing Clear Wood Strength Values
D2915 Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
D4442 Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
D4444 Test Method for Laboratory Standardization and Calibration of Hand-Held Moisture Meters
D4761 Test Methods for Mechanical Properties of Lumber and Wood-Based Structural Materials
E380 Practice for Use of the International System of Units (SI) (the Modernized Metric System) (Withdrawn 1997)
IEEE/ASTM SI 10 Standard for Use of the International System of Units (SI): The Modern Metric System
2.2 American Softwood Lumber Standard:
National Institute of Standards and Technology Voluntary Product Standard PS 20-94
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms related to wood, refer to Terminology D9.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 characteristic size—the standard dimensions of the piece at which the characteristic value is calculated (Note 2).
NOTE 2—In the North American In-Grade program, the characteristic size used was 1.5 in. (38 mm) thick by 7.25 in. (184 mm) wide by 144 in. (3.658
m) in length at 15 % moisture content.
3.2.2 characteristic value—the population mean, median or tolerance limit value estimated from the test data after it has been
adjusted to standardized conditions of temperature, moisture content and characteristic size.
3.2.2.1 Discussion—
The characteristic value is an intermediate value in the development of allowable stress and modulus of elasticity values. Typically
for structural visual grades, standardized conditions are 73°F (23°C), and 15 % moisture content (Note 3). A nonparametric
estimate of the characteristic value is the preferred estimate. If a distributional form is used to characterize the data at the
standardized conditions, its appropriateness shall be demonstrated. (See Practice D2915 for guidance on selection of distribution.)
NOTE 3—The described adjustment factors and allowable stress and modulus of elasticity value assignment procedures were developed based on test
data of visual grades of major volume, commercially available North American softwood species groups. For other species (see Nomenclature D1165)
and for other grading methods, it may be necessary to verify that the listed adjustments are applicable. The commercial species groups and grading criteria
used in the development of these procedures were as described in the grading rules for Douglas Fir-Larch, Hem-Fir and Southern Pine from the United
States, and Spruce-Pine-Fir, Douglas fir(N), and Hem-Fir(N) from Canada (1, 2, 3, and 4) . The specific species groupings, together with botanical names
are given in Nomenclature D1165.
3.2.3 grade quality index (GQI)—A numerical assessment of the characteristics found in the sample specimens which are
considered to be related to strength and are limited as part of the grade description. The grade quality index is a scaling parameter
which allows modeling of strength and modulus of elasticity with respect to grade (Note 4).
NOTE 4—In the North American In-Grade test program, lumber produced in accordance with visual stress grading rules (1, 2, 3, 4, 5, and 6) developed
from the procedures of Practice D245 was sampled. For each test specimen a strength ratio was calculated for the particular type of failure indicated by
the failure code (see Test Methods D4761). Strength ratios were calculated according to the formulas given in the appendix of Practice D245 for bending
and compression parallel to grain test specimens. Strength ratios for lumber tested in tension and compression parallel to grain were calculated as for
bending. The sample grade quality index for each sample was calculated as the nonparametric five percentile point estimate of the distribution of strength
ratios. Specimens which failed in clear wood were excluded from the sample for determining the sample GQI.
3.2.4 In-Grade—samples collected from lumber grades as commercially produced.
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.
The last approved version of this historical standard is referenced on www.astm.org.
Available from U.S. Government Printing Office Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
www.access.gpo.gov.
The boldface numbers in parentheses refer to the references listed at the end of this practice.
D1990 − 19
3.2.4.1 Discussion—
Samples collected in this manner are intended to represent the full range of strength and modulus of elasticity values normally
found within a grade.
3.2.5 monitoring, n—a periodic review of a subset of structural properties of a lumber cell to determine if a potential downward
shift from the assigned values indicates a need for an evaluation or reassessment, or both, of allowable properties developed with
this practice (Stage 1).
3.2.6 evaluation, n—The process of examining data, including that collected over the course of a monitoring program that has
detected a shift in cell properties, to determine the likely cause for the detected shift in cell properties, developing the best response
to the data, and establishing that the actions are sufficient (Stage 2).
3.2.6.1 Discussion—
The response to the evaluation can include altering the grade description, or the input resource, or changing the method of
processing. Testing is conducted to confirm that the action taken corrected the affected properties.
3.2.7 reassessment, n—The recalculation of allowable properties derived by this practice because of a change in product
properties (Stage 3).
3.2.8 statistically significant downward shift, n—A statistically significant downward change in the monitored size grade cell
property in relation to a single cell from the matrix used to derive the current allowable property for which further action is required
in this Practice.
3.2.8.1 Discussion—
The Wilcoxon nonparametric statistical test showing a change that is significant at the 0.05 level has been selected as the consensus
statistical method for determining when further action is required in this Standard.
3.2.9 action level—The lower property boundary, representing a statistically significant downward shift, used in monitoring to
define the property level at which additional confirmation testing during monitoring, or further action beyond monitoring is
necessary.
3.2.10 sampling matrix—the collective designation used to describe all of the individual test cells. The sampling matrix is
intended to characterize the property trends for a range of grades for a single size or a range of sizes for a single grade or a
combination of both sizes and grades for a species or species group.
3.2.10.1 Discussion—
The sampling matrix is intended to characterize the property trends for a range of grades for a single size or a range of sizes for
a single grade or a combination of both sizes and grades for a species or species group.
3.2.11 test cell—the combined test data for a single size/grade/species/property which is intended to characterize that sampling
unit.
3.2.12 thickness—the lesser dimension perpendicular to the long axis of lumber.
3.2.13 tolerance limit (TL)—refers to the tolerance limit with 95 % content and 75 % confidence.
3.2.14 width—the greater dimension perpendicular to the long axis of lumber.
4. Significance and Use
4.1 The procedures described in this practice are intended to be used to establish allowable stress and modulus of elasticity
values for solid sawn, visually graded dimension lumber from In-Grade type test data. These procedures apply to the tested and
untested sizes and grades when an adequate data matrix of sizes and grades exists. In addition, the methodology for establishing
allowable stress and modulus of elasticity values for combinations of species and species groups is covered. Allowable stress and
modulus of elasticity values may also be developed for a single size or a single grade of lumber from test data.
4.2 Methods for establishing allowable stress and modulus of elasticity values for a single size/grade test cell are covered in
Practice D2915. The appropriateness of these methods to establish allowable stress and modulus of elasticity values is directly
dependent upon the quality and representativeness of the input test data.
4.3 A monitoring program shall be established to periodically review the continued applicability of allowable properties derived
by this practice. A monitoring program will establish data sets that are either the same as, above, or below the data that was used
to develop the current allowable properties. Upon detection of a statistically significant downward shift, evaluation of the data and
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confirmation of remedial actions shall be undertaken. When evaluation is not undertaken or the results of the evaluation indicate
an adjustment to allowable properties is appropriate, a reassessment shall be conducted to re-establish allowable properties.
NOTE 5—It is recognized that over time there is the potential for changes in the raw material or product mix. In response to this a monitoring program
must be conducted to ensure design values derived by this practice are not invalidated by such changes. If the data collected with a monitoring provides
evidence of an statistically significant downward shift in lumber properties an evaluation program in accordance with the procedures of this practice is
needed to detect and confirm that responses to such changes are appropriate. Evaluation, if undertaken, provides a means for responding to the data and
assessing if the actions taken are sufficient. Following the confirmation of a statistically significant downward shift, reassessment of values shall be
conducted if evaluation is either not undertaken or does not adequately address the downward shift.
5. Documentation of Results, Adjustments, and Development of Allowable Properties
5.1 Reporting Test Data:
5.1.1 Summarizing Statistics:
5.1.1.1 Provide a set of summarizing statistics that includes sample size, mean, median, standard deviation, confidence intervals,
and nonparametric point estimates and tolerance limits. If parametric methods are used to characterize the data, provide a
description of selection procedures and a tabulation of distribution parameters. Document any “best fit” judgments made in the
selection of a distribution.
5.1.1.2 Provide a description of all statistical methods used with the summarizing statistics.
5.1.2 Unadjusted Test Results—To permit verification of property calculations by regulatory and third party reviewers,
unadjusted individual specimen test results shall be maintained in suitable achival form. The archived records shall be retained as
long as the derived property values are applicable. Archived records shall be retained by the user of this practice and an
independent public institution.
NOTE 6—In the United States, the USDA Forest Products Laboratory, the American Lumber Standards Committee, and colleges and universities are
considered suitable independent public institutions. It may be desirable for historical or other purposes to continue to archive the records after the derived
values are no longer applicable. In such cases, the records should be maintained by a public institution.
5.1.3 Significant Digits—With example calculations, illustrate that adequate significant digits were maintained in intermediate
calculations to avoid round-off errors. Table 3 and Section 4 of Practice E380 provide guidance.
5.2 Graphical Presentation—Graphical presentations are recommended to illustrate typical data sets. If parametric methods are
used, histograms or cumulative distribution functions shall be shown superimposed on the parametric functions. Class widths shall
meet the requirements of Practice D2915, Table 7.
5.3 Preparation of Characteristic Values
5.3.1 Adjustments to Test Data:
5.3.1.1 Document each of the adjustments to the test data.
5.3.1.2 If the adjustments to the test data follow procedures found in other ASTM standards or are documented in other sources,
reference these sources in a manner permitting the reader to recreate the use of these sources in the same application. Indicate the
limitations of application.
5.3.1.3 In the presentation, explain adjustments made to the data which cannot be referenced to acknowledged sources.
5.3.1.4 Provide examples of all adjustment procedures.
5.4 Development of Allowable Properties:
5.4.1 Explain each step of the development of allowable properties with reference to the appropriate paragraph of this practice.
5.4.2 Grouping—Summarize all grouping calculations in tabular form and examples presented to illustrate application of
limiting criteria.
5.4.3 Allowable Property Adjustments—Illustrate each of the adjustments for allowable properties for at least one of the
size/grade combinations presented. Present all adjustments in tabular form. Examples may be presented.
5.5 Summary/Index—Prepare a brief summary of the presentation that highlights each of the major steps. An index or table of
contents shall accompany the document that references the content and the corresponding paragraphs of this practice.
6. Development of Stress Grades
6.1 Stress grades for lumber are designed to separate the raw material source into marketable groups of specific quality levels
to which allowable stress and modulus of elasticity values can be assigned. Stress grading systems used with this practice shall
be internally consistent and continuous (Note 7).
NOTE 7—To be considered internally consistent, a grading system should not be based on two or more methods of determining an allowable property.
A continuous system should not skip levels of material strength. For example, the North American In-Grade test program sampled grades which were
developed using the stress ratio system of Practice D245 (see Refs 1, 2, 3, and 4).
7. Minimum Sampling Matrix
7.1 General Considerations—Development of allowable stress and modulus of elasticity values under this practice may be for
either a single size (7.3) or a single grade (7.2) or a full matrix of sizes and grades (7.4). The required sampling matrix is
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determined by the desired end result. The intent of a sample matrix is to provide sufficient data across the sizes or grades, or both,
to permit interpolation between data points. Extrapolation beyond the sample matrix may be misleading and therefore is not
recommended. Assignment of allowable stress values beyond the sample matrix is permitted when there is additional supporting
information to indicate that the assigned values are conservative estimates.
7.1.1 Population Representativeness—The sampling plan shall be designed to represent the region to be sampled (see Note 8).
NOTE 8—Consideration should be given to potential sources of variability in the allocation of the random sample and the design of the sampling plan.
The North American In-grade test program samples were considered representative because the design of the sampling plan required sampling
proportional to production in at least 3 sub regions of the growing range for each of the species groups with substantial production; this resulted in a
minimum cell size of 360 pieces. Smaller geographic regions equivalent to several U.S. states had representative samples with sample sizes of 200 or
more. The use of large sample sizes is not sufficient by itself to assure that the sample is representative of the population. It is often necessary to sample
sub-regions (or locations) to represent variability due to geography, production and growing conditions; in the North American In-Grade Program, this
was typically a minimum of three sub-regions, but more for the major volume species groups. If this is not possible justification needs to be provided
to demonstrate that an alternate sampling plan adequately represents these sources of variability.
7.1.2 Grade Representativeness—The sampling shall be collected in a random sampling design intended to represent the range
of strength reducing characteristics allowed by the grade.
7.2 Grade—To adequately model grade performance, it is necessary to sample a minimum of two grades representative of the
range of grade quality (Note 4). Grades sampled to model grade relationships shall be separated by no more than one intermediary
grade and no more than one quarter of the total possible range (Note 9) in assumed bending GQI.
NOTE 9—For the grading system sampled in the North American In-Grade test program, the total possible range in strength ratio (GQI) is 0 to 100 %.
The strength ratio concept is described in greater detail in Practice D245.
7.3 Width—In order to adequately develop the data for width, at least three widths per grade shall be tested, and the maximum
difference in width between two adjacent widths shall be 4 in. (10 cm).
7.4 Minimum Full Matrix—A full matrix of grades and sizes shall contain a minimum of six test cells composed of at least two
grades and three widths for each of the grades, meeting the restrictions of 7.2 and 7.3, to be considered adequate for the
development of a full matrix of values, including untested cells (Note 10).
NOTE 10—The sampling matrix judged to be acceptable for the North American In-Grade test program for the major species groups (Note 2) with large
geographic range, consisted of six test cells with large samples (at least 360 pieces per cell). The test cells were nominal 2 by 4, 1.5 in. by 3.5 in. (38
mm by 89 mm); nominal 2 by 8, 1.5 in. by 7.25 in. (38 mm by 184 mm); and nominal 2 by 10, 1.5 in. by 9.25 in. (38 mm by 235 mm) dimension lumber
of select structural grade (65 % minimum bending strength ratio) and No. 2 grade (45 % minimum bending strength ratio). Samples were selected for
tests of four properties (modulus of elasticity, modulus of rupture, ultimate tensile stress parallel to grain, and ultimate compressive stress parallel to
grain). For complete grade descriptions, see Refs. 1, 2, 3, or 4). Samples were selected proportional to production from the entire geographic growth and
production range of each species group.
8. Input Test Data and Adjustments to Input Test Data
8.1 Methods for sampling and analysis of matrix input test data are found in Practice D2915. For testing, use Test Methods D198
or Test Method D4761. Other standards may be employed if demonstrated to be applicable.
8.2 Because the range of quality within any one specific grade may be large, it is necessary to assess the observed grade quality
of the sampled material in relation to the assigned grade quality used to establish the matrix (7.2). The following procedures
provide one way to make this assessment.
8.2.1 The observed GQI determined from failure coded data can be used to assess whether the test cells are representative of
the visual grade that is the target by comparing the 5th percentile point estimate (5th %tle PE) GQI of the test cells with the
assigned GQI for the target grade (Note 4). The observed GQI shall be calculated for all pieces associated with knots, slope of
grain, and distorted grain, or other strength reducing characteristics at point of failure. The calculation methodology shall be
documented (see X12.6)
8.2.2 When calculating strength ratios using the appendix of Practice D245, two strength ratios shall be calculated for
combination knot failures: (1) using the total combined knot cross section in the equation for center of wide face knots, and (2)
using the largest single edge knot from the cross{section in the equation for narrow face knots. The smaller of these two calculated
strength ratios shall be permitted to be used in the calculation of fifth percentile point estimate of the distribution of strength ratios.
8.2.3 Fifth percentile point estimates of the distribution of strength ratios shall be presented to decimal place, using the rounding
procedures of Section 6.4 in Practice E29.
8.2.4 To comply with the requirements of 7.2 and 8.2 both of the following conditions (Note 11) shall be met:
(1) The average of all individual cell GQIs in one grade shall not exceed the assigned grade GQI by more than 5 percentage
points, and
(2) Each individual cell GQI shall not exceed the assigned grade GQI by more than 7 percentage points.
If both conditions are not met one of the options in 8.3 shall be followed.
NOTE 11—GQI evaluation and adjustment is an additional procedure overlaid on the representative sampling requirement to assure final strength
property assignments account for the full range of grade characteristics permitted in each visual grade. The basis for these procedures were developed
using distribution data of GQI measurements of the major North American species groups as part of the North American In-Grade Lumber Testing
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program. A modification of the GQI scale or calculation methodology may be appropriate. The GQI for a sample is determined from defects associated
with the failure of the pieces in the sample after test loading. The determination of a GQI value depends on the assessment and measurement of knot
types, sizes, and their locations as well as the maximum slope of grain of the piece. Sample size, measurement variation, species variability, and methods
of analysis can significantly impact the final GQI value (See X12).
8.3 Standardized Conditions:
8.3.1 Grade Quality
8.3.1.1 If the average of all individual cell GQIs in one grade for a sample is no more than 5 percentage points above the grade
GQI, and each individual cell GQI for a sample is no more than 7 percentage points above the grade GQI that sample shall be
considered to support the intent of 7.2. Otherwise, it is permissible to re-sample or collect more samples to address non-compliance
and re-evaluate the new or augmented sample for grade representativeness using GQI procedures (Note 11). Sampling used for
augmentation or re-sampling shall follow the same sampling protocol applied to the original sample and be representative of
population and grade as specified in 7.1.1 and 7.1.2. If the requirements of this clause are not met or if re-sampling is not possible,
then the following are possible actions to address non-compliance:
(1) If the average of all cell GQIs in one grade does not exceed the grade GQI by more than 5 points, reduce the property value
for all specimens in any cell whose GQI exceeds the grade GQI by more than 7 points using the formula in 8.3.1.2. If the average
of all individual cell GQIs in the grade exceeds the grade GQI by more than 5 points, reduce the property value for all specimens
in each cell that exceeds the grade GQI by more than 5 points using the formula in 8.3.1.2. Cells adjusted, using this procedure,
are assumed to be compliant and no further grade quality adjustment is required for the grade in question.
(2) Adjust the grade definition to support a higher grade GQI so that it is within 5 points of the observed GQI.
NOTE 12—Failure of the sample to meet these criteria could be a result of several causes, some of which may be acceptable or correctable by using
another method. It could be desirable to reassess the appropriateness of the GQI scale used. A proposal for replacement or augmentation of existing data
should include adequate statistical analyses and information to determine if the new data substantiates retaining existing data, augments existing data,
or replaces existing data.
8.3.1.2 Where structural property data of a cell is required to be modified to adjust to standardized conditions of assigned GQI,
the data for all specimens in the cell shall be multiplied by the following factor (Note 13):
Factor 5 ~assigned GQI15% points!/~observed GQI! (1)
An alternative relationship shall be permitted to be used to modify the modulus of elasticity to standardized GQI conditions,
provided this relationship is based on documented evidence. An example equation for the adjustment of modulus of elasticity can
be found in X12.5.6.
NOTE 13—The GQI evaluation and adjustment is an additional procedure applied to the final strength property assignments to account for the maximum
size of grade characteristics permitted in each visual grade. The adjustment factor is an override that can be applied without further sampling. It has been
shown that application of GQI adjustment factors ranging from 0.95 to 0.89 can leave the final design values unchanged or can change the final design
values by 1 rounding rule.
8.3.2 Temperature—Test samples at 736 5°F (23 6 3°C). When this is not possible, adjust individual test data to 73°F (23°C)
by an adjustment model demonstrated to be appropriate.
8.3.3 Moisture:
8.3.3.1 Where possible, test the samples at the moisture content (15 %) at which the characteristic value is to be determined.
When this is not possible, adjust the data to 15 % moisture content by the adjustment procedures in Annex A1 or by procedures
documented as adequate for the method adopted prior to developing the characteristic values.
8.3.3.2 Determination of specimen moisture content shall be made in accordance with Test Methods D4442 and D4444.
8.4 Size:
8.4.1 Adjust specimen dimensions to 15 % moisture content using the adjustment procedure given in Appendix XI or other
demonstrably appropriate adjustment model.
8.4.2 For the purposes of the equation in 8.4.3, the standard dressed size may be used in place of actual specimen dimensions
1 1
when the moisture content adjusted specimen dimensions are within 6 ⁄16 in. (2 mm) in thickness and 6 ⁄4 in. (6 mm) in width
of the standard dressed size.
8.4.3 The property values of all test data shall be adjusted to the characteristic size (for example, 1.5 by 7.25 by 144 in. [38
by 184 by 3658 mm] at 15 % MC) using the following equation (Note 14) or other appropriate size adjustment prior to developing
the characteristic value:
w l t
W L T
1 1 1
F 5 F (2)
S D S D S D
2 1
W L T
2 2 2
where:
F = property value at Volume 1, psi,
F = property value at Volume 2, psi,
W = width at F , in.,
1 1
W = width at F , in.,
2 2
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L = length at F , in.,
1 1
L = length at F , in.,
2 2
T = thickness at F , in.,
1 1
T = thickness at F , in.,
2 2
w = 0.29 for modulus of rupture (MOR) and ultimate tensile stress parallel to grain (UTS); 0.13 for ultimate compressive
stress parallel to grain (UCS); 0 for modulus of elasticity (MOE),
l = 0.14 for modulus of rupture and UTS parallel to grain: 0 for UCS parallel to grain and modulus of elasticity, and
t = 0 for modulus of rupture, UTS parallel to grain, UCS parallel to grain, and modulus of elasticity.
NOTE 14—The adjustments to mechanical properties for piece geometry given in 8.4.2 were developed from test data (adjusted to 15 % MC and 73°F)
of visual grades of lumber (1, 2, 3, 4) using Test Methods D4761. The length adjustments given above are based on the actual test clear span between
reactions or grips. The bending tests used third point loading with a constant span to depth ratio of 17 to 1. The tension tests were conducted with an
8 ft (2.4 m) clear span for 2 by 4 (Southern Pine was tested on a 12 ft (3.7 m) span) and a 12 ft (3.7 m) clear clear span for 2 by 6 ft and wider. The
adjustment equation of 8.4.2 has not been verified for widths less than 3.5 in. (89 mm) nor greater than 9.25 in. (286 mm). Additional information
regarding the basis for and recommended limitations to Eq 2 is given in Appendix X2.
9. Establishment of Characteristic Values
9.1 For strength values, the characteristic value (see 3.2.2) for each grade (GQI class) tested shall be the tolerance limit (see
3.2.13) from the data adjusted by the procedures in Section 8 to standardized conditions of temperature, moisture content and size.
9.2 When more than one width is tested, the characteristic value shall be developed using the combined data of all widths
adjusted to standardized conditions modified as necessary by the test data check given in 9.3.
9.3 Test Cell Data Check:
9.3.1 The purpose of the test cell data check is to minimize the probability of developing nonconservative property estimates
by comparing the model generated property values against the confidence interval for each cell in the test matrix. This test ensures
that the individual matrix cell estimates generated with the volume adjustment procedures of 8.4.3 and the tolerance limit of the
combined data do not lay above the upper limit of the confidence interval for the fifth percentile of any tested cell.
9.3.2 When species are grouped (Section 10), the test cell data check shall be performed after grouping using the combined data
of the controlling species in each test cell. An example is given in Appendix X3.
9.3.3 All individual data values shall be converted to the characteristic size by the procedures of 8.4.3, and the tolerance limit
shall be determined for the combined data set.
9.3.4 The calculated tolerance limit from 9.3.3 shall be used with the procedures of 8.4.3 to generate a size-adjusted estimate
for each cell in the test matrix.
9.3.5 The size-adjusted estimate from 9.3.4 for each test cell shall be compared to the upper limit of the 75 % confidence interval
on the nonparametric fifth percentile estimate for the test data in that cell. If the size-adjusted estimate from 9.3.4 for any cell does
not exceed the confidence interval limit, the characteristic value shall be the tolerance limit as calculated in 9.3.3.
9.3.6 If the size-adjusted estimate from 9.3.4 does exceed the upper limit of the 75 % confidence interval from 9.3.5 for any
cell, reduce the tolerance limit calculated in 9.3.3 until this condition does not exist. The reduced tolerance limit estimate shall be
the characteristic value for that grade.
9.4 For modulus of elasticity, the characteristic values for each grade are the mean, median, and the lower tolerance limit (or
other measure of dispersion).
9.4.1 When more than one width is tested, the characteristic value shall be based on the combined data of all widths adjusted
by the procedures of Section 8 to the standardized conditions.
9.5 Estimates of Characteristic Values for Untested Properties:
9.5.1 These formulas were developed from large data bases of several North American commercial species groups, and are
intended to produce conservative property estimates when only one property was tested. The derivation of these formulas is
discussed in detail in Appendix X4.
9.5.2 Estimates Based on Modulus of Rupture:
9.5.2.1 An estimate of the ultimate tensile stress characteristic value (T), in psi, may be calculated from the modulus of rupture
characteristic value (R), in psi, with the following formula:
T 5 0.45 3R (3)
9.5.2.2 An estimate of the ultimate compressive stress characteristic value (C), in psi, may be calculated from the modulus of
rupture characteristic value (R), in psi, with the following formula:
For R # 7200 psi (4)
C 5 @1.55 2 ~0.32 3R/1000! 1 ~0.022 3~R/1000! !# 3R
For R.7200 psi
C 5 0.39 3R
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9.5.3 Estimates Based on Ultimate Tensile Stress:
9.5.3.1 An estimate of the modulus of rupture characteristic value (R), in psi, may be calculated from the ultimate tensile stress
characteristic value (T), in psi, with the following formula:
R 5 1.2 3T (5)
9.5.3.2 An estimate of the ultimate compressive stress characteristic value (C), in psi, may be calculated from the ultimate
tensile stress characteristic value (T), in psi, with the following formula:
For T # 5400 psi (6)
C 5 @2.40 2 ~0.70 3T/1000!1~0.065 3~T/1000! !# 3T
For T.5400 psi
C 5 0.52 3T
9.5.4 When both bending and tension parallel to grain data are available, use the lower of the two estimates for the compression
parallel to grain value.
9.5.5 Compression parallel to grain tests shall not be used to estimate either the modulus of rupture (R) characteristic value or
the ultimate tensile stress (T) characteristic value.
10. Adjustments to Characteristic Values
10.1 Grouping of Data to Form a New Species Grouping—Frequently, because of species similarities or marketing convenience,
it is desirable to combine two or more species into a single marketing group (Note 15). When this is done, it is necessary to
determine the characteristic values for the combined group of species. There are no limitations as to how many or which species
can be combined to form a new species grouping, but the group characteristic values shall be determined from the procedures of
10.2 for each median or mean property to be established, and the procedures of 10.3 for each tolerance limit property to be
established. When a mean value is to be determined, the group shall be formed using the median values. Sections 10.2 and 10.3
cover procedures for establishing entirely new species groups, as well as adding a new species to an existing species grouping. All
grouping is done after the data have been adjusted to standardized conditions of temperature, moisture content and characteristic
size in accordance with 8.3 and 8.4 (see Appendix X3 for example).
NOTE 15—For grouping by other appropriate technical criteria, see Appendix X9.
10.2 Grouping for Median Properties
10.2.1 New Species Grouping:
10.2.1.1 To assign a median or mean characteristic value to a new grouping of species, begin by conducting a nonparametric
analysis of variance (Appendix X5) to test for equality of median values of the separate species. This can be done for either a single
grade or a matrix of grades. Where the goal is to assign values to a matrix of grades, this grouping procedure shall be conducted
on each grade. Perform grouping tests on the data only after it has been adjusted to the characteristic size by the procedures in 8.4.3.
10.2.1.2 If the test is not significant at the 0.01 level, the median or mean characteristic value for the group shall be the median
or mean of the combined group data.
10.2.1.3 If the test is significant at the 0.01 level, determine the subgroup of species in the grouping which are indistinguishable
from the species with the lowest median characteristic value using a Tukey multiple comparison test (Appendix X4 and Ref (7))
on the medians at a 0.01 significance level. The median or mean characteristic value for the group shall be determined from the
combined data of all the species in this subgroup.
10.2.2 Adding New Species to Existing Group:
10.2.2.1 A new species may be added to an existing species grouping without modification of the group median or mean
characteristic value if the median value of the new species is greater than or equal to the existing group median characteristic value.
10.2.2.2 If the requirements of 10.2.2.1 are not met, determine the combined group median or mean characteristic value in
accordance with 10.2.1. If the data will not permit the use of 10.2.1, then the group median or mean characteristic value shall be
the median or mean of the newly included species.
10.3 Grouping for Tolerance Limit Properties:
10.3.1 New Species Grouping:
10.3.1.1 To assign a tolerance limit characteristic value to a new grouping, determine the tolerance limit value for the combined
grouping (Note 16). Determine the number of pieces in each species group below the group tolerance limit value. Conduct a Chi
Square test (Appendix X7) to determine if the percent of pieces below the group value is statistically significant for each species
in the group.
NOTE 16—To determine a group tolerance limit value, each species to be included in the group should have a minimum sample size of at least 100
per property in order for the Chi Square test to be sufficiently sensitive (8) .
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10.3.1.2 If the test is not significant at the 0.01 level, the group characteristic value shall be determined from the grouped data
of all the species in the new grouping.
10.3.1.3 If the test is significant at the 0.01 level, begin with a subgroup consisting of the two species with the highest percent
of pieces below the group value. Use the Chi Square test to determine if the percent of pieces below the group value are
comparable. Repeat this process, adding the species with the next highest percent of pieces below the group value to the previous
group. Continue adding species until the test is significant at the 0.01 level. The group tolerance limit is determined from the
combined data of the last subgroup of species for which the Chi Square test was not significant at the 0.01 level.
10.3.2 Adding New Species to Existing Group:
10.3.2.1 A new species may be included with an existing species grouping if the tolerance limit of the new species is equal to
or greater than the current characteristic value for the group.
10.3.2.2 If the requirements of 10.3.2.1 are not met, determine the combined species group value in accordance with 10.3.1. If
the data will not permit the use of 10.3.1, the group characteristic value shall be the tolerance limit value of the newly included
species.
11. Establishing Grade Relationships for Stress and Modulus of Elasticity
11.1 The adjustment model for grade shall be based on relating the characteristic values determined in Section 9 modified for
species grouping (Section 10), if appropriate, to the corresponding assumed minimum GQI values (see Appendix X8). The grade
model constructed from the data may consist of either a linear relationship connecting the adjacent points or a mathematically fitted
curve. The selected relationship shall be demonstrated to be appropriate (Note 17).
NOTE 17—The structural visual grade No. 1 (1, 2, 3, 4) has a highly restricted grade description. In the North American In-Grade test program, it was
deemed appropriate for bending and tension to use only 85 % of the No. 1 value that linear interpolation between select structural and No. 2 permitted.
For compression, 95 % of the permitted No. 1 value was used (see Appendix X8). Alternatively, the No. 1 values could have been set equal to the No.
2 values.
11.2 Estimate the characteristic values for untested grades from the model selected in 11.1. Use the assumed minimum GQI for
the grade determined from the minimum grade requirements (see Appendix X8).
11.2.1 If the grade adjustment model is used to extrapolate beyond the sample matrix, provide additional supporting
documentation to demonstrate that the procedure is conservative.
12. Establishing Allowable Properties
12.1 The characteristic values established in Section 9 and modified in Sections 10 and 11, and the estimated values for untested
grades are based on short term tests adjusted to standardized conditions. These characteristic values shall be further modified for
thickness, width, length, moisture content, load duration and safety. The adjustments in this section will convert the characteristic
values to allo
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