ASTM D7341-21

Standard Practice for Establishing Characteristic Values for Flexural Properties of Structural Glued Laminated Timber by Full-Scale Testing

SIGNIFICANCE AND USE
10.1 Full-scale bending testing is an effective way to determine flexural properties of structural glued laminated timber (glulam) beams. However, testing of large glulam members is cost prohibitive. Mathematical models, when confirmed by full-scale test results, are useful tools to assign flexural properties for glulam. This practice provides guidelines for sampling and testing full-scale glulam beams to determine their flexural properties and to validate mathematical models intended for use in assigning flexural design values.
SCOPE
1.1 This practice describes procedures for full scale testing of structural glued laminated timber (glulam) to determine or verify characteristic values used to calculate flexural design properties. Guidelines are given for: (1) testing individual structural glued laminated timber lay-ups (with no modeling), (2) testing individual glulam combinations (with limited modeling), and (3) validating models used to predict characteristic values.  
1.2 This practice is limited to procedures for establishing flexural properties (Modulus of Rupture, MOR, and Modulus of Elasticity, MOE). Some of the principles for sampling and analysis presented may be applicable to other properties. However, other properties may require additional testing considerations that are beyond the scope of this practice.  
1.3 This practice is not intended to supersede the provisions of Practice D3737, but provides an alternative method for establishing characteristic values. Lay-up combinations developed in accordance with Practice D3737 are not required to be governed by this standard.
Note 1: The models described by Practice D3737 have been developed and modified based on more than 50 years of experience and many test programs. In some cases, however, it may be desirable to develop a new model based on other input properties or using lumber materials or grades not covered by that standard.  
1.4 Details of production, inspection, and certification are beyond the scope of this document. However, for test results to be representative of production, quality control systems shall be in place to ensure consistent quality. Manufacturing shall conform to recognized manufacturing standards such as ANSI A190.1 or CSA O122.  
1.5 The values stated in inch-pound units are to be regarded as standard. No other units of measurement are included in this standard.  
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2021
• ICS: 79.060.99 - Other wood-based panels
• Technical Committee: D07 - Wood
• Drafting Committee: D07.02 - Lumber and Engineered Wood Products

Relations

• Refers: ASTM D3737-18(2023)e1 - Standard Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam)
• Effective Date: 01-Oct-2023
• 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 D5456-18 - Standard Specification for Evaluation of Structural Composite Lumber Products
• Effective Date: 01-Apr-2018
• Refers: ASTM D3737-18e1 - Standard Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam)
• Effective Date: 01-Apr-2018
• Refers: ASTM D3737-18 - Standard Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam)
• Effective Date: 01-Apr-2018
• Refers: ASTM D5456-17 - Standard Specification for Evaluation of Structural Composite Lumber Products
• Effective Date: 01-Mar-2017
• Refers: ASTM D5456-17e1 - Standard Specification for Evaluation of Structural Composite Lumber Products
• Effective Date: 01-Mar-2017
• Refers: ASTM D5456-14b - Standard Specification for Evaluation of Structural Composite Lumber Products
• Effective Date: 01-Oct-2014
• Refers: ASTM D5456-14a - Standard Specification for Evaluation of Structural Composite Lumber Products
• Effective Date: 01-May-2014
• Refers: ASTM D5456-14 - Standard Specification for Evaluation of Structural Composite Lumber Products
• 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
• Refers: ASTM D198-14 - Standard Test Methods of Static Tests of Lumber in Structural Sizes
• Effective Date: 01-Feb-2014
• Refers: ASTM D5456-13a - Standard Specification for Evaluation of Structural Composite Lumber Products
• Effective Date: 01-Oct-2013
• Refers: ASTM D198-13 - Standard Test Methods of Static Tests of Lumber in Structural Sizes
• Effective Date: 01-Oct-2013

Overview

ASTM D7341-21 is the international standard practice developed by ASTM International for establishing characteristic values for flexural properties of structural glued laminated timber (glulam) through full-scale testing. This standard outlines detailed procedures for the sampling and testing of glulam beams, enabling verification or determination of key flexural properties such as Modulus of Rupture (MOR) and Modulus of Elasticity (MOE). ASTM D7341-21 is essential for building professionals, structural engineers, and manufacturers who need reliable flexural design values for engineered timber products. The practice also supports the validation of mathematical models used in deriving design values, increasing the efficiency and accuracy of glulam beam evaluations.

Key Topics

• Full-Scale Bending Testing: Procedures for testing full-size structural glued laminated timber beams to establish characteristic flexural properties.
• Model Validation: Provides guidelines for validating mathematical models with empirical full-scale testing results to assign flexural design values.
• Sampling and Lay-Up Guidelines: Outlines minimum sample sizes, selection of lay-ups and combinations, as well as procedures to ensure samples are representative of actual production.
• Analysis and Applicability: Details analytical methods, including transformed section analysis, for evaluating test results and determining the applicability of findings.
• Quality Assurance: Emphasizes the importance of quality control systems and conformance with manufacturing standards such as ANSI A190.1 and CSA O122 to ensure consistent glulam product performance.
• Safety and Regulatory Compliance: Reminds users to address relevant safety, health, and environmental practices during testing.

Applications

ASTM D7341-21 is widely used in the timber and construction industries to:

• Establish Design Values: Assign reliable structural flexural properties for glulam beams used in buildings, bridges, and other timber structures.
• Validate New Material Models: Confirm the performance of engineered wood products or new lumber grades not previously covered by existing standards.
• Support Product Certification: Provide a reproducible testing protocol that supports manufacturers and third-party agencies in product approval processes.
• Optimize Product Design: Allow engineers to use validated data and modeling for efficient glulam design, reducing material waste and cost.
• Quality Control and Consistency: Ensure that production meets specified performance criteria, supporting ongoing quality assurance and regulatory compliance.

Related Standards

Several standards are referenced in ASTM D7341-21 and are integral to its implementation:

• ASTM D198: Test Methods of Static Tests of Lumber in Structural Sizes - Primary mechanical testing reference.
• 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 D3737: Practice for Establishing Allowable Properties for Glulam - Offers alternative procedures and modeling.
• ASTM D4761: Test Methods for Mechanical Properties of Lumber and Wood-Based Materials.
• ANSI A190.1: American National Standard for Structural Glued Laminated Timber.
• CSA O122: Canadian Standard for Glulam.
• AITC Test T119: Full Size End Joint Tension Test.
• PS-20: Voluntary Product Standard for Softwood Lumber.

Practical Value

Following ASTM D7341-21 ensures that glulam beams used in structural applications are assigned accurate, verified flexural properties. This enables safe, efficient design and application of engineered timber, supports regulatory compliance, and builds confidence with stakeholders ranging from manufacturers to project designers and regulatory bodies. Adherence to this standard guarantees that products are evaluated through robust sampling, testing, and analysis methods, making it a critical document for anyone involved in the production, design, or specification of structural glued laminated timber.

Keywords: ASTM D7341-21, glued laminated timber, glulam, flexural properties, Modulus of Rupture, Modulus of Elasticity, full-scale testing, lay-up, characteristic value, timber design, structural wood standards.

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: D7341 − 21
Standard Practice for
Establishing Characteristic Values for Flexural Properties of
Structural Glued Laminated Timber by Full-Scale Testing
This standard is issued under the fixed designation D7341; 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.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice describes procedures for full scale testing
responsibility of the user of this standard to establish appro-
of structural glued laminated timber (glulam) to determine or
priate safety, health, and environmental practices and deter-
verify characteristic values used to calculate flexural design
mine the applicability of regulatory limitations prior to use.
properties. Guidelines are given for: (1) testing individual
1.7 This international standard was developed in accor-
structural glued laminated timber lay-ups (with no modeling),
dance with internationally recognized principles on standard-
(2) testing individual glulam combinations (with limited
ization established in the Decision on Principles for the
modeling), and (3) validating models used to predict charac-
teristic values. Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.2 This practice is limited to procedures for establishing
Barriers to Trade (TBT) Committee.
flexural properties (Modulus of Rupture, MOR, and Modulus
of Elasticity, MOE). Some of the principles for sampling and
2. Referenced Documents
analysis presented may be applicable to other properties.
However, other properties may require additional testing con-
2.1 ASTM Standards:
siderations that are beyond the scope of this practice.
D198 Test Methods of Static Tests of Lumber in Structural
Sizes
1.3 This practice is not intended to supersede the provisions
D245 Practice for Establishing Structural Grades and Re-
of Practice D3737, but provides an alternative method for
lated Allowable Properties for Visually Graded Lumber
establishing characteristic values. Lay-up combinations devel-
D2915 Practice for Sampling and Data-Analysis for Struc-
oped in accordance with Practice D3737 are not required to be
governed by this standard. tural Wood and Wood-Based Products
D3737 Practice for Establishing Allowable Properties for
NOTE 1—The models described by Practice D3737 have been devel-
oped and modified based on more than 50 years of experience and many
Structural Glued Laminated Timber (Glulam)
test programs. In some cases, however, it may be desirable to develop a
D4761 Test Methods for Mechanical Properties of Lumber
new model based on other input properties or using lumber materials or
and Wood-Based Structural Materials
grades not covered by that standard.
D5456 Specification for Evaluation of Structural Composite
1.4 Details of production, inspection, and certification are
Lumber Products
beyond the scope of this document. However, for test results to
D6815 Specification for Evaluation of Duration of Load and
be representative of production, quality control systems shall
Creep Effects of Wood and Wood-Based Products
be in place to ensure consistent quality. Manufacturing shall
2.2 Other Standards:
conform to recognized manufacturing standards such as ANSI
AITC Test T119 Full Size End Joint Tension Test
A190.1 or CSA O122.
ANSI A190.1 American National Standard for Wood Prod-
1.5 The values stated in inch-pound units are to be regarded
ucts – Structural Glued Laminated Timber
as standard. No other units of measurement are included in this
standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This practice is under the jurisdiction of ASTM Committee D07 on Wood and Standards volume information, refer to the standard’s Document Summary page on
is the direct responsibility of Subcommittee D07.02 on Lumber and Engineered the ASTM website.
Wood Products. Available from the Pacific Lumber Inspection Bureau, 1010 South 336th St.
Current edition approved April 1, 2021. Published April 2021. Originally #210 Federal Way, WA 98003, http://www.aitc-glulam.org.
approved in 2008. Last previous edition approved in 2014 as D7341 – 14. DOI: Available from APA—The Engineered Wood Association, 7011 South 19th
10.1520/D7341-21. Street, Tacoma, WA 98466, http://www.apawood.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7341 − 21
ANSI/AWC NDS National Design Specification for Wood 3.2.8 well-defined grade, n—A lumber grade with specific
Construction limits on acceptable characteristics, such as knots, slope of
CSA O122 Structural Glued Laminated Timber grain, density, modulus of elasticity, tensile strength, etc., to
PS 20 American Softwood Lumber Standard ensure reproducibility in production.
3. Terminology
4. Modeling Requirements
3.1 Definitions—For definitions of terms related to wood,
4.1 General:
refer to Terminology D9.
4.1.1 Purpose for Modeling—For test results to be appli-
3.2 Definitions of Terms Specific to This Standard: cable to structural glued laminated timber sizes that are not
tested, it is necessary to relate the properties of the component
3.2.1 apparent properties, n—Mechanical properties as re-
lated to the actual cross-sectional dimensions of the structural laminations to the beam properties through the use of an
analytical model.
glued laminated timber.
4.1.2 Predictive Models—Models that will be used to de-
3.2.2 characteristic value, n—A test statistic from which
velop new combinations, predict characteristic values, and
design values can be derived by the application of appropriate
assign design values shall be able to predict accurately these
adjustment factors.
valuesforabroadrangeofcombinations.Theseresultsmustbe
3.2.2.1 Discussion—For strength properties of structural
validated by full-scale tests according to appropriate test
glued laminated timber, this value is typically a fifth percentile
methods for the property of interest.
estimate with 75 % confidence. For deformation-based
4.1.3 Single Combination—For comparing different lay-ups
properties, such as modulus of elasticity, this value is repre-
and identifying critical sizes for testing within a single
sented by the average value. Other statistics are permitted to be
combination, transformed section analysis is sufficient to
used as characteristic values for input properties of laminations
predict the stresses on each grade in the lay-up relative to the
depending on the model. Characteristic values for structural
stresses in the tested lay-up. No further modeling shall be
glued laminated timber are typically based on apparent prop-
required.
erties.
4.1.4 Single Lay-Up—All modeling requirements shall be
3.2.3 combination, n—A series of lay-ups having similar
waived if the test results are limited to a single, well-defined
lamination properties (grades, species, and end joint strengths),
lay-up (that is, the number of laminations is fixed, the
similar percentages of grade placement in the areas of critical
lamination properties are well defined, and the size (depth)
stresses, and similar predicted properties, that are grouped
tested is representative of the size intended for production).
together for design purposes.
4.2 Minimum Model Inputs:
NOTE2—Anexampleofalay-upcombinationbasedonPracticeD3737
4.2.1 General—At a minimum, a suitable model shall be
would be a 24F-V4 Douglas fir combination.
based on defined lamination properties representative of the
3.2.4 lay-up, n—The specific arrangement of well-defined
material used for each lamination and shall account for the
laminationgradesforasinglestructuralgluedlaminatedtimber
placement of different qualities of laminations throughout the
depth.
cross section.
4.2.2 Lamination Properties—The model shall account for
3.2.5 model, n—Amathematicalmethodforpredictingchar-
both lumber and end joint properties.
acteristic values for full-scale laminated timber based on the
input properties of the individual laminations. 4.2.2.1 Lumber Grade—The species and grades of lumber
used in structural glued laminated timber shall be well defined
3.2.6 reference value, n—The characteristic value of a
to ensure consistent performance between the grades used in
material that has been adjusted by the procedures in Practice
test members and future production members. Strength and
D2915 for use in design equations, but has not been adjusted
stiffness properties for the laminations shall be assigned
for end-use conditions.
according to the lumber grade. For deterministic models, the
3.2.7 structural-glued-laminated timber, n—An engineered,
properties assigned to the grade shall be a representative
stress-rated product of a timber laminating plant comprising
characteristic value for the grade. For probabilistic models, a
assemblies of specially selected and prepared wood lamina-
parametric distribution of values shall be determined to repre-
tions securely bonded together with adhesives, with the fol-
sent the grade.
lowing characteristics: (1) the grain of all laminations is
(1) Species—The species or groups of species permitted by
approximately parallel longitudinally; and (2) the laminations
the grade shall be well defined and shall be represented in the
may be comprised of pieces end-joined to form any length, of
tested members.
pieces placed or glued edge-to-edge to make wider ones or
(2) Modulus of Elasticity—For each grade of lumber used,
pieces bent to curved form during gluing.
the modulus of elasticity shall be determined in accordance
with Test Methods D198 or D4761 or by the procedures of
Specification D5456 or Practice D245.
Available from American Wood Council, 222 Catoctin Circle, SE, Suite 201,
Leesburg, VA 20175, http://www.awc.org
(3) Strength—Strength values shall be assigned to each
Available from Canadian Standards Association (CSA), 5060 Spectrum Way,
grade of lumber used in the laminated timber. Values shall be
Mississauga, ON L4W 5N6, Canada, http://www.csa.ca.
determined by testing in accordance with Test Methods D198
Available fromAmerican Lumber Standard Committee, 7470 New Technology
Way, Suite F, Frederick, MA 21703, http://www.alsc.org. or D4761 or by the procedures of Specification D5456 or
D7341 − 21
Practice D245. Strength values are also permitted to be temperature of the test specimens shall not be less than 50°F
assigned to a grade zone based on its interaction with the beam nor more than 90°F at the time of the tests.
as a whole. (For example, the I /I model used in Practice
K G
5.4 Sampling Requirements for a Single Lay-Up:
D3737 assigns strength values in this way.)
5.4.1 Grading and Lay-Up—Lamination quality (grades,
(4) Creep—Structural composite lumber for use in struc-
species, and end joint strength) and grade placement shall be
tural glued laminated timber shall demonstrate creep perfor-
well defined and verified prior to testing.
mance similar to solid wood as demonstrated by Specification
5.4.2 Specimen Size(s)—Specimens for testing shall be the
D6815.
specific size (depth) of a single, well-defined lay-up in accor-
4.2.2.2 End Joint Strength—The model shall include the
dance with 4.1.4. Width of the specimens shall be representa-
effect of end joints (if used) stressed in tension. Appropriate
tive of the size intended for production. For horizontally
end joint tensile strengths shall be determined by full-scale
laminated beams, a single width is permitted to be considered
tension testing in accordance with AITC Test T119 and main-
representative of members with widths not more than 2 in.
tained through in-plant quality control procedures.
wider nor 2 in. narrower than the tested width, provided that
4.2.3 Arrangement of Grades (Lay-Up)—The arrangement
the selection (grading) criteria relative to the cross-sectional
of laminations of varying quality throughout a laminated
sizeisthesameforeachwidth.Forverticallylaminatedbeams,
timber can significantly alter the stress distribution and perfor-
the depth of test specimens shall be representative of intended
manceofthemember.Themodelshallaccountfortheseeffects
productionsizes,andthewidthshallbebasedonthenumberof
if more than one grade of laminations is to be used. The
laminations and shall be equal to the number of laminations
placement of grades shall be well defined to ensure proper
intended for use in productio
...

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: D7341 − 14 D7341 − 21
Standard Practice for
Establishing Characteristic Values for Flexural Properties of
Structural Glued Laminated Timber by Full-Scale Testing
This standard is issued under the fixed designation D7341; 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.
1. Scope
1.1 This practice describes procedures for full scale testing of structural glued laminated timber (glulam) to determine or verify
characteristic values used to calculate flexural design properties. Guidelines are given for: (1) testing individual structural glued
laminated timber lay-ups (with no modeling), (2) testing individual glulam combinations (with limited modeling), and (3)
validating models used to predict characteristic values.
1.2 This practice is limited to procedures for establishing flexural properties (Modulus of Rupture, MOR, and Modulus of
Elasticity, MOE). Some of the principles for sampling and analysis presented may be applicable to other properties. However, other
properties may require additional testing considerations that are beyond the scope of this practice.
1.3 This practice is not intended to supersede the provisions of Practice D3737, but provides an alternative method for establishing
characteristic values. Lay-up combinations developed in accordance with Practice D3737 are not required to be governed by this
standard.
NOTE 1—The models described by Practice D3737 have been developed and modified based on more than 50 years of experience and many test programs.
In some cases, however, it may be desirable to develop a new model based on other input properties or using lumber materials or grades not covered
by that standard.
1.4 Details of production, inspection, and certification are beyond the scope of this document. However, for test results to be
representative of production, quality control systems shall be in place to ensure consistent quality. Manufacturing shall conform
to recognized manufacturing standards such as ANSI A190.1 or CSA O122.
1.5 Adjustments to characteristic values to determine reference values for design shall be in accordance with Practice D2915 for
allowable stress design (ASD) or Specification D5457 for load and resistance factor design (LRFD).
1.6 Adjustments to ASD reference values for end-use conditions intended for design purposes shall be performed in accordance
with Practice D3737. The same adjustment factors shall apply to LRFD reference values, except that the ASD load duration factor
shall be replaced by an appropriate LRFD time effect factor as determined in accordance with recognized industry practice.
1.5 The values stated in inch-pound units are to be regarded as standard. No other units of measurement are included in this
standard.
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 Feb. 1, 2014April 1, 2021. Published March 2014April 2021. Originally approved in 2008. Last previous edition approved in 20092014 as
D7341 – 09.D7341 – 14. DOI: 10.1520/D7341-14.10.1520/D7341-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7341 − 21
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.7 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:
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
D2915 Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
D3737 Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam)
D4761 Test Methods for Mechanical Properties of Lumber and Wood-Based Structural Materials
D5456 Specification for Evaluation of Structural Composite Lumber Products
D5457 Specification for Computing Reference Resistance of Wood-Based Materials and Structural Connections for Load and
Resistance Factor Design
D6815 Specification for Evaluation of Duration of Load and Creep Effects of Wood and Wood-Based Products
2.2 Other Standards:
AITC Test T119 Full Size End Joint Tension Test
ANSI A190.1 American National Standard for Wood Products – Structural Glued Laminated Timber
ANSI/AWC NDS National Design Specification for Wood Construction
CSA O122 Structural Glued Laminated Timber
PS-20PS 20 Voluntary Product Standard, ALSAmerican Softwood Lumber Standard
3. Terminology
3.1 Definitions—For definitions of terms related to wood, refer to Terminology D9.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 apparent properties, n—Mechanical properties as related to the actual cross-sectional dimensions of the structural glued
laminated timber.
3.2.2 characteristic value, n—A test statistic from which design values can be derived by the application of appropriate adjustment
factors.
3.2.2.1 Discussion—
For strength properties of structural glued laminated timber, this value is typically a fifth percentile estimate with 75 % confidence.
For deformation-based properties, such as modulus of elasticity, this value is represented by the average value. Other statistics are
permitted to be used as characteristic values for input properties of laminations depending on the model. Characteristic values for
structural glued laminated timber are typically based on apparent properties.
3.2.3 combination, n—A series of lay-ups having similar lamination properties (grades, species, and end joint strengths), similar
percentages of grade placement in the areas of critical stresses, and similar predicted properties, that are grouped together for
design purposes.
NOTE 2—An example of a lay-up combination based on Practice D3737 would be a 24F-V4 Douglas fir combination.
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.
Available from the West Coast Lumber Inspection Bureau (WCLIB), 6980 S. W. Varns, Tigard, OR 97223, http://www.wclib.org.Pacific Lumber Inspection Bureau, 1010
South 336th St. #210 Federal Way, WA 98003, http://www.aitc-glulam.org.
Available from APA—The Engineered Wood Association, 7011 South 19th Street, Tacoma, WA 98466, http://www.apawood.org.
Available from American Wood Council, 222 Catoctin Circle, SE, Suite 201, Leesburg, VA 20175, http://www.awc.org
Available from Canadian Standards Association (CSA), 5060 Spectrum Way, Mississauga, ON L4W 5N6, Canada, http://www.csa.ca.
Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov. American
Lumber Standard Committee, 7470 New Technology Way, Suite F, Frederick, MA 21703, http://www.alsc.org.
D7341 − 21
3.2.4 lay-up, n—The specific arrangement of well-defined lamination grades for a single structural glued laminated timber depth.
3.2.5 model, n—A mathematical method for predicting characteristic values for full-scale laminated timber based on the input
properties of the individual laminations.
3.2.6 reference value, n—The characteristic value of a material that has been adjusted by the procedures in Practice D2915 or
Specification D5457for use in design equations, but has not been adjusted for end-use conditions.
3.2.7 structural-glued-laminated timber, n—An engineered, stress-rated product of a timber laminating plant comprising
assemblies of specially selected and prepared wood laminations securely bonded together with adhesives, with the following
characteristics: (1) the grain of all laminations is approximately parallel longitudinally; and (2) the laminations may be comprised
of pieces end-joined to form any length, of pieces placed or glued edge-to-edge to make wider ones or pieces bent to curved form
during gluing.
3.2.8 well-defined grade, n—A lumber grade with specific limits on acceptable characteristics, such as knots, slope of grain,
density, modulus of elasticity, tensile strength, etc., to ensure reproducibility in production.
4. Modeling Requirements
4.1 General:
4.1.1 Purpose for Modeling—For test results to be applicable to structural glued laminated timber sizes that are not tested, it is
necessary to relate the properties of the component laminations to the beam properties through the use of an analytical model.
4.1.2 Predictive Models—Models that will be used to develop new combinations, predict characteristic values, and assign design
values shall be able to predict accurately these values for a broad range of combinations. These results must be validated by
full-scale tests according to appropriate test methods for the property of interest.
4.1.3 Single Combination—For comparing different lay-ups and identifying critical sizes for testing within a single combination,
transformed section analysis is sufficient to predict the stresses on each grade in the lay-up relative to the stresses in the tested
lay-up. No further modeling shall be required.
4.1.4 Single Lay-Up—All modeling requirements shall be waived if the test results are limited to a single, well-defined lay-up (that
is, the number of laminations is fixed, the lamination properties are well defined, and the size (depth) tested is representative of
the size intended for production).
4.2 Minimum Model Inputs:
4.2.1 General—At a minimum, a suitable model shall be based on defined lamination properties representative of the material used
for each lamination and shall account for the placement of different qualities of laminations throughout the cross section.
4.2.2 Lamination Properties—The model shall account for both lumber and end joint properties.
4.2.2.1 Lumber Grade—The species and grades of lumber used in structural glued laminated timber shall be well defined to ensure
consistent performance between the grades used in test members and future production members. Strength and stiffness properties
for the laminations shall be assigned according to the lumber grade. For deterministic models, the properties assigned to the grade
shall be a representative characteristic value for the grade. For probabilistic models, a parametric distribution of values shall be
determined to represent the grade.
(1) Species—The species or groups of species permitted by the grade shall be well defined and shall be represented in the tested
members.
(2) Modulus of Elasticity—For each grade of lumber used, the modulus of elasticity shall be determined in accordance with
Test Methods D198 or D4761 or by the procedures of Specification D5456 or Practice D245.
(3) Strength—Strength values shall be assigned to each grade of lumber used in the laminated timber. Values shall be
determined by testing in accordance with Test Methods D198 or D4761 or by the procedures of Specification D5456 or Practice
D245. Strength values are also permitted to be assigned to a grade zone based on its interaction with the beam as a whole. (For
example, the I /I model used in Practice D3737 assigns strength values in this way.)
K G
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(4) Creep—Structural composite lumber for use in structural glued laminated timber shall demonstrate creep performance
similar to solid wood as demonstrated by Specification D6815.
4.2.2.2 End Joint Strength—The model shall include the effect of end joints (if used) stressed in tension. Appropriate end joint
tensile strengths shall be determined by full-scale tension testing in accordance with AITC Test T119 and maintained through
in-plant quality control procedures.
4.2.3 Arrangement of Grades (Lay-Up)—The arrangement of laminations of varying quality throughout a laminated timber can
significantly alter the stress distribution and performance of the member. The model shall account for these effects if more than
one grade of laminations is to be used. The placement of grades shall be well defined to ensure proper modeling and reproducibility
in production.
4.3 Minimum Model Analyses:
4.3.1 Transformed-Section Analysis—The stresses at the location of each change of grade in a cross section shall be determined
using transformed section analysis. For deterministic analyses, the average modulus of elasticity of each lumber grade shall be
used. The use of probabilistic models with simulated values of modulus of elasticity is also acceptable.
4.3.2 Prediction of Propert
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