ASTM D6815-22a

Standard Specification for Evaluation of Duration of Load and Creep Effects of Wood and Wood-Based Products

ABSTRACT
This specification covers the procedure for testing and evaluating duration of load and creep effects of wood and wood-based materials relative to an accepted duration of load adjustment model. This specification is proposed for use for products that are covered by a consensus standard such as lumber, structural composite lumber and structural use panels. The procedure covered in this specification, however, is not intended to evaluate performance of products under impact loading.
SCOPE
1.1 This specification provides a procedure for testing and evaluating duration of load and creep effects of wood and wood-based materials relative to an accepted duration of load adjustment model. This specification was created for products that are currently covered by a consensus standard (for example, lumber, structural composite lumber, and structural-use panels). This procedure is intended to demonstrate the engineering equivalence to the duration of load and creep effects of visually graded lumber as specified in Practice D245 for a product under evaluation used in dry service conditions. This procedure is not intended to evaluate the performance of products under impact loading. Quantification of specific duration of load or creep factors is beyond the scope of this specification. For further guidance regarding the applicability of this specification refer to X1.1 in the Commentary.  
1.2 Use of the procedure in this specification to determine equivalence to the Practice D245 duration of load relationship is limited to solid wood and wood-based products whose long term load behavior is similar to that of solid wood. Equivalence demonstrated in this specification is dependent upon evaluation of a product's 90-day (minimum) creep-rupture performance. In this evaluation, three criteria must be satisfied: (1) adequate strength over a 90-day period, (2) decreasing creep rate, and (3) limited fractional deflection. A summary of the development of these criteria and the underlying assumptions behind them is provided in the Commentary in Appendix X1 and Appendix X2.  
1.3 Long term degradation phenomena not described by a creep-rupture model are not addressed in this specification (see Commentary X1.2.4).  
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.5 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-Oct-2022
• ICS: 79.080 - Semi-manufactures of timber
• Technical Committee: D07 - Wood
• Drafting Committee: D07.01 - Fundamental Test Methods and Properties

Relations

• 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 D3043-17 - Standard Test Methods for Structural Panels in Flexure
• Effective Date: 15-Nov-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 D4442-15 - Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• Effective Date: 01-Jun-2015
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• 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
• Refers: ASTM D198-13 - Standard Test Methods of Static Tests of Lumber in Structural Sizes
• Effective Date: 01-Oct-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM D4761-13 - Standard Test Methods for Mechanical Properties of Lumber and Wood-Base Structural Material
• Effective Date: 01-Apr-2013
• Refers: ASTM D9-12 - Standard Terminology Relating to Wood and Wood-Based Products
• Effective Date: 15-Oct-2012
• Refers: ASTM D3043-00(2011) - Standard Test Methods for Structural Panels in Flexure
• Effective Date: 01-Nov-2011

Overview

ASTM D6815-22a is a standard specification developed by ASTM International to provide a procedure for evaluating the duration of load and creep effects in wood and wood-based products. This standard is crucial for manufacturers, engineers, and regulators seeking to verify that new engineered wood products perform comparably to traditional solid sawn lumber under sustained loading conditions. The specification is primarily intended for products such as lumber, structural composite lumber, and structural-use panels that are covered by consensus standards.

ASTM D6815-22a focuses on evaluating products under dry service conditions and is not intended for assessing impact loading or effects unrelated to creep-rupture mechanisms. By following this standardized procedure, stakeholders can ensure proper product performance over time when subjected to constant mechanical stresses.

Key Topics

Core Elements of ASTM D6815-22a:

• Scope of Evaluation: Applies to wood and wood-based products with long-term load behavior similar to solid wood, such as lumber and structural panels. Excludes impact loading performance assessment.
• Testing Procedures: Outlines methods for conducting both short-term bending tests and long-term creep-rupture tests over a minimum of 90 days.
• Acceptance Criteria: Establishes benchmarks for:
  • Adequate strength throughout the test period
  • Decreasing creep rate over time
  • Limited fractional deflection after 90 days
• Comparative Approach: Uses engineering equivalence to visually graded lumber standards (referencing ASTM D245), which helps qualify products for duration of load and creep adjustments defined in design codes.
• Environmental Control: Specifies dry service conditions and detailed protocols for moisture content and temperature during testing.
• Test Reporting: Requires detailed documentation of material characteristics, test setup, environmental conditions, and statistical analyses.
• Retest and Acceptance Options: Provides procedures for retesting at reduced stress levels if initial acceptance criteria are not met, along with guidelines for allowable property adjustments.

Keywords: wood creep testing, duration of load, wood-based products, structural lumber, ASTM D6815, structural composite lumber, performance evaluation.

Applications

ASTM D6815-22a has practical applications throughout the wood products supply chain, particularly in:

• Product Development: Enables manufacturers of new engineered wood products (e.g., laminated veneer lumber, oriented strand board) to confirm that their materials will perform reliably under typical building service loads.
• Regulatory Compliance: Supports code bodies and regulatory authorities in determining if a product can be safely specified under existing building codes that assume solid wood performance.
• Quality Assurance: Assists quality control professionals in benchmarking new products against established standards for creep and long-term strength.
• Structural Design: Provides engineers and specifiers with validated performance data, ensuring safety and serviceability of structures using these products.
• Technical Documentation: Offers a basis for preparing technical datasheets and certification reports for both domestic and international markets.

Related Standards

Several other standards and documents are directly referenced or relevant when working with ASTM D6815-22a:

• ASTM D245 – Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber
• ASTM D198 – Test Methods of Static Tests of Lumber in Structural Sizes
• ASTM D1037 – Test Methods for Evaluating Properties of Wood-Base Fiber and Particle Panel Materials
• ASTM D2915 – Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
• ASTM D3043 – Test Methods for Structural Panels in Flexure
• ASTM D4442 – Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
• ASTM D4761 – Test Methods for Mechanical Properties of Lumber and Wood-Based Structural Materials
• ANSI/AWC NDS – National Design Specification for Wood Construction

By following ASTM D6815-22a and its related standards, stakeholders ensure a robust evaluation of the duration of load and creep effects, reinforcing product reliability and safety in the built environment.

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:D6815 −22a
Standard Specification for
Evaluation of Duration of Load and Creep Effects of Wood
and Wood-Based Products
This standard is issued under the fixed designation D6815; 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 1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This specification provides a procedure for testing and
ization established in the Decision on Principles for the
evaluating duration of load and creep effects of wood and
Development of International Standards, Guides and Recom-
wood-based materials relative to an accepted duration of load
mendations issued by the World Trade Organization Technical
adjustment model. This specification was created for products
Barriers to Trade (TBT) Committee.
that are currently covered by a consensus standard (for
example, lumber, structural composite lumber, and structural-
2. Referenced Documents
use panels). This procedure is intended to demonstrate the
2.1 ASTM Standards:
engineering equivalence to the duration of load and creep
D9 Terminology Relating to Wood and Wood-Based Prod-
effects of visually graded lumber as specified in Practice D245
ucts
for a product under evaluation used in dry service conditions.
D198 Test Methods of Static Tests of Lumber in Structural
This procedure is not intended to evaluate the performance of
Sizes
products under impact loading. Quantification of specific
D245 Practice for Establishing Structural Grades and Re-
duration of load or creep factors is beyond the scope of this
lated Allowable Properties for Visually Graded Lumber
specification. For further guidance regarding the applicability
D1037 Test Methods for Evaluating Properties of Wood-
of this specification refer to X1.1 in the Commentary.
Base Fiber and Particle Panel Materials
1.2 Use of the procedure in this specification to determine
D2915 Practice for Sampling and Data-Analysis for Struc-
equivalence to the Practice D245 duration of load relationship
tural Wood and Wood-Based Products
is limited to solid wood and wood-based products whose long
D3043 Test Methods for Structural Panels in Flexure
termloadbehaviorissimilartothatofsolidwood.Equivalence
D4442 Test Methods for Direct Moisture Content Measure-
demonstratedinthisspecificationisdependentuponevaluation
ment of Wood and Wood-Based Materials
of a product’s 90-day (minimum) creep-rupture performance.
D4761 Test Methods for Mechanical Properties of Lumber
In this evaluation, three criteria must be satisfied: (1) adequate
and Wood-Based Structural Materials
strengthovera90-dayperiod,(2)decreasingcreeprate,and(3)
E4 Practices for Force Calibration and Verification of Test-
limited fractional deflection.Asummary of the development of
ing Machines
these criteria and the underlying assumptions behind them is
E6 Terminology Relating to Methods of Mechanical Testing
provided in the Commentary in Appendix X1 and Appendix
E177 Practice for Use of the Terms Precision and Bias in
X2.
ASTM Test Methods
2.2 Other References:
1.3 Long term degradation phenomena not described by a
ANSI/AWS NDS National Design Specification (NDS) for
creep-rupture model are not addressed in this specification (see
Wood Construction
Commentary X1.2.4).
1.4 The values stated in inch-pound units are to be regarded
3. Terminology
as standard. The values given in parentheses are mathematical
3.1 Definitions—See Terminologies D9 and E6 and Prac-
conversions to SI units that are provided for information only
tices E4 and E177 for definitions of terms used in this
and are not considered standard.
specification.
1 2
This specification is under the jurisdiction ofASTM Committee D07 on Wood For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and is the direct responsibility of Subcommittee D07.01 on Fundamental Test contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Methods and Properties. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2022. Published November 2022. Originally the ASTM website.
approved in 2002. Last previous edition approved in 2022 as D6815– 22. DOI: Available fromAmerican Wood Council (AWC), 222 Catoctin Circle SE, Suite
10.1520/D6815-22A. 201, Leesburg, VA 20175, https://www.awc.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6815−22a
NOTE 1—Matching is a technique that attempts to subdivide the initial
3.2 Definitions of Terms Specific to This Standard:
sample population into two or more separate groups that possess near
3.2.1 breadth, n—dimension of the test specimen in the
identical distributional form and scale for bending properties. Matching
direction perpendicular to the span and perpendicular to the
specimens for the purposes of 5.1.1 should be done with care, considering
direction of an applied bending load.
errors introduced by the process and the characteristics of the material
under test.
3.2.2 creep, n—time-dependent increase of deformation of
the test material under a constant load. 5.1.2 Each test specimen shall be simply supported and
loaded by two equal concentrated forces spaced a distance of
3.2.3 creep deflection, n—total measured deflection at a
one-third the total span from the end supports (that is,
specific time minus the initial deflection.
third-point bending). Loads shall be applied in the product
3.2.4 creep rate, n—change in creep deflection over time.
orientation that represents the general intended use of the
3.2.5 creep-rupture, n—failure phenomenon described by a
product.
relationship between applied stress and time-to-failure.
5.1.2.1 Forjoist-formmaterials,thespantodepthratioshall
3.2.6 depth, n—dimension of the test specimen in the beasspecifiedinapplicableteststandards(seeNote2).Lateral
restraints shall be used when necessary to maintain lateral
direction perpendicular to the span and parallel to the direction
of an applied bending load. stability.The minimum test specimen cross section shall be 2.5
in. (63.5 mm) in depth and 1.0 in. (25.4 mm) in width.
3.2.7 dry service conditions, n—conditions in most covered
structures, where the moisture content of lumber will not
NOTE 2—For lumber sized products, span to depth ratios typically used
for flexural tests range between 17 and 21.
exceed 19 % (ANSI/AWC NDS).
3.2.8 duration of load factor, n—factor customarily used to 5.1.2.2 For sheathing-form materials, the test span shall be
not less than 48 times specimen thickness or 24 in., whichever
account for the effect of duration of load on the strength of
wood products. is greater.The specimen width for all sheathing-form materials
shall not be less than 12 in. (305 mm).
3.2.9 failure, n—point at which the test member can no
5.1.3 Moisture content shall be measured on the short-term
longer support the applied constant load.
specimens immediately after destructive testing and on the
3.2.10 fractional deflection, n—ratio of total deflection to
long-term specimens at the termination of the long–term test.
the initial deflection.
Measurement of moisture content shall be in accordance with
3.2.11 initial deflection, n—deflection at approximately one
Test Methods D4442. The average moisture content of all the
minute after the application of load.
long-term test specimens shall not deviate more than 62%
from the average moisture content of all the short–term test
3.2.12 span, n—distance between the centerlines of end
specimens (see Note 3).
reactions on which a test specimen is supported to accommo-
5.1.4 The test environment temperature and relative humid-
date a transverse bending load.
ity shall be recorded daily (see Commentary X1.4.5).The daily
average temperature of the test environment shall not decrease
4. Significance and Use
more than 5 °C (9 °F) below the temperature at which the
4.1 This specification provides a method for evaluating
short–term tests were conducted. At no time shall the test
duration of load and creep effects of wood and wood-based
environment reach a temperature less than 0 °C (32 °F).
products subjected to bending stress. This method is intended
NOTE 3—Conditioning the short-term and long-term test material for at
to demonstrate the engineering equivalence to the duration of
least 30 days in the anticipated test environment conditions generally
load and creep effects of visually graded lumber as specified in
provides compliance with the 62 % moisture content change criterion.
Practice D245 for a product under evaluation. Equivalence is
NOTE 4—In experiments where the temperature falls below the pre-
based on evaluating a product’s creep-rupture performance
scribed limit, it may be possible to demonstrate the validity of the data by
over a minimum of 90 days and meeting the requirements of continuing the experiment for an additional period at least equal to, and
possibly greater than, the amount of time the temperature was below the
this specification. This specification does not attempt to quan-
prescribed limit.
tify the effect of damage accumulation or to establish product-
specific duration of load factors for the product under evalua- 5.2 Short-Term Bending Tests:
tion. 5.2.1 The loading rate for the short-term tests shall be such
that the sample target failure load would be achieved in
5. Test Methods and Acceptance Criteria approximately 1 min. Failure load shall not be reached in less
than 10 s nor more than 10 min. The procedures of Test
5.1 Test Methods:
Methods D198 or D4761 shall be followed for joist-form
5.1.1 A test population shall be sampled from production
materials and Test Methods D1037 or D3043 for sheathing-
that is representative of the product under evaluation. Two
form materials.
matched test groups shall be selected, one for short-term
5.2.2 The sample standard deviation and the lower five
bending tests, and one for long-term creep-rupture bending
percent point estimate of the short-term test group (5 % PE)
tests. A minimum sample size of 28 is required for each test
shall be determined in accordance with Practice D2915.
group. If further testing is contemplated, additional test speci-
mens shall be sampled from the initial test population. Long- 5.3 Creep-Rupture Bending Tests:
term and short-term test specimens shall have the same cross 5.3.1 The creep-rupture test specimens shall be loaded such
section dimensions and length. that the average time to attain the pre-selected constant stress
D6815−22a
level does not exceed the average time to failure of the critical order statistic (N ≥ N ) then the product under evalu-
90 c
short-term tests (see 5.2.1). Thereafter, the specimens shall be ation fails to meet the adequate strength criterion with the
subjected to the constant stress for a minimum period of 90 sample population, N.
days. During this period, mid-span deflection readings shall be 5.4.1.3 If the number of failures at 90 days is equal to the
taken for each test specimen, until the 90-day period has critical order statistic (N = N)in 5.4.1.2, then additional
90 c
elapsed or until the occurrence of a failure.At a minimum, the testing may be conducted. In this case the sample population
deflection readings shall be taken at approximately one minute shall be increased by sampling an additional set of matched
after the application of the constant load (initial deflection), specimens in accordance with 5.1.1 sufficient to allow the use
and at the end of one hour, day 1, day 7, day 14, day 30, day of a higher non-parametric order statistic (see Note 6). The
60, and day 90. When better characterization of the creep rate additional specimens shall be tested for another 90-day test
is desired, more frequent deflection measurements should be duration. The adequate strength requirement of 5.4.1.1 is met
taken.Additionaldeflectionreadingsarerequiredwhenthetest when,attheendoftheadditionaltesting,thecombinednumber
extends beyond 90 days. When a specimen failure occurs, of specimen failures during these two test series (N com-
time-to-failure shall be recorded. bined) is less than the critical order statistic (N combined)
c
5.3.2 The specimens selected for these tests shall be tested based on the combined number of specimens evaluated (N
at a constant stress level, f , as determined in accordance with
combined).
b
Eq 1 (see Commentary Appendix X1).
NOTE 6—From Practice D2915 the order statistic for the lower 5 %
f 5 0.55 3 5% PE (1) tolerance limit with 75 % confidence, N , for various sample populations,
~ !
b c
N, is as follows:
where:
N 28 53 78 102
f = minimum applied bending stress, and N 1234
b c
5%PE = the lower five percent point estimate, as deter-
5.4.2 Decreasing Creep Rate—All the test specimens that
mined from the short-term bending tests in 5.2.
do not fail during the 90-day constant load period shall show a
The creep rate, fractional deflection (FD), and the total
decreasing creep rate.
number of failures at 90 days (N ) (or greater) shall be used to
90 5.4.2.1 To determine a decreasing creep rate, the change in
evaluate the acceptance of the product.
creep deflection shall be calculated between a minimum of
three equally spaced time segments that cover the full period
NOTE5—Examplesofacceptablecreepandcreep-rupturetestapparatus
under load. The change in calculated creep deflection shall
are given in Ref 1.
progressively decrease for each specimen. As an example, for
5.4 Acceptance Criteria—The product is considered accept-
the three equal periods of 0 to 30 days, 30 to 60 days, and 60
able for using the duration of load and creep factors applicable
to90days,thedecreasingcreepratefor90daysunderloadcan
to lumber if the following three criteria are all satisfied: (1)
be expressed as (see Commentary Appendix X2):
adequate strength over the test duration, (2) decreasing creep
D 2 D , D 2 D , D 2 D (3)
rate, and (3) a limited fractional deflection. ~ ! ~ ! ~ !
90 60 60 30 30 i
5.4.1 Adequate Strength—The total number of failures over
where:
the test duration shall be used to determine acceptance.
D = initial deflection (measured one-minute af-
i
5.4.1.1 The total number of failures at 90 or more days shall
ter application of the load in accordance
be less than the critical order statistic, N , of the lower 5 %
c
with 5.3.1), and
non-parametric tolerance limit with 75 % confidence:
D ,D ,D = deflections measured on 30th, 60th, and
30 60 90
N ,N (2)
90 c 90th day respectively.
NOTE 7—To better define the creep rate, additional segments with a
where:
shorter frequency (for example, five 18-day segments) may be used.
N = number of specimen failures at the end of the 90-day
5.4.2.2 If the difference in incremental creep deflection for
test period, and
the last two 30-day periods under load (for example, (D –
N = critical order statistic used to estimate the lower 5 %
c
D )–(D – D )) are within the precision of the deflection
60 60 30
non-parametric tolerance limit based on the number
measuring devices, it shall be permitted to override the
of specimens under long-term load (see Note 6).
decreasing creep rate criterion of 5.4.2.1 for not more than
For example, if 53 specimens are used in the creep-rupture
15 % of the surviving specimens if the difference in incremen-
tests, then N = 2 and no more than one specimen shall fail
c
tal creep deflection between the final two consecutive 30-day
within the 90-day period (N ≤ 1) for the product to be
periods is less than 0.5 % of the initial deflection of the same
accepted as meeting the adequate strength criterion.
specimen (for example, (D – D )–(D – D ) < 0.005D)
90 60 60 30 i
Alternatively, if 28 specimens are tested, then N = 1, and no
c
(see X2.4.4 in the Commentary).
failures shall occur (N = 0).
5.4.2.3 If the criteria of 5.4.2.1 and 5.4.2.2 are not satisfied
5.4.1.2 If the requirement of 5.4.1.1 is not met and the
at the end of the 90-day period, the test shall be extended for
number of failures at 90 days is greater than or equal to the
a minimum of 30 additional days. The change in calculated
creep rate for the additional time segment(s) after 90 days shall
progressively decrease relative to the preceding segment.
The boldface numbers in parentheses refer to the list of references at the end of
this standard. NOTE 8—The creep rate may fluctuate due to environmental changes in
D6815−22a
relative humidity or temperature, or both. Extending the test beyond the
∆ = initial deflection gauge reading prior to loading,
initial
90-day period in a controlled environment may demonstrate that the
in. (mm),
beams were not exhibiting tertiary behavior at the end of the period.
∆ = deflectiongaugereadingjustpriortounloading,
load-end
5.4.3 Fractional Deflection—Fractional deflection after
in. (mm), and
ninety (90) days for each surviving specimen shall not be
∆ = deflection gauge reading within 30 days after
unload-30
greater than 2.0:
unloading, in. (mm).
D
6.3.3 Average Residual Strength and Stiffness—The speci-
FD 5 # 2.0 (4)
D
i mens from the long-term loading retest shall be tested in
short-term bending in accordance with 5.1.2. The average
where:
residual strength and stiffness of the test specimens shall be
D = initial deflection (measured one-minute after applica-
i
greater than or equal to ninety percent (90 %) of that measured
tion of the load in accordance with 5.3.1), and
in the short-term bending tests of 5.2.
D = deflection measured on 90th day.
NOTE9—Theselectionofthereducedstresslevelisdefinedbytheuser;
6. Retest Option
and is an careful selection with the desire to assure that the product can
meet all six acceptance criteria.
6.1 If a product fails to meet the strength criterion of 5.4.1,
the product shall not be allowed to use the duration of load or
6.4 AllowablePropertyAdjustment—Iftheretestprovesthat
creep adjustments in the ANSI/AWC NDS. A retest at any
the product meets all the acceptance criteria defined in 6.3, all
stresslevellowerthanthatspecifiedin5.3.2isnotpermittedto
time-dependent member and connection properties defined by
satisfy the strength criterion of 5.4.1.
the NDS shall be reduced by the percent change in stress level
used in the retest(s).
6.2 If a product satisfies the strength criterion of 5.4.1 in the
original test at the stress level specified in 5.3.2, but fails to
7. Report
meet either or both of the deflection-based criteria of 5.4.2 and
7.1 The report content depends on the type of tests con-
5.4.3, the product proponent shall be allowed to conduct a
ducted. As a minimum, the report shall include the following
retest at a reduced stress level. The reduced stress level is
information:
defined by the user. The user shall be permitted to repeat this
7.1.1 Description of the material under evaluation, includ-
procedure until the acceptance criteria of 6.3 are satisfied.
ing species, grade (or grade combination), specimen geometry,
However, if a product fails to meet the strength criterion of
and grain orientation, and other specific process parameters
5.4.1 during any retest at a stress level less than that specified
involved in its manufacture.
in 5.3.2, then the material is not allowed to use the duration of
7.1.2 Description of the sampling and matching protocol
load or creep adjustments in the NDS and no further retesting
used.
shall be permitted.
7.1.3 Descriptions of the test setup, including detailed
6.3 Acceptance Criteria for Retest at Lower Stress Level—
drawings, the span, and the deflection measuring apparatus.
The acceptance criteria for the retest(s) shall include the three
7.1.4 Description and frequency of calibration procedures.
acceptance criteria from 5.4 plus all of the following:
7.1.5 Records of test environmental conditions.
6.3.1 Average Fractional Deflection—The average frac-
7.1.6 Testdata,including(1)specimenmoisturecontent,(2)
tional deflection after 90 days shall be less than or equal to 1.6.
applied loads, (3) deflection measurements at various test
6.3.2 Average Creep-Recovery—The average creep-
durations, (4) test specimen time-to-failure, (5) creep rate, and
recovery within 30 days of unloading shall be greater than or
(6) fractional deflection for each surviving test specimen.
equal to twenty percent (20 %). Creep-recovery shall be
7.1.7 Statistical calculations, including parametric statistics
defined as:
on short-term bending tests (if applicable) and description of
~∆ ! ~∆ 2∆ !
procedure used to calculate the five percent point estimate.
recovered unload230 initial
CR 5 5 1 2 $ 0.20 (5)
∆ ∆ 2∆
~ ! ~ !
creep load2end 12min
8. Precision and Bias
where:
8.1 Theprecisionoftheprovisionsinthisspecificationhave
CR = creep-recovery, unitless,
not yet been determined. When data become available, a
∆ = the total creep deflection recovered within 30
recovered
precision and bias statement will be included.
days after unloading, in. (mm),
∆ = the total creep deflection accumulated over the 9. Keywords
creep
long-term load test, in. (mm)
9.1 creep rate; creep-rupture; duration of load; fractional
∆ = deflection gauge reading after 1 min of loading,
1-min
deflection; lumber; structural composite lumber; structural-use
in. (mm),
panels
D6815−22a
APPENDIXES
(Nonmandatory Information)
X1. COMMENTARY ON DURATION OF LOAD EFFECTS IN WOOD PRODUCTS
X1.1 Scope X1.2.4 Typically, creep-rupture models are empirical, rely-
ing on events observable only at a macro level. This type of
X1.1.1 Appendix X1 provides general background informa-
model, in the context of the proposed short term test, is only
tion on the underlying assumptions used in establishing the
sensitive to the actual micro level degradation phenomena
creep-rupture (duration of load) evaluation procedures in this
(chemicalbonds)leadingtofailurewhenthatdegradationleads
specification.Theprocedureinthisspecificationwasoriginally
to creep or rupture during the test. The traditional DOL
developed to provide for the evaluation of duration of load
behavior as presented in Practice D245 is based on observation
(DOL) and creep adjustment factors for structural composite
and judgement of solid wood only. In that model, relatively
lumber (SCL) products. Much research has since been con-
short-term test results (like 90 days) appear to fit within a
ducted on SCL products to demonstrate their long-term load
projection that can cover a longer period of degradation.
performance. It was considered important to provide the
However all degradation phenomena embodied in that state-
engineering community with a standard procedure for evalu-
ment of DOL are those of solid wood with limited processing.
ating DOL effects in these and other wood products. It is the
Materials or combinations of materials that may degrade under
intent of the Committee to limit the application of the concepts
load and time with mechanisms different than those of solid
inthisspecificationtoproductsthatexhibitDOLeffectssimilar
wood may experience a different failure history than that
to solid wood. Creep-rupture tests of sawn lumber, structural
predicted by the Practice D245 model.This specification is not
composite lumber, plywood, and oriented strand board (X1.5.1
designed to project duration of load performance beyond the
– X1.5.3) indicate that wood products whose strength is
period of the test for processing methods or materials having
controlled by the properties of the wood fibers, wood strand or
degradationmechanismsdifferentfromtraditionallydriedsolid
otherwoodelementsintheproductexhibitdegradationmecha-
wood (possible examples of this may be chemically modified
nismsgenerallysimilartothoseofsolidwoodusedtoestablish
wood products or wood-plastic composites). Some composite
the DOL relationship in Practice D245.
materials, such as plywood and glued laminated beams fabri-
X1.
...

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: D6815 − 22 D6815 − 22a
Standard Specification for
Evaluation of Duration of Load and Creep Effects of Wood
and Wood-Based Products
This standard is issued under the fixed designation D6815; 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 specification provides a procedure for testing and evaluating duration of load and creep effects of wood and wood-based
materials relative to an accepted duration of load adjustment model. This specification was created for products that are currently
covered by a consensus standard (for example, lumber, structural composite lumber, and structural-use panels). This procedure is
intended to demonstrate the engineering equivalence to the duration of load and creep effects of visually graded lumber as specified
in Practice D245 for a product under evaluation used in dry service conditions. This procedure is not intended to evaluate the
performance of products under impact loading. Quantification of specific duration of load or creep factors is beyond the scope of
this specification. For further guidance regarding the applicability of this specification refer to X1.1 in the Commentary.
1.2 Use of the procedure in this specification to determine equivalence to the Practice D245 duration of load relationship is limited
to solid wood and wood-based products whose long term load behavior is similar to that of solid wood. Equivalence demonstrated
in this specification is dependent upon evaluation of a product’s 90-day (minimum) creep-rupture performance. In this evaluation,
three criteria must be satisfied: (1) adequate strength over a 90-day period, (2) decreasing creep rate, and (3) limited fractional
deflection. A summary of the development of these criteria and the underlying assumptions behind them is provided in the
Commentary in Appendix X1 and Appendix X2.
1.3 Long term degradation phenomena not described by a creep-rupture model are not addressed in this specification (see
Commentary X1.2.4).
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.5 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
This specification is under the jurisdiction of ASTM Committee D07 on Wood and is the direct responsibility of Subcommittee D07.01 on Fundamental Test Methods
and Properties.
Current edition approved Aug. 1, 2022Nov. 1, 2022. Published September 2022November 2022. Originally approved in 2002. Last previous edition approved in 20152022
as D6815 - 09 (2015).D6815– 22. DOI: 10.1520/D6815-22.10.1520/D6815-22A.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6815 − 22a
D245 Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber
D1037 Test Methods for Evaluating Properties of Wood-Base Fiber and Particle Panel Materials
D2915 Practice for Sampling and Data-Analysis for Structural Wood and Wood-Based Products
D3043 Test Methods for Structural Panels in Flexure
D4442 Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based Materials
D4761 Test Methods for Mechanical Properties of Lumber and Wood-Based Structural Materials
E4 Practices for Force Calibration and Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
2.2 Other References:
ANSI/AWS NDS National Design Specification (NDS) for Wood Construction
3. Terminology
3.1 Definitions—See Terminologies D9 and E6 and Practices E4 and E177 for definitions of terms used in this specification.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 breadth—breadth, n—dimension of the test specimen in the direction perpendicular to the span and perpendicular to the
direction of an applied bending load.
3.2.2 creep—creep, n—time-dependent increase of deformation of the test material under a constant load.
3.2.3 creep deflection—deflection, n—total measured deflection at a specific time minus the initial deflection.
3.2.4 creep rate—rate, n—change in creep deflection over time.
3.2.5 creep-rupture—creep-rupture, n—failure phenomenon described by a relationship between applied stress and time-to-failure.
3.2.6 depth—depth, n—dimension of the test specimen in the direction perpendicular to the span and parallel to the direction of
an applied bending load.
3.2.7 dry service conditions—conditions, n—conditions in most covered structures, where the moisture content of lumber will not
exceed 19 % (ANSI/AWC NDS).
3.2.8 duration of load factor—factor, n—factor customarily used to account for the effect of duration of load on the strength of
wood products.
3.2.9 failure—failure, n—point at which the test member can no longer support the applied constant load.
3.2.10 fractional deflection—deflection, n—ratio of total deflection to the initial deflection.
3.2.11 initial deflection—deflection, n—deflection at approximately one minute after the application of load.
3.2.12 span—span, n—distance between the centerlines of end reactions on which a test specimen is supported to accommodate
a transverse bending load.
4. Significance and Use
4.1 This specification provides a method for evaluating duration of load and creep effects of wood and wood-based products
subjected to bending stress. This method is intended to demonstrate the engineering equivalence to the duration of load and creep
effects of visually graded lumber as specified in Practice D245 for a product under evaluation. Equivalence is based on evaluating
Available from American Wood Council (AWC), 222 Catoctin Circle SE, Suite 201, Leesburg, VA 20175, https://www.awc.org.
D6815 − 22a
a product’s creep-rupture performance over a minimum of 90 days and meeting the requirements of this specification. This
specification does not attempt to quantify the effect of damage accumulation or to establish product-specific duration of load factors
for the product under evaluation.
5. Test Methods and Acceptance Criteria
5.1 Test Methods:
5.1.1 A test population shall be sampled from production that is representative of the product under evaluation. Two matched test
groups shall be selected, one for short-term bending tests, and one for long-term creep-rupture bending tests. A minimum sample
size of 28 is required for each test group. If further testing is contemplated, additional test specimens shall be sampled from the
initial test population. Long-term and short-term test specimens shall have the same cross section dimensions and length.
NOTE 1—Matching is a technique that attempts to subdivide the initial sample population into two or more separate groups that possess near identical
distributional form and scale for bending properties. Matching specimens for the purposes of 5.1.1 should be done with care, considering errors introduced
by the process and the characteristics of the material under test.
5.1.2 Each test specimen shall be simply supported and loaded by two equal concentrated forces spaced a distance of one-third
the total span from the end supports (that is, third-point bending). Loads shall be applied in the product orientation that represents
the general intended use of the product.
5.1.2.1 For joist-form materials, the span to depth ratio shall be as specified in applicable test standards (see Note 2). Lateral
restraints shall be used when necessary to maintain lateral stability. The minimum test specimen cross section shall be 2.5 in. (63.5
mm) in depth and 1.0 in. (25.4 mm) in width.
NOTE 2—For lumber sized products, span to depth ratios typically used for flexural tests range between 17 and 21.
5.1.2.2 For sheathing-form materials, the test span shall be not less than 48 times specimen thickness or 24 in., whichever is
greater. The specimen width for all sheathing-form materials shall not be less than 12 in. (305 mm).
5.1.3 Moisture content shall be measured on the short-term specimens immediately after destructive testing and on the long-term
specimens at the termination of the long–term test. Measurement of moisture content shall be in accordance with Test Methods
D4442. The average moisture content of all the long-term test specimens shall not deviate more than 62 % from the average
moisture content of all the short–term test specimens (see Note 3).
5.1.4 The test environment temperature and relative humidity shall be recorded daily (see Commentary X1.4.5).The daily average
temperature of the test environment shall not decrease more than 5 °C (9 °F) below the temperature at which the short–term tests
were conducted. At no time shall the test environment reach a temperature less than 0 °C (32 °F).
NOTE 3—Conditioning the short-term and long-term test material for at least 30 days in the anticipated test environment conditions generally provides
compliance with the 62 % moisture content change criterion.
NOTE 4—In experiments where the temperature falls below the prescribed limit, it may be possible to demonstrate the validity of the data by continuing
the experiment for an additional period at least equal to, and possibly greater than, the amount of time the temperature was below the prescribed limit.
5.2 Short-Term Bending Tests:
5.2.1 The loading rate for the short-term tests shall be such that the sample target failure load would be achieved in approximately
1 min. Failure load shall not be reached in less than 10 s nor more than 10 min. The procedures of Test Methods D198 or D4761
shall be followed for joist-form materials and Test Methods D1037 or D3043 for sheathing-form materials.
5.2.2 The sample standard deviation and the lower five percent point estimate of the short-term test group (5 % PE) shall be
determined in accordance with Practice D2915.
5.3 Creep-Rupture Bending Tests:
5.3.1 The creep-rupture test specimens shall be loaded such that the average time to attain the pre-selected constant stress level
D6815 − 22a
does not exceed the average time to failure of the short-term tests (see 5.2.1). Thereafter, the specimens shall be subjected to the
constant stress for a minimum period of 90 days. During this period, mid-span deflection readings shall be taken for each test
specimen, until the 90-day period has elapsed or until the occurrence of a failure. At a minimum, the deflection readings shall be
taken at approximately one minute after the application of the constant load (initial deflection), and at the end of one hour, day
1, day 7, day 14, day 30, day 60, and day 90. When better characterization of the creep rate is desired, more frequent deflection
measurements should be taken. Additional deflection readings are required when the test extends beyond 90 days. When a
specimen failure occurs, time-to-failure shall be recorded.
5.3.2 The specimens selected for these tests shall be tested at a constant stress level, f , as determined in accordance with Eq 1
b
(see Commentary Appendix X1).
f 5 0.55 3~5% PE! (1)
b
where:
f = minimum applied bending stress, and
b
5 % PE = the lower five percent point estimate, as determined from the short-term bending tests in 5.2.
The creep rate, fractional deflection (FD), and the total number of failures at 90 days (N ) (or greater) shall be used to evaluate
the acceptance of the product.
NOTE 5—Examples of acceptable creep and creep-rupture test apparatus are given in Ref 1.
5.4 Acceptance Criteria—The product is considered acceptable for using the duration of load and creep factors applicable to
lumber if the following three criteria are all satisfied: (1) adequate strength over the test duration, (2) decreasing creep rate, and
(3) a limited fractional deflection.
5.4.1 Adequate Strength—The total number of failures over the test duration shall be used to determine acceptance.
5.4.1.1 The total number of failures at 90 or more days shall be less than the critical order statistic, N , of the lower 5 %
c
non-parametric tolerance limit with 75 % confidence:
N ,N (2)
90 c
where:
N = number of specimen failures at the end of the 90-day test period, and
N = critical order statistic used to estimate the lower 5 % non-parametric tolerance limit based on the number of specimens
c
under long-term load (see Note 6).
For example, if 53 specimens are used in the creep-rupture tests, then N = 2 and no more than one specimen shall fail within
c
the 90-day period (N ≤ 1) for the product to be accepted as meeting the adequate strength criterion. Alternatively, if 28 specimens
are tested, then N = 1, and no failures shall occur (N = 0).
c 90
5.4.1.2 If the requirement of 5.4.1.1 is not met and the number of failures at 90 days is greater than or equal to the critical order
statistic (N ≥ N ) then the product under evaluation fails to meet the adequate strength criterion with the sample population, N.
90 c
5.4.1.3 If the number of failures at 90 days is equal to the critical order statistic (N = N ) in 5.4.1.2, then additional testing may
90 c
be conducted. In this case the sample population shall be increased by sampling an additional set of matched specimens in
accordance with 5.1.1 sufficient to allow the use of a higher non-parametric order statistic (see Note 6). The additional specimens
shall be tested for another 90-day test duration. The adequate strength requirement of 5.4.1.1 is met when, at the end of the
additional testing, the combined number of specimen failures during these two test series (N combined) is less than the critical
order statistic (N combined) based on the combined number of specimens evaluated (N combined).
c
NOTE 6—From Practice D2915 the order statistic for the lower 5 % tolerance limit with 75 % confidence, N , for various sample populations, N, is as
c
follows:
N 28 53 78 102
N 1 2 3 4
c
The boldface numbers in parentheses refer to the list of references at the end of this standard.
D6815 − 22a
5.4.2 Decreasing Creep Rate—All the test specimens that do not fail during the 90 day 90-day constant load period shall show
a decreasing creep rate.
5.4.2.1 To determine a decreasing creep rate, the change in creep deflection shall be calculated between a minimum of three
equally spaced time segments. segments that cover the full period under load. The change in calculated creep deflection shall
progressively decrease for each specimen. For As an example, for the three equal periods of 0 to 30 days, 30 to 60 days, and 60
to 90 days, the decreasing creep rate for 90 days under load can be expressed as (see Commentary Appendix X2):
D 2 D .D 2 D .D 2 D (3)
30 i 60 30 90 60
~D 2 D ! , ~D 2 D ! , ~D 2 D ! (3)
90 60 60 30 30 i
where:
D = initial deflection (measured one-minute after application of the load in accordance with 5.3.1), and
i
D , D , D = deflections measured on 30th, 60th, and 90th day respectively.
30 60 90
NOTE 7—To better define the creep rate, additional segments with a shorter frequency (for example, five 18-day segments) may be used.
5.4.2.2 If the difference in incremental creep deflection for the last two 30-day periods under load (for example, (D – D ) – (D
90 60 60
– D )) are within the precision of the deflection measuring devices, it shall be permitted to override the decreasing creep rate
criterion of 5.4.2.1 for not more than 15 % of the surviving specimens if the difference in incremental creep deflection between
the final two consecutive 30-day periods is less than 0.5 % of the initial deflection of the same specimen (for example, (D – D )
90 60
– (D – D ) < 0.005D ) (see X2.4.4 in the Commentary).
60 30 i
5.4.2.3 If the creep rate forcriteria of 5.4.2.1 a givenand 5.4.2.2 specimen is are not decreasingsatisfied at the end of the 90-day
period, the periodtest shall be extended for a minimum of 30 additional days. The change in calculated creep rate for the additional
time segment(s) after 90 days shall progressively decrease relative to the preceding segment.
NOTE 8—The creep rate may fluctuate due to environmental changes in relative humidity or temperature, or both. Extending the test beyond the 90-day
period in a controlled environment may demonstrate that the beams were not exhibiting tertiary behavior at the end of the period.
5.4.3 Fractional Deflection—Fractional deflection after ninety (90) days for each surviving specimen shall not be greater than 2.0:
D
FD 5 # 2.0 (4)
D
i
where:
D = initial deflection (measured one-minute after application of the load in accordance with 5.3.1), and
i
D = deflection measured on 90th day.
6. Retest Option
6.1 If a product fails to meet the strength criterion of 5.4.1, the product shall not be allowed to use the duration of load or creep
adjustments in the ANSI/AWC NDS. A retest at any stress level lower than that specified in 5.3.2 is not permitted to satisfy the
strength criterion of 5.4.1.
6.2 If a product satisfies the strength criterion of 5.4.1 in the original test at the stress level specified in 5.3.2, but fails to meet
either or both of the deflection-based criteria of 5.4.2 and 5.4.3, the product proponent shall be allowed to conduct a retest at a
reduced stress level. The reduced stress level is defined by the user. The user shall be permitted to repeat this procedure until the
acceptance criteria of 6.3 are satisfied. However, if a product fails to meet the strength criterion of 5.4.1 during any retest at a stress
level less than that specified in 5.3.2, then the material is not allowed to use the duration of load or creep adjustments in the NDS
and no further retesting shall be permitted.
6.3 Acceptance Criteria for Retest at Lower Stress Level—The acceptance criteria for the retest(s) shall include the three
acceptance criteria from 5.4 plus all of the following:
6.3.1 Average Fractional Deflection—The average fractional deflection after 90 days shall be less than or equal to 1.6.
D6815 − 22a
6.3.2 Average Creep-Recovery—The average creep-recovery within 30 days of unloading shall be greater than or equal to twenty
percent (20 %). Creep-recovery shall be defined as:
~Δ ! ~Δ 2 Δ !
recovered unload230 initial
CR 5 5 12 $ 0.20 (5)
Δ Δ 2 Δ
~ ! ~ !
creep load2end 12min
where:
CR = creep-recovery, unitless,
Δ = the total creep deflection recovered within 30 days after unloading, in. (mm),
recovered
Δ = the total creep deflection accumulated over the long-term load test, in. (mm)
creep
Δ = deflection gauge reading after 1 min of loading, in. (mm),
1-min
Δ = initial deflection gauge reading prior to loading, in. (mm),
initial
Δ = deflection gauge reading just prior to unloading, in. (mm), and
load-end
Δ = deflection gauge reading within 30 days after unloading, in. (mm).
unload-30
6.3.3 Average Residual Strength and Stiffness—The specimens from the long-term loading retest shall be tested in short-term
bending in accordance with 5.1.2. The average residual strength and stiffness of the test specimens shall be greater than or equal
to ninety percent (90 %) of that measured in the short-term bending tests of 5.2.
NOTE 9—The selection of the reduced stress level is defined by the user; and is an careful selection with the desire to assure that the product can meet
all six acceptance criteria.
6.4 Allowable Property Adjustment—If the retest proves that the product meets all the acceptance criteria defined in 6.3, all
time-dependent member and connection properties defined by the NDS shall be reduced by the percent change in stress level used
in the retest(s).
7. Report
7.1 The report content depends on the type of tests conducted. As a minimum, the report shall include the following information:
7.1.1 Description of the material under evaluation, including species, grade (or grade combination), specimen geometry, and grain
orientation, and other specific process parameters involved in its manufacture.
7.1.2 Description of the sampling and matching protocol used.
7.1.3 Descriptions of the test setup, including detailed drawings, the span, and the deflection measuring apparatus.
7.1.4 Description and frequency of calibration procedures.
7.1.5 Records of test environmental conditions.
7.1.6 Test data, including (1) specimen moisture content, (2) applied loads, (3) deflection measurements at various test durations,
(4) test specimen time-to-failure, (5) creep rate, and (6) fractional deflection for each surviving test specimen.
7.1.7 Statistical calculations, including parametric statistics on short-term bending tests (if applicable) and description of
procedure used to calculate the five percent point estimate.
8. Precision and Bias
8.1 The precision of the provisions in this specification have not yet been determined. When data become available, a precision
and bias statement will be included.
9. Keywords
9.1 creep rate; creep-rupture; duration of load; fractional deflection; lumber; structural composite lumber; structural-use panels
D6815 − 22a
APPENDIXES
(Nonmandatory Information)
X1. COMMENTARY ON DURATION OF LOAD EFFECTS IN WOOD PRODUCTS
X1.1 Scope
X1.1.1 Appendix X1 provides general background information on the underlying assumptions used in establishing the
creep-rupture (duration of load) evaluation procedures in this specification. The procedure in this specification was originally
developed to provide for the evaluation of duration of load (DOL) and creep adjustment factors for structural composite lumber
(SCL) products. Much research has since been conducted on SCL products to demonstrate their long-term load performance. It
was considered important to provide the engineering community with a standard procedure for evaluating DOL effects in these and
other wood products. It is the intent of the Committee to limit the application of the concepts in this specification to products that
exhibit DOL effects similar to solid wood. Creep-rupture tests of sawn lumber, structural composite lumber, plywood, and oriented
strand board (X1.5.1 – X1.5.3) indicate that wood products whose strength is controlled by the properties of the wood fibers, wood
strand or other wood elements in the product exhibit degradation mechanisms generally similar to those of solid wood used to
establish the DOL relationship in Practice D245.
X1.1.2 This specification does not address the conditions of extremely rapid loading or impact loading. Consequently the sections
in Practice D245 related to this type of loading cannot be applied to new products evaluated with this specification. Verification
of the DOL adjustment for impact load conditions requires separate evaluation and is considered beyond the scope of this
specification.
X1.2 Background
X1.2.1 The phenomenon of creep-rupture, usually called the duration of load (DOL) effect in wood and wood-based products has
been of particular interest to the wood science and timber engineering community as well as wood product manufacturers
concerned with the introduction of new building products and implementation of new codes for engineering design in wood. Since
the early 1970s, a significant amount of work has been conducted on measuring and empirically modeling the time-dependent
strength behavior of structural size lumber. A historical perspective of this issue and a review of the major test studies conducted
are provided by Barrett (2).
X1.2.2 If new engineered wood products are to use the duration of load adjustments recommended in the design codes for solid
sawn lumber and o
...