ASTM D3957-09
(Practice)Standard Practices for Establishing Stress Grades for Structural Members Used in Log Buildings
Standard Practices for Establishing Stress Grades for Structural Members Used in Log Buildings
ABSTRACT
These practices cover the visual stress-grading principles applicable to structural wood members of nonrectangular shape, as typically used in log buildings. Both sawn lumber and round timber stress-grading methodologies are applied to two different types of structural members used in log buildings: wall-logs and round timber beams. The development of design stress values from clear wood strength values for wall-logs and round timber beams for used in log buildings is demonstrated in this standard. However, the grading provisions presented herein are not intended to establish grades for purchase, but rather to show how stress-grading principles are applied to members used in log buildings.
SCOPE
1.1 These practices cover the visual stress-grading principles applicable to structural wood members of nonrectangular shape, as typically used in log buildings. These practices are meant to supplement the ASTM standards listed in Section 2, which cover stress-grading of sawn lumber and round timbers. Pieces covered by these practices may also be used in building types other than log buildings.
1.2 The grading provisions used as illustrations herein are not intended to establish grades for purchase, but rather to show how stress-grading principles are applied to members used in log buildings. Detailed grading rules for commercial stress grades which serve as purchase specifications are established and published by agencies that formulate and maintain such rules and operate inspection facilities covering the various species.
1.3 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.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
NF—Narrow Face
WF—Wide FaceFIG. 1 Typical Wall-Log Sections Showing Wide and Narrow Faces as Determined by Inscribed Rectangle
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Designation: D3957 − 09
StandardPractices for
Establishing Stress Grades for Structural Members Used in
1
Log Buildings
This standard is issued under the fixed designation D3957; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
These practices are based on the assumption that structural members in log buildings can be
stress-gradedbymethodsthatderivefromacceptedstandardsforconventionalsolidsawnlumberand
round timbers. It is assumed that the material to be graded bears enough similarity to either sawn
lumber or round timber, both in dimensional properties and in use, to warrant application of
stress-grading standards written for sawn-lumber or round-timber, or both. These practices, such as
Practices D245 and D2899, cannot be applied directly because the structural members used in log
buildingsaregenerallyneitherperfectlyrectangularnorperfectlyroundinsection.Thesepracticesuse
certain conventions regarding cross-sectional dimensions that make it possible to extend established
stress-grading methodologies to cover the members used in log buildings.
Where log member characteristics deviate from sawn lumber or round timber standards, there may
be uncertainty as to the exact effect of the deviation on strength properties. To compensate for this
uncertainty, some design stress values are herein derived with practices that are, by engineering
judgment, conservative. The philosophy guiding this approach is that while the absence of
experimental data may make a measure of conservatism unavoidable, the reliability of design stress
valuesmustnotbeachievedthroughwoodqualityorsizerequirementsthatareanunnecessaryburden
on the wood resource.
In general, the sawing, cutting, and shaving required to bring a piece to its final shape must be
completed before it can be visually graded using the principles in these practices. Small cuts may be
allowedaftergradingifitcanbeshownthateither(1)thecutsdonotaffectthegrade,or(2)thegrade
takes the additional cuts into consideration.
Both sawn lumber standards and round timber standards are herein referenced, because these two
stress-grading methodologies can be assumed to apply to two different types of structural members
used in log buildings: wall-logs and round timber beams. Since wall-logs must be provided with a
meansofjoiningtogether(forexample,tongue-and-groovejoints),theyresemblesawnlumberandare
treated as such in the standard. Rafters, purlins, and beams, on the other hand, are sometimes left as
roundlogs,exceptforasmallamountofsawingtoprovideaflatnailingsurface.Thesepracticesthus
deal with stress-grading of wall-logs and round-timber beams separately.
1. Scope Pieces covered by these practices may also be used in building
types other than log buildings.
1.1 These practices cover the visual stress-grading prin-
ciples applicable to structural wood members of nonrectangu-
1.2 The grading provisions used as illustrations herein are
larshape,astypicallyusedinlogbuildings.Thesepracticesare
not intended to establish grades for purchase, but rather to
meant to supplement the ASTM standards listed in Section 2,
show how stress-grading principles are applied to members
which cover stress-grading of sawn lumber and round timbers.
used in log buildings. Detailed grading rules for commercial
stress grades which serve as purchase specifications are estab-
lished and published by agencies that formulate and maintain
1
These practices are under the jurisdiction ofASTM Committee D07 on Wood
suchrulesandoperateinspectionfacilitiescoveringthevarious
and are the direct responsibility of Subcommittee D07.02 on Lumber and Engi-
species.
neered Wood Products.
Current edition approved May 1, 2009. Published June 2009. Originally
1.3 Thevaluesstatedininch-poundunitsaretoberegarded
approved in 1980. Last previous edition approved in 2006 as D3957–06. DOI:
10.1520/D3957-09. as standard. The values given in parentheses are mathematical
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
D3957 − 09
conversions to SI units that are provided for information only methodologies for wall-logs and round timber beams, as
and are not considered standard. typically used in log buildings.The clear wood strength values
are used as the basis for deriving the design stress values in
1.4 This standard does not purport to address all of the
these applications.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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:D3957–06 Designation:D3957–09
Standard Practices for
Establishing Stress Grades for Structural Members Used in
1
Log Buildings
This standard is issued under the fixed designation D3957; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
These practices are based on the assumption that structural members in log buildings can be
stress-gradedbymethodsthatderivefromacceptedstandardsforconventionalsolidsawnlumberand
round timbers. It is assumed that the material to be graded bears enough similarity to either sawn
lumber or round timber, both in dimensional properties and in use, to warrant application of
stress-grading standards written for sawn-lumber or round-timber, or both. These practices, such as
Practices D245 and D2899, cannot be applied directly because the structural members used in log
buildingsaregenerallyneitherperfectlyrectangularnorperfectlyroundinsection.Thesepracticesuse
certain conventions regarding cross-sectional dimensions that make it possible to extend established
stress-grading methodologies to cover the members used in log buildings.
Where log member characteristics deviate from sawn lumber or round timber standards, there may
be uncertainty as to the exact effect of the deviation on strength properties. To compensate for this
uncertainty, some design stress values are herein derived with practices that are, by engineering
judgment, conservative. The philosophy guiding this approach is that while the absence of
experimental data may make a measure of conservatism unavoidable, the reliability of design stress
valuesmustnotbeachievedthroughwoodqualityorsizerequirementsthatareanunnecessaryburden
on the wood resource.
In general, the sawing, cutting, and shaving required to bring a piece to its final shape must be
completed before it can be visually graded using the principles in these practices. Small cuts may be
allowedaftergradingifitcanbeshownthateither(1)thecutsdonotaffectthegrade,or(2)thegrade
takes the additional cuts into consideration.
Both sawn lumber standards and round timber standards are herein referenced, because these two
stress-grading methodologies can be assumed to apply to two different types of structural members
used in log buildings: wall-logs and round timber beams. Since wall-logs must be provided with a
meansofjoiningtogether(forexample,tongue-and-groovejoints),theyresemblesawnlumberandare
treated as such in the standard. Rafters, purlins, and beams, on the other hand, are sometimes left as
roundlogs,exceptforasmallamountofsawingtoprovideaflatnailingsurface.Thesepracticesthus
deal with stress-grading of wall-logs and round-timber beams separately.
1. Scope
1.1 These practices cover the visual stress-grading principles applicable to structural wood members of nonrectangular shape,
as typically used in log buildings. These practices are meant to supplement theASTM standards listed in Section 2, which cover
stress-grading of sawn lumber and round timbers. Pieces covered by these practices may also be used in building types other than
log buildings.
1.2 Thegradingprovisionsusedasillustrationshereinarenotintendedtoestablishgradesforpurchase,butrathertoshowhow
stress-grading principles are applied to members used in log buildings. Detailed grading rules for commercial stress grades which
serve as purchase specifications are established and published by agencies that formulate and maintain such rules and operate
inspection facilities covering the various species.
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
1
ThesepracticesareunderthejurisdictionofASTMCommitteeD07onWoodandarethedirectresponsibilityofSubcommitteeD07.02onLumberandEngineeredWood
Products.
Current edition approved May 15, 2006.1, 2009. Published May 2006.June 2009. Originally approved in 1980. Last previous edition approved in 20032006as
D3957–036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
1
---------------------- Page: 1 ----------------------
D3957–09
NF—Narrow Face
WF—Wide Face
FIG. 1 Typical Wall-Log Sections Showing Wide and Narrow Faces as Determined by Inscribed Rectangle
conversions to SI units that are provided for information only and are not consid
...
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