ASTM D3957-06

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Designation:D3957–06
Standard Practices for
Establishing Stress Grades for Structural Members Used in
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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 which cover stress-grading of sawn lumber and round timbers.
Pieces covered by these practices may also be used in building
1.1 These practices cover the visual stress-grading prin-
types other than log buildings.
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
used in log buildings. Detailed grading rules for commercial
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These practices are under the jurisdiction ofASTM Committee D07 on Wood
stress grades which serve as purchase specifications are estab-
and are the direct responsibility of Subcommittee D07.02 on Lumber and Engi-
lished and published by agencies that formulate and maintain
neered Wood Products.
suchrulesandoperateinspectionfacilitiescoveringthevarious
Current edition approved May 15, 2006. Published May 2006. Originally
approved in 1980. Last previous edition approved in 2003 as D3957–03. species.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D3957–06
NF—Narrow Face
WF—Wide Face
FIG. 1 Typical Wall-Log Sections Showing Wide and Narrow Faces as Determined by Inscribed Rectangle
1.3 Thevaluesstatedininch-poundunitsaretoberegarded wall, in any building. These structural members can vary
as standard. greatly in dimension and section profile, and therefore previ-
1.4 This standard does not purport to address all of the ously developed standards for solid sawn lumber are not
safety concerns, if any, associated with its use. It is the readily applied to them (Fig. 1).
responsibility of the user of this standard to establish appro-
3.1.2 Wall-logs,asreferredtointhesep
...