Home>ASTM Standards>ASTM D3957-09(R2020) pdf free download

ASTM D3957-09(R2020) pdf free download

ASTM D3957-09(R2020) pdf free download.Standard Practices for Establishing Stress Grades for Structural Members Used in Log Buildings
3. Significance and Use
3.1 It is useful to grade logs to improve the consistency in performance. Using the visual stress-grading principles appli- cable to rectangular and round shape structural wood members, these practices illustrate the development of stress grading methodologies for wall-logs and round timber beams, as typically used in log buildings. The clear wood strength values are used as the basis for deriving the design stress values in these applications.
4. Stress-Grading of Wall-Logs
4.1 General: 4.1.1 This section is intended to apply to wood members, referred to as wall-logs, which are normally stacked horizon- tally or laid-up vertically to form a load-bearing, solid-wood wall, in any building. These structural members can vary greatly in dimension and section profile, and therefore previ- ously developed standards for solid sawn lumber are not readily applied to them (Fig. 1). 4.1.2 Wall-logs, as referred to in these practices, can also be used as beams, joists, and so forth, and do not have to be used as wall components. 4.1.3 Unless they qualify as round-timber beams under Section 5 of these practices, wall-logs must be considered as sawn lumber and therefore must respect the provisions of stress-grading described in Practice D245. The manner in which Practice D245 is applied to wall-logs is described in Use of Rectangular Section Inscribed in Actual Sec- tions: 4.2.1 A wall-log is to be graded as the largest piece of rectangular lumber that can be embedded in the wall-log without protrusion from any wall-log surface except that each corner may protrude up to 1 ⁄ 2 in. (12.7 mm) in either or both directions (Fig. 2). All provisions of Practice D245 that would apply to a piece with the same cross-section as the inscribed rectangle shall apply to the wall-log. 4.2.2 Maximum knot sizes shall be determined by the wide and narrow face dimensions of the inscribed rectangle, using knot tables in Practice D245. Boundaries between portions of the wall-log surface considered wide-face and portions consid- ered narrow-face shall be found by extending the diagonals of the inscribed rectangle to the wall-log surface (Fig. 2). Just as the wide and narrow faces of the inscribed rectangle belong to a quadrant between diagonals, so shall the wide and narrow faces of the wall-log surface belong to the same quadrants. In general, then, the surface boundaries between wide and narrow faces may not coincide with actual edges on the wall-log. 4.2.3 Knot size limitations, as determined by the dimensions of the inscribed rectangle, shall apply to knot measurements taken at the surface of the wall-log. The slight difference between the knot size at the surface of the wall-log, and the knot size at the inscribed rectangle is, for practical purposes, disregarded.4.2.4 If the wall-log design has saw-cuts that penetrate deeply into the piece, then any inscribed rectangle that remains unpenetrated by sawing may be too small to use for determin- ing knot limitations. To accommodate wall-logs of this type, cuts into the inscribed rectangle may be treated as follows. If a face of an inscribed rectangle has a maximum allowable knot size of D inches when the face is unpenetrated by any cuts, then the maximum allowable knot size for knots that do not encompass the sawcut is reduced to D − d inches when the face is penetrated by a cut d inches wide. That is, a saw cut 1 ⁄ 2 in. (12.7 mm) wide could effectively increase a 2-in. (50.8 mm) knot to 2 1 ⁄ 2 in. (63.5 mm), as when the knot and the cut are tangent to each other. Therefore, a cut 1 ⁄ 2 in. wide will reduce the maximum allowable knot by 1 ⁄ 2 in. (Fig. 3). As an alternate to, reduce the maximum allowable knot displacement D to D − 2d where d is the displacement of the sawcut(s) when the knot does not encom- pass the sawcut. For example, a 6 by 12 in. (152.4 by 304.8 mm) with maximum knot displacement of 50 %, and two grooves 3 ⁄ 4 by 1 in. (19.1 by 25.4 mm) each on one narrow face, a groove displacement of2 %, the allowable knot displacement for knots that do not encompass the grooves would by reduced to 50 − 2(2) = 46 %.

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