Shear and compression perpendicular to grain property estimation for 2400f MSR lumber

In 1992, the American Lumber Standard Committee approved alternative procedures for assigning allowable shear parallel and compression perpendicular to grain values to machine stress rated (MSR) lumber. This paper compares the newly approved procedures to results of clear wood tests on remnants of bending specimens for Douglas-fir/larch, hem-fir, and Engelmann spruce-lodgepole pine 2400f-2.0E MSR lumber. Approximately 130 shear strength parallel to the grain (shear), compression perpendicular to the grain (C-perp), and specific gravity tests were conducted for each species at 13 percent moisture content. Shear and C-perp tests used nonstandard test specimens that had been evaluated in the literature and found to give equivalent results to the standard specimens. This study indicates that the alternative method for assigning shear to MSR lumber based on specific gravity, recently approved by the American Lumber Standards Committee, is overly conservative for 2400f-2.0E. A similar equation that uses the dry-green ratios in ASTM D 2555, rather than the moisture content adjustment factor given in ASTM D 245, gives a more realistic prediction of 5th percentile shear. The alternative procedure for assigning C-perp fiber stress at 0.04- inch deformation follows the slope of the mean trend but gives a conservative estimate of the mean values for C-perp in 2400f-2.0E MSR lumber.

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