Recommended Bearing Stresses for Design in Light-Frame Construction

Compression perpendicular to grain tests of Pacific silver fir (Abies amabilis (Dougl.) Forbes) and subalpine fir (Abies lasiocarpa (Hook.) Nutt) lumber were conducted using three different test specimen configurations in order to evaluate present design stress development. Results show that there is a significant difference between the present ASTM practice, which examines compression perpendicular to grain deformations of steel-on-wood bearing interfaces, and wood-on-wood interfaces typical of light-frame construction. The wood-on-wood compression perpendicular to grain stresses at any given deflection level within the range of the tests reached a maximum of 68 to 85 percent of the corresponding ASTM steel-on-wood stresses for Pacific silver fir and subalpine fir, respectively. However, the deformation due to shrinkage of the framing members, soil settlement, and construction irregularities is considered to be of a higher order of magnitude than bearing deformations.

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