Effect of Moisture Content on the Flexural Properties of Douglas-Fir Plywood

This study was undertaken to estimate the effect of MC on the MOR and flexural MOE of commercial (in-grade) Douglas-fir plywood. A random sample of 40, 5-ply, 1/2-inch (12.5-mm)-thick, unsanded, standard sheathing-grade Douglas-fir plywood panels, collected from three British Columbia mills, were cut into 240 flexural specimens, each measuring 48 by 45 inches (1220 by 1140 mm). The specimens were grouped into four matching sets, and conditioned to MCs of 7, 15, 24, and 100 percent. All specimens were bent with face-grain parallel to span. Simple linear equations were fitted to the pooled experimental data by least squares techniques, to provide estimates of both mean and exclusion limit values of flexural properties as a function of MC. While most of the earlier efforts centered on evaluating the effect of MC upon the flexural properties of small clear plywood specimens, the proposed equations are applicable to large, in-grade, plywood structural elements.

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