Effect of Moisture Content on Shear-Through-Thickness Strength of Douglas-Fir Plywood

A random sample of 52, 5-ply, 1/2-inch-thick commercial sheathing grade Douglas-fir plywood panels was cut into a total of 400 15-inch by 24-inch shear-through-thickness specimens. These were grouped into four matching sets and conditioned to nominal moisture contents of 7 percent, 16 percent, 24 percent and soaked. All specimens were tested parallel to their face grain. Load-deformation curves to failure were recorded for each specimen. The effect of moisture content upon the mechanical properties in shear-through-thickness was examined to provide realistic correction factors from laboratory test results to dry and wet service conditions. Simple linear regression equations were found to provide fairly accurate estimates below the fiber saturation point for both the mean and five percent exclusion limit values of ultimate stress and modulus of rigidity in shear-through-thickness.

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