Effect of knots on longitudinal shear strength of Douglas-fir using shear blocks

An investigation of the effect of knots on the parallel to grain shear strength of wood was conducted using shear block specimens. This included testing of 40 specimens with knots and 40 matched clear specimens. The 40 knot specimens tested included 20 knot specimens with knots parallel to the shear plane as well as 20 specimens with knots perpendicular to the shear plane. Twenty matched specimens of clear wood were tested for each of the two orientations of the knot in the shear plane. All specimens were Douglas-fir and the tests were conducted according to ASTM D 143. Statistical analysis of the data showed no significant difference in the mean shear strength of clear and knotted specimens.