EFFECT OF INCISING AND PRESERVATIVE TREATMENT ON SHEAR-STRENGTH OF NOMINAL 2-INCH LUMBER

This study evaluated the effects of pretreatment incising of dry lumbe r and preservative treatment on the shear strength of 1980 pieces of 2 X 4 dimension lumber (nominal 50 mm X 100 mm X 3.6 m long). Three spe cies groups (Douglas-fir, Hem-Fir, and Spruce-Pine-Fir-South) and two commercially produced machine-stress-rated grades per species group we re tested in torsion to determine their shear strength. Incising and p reservative treatment produced significant reductions in the average s hear strength of Douglas-fir, Hem-Fir, and Spruce-Pine Fir-South dimen sion lumber. These effects need to be addressed through the developmen t of more appropriate design values for uses of preservative-treated w ood of these species when shear is a governing factor. An adjustment f actor of 0.70 is proposed for incised and preservative-treated nominal 2-inch lumber.