Tensile Strength of L3 Douglas-Fir Glulam Members

Tensile tests were performed on 335 full-size glued-laminated members made up wholely of grade L3 Douglas-fir and larch laminations. The variable studies were: thickness of laminations, number of laminations, and width of laminations. The modulus of elasticity, specific gravity, and knot sizes and locations were determined for all laminations. Eleven parameters based on the aforementioned data were related to tensile strength by multiple linear regression analysis. The most closely related parameters were: modulus of elasticity, lamination thickness, and lamination width. The knot parameter K/b (from USDA Bulletin 1069) was found to be ineffective as a predictor of strength. Tensile strength was generally related to the projected area of the largest knot or knots, nor the proportion of their width to lamination width. Number of laminations between the limits of 2 and 7 did not have significant influence on tensile strength.