THE EFFECT OF EDGE KNOTS ON THE STRENGTH OF SPF MSR LUMBER

An experimental program has been performed to evaluate the impact of a djustments of edge knot visual quality level on the tension and bendin g strengths of 1650f-1.5E 38- by 89-mm Spruce-Pine-Fir machine-stress- rated lumber. A closed-form solution has been developed to establish t he strength property probability distribution of a new combined grade containing visual quality level knots (edge knots). Simulations have b een conducted verifying the closed-form solution. The results indicate that the level of edge knots to be included in the new grade is impor tant. In this study, the new grade exceeded the bending strength and e dgewise modulus of elasticity requirements but failed to meet the tens ion strength requirement due to the quality and quantity of visual qua lity level knots included in the grade mix.