Species and Core Joint Design Affect Tensile Strength and Stiffness of Composite Truss Lumber

Composite truss lumber 2 by 4’s made with southern pine veneer and sweetgum veneer were tested in tension. Veneer species, type of core joint, and core orientation index significantly affected tensile strength of composite 2 by 4’s. Sweetgum veneer was superior to southern pine veneer. Scarf joints were superior to butt joints. High orientation index core was superior to low orientation index core. (The core orientation index is a measure of the degree of flake orientation.) Testing of a limited number of samples indicated that allowable tensile stress of the composite was generally equivalent to the allowable tensile stress for southern pine No. 1 kiln-dried (KD) dimension lumber (1,050 psi). None of the factors studied had a statistically significant effect on the tensile modulus of elasticity (MOE).

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