Strength of Beams with Laminae Located According to Stiffness

Southern pine veneers 1/3 inch thick were assembled into beams containing 21 laminae located with the stiffest on the outside and the most limber in the center. Modulus of elasticity of the veneers averaged 1,700,000 psi and ranged from 740,000 to 3,370,000 psi. The beams had an average modulus of rupture of 9,900 psi and a modulus of elasticity (corrected for shear) of 1,820,000 psi. Ninety-five percent of the population represented by the 25-beam sample could be expected to have a modulus of rupture in excess of 8,060 psi. With beams made by this system, allowable design stress apparently is equivalent to the maximum allowable stresses now in use for high grade lumber randomly assembled into beams. If the laminae contain properly spaced finger joints, the average modulus of rupture should not fall below 7,300 psi (with a 95-percent exclusion limit of 5,250 psi).

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member