Super-Strength Beams Laminated from Rotary-Cut Southern Pine Veneer

Very strong beams were made by arranging 42 laminae of 1/6-inch rotary-cut southern pine veneer so that the stiffest veneers were on the tension and compression flanges and the most limber in the center. Beams thus fabricated to a 3-inch width and a 100-inch length averaged 13,280 psi stress in the outer laminae when failed in flexure. Modulus of elasticity averaged 2,330,000 psi. Similarly arranged beams were further strengthened by having the outer six veneers on both tension and compression sides impregnated with methylmethacrylate and then irradiated. These beams withstood 15,030 psi stress and had a MOE of 2,570,000. Comparable beams strengthened by having the outer six laminae on both sides densified by heat and pressure averaged 22,090 psi stress in the outer laminae at failure; MOE was 3,040,000. When laminae were arranged by stiffness, but not densified or impregnated, 2-inch-wide beams were stronger per inch of width than 3-inch beams; they also were less variable. The reason probably is that the narrowness of the laminae increases the probability of finding very strong pieces. There appear to be possibilities in assembling wide beams from narrow beams of 2 inches or some other standard width. Further tests of these narrow beams might justify an allowable stress of 4,000 psi. Ultimate horizontal shear stress (transformed section) of the stiffness-arranged beams averaged in excess of 550 psi. While this is a very respectable value for wood beams, it does become a design limitation on these exceptionally strong, stiff beams.

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