Red maple lumber resources for glued-laminated timber beams

This paper presents test evaluation results for red maple structural glued-laminated (glulam) beams manufactured from two different lumber resources. Two types of red maple glulam beam combinations were evaluated: 1) a glulam combination designed with E-rated lumber in 25 percent of the outer laminations (top and bottom) and visually graded lumber in 50 percent of the center laminations; and 2) a wide-width glulam combination with laminations made from nominal 2- by 4- and 2- by 6-inch No. 2 grade lumber laid edge-to-edge having staggered end joints (termed 2 by 4/2 by 6 glulam combination). The two research studies differed in that one study obtained red maple lumber using common sawing practices used for appearance hardwood lumber recovery, whereas the other study exclusively obtained lumber from the red maple log cants that had been processed for removal of furniture-grade material. Given these two lumber resources, the test results from the two studies showed that it was feasible to develop structural glulam combinations made from E-rated lumber that would meet or exceed a target design bending stress of 2,400 psi and a target modulus of elasticity (MOE) of 1.8 × 10⁶ psi. In addition, the 2 by 4/2 by 6 glulam combination exceeded published design stresses for vertically laminated bending strength, MOE in both the horizontally and vertically laminated orientations, and horizontal shear stress in the vertically laminated orientation. Based on the results of the 2 by 4/2 by 6 glulam combination, it was determined that edge gluing the laminations to form wide-width lumber is not required to achieve targeted strength and stiffness levels. Data analysis showed that ASTM D 3737 procedures developed for softwood species accurately predict beam stiffness and provide conservative bending and horizontal shear strength estimates for red maple glulam beams. Also, it was shown that results from ASTM D 143 shear-block tests could be used to accurately predict horizontal shear strength of 2 by 4/2 by 6 red maple glulam beams.