InTrans / Aug 14, 2018

Efficient utilization of red maple lumber in glued-laminated timber beams

The feasibility of utilizing cant-sawn hardwood lumber, which
would not usually be desired for furniture manufacture, was studied for the manufacture of structural glued-laminated (glulam) timber. Two red maple beam combinations were evaluated: (1) a glulam combination designed with E-rated lumber in 25 percent of the outer laminations (top and bottom) and No. 3 grade 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-in. No. 2 grade lumber laid edge-to-edge having staggered end joints (termed 2 by 4/2 by 6 glulam combination). Test results of 42 red maple glulam beams showed that it was feasible to develop structural glulam timber from cant-sawn lumber. The glulam combinations made from E-rated lumber exceeded the target design bending stress of 2,400 lb/in2 and met the target modulus of elasticity (MOE) of 1.8 å« 106 lb/in2. 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 D3737 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 D143 shear-block tests could be used to accurately predict horizontal shear strength of 2 by 4 and 2 by 6 red maple glulam beams.