Edge-Glued Dimension Lumber from Low-Grade Southern-Pine

Edge-glued beams were made from laminae of 2 by 4 (No. 3) and 2 by 6 (No. 2) southern pine dimension lumber of known modulus of elasticity. Four groups of eight beams each were made as follows; 2 by 6 with above-average MOE and 2 by 4 with above-average MOE; 2 by 6 with above-average MOE and 2 by 4 with below-average MOE; 2 by 6 with below-average MOE and 2 by 4 with above-average MOE; 2 by 6 with below-average MOE and 2 by 4 with below-average MOE. The experimental design was chosen to provide a large estimate of population variance. The 32 beams were tested for stiffness in flexure twice, once with the 2 by 6 on the compression face and again with the 2 by 6 on the tension faces. Half of each group of beams were tested in flexure destruction with the 2 by 6 on the tension face of the beam and the other half with the 2 by 6 on the compression face. The results were subjected to multiple regression analysis and analysis of variance. The analysis indicated that there was no effect of lamina location on either the strength or stiffness of the edge-glued beams. The allowable stress in bending for the 32 beams was equivalent to the published values for kiln-dried, southern pine, No. 2, dimension lumber. Indications are that edge-glued beams equivalent in stiffness and strength to southern pine, No. 2, dimension lumber can be produced with random selection and layup procedures without regard to defect location.

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