Strength Characteristics of Two-Ply Vertically Laminated Beams of Southern Pine

Two-ply vertically laminated beams were made from southern pine No. 2 boards, which have defect characteristics similar to No. 3 dimension lumber. Fabrication variables were nail-laminating, mastic adhesive, and phenol-resorcinol adhesive. Controls were beams with no fastening between the plies. Thirty beams in each fabrication group and 50 solid beams of southern pine No. 2 dimension were tested. Calculated allowable stress in bending for the 2-ply beams exceeded the published values for southern pine No. 2 dimension, even for the control group with no fastening between the plies. Beams made with either adhesive exceeded the allowable stress value for No. 1 dimension. Average stiffness of the lamina pairs was very close to the beam stiffness. Substitution of 2-ply beams, made from southern pine No. 2 boards, for No. 2 dimension lumber is technically feasible. Although the study was confined to southern pine boards 1 by 6 feet long, there is no reason to believe that the results would not apply to other widths and lengths of boards and to softwood species graded to the same standards.

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