Structural Engineering Research in Wood

Four structural engineering studies of wood beams, in progress or recently completed at the U. S. Forest Products Laboratory, are presented. A mathematical theory is presented to explain the size-bending strength relationship for wood beams. The approach considers a volume-strength relationship rather than a depth-strength relationship as has been used in the past. Results show that the relationship developed applies to small as well as relatively large beams. Principal results of research on the lateral stability of deep beams, tapered bending members, and prestressed laminated wood beams are also summarized, with references to complete papers indicated. In the lateral stability study, the stability of roof and floor systems, whose proportions allow lateral buckling of the supporting beams, is analyzed. Particular attention is given to the stabilizing influence of the shear stiffness of the attached deck. The study of tapered bending members shows that bending, shear, and vertical stresses can occur at one point and the effect of combined stresses should be considered in design. In the study of prestressed laminated wood beams, it is shown that increased strength and decreased variability of strength can be attained by prestressing wood members.