Lateral Stability of Wood Beam-and-Deck Systems

Modern timber structures frequently employ large wood beams bridged by 2 in. wood decking. Economy of material dictates the use of deep narrow beams whose design is limited by considerations of lateral instability. Such constructions must rely upon the in-plane shear rigidity of the attached deck to prevent collapse, yet when decks of low rigidity such as 2 in. decks are employed, the stability of the resulting structure is seriously in question. This report quantitatively answers the question of how much shear rigidity a deck must possess in order to provide adequate lateral support when attached to the top of a set of deep beams. A variational method of derivation is employed, and buckling curves are presented for five cases of load and support. The use of these results by structural engineers will facilitate the safe design of lightweight economical wood structures.