Elastic lateral torsional buckling of two-ply built-up wooden beams connected with discrete fasteners

Abstract

The present study investigates the elastic lateral torsional buckling of built-up wooden beams formed by two plies of equal depth connected through fasteners at their vertical interface. Towards this goal, the study develops a variational principle for the problem and then develops a finite element formulation, leading to an eigenvalue problem. The formulation captures the transverse, longitudinal slippage between both plies and the shear stiffness provided by the fasteners at the interface. A systematic parametric study is then conducted to investigate the effect of the fasteners' stiffness, their distribution, moment gradient, load height, and beam dimensions on the resulting elastic critical moment. The model provides a basis to quantify the level of the composite action achieved by various nailing patterns and stiffnesses and their effect on the lateral torsional buckling capacity of two-ply built-up beams. The study then explores the effect of uniform and non-uniform nail patterns in a bid to optimize the design of built-up beams. The study shows that the critical moment of built-up beams with fastener spacings conforming with the Canadian Standards requirements is considerably lower than that of a monolithic beam with identical total width.