Effect of Fastener Stiffness on Buckling Behaviour of Wooden Built-Up Beams

The present study investigates the lateral-torsional buckling (LTB) behaviour of wood built-up beams formed by individual members of the same depth that are fastened or glued together. The LTB capacity of a built-up beam is primarily affected by the level of composite action achieved between individual plies, which is influenced by the fastener properties and locations. The Canadian wood design standard (CSA O86:19) permits full composite action for built-up beam design but is silent on the types and geometries of fasteners necessary to sustain full composite action. The lack of guidance on this topic is also observed in wood design standards in the U.S. and Europe. Within the above context, the present study aims to quantify the effects of fastener stiffness and spacings on the LTB capacity. Towards this goal, a 3D finite element (FE) model, capable of capturing fastener flexibility and predicting the elastic buckling capacity of built-up beams, is developed. The stiffness of fasteners commonly used to connect the plies of the built-up beam is obtained from literature and used as inputs in the FE model. The results obtained from the FE model indicate that the LTB capacities of built-up beams are sensitive to the fastener lateral stiffness and spacings, although the correlation is not linear. It is anticipated that the outcome of this study will help develop clear design guidelines and detailing for the buckling capacity of built-up beams.