Non-linear analysis of multi-span composite beams under combined flexure and torsion

Multi-span steel-concrete composite beams fabricated from two steel joists and one concrete slab are widely utilised in bridges and highway interchanges, and are commonly subjected to combined actions of flexure and torsion. However, few national standards involve such loading combinations for the design of composite beams, and little research reported in the literature concerns the multi-span composite beams. With the aim of understanding the strength characteristics of such members subjected to combined flexure and torsion, a three-dimensional finite element (FE) model is introduced herein, and is calibrated against experimental results in terms of the loading capacities, the ultimate strength in torsion as well as the load-deformation response. A large number of parametric analyses are subsequently presented by using the FE model, and the effects of various parameters relating to the degree of shear connection, material strengths, stirrups and geometries are elucidated. Based on the non-linear analysis results, the degree of shear interaction, the spacing of the joists and the span-to-depth ratio are found to be influential in the ultimate strength in pure torsion of multi-span composite beams, in addition to the well-known parameters relating to the plain concrete and stirrups. Regarding the flexure-torsion interaction relation, the torsional and bending strengths are decreased within the presence of combine flexure and torsion, respectively. Furthermore, the interaction is generally consistent with varying parameters being incorporated. In accordance with a review of previous methodologies reported in the literature and the non-linear analysis results, practical design guidance and equations are developed for evaluating the torsional strength and the flexure-torsion interaction relation