Behaviour and design of composite beams under generalised actions

Steel-concrete composite beams can be subjected to combined bending and axial forces; however, the behaviour of composite beams under combined loading is not covered by the current design standards. An extensive experimental investigation comprising twenty-four full-scale tests was conducted recently in the University of Western Sydney, aiming to investigate the behaviour and ultimate strength of compact composite beams under sagging or hogging bending and compressive or tensile axial forces. The research was accompanied by theoretical analyses, including detailed finite element simulations and parametric studies. This paper gives a summary of the research outcome on this topic. It was found that the moment capacity of a composite beam is reduced in most situations under simultaneous axial loading. Partial shear connection does not alter the shape of the interaction curve, but it affects the ductility of the beam and the amount of axial load transferred to the slab. Based on the experimental and numerical results, simplified design rules are proposed to account for the effect of axial loads on the bending capacity of composite beams.