Behaviour and Design of Composite Beams Subjected to Combined Bending and Axial Forces

Steel-concrete composite beams can often be subjected to combined bending and high axial forces. However, the moment-axial force interaction in composite beams is not covered by the current codes of practice. An 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 composite beams under bending and axial forces. Nonlinear finite element simulations and parametric studies complemented the tests. 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.