Behaviour and design of composite beams under bending and axial tension

![CDATA[Steel-concrete composite structural systems are widely used in modern construction due to their numerous advantages in terms of economy and efficiency. There are many situations where composite beams are subjected to a combination of bending moment, axial loads and shear forces. Nevertheless, the design of composite beams under combined actions is not yet fully covered by the current codes of practice. This paper describes a series of experiments conducted in the University of Western Sydney in order to investigate the ultimate flexural strength of composite beams when subjected to simultaneous axial forces. Twelve composite beams were tested under both sagging and hogging bending moments and the moment axial force interaction curves were identified. Following the tests, advanced finite element models were established in order to simulate the nonlinear behaviour of the specimens and the accuracy of the numerical methods were assessed against the available experimental data. The model was then used to carry out parametric studies and to cover a series of beam sizes and spans used in practice. The effect of partial shear connection and its implications to the design were also considered. It was found that the flexural capacity of composite beams is considerably deteriorated when a high axial load acts in the steel beam. This deterioration in flexural strength follows different rules in hogging and sagging bending regions. Based on the experimental results and the finite element analyses, design interaction curves we constructed and simple design models are proposed for use in engineering practice.]]