This paper investigates the behaviour of steel–concrete composite beams subjected to the combined effectsof negative bending and axial compression. For this study, six full-scale tests were conducted on compositebeams subjected to negative moment while compression was applied simultaneously. The level of the appliedaxial compression varied from low to high. Following the tests, a nonlinear finite elementmodel was developedand calibrated against the experimental results. The model was found to be capable of predicting the nonlinearresponse and the ultimate failure modes of the tested beams. The developed finite element model was furtherused to carry out a series of parametric analyses on a range of composite sections commonly used in practice.It was found that, when a compressive load acts in the composite section, the negative moment capacity of acomposite beamis significantly reduced and local buckling in the steel beamismore pronounced, compromisingthe ductility of the section. Rigid plastic analysis based on sectional equilibrium can reasonably predict the combinedstrength of a composite section and, thus, can be used conservatively in the design practice. Detailingwithlongitudinal stiffeners in the web of the steel beam in the regions of negative bending eliminate web bucklingand increase the rotational capacity of the composite section. Based on the experimental outcomes and the finiteelement analyses a simplified design model is proposed for use in engineering practice.
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