Steel-concrete composite beams behaviour under combined hogging moment and axial tension

Composite steel-concrete beams are used in many types of structures, including steel framed buildings, bridges, stadiums and car parks. Composite beams are being increasingly used in situations where combinations of bending, shear and axial force may be introduced into the beam. This may occur via the installation of post-tensioning cables; by the inclination of the beam such as in stadia or bridge approaches; in cable-stayed bridges; or by the necessity to transfer diaphragm forces from the floor plate into the shear core of a building. However, modem steel and composite structural codes, including Eurocode 4 [1], Australian codes AS2327 and AS5100 [2, 3] and American AISC [4], currently do not address the effects of combined actions in composite beams. The ultimate capacity of steel-concrete composite beams under the combined effects of axial tension and negative bending moment is investigated in the present study. Firstly, details of an experimental investigation into composite beams under combined axial tension and negative bending are provided. Six composite beams of identical cross-section were tested in the laboratory of the University of Western Sydney under different combinations of tension and bending and the plastic capacities and failure modes were identified. The results were compared with the capacities provided by rigid plastic analysis through the composite section and reasonable agreement was found. The last section of the paper provides details of an extensive numerical study using the finite element method. The tested beams were modelled by a nonlinear finite element model in the ABAQUS commercial software. The three-dimensional model was compared against experimental results and found to be capable of simulating the inelastic behaviour of the composite beams with efficiency and to trace the failure modes up to ultimate load levels