Interaction Equations for Composite I-Girders under Combined Axial Compression and Positive Moment

Abstract

A composite I-girder is compose of steel beam and reinforced concrete slab by effectively using structural advantage and widely designed as the beams subjected to moment. However, in cable-stayed bridges, composite I-girders should be designed as beam-column members since they are subjected to combined bending moments and axial forces caused by the inclined cables. Accordingly, when a design for the composite I-girders in the cable-stayed bridge is performed by the equations of current construction codes, it could be a conservative design. For the reasonable design of the composite I-girders in the cable-stayed bridges, a research on a behaviour of composite I-girders under the combined loadings is essential. But, there is only a little research on the composite I-girders under the combined loadings. In this study, design model of the composite I-girders of two actual cable-stayed bridges are modelled by using the ABAQUS commercial finite element analysis program. Subsequently, it assesses the ultimate positive moment strength of composite I-girders at each level of axial force for investigating the effect of the interaction relation under combined axial compression and positive moment. As a result, the P-M interaction curves of the composite I-girders commonly show bilinear shape. Furthermore, it is found that the moment strength increase when relatively low axial compressive forces exist and affected by size of tension flange. Based on the FEA results, the interaction equations for composite I-girders are proposed for reasonable design. Then the applicability and validity of the proposed equations are verified by comparing with the current interaction equations of design specifications.