Finite element analysis of square concrete-filled steel tube (CFST) columns under axial compressive load

The confinement provided in concrete-filled steel tube (CFST) columns can significantly increase the strength and ductility of the concrete columns. However, in non-circular CSFT, the confining stresses are non-uniform and anisotropic, making their incorporation in structural analysis and design fairly difficult. Herein, a novel finite element (FE) model, which takes into account the lateral expansion and triaxial behaviour of the confined concrete, plastic behaviour of the steel tube and interaction at the concrete-steel tube interface in the evaluation of the confining stress field, is developed. It is applied to analyse a total of 92 axially loaded square CFST specimens published in the literature with concrete cylinder strength ranging from 24 to 110 MPa, steel yield strength from 262 to 835 MPa and steel tube depth-to-thickness ratio from 18 to 102. Overall, the FE analysis yielded full-range load-strain curves in good agreement with the experimental results. Using the new FE model, parametric studies on the effects of corner radius have been conducted and it is found that increasing the corner radius would produce better confinement at post-peak stage and thus would improve the post-peak behaviour of square CFST columns.