Behaviour of concrete filled-steel tubes under axial load

In order to study the mechanical mechanism of concrete-filled steel tubes (CFSTs) under axial compression, a theoretical model for analysing the behaviour of axially loaded CFST columns is presented in this paper. The model is derived from the theory of elasto-plasticity, non-linear elastic mechanics and materials properties. Based on a related numerical program, analytical results were compared with experimental data. The complete load-deformation relationship of specimens, steel tube stress, performance of the confined core concrete and the interaction between the outer tube and the core concrete were investigated. The analytical results indicated that this model is able to capture the mechanical behaviour of concrete-filled circular steel tubes. It was found that the axial and circumferential stresses of the steel tubes behaved non-linearly during the loading history. It was concluded that the behaviour of the confined core concrete was significantly influenced by the confining pressure. The constraining factor had an important effect on the improvement of the core concrete strength. The analytical results also indicated that the axial stress-strain relationship of concrete under constant confinement was not appropriate for the core concrete in CFST specimens. Finally, a comparison between the confining pressure and the confined concrete response is presented.