Study on axial compression bearing capacity of reinforced concrete filled steel tube members

The bearing capacity equation of reinforced concrete filled steel tube (RCFST) members under axial loads is derived by using the combined unified and limit equilibrium theories. The concrete strength increase due to the constraint effect of the steel tube is taken into account through the use of unified theory; whereas the concrete strength increase due to the constraint effect of the stirrups is considered through the use of the limit equilibrium theory. Three-dimensional nonlinear finite element analysis and experimental tests were carried out and the corresponding results are reported in this paper. The comparisons of the numerical, experimental and theoretical results show that there are in good agreement between these three different methods. However, the present theoretical analysis model is not only simple and convenient to use but also consistent with existing Chinese design codes for CFST columns.