Evaluation and improvement of shear-strength expressions for circular concrete-filled steel tubes

The accuracy of the shear resistance design equation for concrete-filled steel tubes (CFSTs) is crucial to ensure the safety of CFST structures. However, the current design equations underestimate the test data, and cannot accurately predict the relative shear resistance of the steel and concrete fill. To solve this problem, this paper developed an advanced finite element model in the LS-Dyna program, which was validated using experimental results of CFST members failing in shear. A systematic parametric study was then conducted. The result showed that the contribution of the steel increased significantly with the strain-hardening ratio (F_u/F_y) while the contribution of concrete fill was greatly influenced by the internally reinforced ratio (ρ_int) and axial load level (P/P_0). These predictions were combined with the experimental results to develop a more accurate and reliable design expression for the shear strength of circular CFSTs.