Numerical study on seismic performance of steel jacket-confined square ultra-high-strength concrete-filled steel tube columns

The application of steel jacket confinement in plastic hinge regions is an effective measure to enhance the deformability of square ultra-high-strength concrete-filled steel tube (CFST) columns. To investigate the influence of key parameters on the seismic performance of jacket-confined CFST (JCCFST) columns, this study established a refined finite element model using the ABAQUS platform and conducted a parametric analysis. The results indicate that the confining jacket significantly improves the load-carrying capacity and ductility of the composite columns by restraining the crushing of core concrete and inhibiting bulging of the steel tube, while also slowing the accumulation of axial shortening. The ultimate drift ratio θu of JCCFST columns increases approximately linearly with the effective jacket confinement index λm and the steel tube confinement coefficient ξs, whereas it decreases significantly with an increase in the axial load ratio n. The ratio of the flexural capacity Mju of JCCFST columns to that of CFST columns M0u, denoted as (Mju/M0u), increases with λm but at a gradually diminishing rate, while ξs and n exhibit negligible effects on the Mju/M0u ratio. Finally, calculation formulas were derived to determine the minimum required jacket confinement index and jacket height to meet specified deformation capacity demands.