Seismic performance of composite jacket-confined square high-strength concrete-filled steel tube columns

Abstract

Adding external confining jackets in the potential plastic hinge regions is a practical approach to improving the deformation capacity of square concrete-filled steel tube (CFST) columns with high-strength concrete (HSC). To investigate the seismic behavior of composite jacket-confined square CFST columns with HSC, three jacket-confined CFST (JCCFST) columns and two CFST counterparts with concrete compressive strength of approximately 125 MPa were tested. The test variables included the jacket configuration and steel tube strength. The test results demonstrated that both the jacket-confined region and the adjacent unconfined region could be damaged when the jacket length was 1.25 times the steel tube width. Finite element analyses were also performed to comprehensively investigate the influence of the parameters on the column behavior. It was found that the ultimate drift ratio, θu, increased approximately in proportion to the effective jacket confinement index, λm, and the confinement index of the CFST section, ξs, and decreased rapidly as the axial load ratio, n, increased. The ratio of the moment capacity of a JCCFST column to that of the corresponding CFST column, Mju/M0u, increased as λm increased. The influence of n and ξs on Mju/M0u was not significant. Formulas for designing the confining jacket were also developed.