Seismic behavior of confined square CFT columns

The failure of conventional concrete filled tubes (CFT) under seismic loading is typically governed by the inelastic buckling and low cycle fatigue rupture. The second author has proposed to use additional confinement to control or delay the inelastic buckling of the steel tube at the potential plastic hinge zones of CFT members. Following the success of the previous studies on confined concrete filled tubes (CCFT) with circular sections, this paper reports the experimental results on square CCFT columns. One conventional CFT and five CCFT model columns were tested under constant axial load and cyclic lateral forces. Test results validated the concept of CCFT for square sections. Compared with the conventional CFT column model, the CCFT columns exhibited significantly improved seismic performance with large ductility. A design method for the additional confinement to the plastic hinge region was also developed and validated.