Analytical and experimental studies on mechanical behavior of confined concrete filled tubular columns

Unrestricted Composite materials composed of Concrete filled steel tube (CFT) have been widely applied in high strength column design due to their advantages such as high strength, stiffness, ductility and better seismic resistance. However, the conventional CFT system has a critical disadvantage which is the significant strength reduction after yield of steel tube caused by plastic local buckling. To resolve this problem, new CFT column system with additional transverse confinement is proposed. This study is intended to study confined CFT (CCFT) columns for better ductility and improved seismic design. To validate the effectiveness of confinement in CCFT, new confinement scheme is experimentally examined through axial compression test. The results show that it is possible to increase the compressive strength and reduce the local plastic buckling by using carbon-fiber-reinforced plastics confinement jacket. Also, the ultimate strength of the confined CFT columns is mainly dominated not by the existence of the cushion gap but by the ultimate strength of the CFRP confinement. In addition to experimental approaching, analytical and numerical methods are adopted to provide comparative studies with experimental results.