Seismic performance of concrete-encased column base for hexagonal concrete-filled steel tube: experimental study

Abstract

The concrete-encased column base investigated in this paper is composed of an inner base plate column base partially encased by an outer reinforced concrete (RC) component. The seismic behavior of the column base for hexagonal concrete-filled steel tube (CFST) along the strong axis is studied experimentally. Twelve composite specimens are tested under constant axial loading and cyclic lateral loading applied on the hexagonal CFST columns. The test parameters are the height of the outer RC component, with or without shear studs outside the tube and the axial load level on the hexagonal CFST column. Two typical failure modes are observed in the test, and the experimental results show that the concrete-encased column bases exhibit a high strength with good ductility and high energy dissipation capacity. The damage modes of the outer RC component are investigated, and the load transfer mechanism of the concrete-encased column base is analyzed. The load versus displacement relation, strain development, lateral deflection distribution and bottom rotation are compared for specimens under different failure modes. Further analysis is conducted to investigate the effects of parameters on various seismic performance indexes, such as the elastic stiffness, the maximum strength, the ductility coefficient, the strength and stiffness degradation, and the equivalent viscous damping ratio. Finally, a simplified strength model of the concrete-encased column base for hexagonal CFST is also proposed.