Seismic performance of concrete-encased column connections for concrete filled thin-walled steel tube piers

An improved type of concrete-encased column connections (CECCs) for circular concrete filled steel tube (CFST) piers is proposed in this paper, which does not require the use of base plates and anchor bolts. The seismic performance of the proposed CECC for circular CFST piers was experimentally investigated. Four CECC specimens were tested under a constant axial load and cyclic lateral loads to investigate the effects of the reinforcement ratio in the steel tube and the thickness of outer reinforced concrete component. The test results show that all test specimens failed flexurally primarily and the lateral load versus displacement hysteresis curve was generally full, indicating a good energy dissipation capacity (with a ductility coefficient >3.5). The strength degradation, stiffness degradation, and energy dissipation coefficient were calculated to study the seismic performance of proposed CECCs. The axial and lateral load versus the strain development of steel tube and anchor bars curves were further investigated to analyze the load transfer mechanism. The calculation methods for the sectional strengths of both CFST section and bottom section are proposed, which are found to be in good agreement with the test results.