Experimental investigation into seismic performance of self-centering rocking piers of concrete-filled steel tubes with bottom encasements

Abstract

This paper presents an advanced structural system of self-centering (SC) rocking piers made of concrete filled steel tubes (CFST) with bottom encasements, and a number of unbonded post-tensioned (PT) strands and energy dissipation (ED) steel bars are also provided to enhance their performance under seismic actions. A total of seven CFST pier specimens were tested under quasi-static lateral loads, and their seismic responses were described thoroughly in this paper. Key parameters included various geometrical dimensions in the CFST piers, the bottom encasements, the PT strands and the ED steel bars together with their axial load ratios, and typical failure modes and deformation characteristics of these piers were identified. All the test specimens failed due to extensive yielding of ED bars and damage to the concrete at the bottom encasement. It is shown that with an increase in the ED bar ratio, the deformation characteristics of the CFST piers, including bending stiffness and resistance, and energy dissipation capacity are significantly increased while the self-centering capacity is decreased correspondingly. Moreover, increasing the diameter of the bottom encasements is able to enhance significantly the bending stiffnesses and resistances of the piers, but this also causes a minor reduction to both the self-centering and the energy dissipation capacities of the SC-CFST piers. With an increase in the applied compression forces to the SC-CFST piers and also the forces in the PT strands, all their deformation characteristics together with their self-centering capacities are increased. After calibration against measured data, a simplified theoretical model is proposed which is shown to be able to estimate the lateral load-drift skeleton curves of these self-centering piers with a high level of accuracy.