New rocking column with control of negative stiffness displacement range and its application to RC frames

Abstract

This paper investigates the use of rocking columns with central steel bars in RC building frames. Motivated by the adverse effects of conventional steel bars anchored at both ends, a new rocking column is proposed that allows the slippage of the steel bar at the bottom end within a controlled range of displacements (gap). A numerical model of the new rocking column is developed and implemented in Opensees. A parametric study is conducted to investigate the overall response of several RC frames featuring the proposed rocking columns in the first story. It was found that the response is controlled by (i) the maximum restoring force provided by the rocking columns, (ii) the lateral strength provided by the dampers, and (iii) the dimensions of the gap. In comparison with conventional RC frames, the proposed solution reduces the maximum inter-story drifts in the upper stories by about 3 times, the story accelerations about 1.5 times and the energy dissipation demand about 20 times. The results of this research are expected to enhance the use of rocking columns for seismic isolation of RC frame structures, through a new solution that takes full advantage of the negative stiffness and prevents collapse.