Seismic retrofitting of RC columns using stainless steel grid-reinforced UHPC jackets in plastic hinge zone

Abstract

This study aims to propose a new seismic retrofitting method for reinforced concrete (RC) columns in buildings with insufficient or flawed design in early standards by locally using stainless steel grid-reinforced ultra-high performance concrete (UHPC) jackets in the plastic hinge zone. For this purpose, pseudo-static loading tests were conducted on four rectangular columns with economical reinforcement ratios, including three retrofitted columns and one traditional RC column, and the effects of the number of stainless steel grid layers and the height of UHPC jackets were investigated. Additionally, a fiber-based finite element model was developed for the retrofitted columns and its accuracy was verified. The influence of other parameters not considered in the experiment, such as the axial compression ratio, UHPC jacket thickness and concrete compressive strength on the seismic performance of the retrofitted columns were also analyzed. The results demonstrated that the proposed retrofitting method effectively improves the seismic behavior of RC columns in a quick and cost-effective manner. The combination of stainless steel grids and UHPC jackets provided stable confinement for the internal RC columns, significantly reducing the damage in the plastic hinge zone and the residual displacements. Compared with the RC column, the ductility, bearing capacity and energy dissipation of the retrofitted columns were enhanced. Especially, the ductility coefficient of the specimens using a two-layer stainless steel grid increased by 27.19 %–36.56 %.