Retrofitting of Severely Seismically Damaged Bridge Piers Using Ultrahigh-Performance Concrete

This study presents an innovative retrofitting strategy for severely damaged bridge piers, incorporating concrete-filled steel tubes (CFSTs), which utilize ultrahigh-performance concrete (UHPC) jacket within the plastic hinge region. Four seismically damaged bridge piers comprising two precast and two cast-in-place (CIP) specimens were retrofitted with the proposed jacketing approach and subsequently tested under lateral cyclic loading. The retrofit design aims to relocate the plastic hinge formation above the previously damaged zone and restore the stiffness, strength, and ductility of the bridge columns. Experimental results demonstrate that the jacketing system successfully shifted the plastic hinge formation above the retrofitted region in all specimens while maintaining the integrity of the UHPC jacket without visible damage. Both precast and CIP retrofitted piers effectively restored their load-carrying capacity, with precast specimens achieving maximum forces of 136.56 kN (30.7 kips) and CIP specimens reaching 111.21 kN (25 kips). The use of dowels in Precast 1 enhanced initial stiffness by 61.7% compared to Precast 2 (without dowels), while Precast 2 achieved higher displacement ductility and overstrength due to rocking behavior at the base. Similarly, among CIP specimens, CIP 1 (retrofitted with a 76.2 mm (3 in.) thick UHPC jacket) showed higher initial stiffness, whereas CIP 2 (retrofitted with a 50.8 mm (2 in.) thick UHPC jacket) demonstrated improved ductility and energy dissipation capacity. The results confirm the efficacy of the proposed jacketing method in restoring and enhancing the seismic performance of severely damaged bridge piers.