Seismic performance of reinforced concrete columns with precast ultra-high performance concrete (UHPC) jacket

To improve the seismic performance of reinforced concrete (RC) columns, ultra-high performance concrete (UHPC) with superior compressive mechanism and durability was adopted to locally strengthen the weaken region (i.e., plastic hinge zone) of the RC column in this paper. Quasi-static tests were conducted on six specimens, including five RC columns strengthened with prefabricated UHPC jackets (called UHPC composite columns) and one conventional RC control column. The influence of axial compression ratio (0.1, 0.2, 0.3), UHPC jackets height (330 mm and 530 mm, corresponding to one and two times the plastic hinge length), and normal-strength concrete (NSC) compressive strength (29.2 MPa and 38.0 MPa) on seismic behavior was systematically examined. The results showed that, compared with RC column, the failure zone in UHPC composite columns shifted outward from the columns foot to the NSC region above the UHPC panels, indicating a successful outward relocation of the plastic hinge. This shift resulted in enhanced lateral load-bearing capacity, yield stiffness, and energy dissipation capacity. While increasing the axial compression ratio improved the peak load and initial effective stiffness of columns, but the displacement ductility and cumulative energy dissipation capacity at failure were declined. Increasing the UHPC panel height further improved both lateral load-bearing capacity and displacement ductility. Moreover, the proposed strengthening method using precast UHPC jackets in the plastic hinge zone demonstrated practical feasibility and offered a viable solution for enhancing the seismic resistance and post-earthquake repairability of RC columns.