Experimental evaluation of bonded/unbonded prestressed precast concrete joints under repetitive loading scenarios: Seismic performance and retrofit intervention

Abstract

Recently, demands for mitigating structural damage and post-earthquake repair costs have spurred considerable research on prestressed precast frames. In this study, quasi-static tests were conducted on bonded and unbonded prestressed precast beam-column joints (BPPJs and UPPJs) to investigate the influences of bonded/unbonded post-tensioned (PT) strands, evaluate the performance of BPPJs under repeated loading, and verify the effectiveness of post-earthquake retrofitting with external buckling-restrained rods (BRRs). Additionally, the difference between the bonded and unbonded joints was further revealed from the perspective of the tensile forces of the strands at the beamcolumn interface. Test results showed that compared with the UPPJ, the BPPJ exhibited superior performance in terms of lateral stiffness, lateral resistance, and energy dissipating capacity, with a 76.4 % increase in the load-bearing capacity. The compressive zone at the beam end was also deeper in the BPPJ, accompanied by a denser distribution of compressive cracks in the concrete. Furthermore, the bond between the strands and grouting material in the duct accelerated the increase in the tensile forces of the strands at the interface, resulting in considerably more prestress loss in the BPPJ after the tests, which was 120.0 % greater than that in the UPPJ. Under repetitive loading scenarios, although the yielding resistance of the BPPJ decreased by 35.0 % compared with that of the first loading owing to the reduced tensile forces in the strands, relatively minor variations in the load-bearing capacity and energy dissipation were observed. After retrofitting with BRRs, the BPPJ exhibited substantial enhancements in both lateral stiffness and resistance, validating the effectiveness of post-earthquake retrofitting with BRRs.