Impact behaviour and residual displacement mitigation of precast hybrid reinforced concrete (HRC) bridge columns

• Hybrid reinforcement reduces post-impact residual displacement by up to 50% • Peak displacement reduced by 22% with improved post-yield stiffness • High-strength reinforcement bars prevent joint opening and mitigates impact damage • Mechanism of impact resistance improvement in precast HRC bridge columns clarified • Similitude-based design framework bridges experimental and prototype conditions Precast reinforced concrete (RC) bridge columns have been widely adopted in modern bridge construction, yet their impact behaviour remains insufficiently investigated. Studies addressing the reduction of post-impact residual displacement in precast bridge columns are particularly scarce. In previous work by the first author[ 1 ], a precast hybrid reinforced concrete (HRC) bridge column incorporating both normal-strength and high-strength steel reinforcement was proposed, with its superior self-centering performance under lateral cyclic loading experimentally demonstrated. The present study further investigates the impact behaviour and post-impact residual displacement of HRC precast bridge columns. A similitude-based design framework was developed for the lateral impact test programme, effectively bridging experimental and prototype conditions. One RC and two HRC precast bridge columns were tested, with the proportion of high-strength reinforcement as the key variable. Each specimen was subjected to three impacts of increasing velocity. Test results demonstrated that, compared to the precast RC specimen, the hybrid reinforcement in HRC specimens effectively prevented opening of the precast column-base joint and mitigated impact damage. The hybrid reinforcement reduced peak displacement by up to 22% and post-impact residual displacement by up to 50%. The mechanisms underlying this reduction in residual displacement were also clarified. Furthermore, a comprehensive numerical model was developed and validated against experimental results. Parametric analyses were subsequently conducted to investigate the impact behaviour of precast HRC columns under varying conditions. The numerical study examined the effects of impact height and tensile strength of high-strength reinforcement on the impact response and post-impact residual displacement.