Seismic Performance of Precast Steel-UHPC Composite Joints in High-Speed Railway Frame Piers

This study proposes a novel precast steel-ultrahigh-performance concrete (UHPC) composite joint for high-speed railway frame piers. Cyclic lateral loading tests were conducted on three 1:4.5 scaled specimens, each comprising a precast pier, a precast foundation, and a postcast joint. The influence of joint materials and the anchorage length of connecting rebars on seismic performance was investigated. All specimens exhibited flexural failure, characterized by concrete crushing in the pier and yielding of longitudinal rebars, while UHPC joints remained intact. Experimental results demonstrated that UHPC joints significantly improved ductility and energy dissipation while reducing residual deformation compared to normal-strength concrete (NSC) joints. The strain distribution of connecting rebars was analyzed, revealing a reduction in equivalent anchorage length from 17Dcr to 23Dcr in NSC joints to 8Dcr to 10Dcr in UHPC joints. Furthermore, the stress distribution factor was introduced, indicating that the upper studs in the steel-UHPC composite joints played a dominant role in load transfer. Displacement component analysis showed that UHPC increased the proportion of bending displacement, thereby delaying damage progression under extreme loading conditions. These findings underscore the potential of the proposed steel-UHPC composite joints for high-speed railway frame piers to enhance seismic resilience, improve structural integrity, and reduce maintenance requirements.