## 12 Seismic Performance of Steel-Concrete Composite Bridges
### Seismic Performance of Steel-Concrete Composite Bridges: State-of-the-Art
They also compared the effects of vertical ground motion on seismic behavior, finding a significant impact on compressive force and shear resistance. [PERSON] et al. (2024) [179] delved into the seismic performance and potential applications of continuous beam bridges with prefabricated concrete-filled steel tubular piers. Initially, two prototype bridges were compared, one with 10 m double-column reinforced concrete piers and another with 35 m double-column reinforced concrete piers. Then, seven bridges were designed with prefabricated concrete-filled steel tube piers to match the lateral stiffness of the reinforced concrete piers. The hysteretic characteristics of composite piers were verified through numerical models and seismic response analysis. Fragility curves were generated through time-history analyses. [PERSON] et al. (2023) [180] proposed a fiber-based nonlinear modeling approach for the seismic analysis of partially concrete-filled steel tubular bridge piers, addressing computation time and convergence issues by considering probable local buckling of the outer steel tube and efficiently captured composite pier behavior. Comparing numerical modeling with experimental data showed the effectiveness of the fiber models in seismic assessments. Thorough cyclic pushover and time-history analyses highlighted the importance of coordinating steel tube and concrete design parameters to improve seismic performance. A new design approach involving layered concrete filling was recommended for enhancing structural seismic performance and was especially useful for retrofitting existing hollow steel piers without increasing foundation forces. Furthermore, a prefabricated steel tube-confined concrete circular pier with a grouted sleeve connection was developed by [PERSON] et al. (2022) [181]. This composite pier could address limitations in typical precast concrete piers, enhancing their use in seismic hazard zones. Scale models of circular piers were tested under cyclic loading, showing tube-confined concrete circular piers had improved flexural  
Figure 11: Dumbbell steel tube confined reinforced concrete pier design, highlighting innovative structural reinforcement techniques (adapted from [PERSON] et al. (2020) [176]). strength and energy dissipation due to steel tube confinement. Ductility and stiffness also increased, with a more even distribution of pier body stiffness. Parametric analysis revealed thicker and stronger steel tubes increased flexural strength and stiffness. [PERSON] et al. (2023) [182] examining hollow bridge piers with concrete-filled double-skin tubular sections evaluated their seismic design and cost-effectiveness. The results showed that these composite piers had higher displacement ductility, lateral force-bearing capacity, cost-performance ratio, and flexural stiffness with reduced residual drift ratio. Certain factors, such as the diameter-to-thickness ratio of outer steel tubes and hollow ratio, significantly influenced the seismic performance of composite piers and recommendations include a diameter-to-thickness ratio between 60 and 150 for effective and ductile seismic design of composite bridge piers. Similarly, [PERSON] et al. (2023) [183] executed experimental tests comparing posttensioned precast segmental concrete-filled double-skin steel tubular piers with cast-in-place concrete-filled double-skin steel tubular piers, showing superior ductility, energy dissipation, and minimal damage to precast segments. The numerical analysis explored design parameters' impact on pier behavior, revealing the crucial roles of energy-dissipating bars, gravity loads, and prestressing loads in energy dissipation and self-centering capacities. Initial stress levels in prestressing strands chiefly influenced failure mode and deformation capacity. [PERSON] et al. (2023) [184] investigated the seismic behavior of steel-concrete composite rigid-frame bridges with posttensioned precast segmental concrete-filled double-skin steel tube piers under across-fault ground motions.