## 12 Seismic Performance of Steel-Concrete Composite Bridges
### Seismic Performance of Steel-Concrete Composite Bridges: State-of-the-Art
Figure 12 depicts the positional relationship between the bridge and the seismic faults. A numerical model was developed using LS-Dyna software ([[https://lsdyna.ansys.com/](https://lsdyna.ansys.com/)]([https://lsdyna.ansys.com/](https://lsdyna.ansys.com/))), validated by previous tests. Two types of ground motions were considered, with several filing steps. The study compared the damages, joint deformations, energy absorption, and seismic responses of the bridges and found that during strike-slip and dip-slip across-fault ground motions, posttensioned precast segmental piers sustained less damage compared to monolithic piers. Monolithic piers exhibited damage along the entire pier, while posttensioned precast segmental piers experienced localized damage at segment-to-segment joints. Under transverse strike-slip ground motions, posttensioned precast segmental piers showed excellent self-centering performance with minimal residual lateral deformations. Posttensioned precast segmental piers could accommodate displacements through torsion slip at joints and showed better seismic resilience and post-earthquake recovery performance compared to monolithic piers. A new type of pier has been developed by [PERSON] et al. (2024) [185] using a composite material made of glass fiber-reinforced polymer, steel, and rubber concrete, featuring a double-skin design. Two 1:4-scale specimens were created for an investigation, where the first specimen underwent a mixed loading test involving pseudo-dynamic loading and quasi-static loading. This loading simulated the phenomenon where, after an earthquake, it is common to experience multiple aftershocks, emphasizing the need to assess the  
Figure 12: Spatial relationship analysis between composite bridge infrastructure and seismic fault lines, demonstrating critical geological risk assessment approach (adapted from [PERSON] et al. (2023) [184]). seismic performance of newly constructed composite piers. On the other hand, the second specimen was exclusively subjected to a quasi-static test. It is also found that composite piers exhibited elastic behavior in frequent seismic events, with glass fiber fracture and steel tube yielding in infrequent events. Despite seismic damage, specimens still showed energy dissipation, capacity, and ductility. A correction coefficient was proposed for calculating the plastic hinge length due to the underestimation of the plastic deformation capacity in existing specifications. [PERSON] et al. (2024) [186] proposed a design method for normal strength and ultrahigh performance concrete composite bridge piers, optimizing ultra-high-performance concrete jacket thickness and pier diameter. They suggested that the jacket thickness should be 0.2-0.3 times the pier radius, while the composite pier diameter should be 0.8 times that of an equivalent reinforced concrete pier. The fragility analysis showed that composite piers reduced damage probabilities under small-to-moderate earthquakes across all damage states. For strong earthquakes, they effectively controlled extensive damage but were less effective for slight and moderate damage levels. Similarly, [PERSON] et al. (2023) [187] investigated ultra-high-performance concrete and normal strength concrete composite bridge piers under cyclic loading, finding that the ultra-high-performance concrete cover effectively prevented compressive crushing and enhanced load-carrying capacity compared to conventional reinforced concrete piers. The composite piers generally failed due to reinforcement fracturing at the bottom. Cracks developed quickly in the ultra-high-performance concrete cover, indicating a need for reinforcement. The ultra-high-performance concrete cover significantly increased the balanced axial load of the composite section, influencing failure modes and load-carrying mechanisms. An optimal axial load ratio of 0.1-0.15 was recommended for composite piers to balance performance and cost-effectiveness. [PERSON] et al.