Seismic performance of bridges retrofitted with riprap for scour countermeasures

Highway bridges across rivers are susceptible to flood-induced scour. Riprap, a widely applicable bridge scour countermeasure, gained popularity due to its flexibility and ease of maintenance compared to other similar measures. Despite extensive research on the design and application of ripraps for bridges, performance of riprap-retrofitted bridges under seismic ground motions remains unexamined. Therefore, the current study presents a complex soil–riprap–foundation interaction analysis to evaluate seismic performance of bridges retrofitted with ripraps. Detailed finite-element (FE) models for superstructure and substructure of a representative reinforced concrete bridge are developed in the STAAD.Pro and Plaxis 3D software programs, respectively. The coupling tool in Plaxis 3D enables interaction between the FE models to capture behaviour of the bridge system under lateral loading. The substructure model is validated using available pile load test data. Time-history analyses of the bridge in original, scoured and riprap-retrofitted conditions are performed under 20 earthquakes. Results show that scour increases mean normalised pier-top displacement of the bridge by approximately 15–20% relative to its original condition, while riprap helps to reduce this mean normalised response and brings it back close to its pre-scour level. Overall, research findings suggest that riprap can enhance multi-hazard performance of bridges under earthquakes and scour.