Effect of bridge design parameters on multi-hazard performance of river-crossing bridges

River-crossing bridges in seismically active regions are typically susceptible to two natural hazards – earthquakes and floods. For such bridges, design parameters related to piers may play major roles in bridge multi-hazard performance. In this study, the same was explored for key bridge design parameters – the aspect ratio and longitudinal reinforcement ratio of piers and the differential ground elevation between multiple bents. The multi-hazard condition in the southeast of Nepal was considered as the test-bed hazard condition. The regional seismic hazard was represented using a suite of earthquakes generated based on regional seismic design spectra. Due to the flood hazard in the region, expected pier scour of investigated bridges was estimated from 100-year flood discharge (including climate change projection) in the Koshi River, Nepal. Three-dimensional finite-element models of the chosen bridges, with and without scour and with ±10% variations in the stated design parameters, were developed. Fragility and risk curves of the bridges were developed and compared in order to assess the relative influence of the design parameters on bridge performance. It was found that the aspect ratio and longitudinal reinforcement ratio of piers can significantly influence the multi-hazard performance of riverine bridges. The findings also demonstrate how design parameters may be revised to perform risk-targeted multi-hazard design of bridges.