Multi-hazard fragility analysis of RC bridges for high seismicity and high scouring scenarios

Both earthquakes and floods occur frequently in the Himalayas. Since bridge structures are designed considering earthquake forces alone, floods are causing significant damage to bridges almost every year across the Himalayas. Thus, it is obvious that floods and earthquakes are the two most important natural hazards that could alter the performance of bridges in the Himalayas. Furthermore, settlement and scouring are commonly observed in many bridges in Nepal and neighbouring regions in the Himalayas. To this end, the conventional earthquake force-based analysis approaches become conservative as the conventional approaches do not account for multi-hazard impacts and design considerations. To fulfil the gap regarding multi-hazard vulnerability characterization, this study presents a comparative assessment of single and multiple natural hazards that are likely to impact Nepali highway bridges. Seismic fragility functions for representative reinforced concrete (RC) bridges are developed for earthquake only and earthquake and scouring scenarios. Parametric variation of likely scouring depth obtained from the hydrological analysis is used to depict the probabilistic scenario to obtain fragility functions for various scouring levels. The sum of the findings outlines that the seismic vulnerability of RC bridges increases significantly when scouring precedes seismic excitation.