Analysis of Bridge Performance Exposed to Earthquake and Flood Induced-Scour for Very Dense Sand: Derivation of Fragility Curves

Bridges play a critical role in maintaining transportation networks, and their resilience to natural disasters is of utmost importance. The bridges’ vulnerability to multiple hazards particularly seismic activities and flood-induced scour is not fully understand. This study focuses on evaluating how bridges respond to the simultaneous threats of earthquakes and flood-induced scour, particularly in very dense sandy soil conditions. The research employs specialized finite element modelling software (CSI Bridge) to derive fragility curves, providing crucial insights into bridge vulnerability in these challenging circumstances. This comprehensive approach allows for a thorough assessment of bridge vulnerability which primarily contribute to the development of fragility curves for minor, moderate and extensive damage. These curves quantify the probability of bridge damage or failure across varying levels of hazard intensity. Nonlinear time history analyses were conducted by 5 earthquakes data from the past events by scaling it within the range of 0.25 g to 1.5 g and various scour depth which ranges from no scour, 1Df, 1.5Df and 2Df. The findings highlighted those bridges exposed to both earthquake and flood-induced scour in very dense sandy soils heightened the risks of damage and the median threshold value of the earthquake intensity measure (IMmi) will show a lower value when the probability of damage is higher. Results demonstrate that the higher the depth of scour, the higher the probability for the bridge to undergo minor, moderate as well as extensive damage in very dense sandy soil type. Thus, it was concluded that the probable multi-hazard impacts of earthquake and scouring in river crossing bridges should be considered in bridge substructure design.