Probability of failure estimation for highway bridges under combined effects of uncorrelated multiple hazards

Majority of the highly populated regions of the United States are susceptible to multiple natural hazards. In such regions, the design and construction of structures under multiple hazards are critical to achieve the appropriate structural performance and infrastructure resilience. Multi-hazard reliability analysis of structural systems evaluates the system response under multiple random loads, some of which may occur simultaneously, or the effect of one may weaken the structural system before the occurrence of the next event. This paper studies the combined effects of scouring and earthquakes, as two uncorrelated extreme events, on the performance of reinforced concrete highway bridges. In a continuous effort to support future improvement in understanding the impact of multi-hazard loading scenario on bridges and to develop mitigation actions, this paper assesses the seismic vulnerability of a reinforced concrete highway bridge experiencing the effect of erosion due to the increase in frequency of flood events. The analytical fragility approach uses a three-dimensional nonlinear finite element model of the bridge cases with various levels of scouring. Because a bridge is system of components, a component level fragility curve is used to track the response of the components for a given ground motion intensity. The system fragility curves are developed to consider the vulnerability of critical components to assess the probability of bridge damage. The results indicate that under multi-hazard scenarios, the component governing the fragility of the bridge system varies depending on the level of scour sustained by the structure.