Scour-dependent empirical fragility modelling of bridge structures under earthquakes

Abstract

Fragility analysis is often employed to evaluate the vulnerability of structures subject to strong earthquakes, and in recent years, it further becomes one of the basic components for assessing the seismic resilience of civil structures and infrastructure systems. For river-crossing bridges that are exposed to both strong earthquakes and flooding events, a significant risk to bridge structures is the conjunct effects of seismic excitation and bridge scour. However, how to consider scour as a secondary hazard in performing fragility analysis and how to achieve balance among physical complexity, simplification and analytical rigour are not fully addressed in the literature. Extended from the traditional fragility modelling and incremental dynamic seismic analysis, a scour-dependent empirical fragility modelling approach is proposed in this article. In the proposed model, the model parameters are associated with scour depths in terms of quadratic polynomials, which provide great flexibility to consider the complex effects of bridge scour. Numerical analysis based on a simple two-span bridge model with pile foundations demonstrates the effectiveness and accuracy of the proposed approach. The fragility surface generated in this work can be used to assess the seismic resilience of scoured bridge under earthquake loads.