Fragility of bridge decks exposed to hydraulic and driftwood actions

A resilient bridge network is vital to a community recovery after natural disasters. Floods are the main cause of bridge collapses, but there is little research on the combined fragility of single-span bridge decks to hydrodynamic forces and driftwood clogging. Moreover, most studies concentrate on multi-span bridges and piers. By using HEC-RAS software and in-house developed Python scripts, this work proposes a method to obtain fragility curves for single-span bridges accounting for hydrodynamic actions and driftwood. Due to the lack of indications from standards concerning uplift and overturning of bridge decks, these limit states are included in the formulation together with slippage. Results revealed that all three limit states must be taken into account and showed that driftwood clogging can have a severe impact on the failure probability of the bridge, with even a minor decrease in clearance causing a significant safety reduction. Additionally, this work discusses the influence of hydrologic model recalibration on the failure probability of a structure.