Flood-Induced Scour Fragility Analysis of Bridges in Different Soil Conditions

Bridges are a significant component of transport infrastructure, yet they are most vulnerable to flood risks, including hydrodynamic forces and erosion. Climate change has increased the frequency and intensity of floods, which is an added threat to the structural integrity of bridges, calling for the development of more reliable risk analysis methods. Fragility curves have been widely used in the assessment of structural vulnerability. However, while the current topic of prominent literature remains seismic- induced bridge failure, insufficient studies specifically concentrating on flood-induced damage can be found. This study investigates the flood vulnerability of bridges, including scour and hydrodynamic load effects. A CSI Bridge finite element model performed 56 analyses to obtain fragility curves for various discharge levels. Through probability of exceedance analysis, bridge response was examined by considering Very Stiff Clay (Ground Type B) and Medium-dense Sand (Ground Type C). This study demonstrates that bridge vulnerability to hydrodynamic forces is highly dependent on foundation soil type and scour depth, with very stiff clay leading to higher failure probabilities due to stress concentration, while medium-dense sand offers greater resilience. This research contributes to the enhancement of bridge resilience, highlighting the necessity for additional investigations into soil conditions and the assessment of the effects of debris and log accumulation during scour events.