Fragility functions for highway RC bridge under various flood scenarios

Bridges are a country's lifeline infrastructure. As a result of climate change and global warming, floods are becoming more frequent and unpredictable. Even well-designed bridges are vulnerable to extreme flooding, as recent flood events have demonstrated. Flood fragility curves are developed for an existing RC rail over bridge considering various loading scenarios such as flood level up to the top of the pier, flood level up to the top of the girder, the impact due to log and debris, the effect of providing shear key and the effect due to scouring. The threshold mean flood velocities for the initiation of serviceability limit state for the above flood scenarios are found out. When there is no shear key, the exceedance probability for the deck displacement is found to increase with the flood water level. This increase is found to be about 92% at a particular mean flood velocity of 8.6 m/s, when the floodwater level increases from 3/4th the height of the girder to the full height of the girder. Typical log impact and debris impact increase the vulnerability of the bridge by about 45% and 80%, respectively, for a particular flood velocity of 6.8 m/s and when the flood level is up to the full height of the girder. The fragility of the bridge increases by about 80% for a scour depth of about 1.5 m at a mean flood velocity of 8.6 m/s.