A Concise Analysis of Hydraulic Bridge Collapse

The New York State Department of Transportation maintains a database of over 428 bridges that have collapsed in the United States between 1992 and 2014. These collapsed bridges are associated with inspection data from the NBI (National Bridge Inventory) dated just prior to collapse. Out of 428 bridges in the compiled-collapse database, 237 (55.4%) have collapsed due to a hydraulic-induced failure. A test of independence between the scour critical rating and hydraulic failure indicates that the two variables are associated. Almost half of the bridges (46.4%) that collapsed due to a hydraulic failure are inspected and rated scour stable, which indicates a discrepancy between the scour critical rating and hydraulic collapse. Evidence of accelerated deterioration is found in conjunction with substructure condition ratings. Underwater inspection of in-service bridges shows decreased substructure condition ratings compared to decks and superstructures. The evaluation of the bridge components for hydraulic collapse (median rating of “5”) and the in-service population (median rating of “7”) yield a lower rating for the substructure. The presence of minor scour at the substructure is a greater hazard than currently described by the inspection system.