Segregation of Bridge Failure Causes and Consequences

A database of United States bridge failures was used to ascertain the probability of bridge failures segregated by cause. The database showed hazards that have caused bridges to fail historically. The probabilities of failure by causes are established and conditional probabilities of failure with consideration for the features under the structures were assessed. The most likely cause of failure was determined to be hydraulic in nature when adjusting for the features under the structure. The probability of a hydraulic failure was unknown from past investigations; however, the value was determined to be an annual probability of 1.52E-4. Similar probabilities were also quantifiably established for other causes. The consequences coupled with the probability of failure by cause were evaluated qualitatively and quantitatively. Consequences of bridge failures were set forth qualitatively using engineering judgment. A sample population from the database was used from one Department of Transportation (DOT) that was linked to National Bridge Inventory (NBI) data. Selective quantitative consequences were assessed for the sample data bridge failures. Life loss occurred in about 4% of bridge failures. An ideological benchmark, set by the United States Army Corps of Engineers interim guideline for dam safety, was used to show that bridge failures within the United States are tolerable comparing probability of failure to life loss.