Catastrophic failures are the ultimate nightmare of structural engineers. The greatest number of bridge failures occur during construction, and the second largest cause of bridge failure is from flood water either from scour or from overtopping. However, the failures that seem to attract the most media attention are those that occur to aging bridges that have been in service for many years, particularly if there is loss of life involved. In many cases, the offending culprit, an overweight truck on a load posted bridge, can be identified because it is trapped in the wreckage. Unfortunately, it is often only a lightly loaded vehicle that is on the bridge when it collapses.
