Observations and Trends among Collapsed Bridges in New York State

Abstract

A collection of condition and appraisal ratings of bridges prior to collapse is presented and analyzed to show commonalities among collapsed bridges in New York State. General observations of bridge collapses are presented in addition to select consequences. Bridge inspection data are collected for the most recent inspection dates prior to the collapse of each collapsed bridge. Trends obtained from statistical analysis of existing data show 45 (46%) of collapsed bridges were structurally deficient prior to collapse, and a collapse rate of structurally deficient bridges is estimated to be 1/1,200 annually. Age and structural deficiency are shown to be related. Structural deficiency and collapse are shown to be related. Age of structure at the time of collapse is contingent on collapse cause. Deterioration-caused and overload-caused bridge collapses are age related, but hydraulic-caused and collision-caused bridge collapses have no age-determined relationship. Fifty-seven percent of hydraulic-caused bridge collapses had a scour vulnerability rating that indicated the foundations were stable for calculated scour and scour conditions. Collision-caused bridge collapses appear to be contingent on the vertical clearance: roughly 90% of bridges analyzed had a vertical clearance less than 4.5 m (14 ft 9 in.). Overload-caused bridge collapses have a relationship with the bridge being load restricted. The overload-caused collapse rate for a bridge that is load restricted is estimated to be 1/3,500 annually. Life loss is associated with 5% of bridge collapses, most of which are collision-caused. The majority of bridge collapses have low consequences related to life loss, average daily traffic, and detour length.