Repairing Distortion-Induced Fatigue Cracking in a Seismically Retrofitted Steel Bridge: Field Test

Many steel bridges in the United States designed before the mid-1980s are highly susceptible to distortion-induced fatigue cracking. This vulnerability is substantially increased if the out-of-plane driving force caused by differential girder displacement is increased for any reason. This research examines one such case where a multi-girder steel bridge, originally built in the 1960s, was retrofitted to improve seismic performance. As part of the retrofit, single angle K-type cross frames were replaced with stiffer double-angle cross-type frames. This seismic retrofit led to an increase in the driving force, and after only a few years following the retrofit, numerous fatigue cracks were identified in the web-gap region. Repairs were implemented to provide a positive connection between the connection plate and the girder flange aimed to reduce the level of distortion in the web-gap. This study presents the results of two field tests, before and after repair, and investigates the efficacy of the repair implemented for the bridge.