Fatigue behavior of welded coverplates treated with Ultrasonic Impact Treatment and bolting

Damage due to traffic-induced fatigue is a common problem in welded steel girder bridges. Engineers tasked with the duty of repairing fatigue-damaged bridges face difficult decisions about the choice of repair method to implement. In some instances different repair methods are used in combination, under the assumption that the combined effects of two techniques that have been shown separately to improve fatigue life will result in greater improvement. This study evaluated the interaction that may take place between different repair methods for a particular type of fatigue vulnerable detail. The detail that was chosen for the study was a welded connection between a plate and a coverplate, often used in older bridges. Specifically, this study investigated the fatigue life enhancement afforded by three retrofit methods: post-installation of tensioned bolts behind the weld, application of Ultrasonic Impact Treatment (UIT) to the weld, and a combination of the two techniques.Results of 15 fatigue tests showed that UIT was a highly effective technique to enhance the fatigue life of coverplate end details. Weld treatment with UIT resulted in an improvement in fatigue life over control specimens by a factor of 25. This translated into an improvement in fatigue life from that of an AASTHO fatigue Category E detail to that of an AASHTO fatigue Category A detail. The bolting procedure, as implemented in this study, had a negligible effect on fatigue life. The combination of the two methods was found to be less effective than using UIT alone due to stresses induced by the bolt on the untreated portion of the weld.