Fatigue Strength Improvement of Bridge Girders by Ultrasonic Impact Treatment (UIT)

Over the past four years, extensive research has been initiated on the application of ultrasonic impact treatment (UIT) for fatigue enhancement of fracture-critical details in steel bridges. The research is particularly relevant in light of the development of high strength steels and their use within the bridge industry. The main investigation involved fatigue tests on full-size fabricated and rolled ASTM A709 GR 50W steel girders with welded attachments (stiffeners and cover plates). These enabled the influence of weld detail design on the benefit of UIT to be investigated. At the same time, a series of fatigue tests was also carried out, aimed at the comparative evaluation of the effectiveness of various post-weld fatigue improvement methods. The results obtained to-date in these investigations are presented in this paper. Specific emphasis is focused on weld design options and the benefits achieved by ultrasonic impact treatment. The fatigue test results obtained to-date from the research are presented in this paper. Conclusions are drawn regarding the improvement in fatigue performance that can be achieved with UIT for consideration in the design of welded bridge structures as well as maintenance and repair procedures.