REPAIR EFFECT OF UIT ON WEB GUSSET WELDED JOINTS WITH FATIGUE CRACKS STAYING ALONG WELD TOES

Abstract

 Metropolitan Expressway has been in service for over 50 years under heavy traffic, so that many fatigue cracks have been detected at web-gusset welded joints of steel I-beam bridges. Most of those cracks are shallow and staying along the weld toes. Commonly, these cracks are repaired by removing them with bar grinder. UIT (Ultrasonic Impact Treatment) has been used for enhancing fatigue strength by impacting weld toes with hard pins and inducing compressive residual stresses there. It was thought that the repair work loads would be much lighter, if UIT could be applied to the repair of those fatigue cracks instead of bar grinder method. For the purpose of verifying the repair effect of UIT on those fatigue cracks, fatigue tests using model specimens were performed. The results suggest that the fatigue life of welded joints with toe cracks is improved more than twice that of the original joints in conditions where the stress range is less than 65N/mm² and the UIT groove depth exceeds 0.23mm.