Fatigue performance of the welded details of an old, demolished steel railway bridge

Abstract

This study investigates the fatigue performance of the welded details of an old disused steel railway bridge. The Saimaa canal railway bridge was demolished after 60 years of service, and as a part of the demolition process, a fillet-welded vertical web stiffener joint of an I-profile girder was taken for experimental testing. Fatigue tests were carried out on the joints tested in both as-welded and post-weld-treated conditions, using burr grinding, high-frequency mechanical impact (HFMI) treatment, and TIG dressing as improvement techniques. To examine the reduction in stress concentration due to the post-weld treatments, numerical analyses were performed as per the effective notch stress (ENS) approach and the theory of critical distance (TCD) methods, and different local approaches were used to assess the fatigue strength of the welded details. According to the obtained results, the fatigue strength of the joints in the as-welded condition was higher than that of recommended by fatigue design standards, indicating good welding quality and suggesting that the tested welded details had not experienced severe fatigue loads during service. HFMI treatment and burr grinding improved the fatigue strength by 30%, meanwhile no failures in the joint area were observed with the TIG dressing. Of the applied local approaches, the structural hot-spot stress method, 4R method, and ENS concept showed the highest accuracy in the fatigue assessments, and had lower scatter than the TCD methods.