ABSTRACT
In the background of requirements to weight reduction and cost saving, the application of high strength steels in steel bridges has been investigated. However, SBHS700 of 780MPa class steels must particularly grasp with respects to fatigue strength of welded joints. In this study, in order to clarify effects of the fatigue strength improvement by ICR (Impact crack retrofit closure) treatment for SBHS700, fatigue tests continuously carried out using small fatigue specimens of out of plane gusset welded joints, which were removed from a girder specimen of a previous study by gas fusion cutting. Before fatigue tests, compressive residual stress is confirmed with the x-ray diffraction method. The test results indicate that the fatigue strength improvement effects on welded joints treated by ICR treatment was at least 3 classes larger in case of using SBHS700. However, the fatigue strength of one specimen is lower than that of another specimen. Therefore, this paper also presents the result evaluated by using the control method of fatigue strength improvement based on the shape of the deformation area after ICR and the crack initiation can be identified based on the observation for a fractured surface using Scanning Electron Microscope (SEM).
