Effect of ultrasonic impact treatment on welding residual stress and fatigue resistance of doubly-welded rib-to-deck joints in OSD

Innovative doubly-welded rib-to-deck joints (DRJ) have been developed to enhance the fatigue life of orthotropic steel decks (OSD) used in steel bridges. However, the welding process and welding residual stress (WRS) dis-tribution of DRJ are more complicated than those of conventional single-side welded rib-to-deck joints. To release WRS and improve the fatigue resistance of DRJ, ultrasonic impact treatment (UIT) and fatigue tests were performed in this study. The effect of the UIT process on the WRS distribution and fatigue resistance of the DRJ was investigated. Furthermore, the welding processes of the DRJ and UIT were simulated using the finite element method and validated against the relevant measurements. Subsequently, they were used to investigate the effect of the UIT process on the WRS distribution and represent the mechanism of fatigue failure of the DRJ. Compared with the as-welded specimens without UIT, the fatigue strength of the DRJ increased by more than 60%, and the UIT process altered the dominant fatigue failure mode of the DRJ. The fatigue crack, caused by a UIT-induced fold defect, tends to initiate at the bottom of the impact pit. Owing to the UIT process, the adverse tensile WRS in the weld toe is eliminated, and beneficial compressive residual stress is introduced, leading to an improvement in the fatigue strength of the DRJ.