Fatigue Evaluation and Crack Propagation Characteristics of Rib-to-Deck Welded Joints in Steel Bridge Decks

To investigate the fatigue crack growth characteristics and establish a fatigue life evaluation method for rib-to-deck (RTD) welded joints in orthotropic steel decks (OSDs), the influence of different simulation methods of fatigue crack propagation and material properties were considered. The OSD under heavy traffic in a highway bridge crossing the Yangtze River was taken as the research object, and fatigue tests and numerical simulation based on fracture mechanics were carried out. The fatigue life of RTD welded joints corresponding to cracks that originated from weld roots was reasonably predicted, and associated fatigue crack growth characteristics were revealed. The research results show that the relative errors between the predicted fatigue life under constant amplitude fatigue loading and measured values are less than 10%, and the assessment results tend to be safe. Fatigue crack growth paths and shape changes are basically consistent with those observed from fatigue testing. Simulation methods for fatigue crack growth, calculation criteria for kink angle, material parameter values, and initial crack depth are key factors that influence fatigue life prediction. Fatigue cracks initiated from weld roots are mixed-mode cracks dominated by mode I. The influence of mode II and mode III should be taken into account in fatigue life prediction. The crack shape shows the typical characteristic of a spatial curved surface with an aspect ratio between 0.20 and 0.63, and the maximum kink angle is 12.7°. The predicted fatigue life is fairly sensitive to the initial crack depth, which should be derived with reasonable consideration of engineering practice.