RESEARCH ON SURFACE DEFECTS AND FATIGUE EFFECTS AT RIB-TO-CROSSBEAM WELDED JOINTS OF ORTHOTROPIC STEEL BRIDGE DECKS

The initial weld defect is one of the key factors which have major influences on the fatigue performance of structures and components. Characteristic initial weld defects were introduced into the fracture mechanics evaluation framework, the interaction energy integral method and mixed-mode fracture criterion were adopted to address the fatigue crack propagation caused by surface defects. On this basis, an analytical approach, which can assess the impact of surface defects on fatigue, was established by means of writing a program of simulating fatigue crack growth. Detailed analysis was carried out to reveal the effects of initial weld defects with different shapes and dimensions on the key indices of crack propagation and fatigue life prediction at the rib-to-crossbeam welded joints of orthotropic steel bridge decks. The results indicate that the proposed approach can be effectively applied to evaluate the influences of surface weld defects on the fatigue properties of weld toes. Planar defects have more remarkable influences on the evaluation indices of crack propagation and of predicted fatigue life; initial depth and shape are both critical factors that have a significant impact on fatigue performance;and the influences of volumetric weld defects are mainly controlled by the size in the depth direction. The shape and geometric parameter values of initial weld defects should be determined according to engineering practice and recommended values from specifications, and the fatigue life could be underestimated if all the defects are roughly simplified as planar defects. Further research should be dedicated to the reliability assessment method considering the uncertainty of weld defects.