Fatigue Crack Behavior at Rib-to-Deck Weld Bead in Orthotropic Steel Deck

One of the typical fatigue cracks observed in orthotropic steel deck is a through-thickness crack which penetrates and propagates along the weld bead. Moreover, according to some reports of the fatigue crack observed in some bridges, the fatigue crack sometimes changes its direction suddenly, and propagates to the rib wall and the deck plate. Such fatigue damage can cause the sudden decrease of stiffness of longitudinal rib. However, the propagation mechanism of the crack has not been investigated clearly. In this study, numerical studies on the through-thickness crack at rib-to-deck weld bead in the orthotropic steel deck were carried out. Finite element model (FEM) of an orthotropic deck with different through-thickness crack at rib-to-deck weld bead was created. In order to identify the propagation behavior of the fatigue crack, stress intensity factors for three deformation modes were estimated by the FE analysis (FEA) and the displacement extrapolation method. Based on the maximum energy release rate (MERR) criterion, the equivalent stress intensity factor and the crack direction were evaluated. From the numerical results, the crack direction change was found to be originated by the Mode II and Mode III deformation near the crack tip due to the out-of-plane bending of the rib wall along the crack.