An investigation on fatigue crack propagation behavior of welded connections in UHPC reinforced OSDs using 3D crack simulation

Fatigue performance of orthotropic steel decks (OSDs) is one of the concerns that should be carefully considered, since OSD is reported as one of the most structures experiencing fatigue defects. In this study, the fatigue crack propagation behavior of welded connections in OSDs was investigated using 3D crack simulation based on the linear elastic fracture mechanics (LEFM). Fatigue testing results of rib-to-deck and rib-to-floorbeam welded specimens were considered to validate the applicability and efficiency of the crack propagation analysis. Stress intensity factors (SIFs) of the test specimens were computed using the M-integral approach, where Mode I (opening mode) and mixed-mode (i.e., combining Mode I, II, and III) of failure were considered. Additionally, the effect of the applied stress range amplitude, initial crack size, and UHPC layer thickness on the crack propagation behavior of welded joints under consideration were explored. The results indicated that the crack simulation analysis is acceptable and applicable for the evaluation of fatigue crack propagation of welded connections in OSDs. The computed SIFs demonstrated that the governing propagation mode of rib-to-deck and rib-to-floorbeam welded joints is Mode I (opening mode) and the effect of shear and tearing is limited. For both details (i.e., RD and RF welded joints) the decrease of the stress range amplitude and the increase of the UHPC layer thickness considerably slowed the crack propagation, while the increase of the initial crack size significantly accelerated the crack propagation. Comparison of the test and numerical results with the S-N curves showed that FAT100 curve of the IIW specification is recommended to predict the fatigue strength of RD and RF welded joints in OSDs reinforced by UHPC layer.