Merging behaviour and fatigue life evaluation of multi-cracks in welds of OSDs

Experimental studies were conducted to investigate the merging behaviour of multiple fatigue cracks (MFCs) in rib-to-deck welds of orthotropic steel decks (OSDs). Numerical simulations were conducted to investigate the mechanism of the merging behaviour of MFCs on fatigue life. In addition, the sensitive parameter in the MFCs affecting the fatigue life were revealed. Finally, a comprehensively failure criterion for MFCs was proposed. Results show that the merging behaviour of MFCs can be effectively observed by the beach marks on the fracture surface of the rib-to-deck weld. The merging behaviour is a key factor driving cracks penetrating through the deck, which significantly increases the crack length and decreases the crack shape ratio. The fatigue life of MFCs with different crack sizes is mostly determined by the larger crack, while the shape ratio effect can be ignored. The crack number has the most significant effect on fatigue life, where the five-cracks case reducing the fatigue life by up to 39 % compared to a single crack. Due to the nonlinear effect of crack spacing on fatigue life, MFCs with the same fatigue life may have significantly different final crack length. Therefore, the proposed failure criterion for MFCs considers the effects of both crack depth and length.