ABSTRACT
Orthotropic steel decks (OSDs) consist of a complex network of longitudinal stiffeners, transverse stiffeners and the deck plate itself. Working as a whole, it takes part in the structural working of the overall bridge concept, resulting in an extremely lightweight and durable deck concept. Orthotropic steel decks are very sensitive to fatigue damage, because of the large number of welded connections in the deck. Historically, designers have tried to improve upon the concept by focusing on: optimization of the overall dimension of the steel plates, determining the shape of the stiffeners and possible cut-outs and investigating the possible influence of the wearing courses in distributing vehicle loads. Most of these approaches have proven successful. However, combined with the ever-increasing vehicular loads and traffic volumes, designers still feel the need to increase the plate thicknesses. A deck plate thickness of 18mm or more has become quite common. This is mainly caused since regulations stick to the existing fatigue concepts. Innovative research focuses on the application of fracture mechanics as well as the influence of residual stresses on the fatigue lifetime. An analysing tool using Linear Elastic Fracture Mechanics (LEFM) is proposed in this paper. Crack propagation and crack growth direction are evaluated with an eXtended Finite Element Model (XFEM), on macro- and meso-scale. In addition, thickness effects are evaluated for both longitudinal stiffener and deck plate. These calculations result in a better understanding of the increased fatigue properties compared to the increased dead load of the structure. Manufacturing processes such as welding operations cause residual stresses, which are present in most civil structures. They are causing plastic deformations without any external loads and are therefore often overlooked during design. Nevertheless, residual stresses can have profound influences on the material strength and the fatigue life. Overall, it can be stated that the OSD remains a valuable bridge concept, especially for larger span bridges, that can be understood better using modern research techniques.
