Multiaxial fatigue assessment of welded connections in railway steel bridge under constant and variable amplitude loading

Fatigue assessment based on the critical plane approach is generally accepted to be more accurate for multiaxial non-proportional loading. Among different critical plane fatigue criteria, the modified Carpinteri-Spagnoli (C-S) criterion is rather a simple approach in which the critical plane orientation can be determined a priori. The aim of this paper is to investigate the applicability and reliability of the critical plane approach-based C-S criterion that can be employed to calculate the fatigue damage of bridge connections under railway traffic loading. A typical half through steel bridge subjected to railway traffic is analysed using Finite Element Modelling in ANSYS 17.2. The averaged principal stress directions determined through appropriate weight functions are used to predict the critical plane orientation. Then, the multiaxial fatigue damage is assessed through an equivalent stress expressed by a nonlinear combination of the normal and the shear stress components acting on the critical plane. Applicability of the C-S criterion is investigated by estimating the fatigue damage of critical welded connections and is compared with the fatigue damage computed according to Eurocode EN1993-1-9 under both constant and variable amplitude loading.