Coupled finite element and multibody systems dynamics modelling for the investigation of the bridge approach problem

Railways are the most common mode of transportation for both people and cargo due to its advantages in economy, safety, and comfort. The finite element method has been broadly used for more than three decades to model the different components of the railroad system such as rails, sleepers (cross ties), and substructure and has been used to investigate a variety of problems associated with rail mechanics. Different multibody systems dynamics software programs have also been developed to investigate the dynamic performance and contact behaviour between the rails and the wheels and to determine the contact forces. In this work, a full three-dimensional model that couples both the finite element method and the multibody systems dynamics has been used to study the railroad system. The main focus of this study is to model the bridge approach problem under dynamic load. The bridge approach problem arises from the sudden change in the foundation's stiffness under the rails at the bridge entry and exit, leading to high levels of stress and settlement that can also cause further problems over time. The effect of using a concrete slab at the bridge entry is also investigated in this study, using two slab designs: rectangular and inclined. The results show the effectiveness of the three-dimensional model and slab implementation on the forces and the vertical deformation, especially the inclined slab that applies a gradual change in the stiffness rather than a sudden change.