Finite Element Modeling of Railroad Track Components

A ballasted railroad track consists of rails, fasteners, ties, ballast and the underlying subgrade. Realistic simulations of the track response to interactive vehicle-rail loads will require detailed models of each component. In this paper, finite element (FE) models are developed for some of the ballasted track components including wood and concrete crossties, ballast and subgrade. A user material subroutine is employed to predict the failure of wood ties based on an orthotropic stress criterion. The concrete tie is modeled as a heterogeneous medium with prestressing tendons embedded in a concrete matrix. The concrete material observes elasticity followed by damaged plasticity. The interfaces between the tendons and concrete are simulated with cohesive elements, and there can be initiation and evolution of damage to the bond between the steel tendons and concrete. Further, the granular and frictional ballast material is modeled with extended Drucker-Prager plasticity, and the subgrade is modeled as an elastic half space. All material parameters are obtained from the open literature. The track component models are then assembled and applied in FE analyses. First, the stress states in concrete ties upon release of the pretention in the prestressing tendons are predicted. Second, individual wood and concrete tie responses to a simplified, uniformly distributed pressure load over the rail seats in a ballasted track are analyzed. The analyses indicate the failure modes in this type of loading as tensile cracking at the tie base below the rail seats of a concrete tie and compressive failure in the rail seats of a wood tie. Future work will include developing and incorporating fastener and rail models in the track assembly. A complete track model will be subjected to more realistic vehicle-rail forces in FE analyses and expected to reproduce the complex stress states in the rail seats of a tie more accurately. Such analyses may provide a better understanding of the mechanisms responsible for the rail seat deterioration failures observed in some concrete ties.