This paper describes work in-progress that applies the finite element (FE) method in predicting the responses of individual railroad crossties to rail seat pressure loading in a ballasted track. Both wood and prestressed concrete crossties are examined. The concrete tie is modeled as a heterogeneous medium with prestressing wires or strands embedded in a concrete matrix. The constitutive relations employed in the models are: elasticity followed by damaged plasticity for the concrete material, linear elastic bond-slip relations with potential initiation and evolution of damage to the bond for the steel-concrete interfaces, orthotropic elasticity followed by failure dictated by orthotropic stress criteria for the wood ties, extended Drucker-Prager plasticity for the granular and frictional ballast material, and elastic half space for the subgrade. The corresponding material parameters are obtained from the open literature.
Under a simplified pressure load uniformly distributed over the rail seat area, the FE method predicts 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. The rail seat force-displacement relations are obtained from the simulations. The resultant rail seat forces at which tie failures occur are compared for concrete and wood ties.
The FE method appears to be a promising tool for studying the railroad tie behavior under rail seat loading conditions in a ballasted track. Experimental data will be sought to calibrate the material parameters and verify the modeling approach. Additional track components, particularly rails, rail pads and fasteners, will be incorporated in future modeling efforts. This detailed modeling approach may help to shed light on the rail seat deterioration failure mechanisms observed in some concrete ties.