Dynamic Vehicle–Track Model to Study the Effects of Track Geometry and Vehicle–Track Interaction on Concrete Tie Rail Seat Load Environment

Rail seat deterioration (RSD) of concrete ties is manifested by the loss of concrete material in the rail seat area supporting the rail. This failure mode can lead to track that performs poorly and, in extreme cases, can result in the loss of rail clip hold down, reverse rail cant, and rail rollover derailments. This paper describes the use of a multibody vehicle–track dynamics model developed to study the load environment of concrete tie rail seats, specifically addressing the failure mode of RSD. Vehicle–track interaction simulations were conducted to determine the effect of track geometry perturbations on the overall load environment. Various types and magnitudes of track geometry perturbations, including combinations of surface (vertical) and alignment (lateral) perturbations were considered. Fastening system parameters such as clip hold-down force, tie pad stiffness, and broken insulator conditions were also considered. Results of these simulations suggest that concrete crushing, a hypothesized mechanism of RSD, is unlikely in realistic revenue service conditions. Under the load environments considered, the results augment support for an abrasion-related mechanism of RSD that may be more dependent on tonnage and infiltration of fine particles in the rail seat, two factors not addressed in this model. Results from in-track testing are also presented to compare model outputs with measured in-track forces under artificial track geometry perturbations installed at the Transportation Technology Center’s Facility for Accelerated Service Testing. More broadly, the use of this model to explore the effects of vehicle track interaction on tie and fastener load environment is also discussed.