Behavior of Integrated Crosstie Trackwork System

Abstract

Light rail systems are an important transportation mode in urban centers. An advanced rail transit system has been developed that utilizes linear induction motors (LIM) for propulsion and braking of the vehicles. Due to the tight motor-to-rail air gap tolerances required for the efficient operation of the LIM system, the trackwork requires special consideration. An innovative crosstie trackwork system has been developed to address competing requirements for high stiffness to ensure efficient operation of the LIM, and low track stiffness for acceptable ride quality. The crosstie incorporates a hollow structural steel section welded at each end to formed steel base plates which are supported by elastomeric pads. The crosstie supports steel running rails. This paper describes a finite-element model developed to predict the response of a crosstie to loads that simulate the passage of a steel wheeled transit vehicle. The model uses tetrahedral elements for the hollow structural steel section and the base plates. The elastomeric pads are modeled using elastic foundation elements. The model predicts stresses and deflections in the crosstie. An experimental program that was carried out on the crosstie to investigate its fatigue performance and to obtain data to verify the finite-element model is also described. The model conservatively predicts crosstie deflections and stresses. The hot spot stress approach is used to provide a conservative fatigue life prediction of the crosstie.