Resilient cross-tie track for a transit guideway.

摘要

The Advanced Light Rail Transit (ALRT) system developed by the Urban B Transportation Development Corporation (UTDC) uses steel-wheeled vehicles which run on steel rails within a direct fixation track on a guideway. Propulsion and braking of the vehicles is by means of vehicle-borne Linear Induction Motors (LIMs) interacting with the LIM reaction rail which is a part of the track and runs parallel to the running rails. Efficient functioning of a LIM requires the air gap between the LIM and its reaction rail to be maintained to a tight tolerance. In the present direct fixation track where the running rails and the LIM reaction rail are connected separately to the concrete guideway and, therefore, deflect separately, the stiffness of the track must be high in order to maintain the air gap. The incompatibility of relatively low wheel loads of the ALRT vehicle and a high stiffness track is known to contribute to corrugation, noise and vibration problems. An alternative resilient track system in which the LIM reaction rail and the steel running rails are interconnected by means of steel cross-ties is examined in this study using both laboratory testing and numerical modelling.;Cyclic load testing of a prototype of the proposed cross-tie is described. The cross-tie endured the 3,000,000 cycles of maximum fatigue level of loading in the laboratory with no obvious sign of distress, and the relative displacement between the rail head and the LIM reaction rail (equivalent to the change in the air gap in an actual track) was found to be within the required tolerance of 1 mm.;An iterative method of analysis developed for numerical modelling of the vehicle-track dynamic interaction is described. The track is modelled by the finite element method and the vehicle is modelled as an assembly of masses, springs and dampers, with the wheel loads being the connection between the vehicle model and the track model. A parametric study conducted on the dynamic response of the track to moving loads and on the influence of a number of parameters on the variation of the air gap is presented. It is concluded that an ALRT vehicle can be modelled as a single truck with the vehicle body being represented as a point mass, and that the displacement response of the track is predicted accurately only when the surface roughness profile of the rail, as well as the interaction between the vehicle and the track, is included. The wheel loads, however, can be predicted, with small error, by considering only the vehicle response to the surface roughness profile of the rail. Non-linearity of the tie pads has a considerable influence on the displacement response of the track, but is of minor significance in the distribution of the wheel and LIM loads among the cross-ties. It is shown that the change in the air gap is not significantly affected by the inertia effects of the track, magnitude of wheel loads, speed of the vehicle, and the stiffness and damping of the tie pads.;It is concluded that the proposed resilient cross-tie track system satisfies all the design requirements and should overcome some of the problems with the existing track work.