Safety of High-Speed Ground Transportation Systems: Analyses of Track Shift under High-Speed Vehicle-Track Interaction

This report describes analysis tools to predict shift under high-speed vehicle- track interaction. The analysis approach is based on two fundamental models developed (as part of this research); the first model computes the track lateral residual deflections under vehicle passage, whereas the second determines the lateral dynamic loads generated as the vehicle negotiates misaligned tangent or curved tracks. The track residual deflection model takes the loads from the vehicle dynamic model as inputs and is based on a quasi-static beam theory and an appropriate trilinear constitutive representation for the tie-ballast lateral resistance under the wheel vertical loads. The vehicle dynamic model is based on a multibody simulation which maintains a wheel-rail rolling contact connection with a complaint track representation. Computer codes (OMNISIM) for track residual deflection and for vehicle multibody simulation with complaint track element have been developed to facilitate parametric study. OMNISM, which has been developed through extensive modifications of previous programs (which do not permit a complaint track element is shown to have several advantages including accuracy in the evaluation of loads and wheel climb predictions. The track shift computer code can be used to identify the stable and unstable regimes of track shift, and is partially validated by test data on panels under stationary load cycles, and SNCF data on TGV track under moving loads. It is shown that moving load simulation is required for an assessment of track shift. Preliminary results are presented for a representative articulated train with high-speed track traversing track with selected alignment irregularities at selected wavelengths. The results are sensitive to flange clearance and wheel profile. For "AAR wheel profile," the net axle force ratio can reach a high value (-0.49) for a misalignment of 8 mm amplitude and 10 m wavelength, at speeds on the order of 93 mph. However, this force is spread over a finite length of the track and its effect on track shift needs to be investigated.