Keywords: high speed railway, dynamic analysis, train-track interaction, stiffness transition, passenger comfort, track safety, parametric study.

One of the complexities associated with the construction of high speed railway lines refers to zones of abrupt changes in track stiffness. These changes in the vertical stiffness of the track cause important variations in the wheel-rail interaction forces and in the vertical acceleration of the locomotive box.

In this work an evaluation is presented for the influence of several parameters of the track-train system in the dynamic behaviour of zones where an abrupt variation in vertical stiffness occurs, caused by the foundations of the soils with distinct deformability moduli. These dynamic analyses were performed based on a numerical analysis program, which enables the dynamic interaction between the train and the track to be considered.

For the circulation of the Eurostar train at speeds of 200, 250, 300 and 350 km/h an analysis has been performed on the deformability moduli ratio of the foundation soil. From this analysis it was concluded that the largest variations of the dynamic interaction force occurs at the second axle of the locomotive and that there is a very significant increase of the wheel-rail interaction force with the increase of the deformability moduli ratio.

Afterwards fixing a deformability moduli ratio of the foundation soils equal to 10 and a train speed of 300 km/h the influence of several constituents of the track (such as pads, foundation soil, ballast and subballast) and the train (such as primary suspension, wheel-rail connection, bogies and wheels) in the dynamic behaviour of the system is analysed.

For the track damping, it is concluded from the results of the analyses that a decrease of the global damping ratio of the structure implies an increase in the wheel-rail interaction force.

The track model adopted for the studies considers the flexural inertia of the ballast and subballast layers, the study performed enables to conclude that the discard of this parameter induces an increase of about 20% in the wheel-rail interaction force and on the vertical acceleration of the locomotive box.

From the analysis performed for the pads it is possible to verify that the pad damping has little influence on the track-train system behaviour but the pad stiffness plays an important role.

The primary suspension parameters has a high influence on the passengers comfort as an increase on the damping or on the stiffness of this suspensions imply an increase on the vertical acceleration of the locomotive box.

By increasing the wheel mass twice the original value, the maximum value of the interaction force registered at the second axle of the locomotive increase significantly (85%). It is important to point out that a decrease of the bogie mass incites an increase of the vertical acceleration of the locomotive box.

From the calculations with train models of different complexities it was concluded that for the assessment of the wheel-rail interaction force simpler models can be adopted but for the analysis of the passengers comfort the more accurate model is required.

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