Keywords: mono-block concrete sleeper, ballasted track, finite element method, natural frequency, numerical simulation, structural damping, sleeper design, sleeper vibration acceleration, pressure on sleeper bottom.

For a ballasted track, it is conceivable that the frequency of the impact load caused by settling and lateral movement of the ballast layer is mainly 100 Hz and less. However, the loading pressure at the bottom of the sleeper is not uniformly distributed [1]. Furthermore, a ballasted layer is locally forced by the bending of the sleeper. Therefore it is important: to examine a degradation mechanism of the ballasted track and to consider bending and twisting of the sleeper.

We created a three-dimensional finite element model of a prestressed concrete sleeper (maximum element size was set to 20 mm, and the number of both nodes and elements were approximately 50,000), expressing the influence of the ballast using a spring based on the experimental modal analysis of the prestressed concrete sleeper on the ballasted layer. In the experiment, a sleeper with some accelerometers was put on the ballast layer. Then, we obtained the frequency characteristics by the excitation with an impulse hammer. In the numerical simulation, we set up some parameters based on the frequency response of the experiment. Then, to examine of the influence of the vibration from the sleeper to the ballast, we investigated transient response analysis with the sleeper model by using the load of the train. Then some structurally varying sleeper models (high rigidity, high density, widely and a thick sleeper) were prepared and the difference of dynamic characteristics compared between a normal sleeper and those with some structural modifications.

We compared the appearance of acceleration and pressure response between those measured on a commercial line and numerical analysis was performed to confirm the accuracy of the numerical model. Both acceleration and the bottom pressure of the analysis was accurate, although the peak value was a little smaller than the measured value.

In the amplitude spectrum analysis of the acceleration, all natural frequencies in the additional cases were not changed when compared with the normal sleeper. In addition, peak values of almost all frequencies areas decreased. However, we need to determine an effective countermeasure method which accounts for the focused frequency area. In addition, acceleration was mainly related to the low frequency domain, and pressure was related to the high one. This means that it is very important to decrease the force through the ballast layer by reducing the peak value of the low frequency domain and by also reducing the peak value of high frequency domain.

1

A. Aikawa, F. Urakawa, A. Kono, A. Namura, "Sensing Sleeper for Dynamic Pressure Measurement on a Sleeper Bottom Induced by Running Trains", Railway Engineering, 2009.

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