MS9.10 - Dynamics of Railway infrastructures

The resonances of railway bridges have often been analysed for short bridges under periodical high-speed trains, for simply supported one-span bridges, for the fundamental bridge mode, and by time-domain analyses. Many time-consuming calculations have been performed to establish simplified rules for standards. In this contribution, the passage of different (existing, new and hypothetic) trains over different bridges will be analysed in frequency domain by using three separated spectra with the purpose to get a better physical insight in the phenomena. At first, the excitation spectrum of the modal forces is built by the mode shape and the passage time of the train over the bridge. The second spectrum is the frequency response function of the bridge which include the modal frequency, damping and mass. The third part is the spectrum of the axle sequence of an arbitrary train which is not limited to periodical or specific (conventional, articulated, regular or standard) trains and which does not include any bridge parameters. The final solution in frequency domain is obtained as the product of these three complex, strongly varying spectra for the dominating bridge mode or in general as the sum of these products over all relevant bridge modes. The time domain solution is obtained via the inverse Fourier transform, and the resulting time histories have been successfully compared with some measurement results. The method is applied to the vertical and torsional modes of a mid-long 1-span bridge on elastomeric bearings under standard train speeds, and to a long multi-span integral bridge under long periodical freight trains. Different resonance and cancellation effects have been found for systematically varied train speeds according to the axle sequence of the whole train which is dominated by the two locomotives in that case. To be more specific, the first torsional mode of the mid-span bridge is excited for a train speed of 100 km/h whereas the second bending mode is excited for a train speed of 160 km/h. In both cases, the other mode is suppressed by the minima of the axle-distance spectra. In addition, the case of the German high-speed train ICE4 and the very high-speed hyperloop case will be discussed briefly. In general, it is shown that resonance effects are also worth to be studied for freight and passenger trains with lower speeds. [1] L. Auersch: Resonances of railway bridges analysed in frequency domain by the modal-force-excitation, bridge-transfer and axle-sequence spectra. Engineering Structures, Volume 249, 2021 Dec., 113282.

Noise barriers, that are built parallel to the railway to reduce the noise pollution, will be subjected to strong and transient aerodynamic pressure from the trains running with high speed and have the significant dynamic responses under such pressure. Geometric of high-speed trains, especially for the shape of train head, is an important factor influencing the amplitude of aerodynamic pressure. In this study, based on the computational fluid dynamics (CFD) method, the numerical simulation of aerodynamic pressure on noise barriers caused by high-speed trains was performed and validated by field data from other studies. Then, the distribution along height and length directions of such pressure on surface of noise barriers from Swedish trains, which have a different geometric design from other countries, was ana-lyzed, and the effect of different factors on results, e.g., the train speed, the distance from noise barriers to the center of track and height of noise barrier, was discussed. Finally, the results obtained by CFD simulation were compared with the existing pressure model from Standard EN 14067-4 to adapt this load model and calculation method to Swedish high-speed trains.