The role of vehicle dynamics in train-induced ground vibrations and the detection of irregular axle-pulse responses due to a varying track support stiffness

Abstract

Train-induced ground vibrations are all generated by the vehicle, by static or dynamic vehicle loads. The most important and most accepted excitation are the dynamic wheel loads from the passage over track irregularities. Dynamic wheel loads will be compared from parallel axle-box and ground vibration measurements at more than seven sites. Some low-frequency excitation of ground vibrations, typically between 10 and 30 Hz, cannot be found in the axle-box measurements. Therefore, other vehicle modes, such as rigid bogie modes, flexible carriage modes, rigid and flexible wheelset modes, have been analysed for additional excitation forces. These vehicle dynamics analyses give an explanation for higher axle-box results at high frequencies, but not for the excitation of the higher low-frequency ground-vibration component. Finally, the effect of the moving static train loads will be analysed. For a regular track and soil, the moving static train loads yield the quasi-static response which exists only in the low-frequency nearfield of the track. If the support stiffness is randomly varying along the track, the pulses on the track generate an additional low-frequency component which is called the irregular pulse responses. This component will be demonstrated by numerical analysis where all axle pulses are superposed in frequency domain.

Effects of a varying track and soil stiffness on ground vibrations near railway lines

“…Moreover, a general trend of the dynamic loads ( 1 kN) has been observed, which has been exceeded by back-calculated axle loads at some more ground-vibration measurement sites (Fig. 5) [13]. 4.…”

“…For the effect of the varying support stiffness on the wave propagation [13], the passage of the static train loads is represented by a number of pulses at a line of discrete excitation points. The passage of a train yields impulses F0dt on the track due to the static axle load F0.…”

“…1. The vehicle dynamics (rigid or flexible car-body, rigid bogie, and flexible wheelset eigenfrequencies have no or only a minor influence on the dynamic load amplitudes [13].…”

“…The purpose of the present work is to find the reason of this component and to compare it with other effects of a varying stiffness or a moving static load. The reasons have been searched in vehicle dynamics [13], the static axle loads passing regularly over the track (the quasi-static response) [14][15][16], the geometric irregularities of the vehicle (wheel) and the track and the corresponding dynamic loads [17], the regular and irregular dynamic loads from stiffness variations of the track [4,10,12,18], and the irregular wave propagation due to stiffness variations of the track support [13,19] or the soil [1,20]. The trans-Rayleigh train effect [21], however, has been excluded because none of the 50 BAMmeasuring sites had a wave velocity that is lower than the train speed.…”