Vertical Natural Vibration Modes of Ballasted Railway Track

Impact loads from running trains induce natural vibration within the ballast layer, which causes ballast deterioration over time. This study measured the natural vibration characteristics of the ballast layer using field measurements, full-scale impact loading experiments and large-scale finite element analysis. Experimental test results indicate that the vibration components in the high-frequency range are dominant in ballast responses under loading and that ballast motions during unloading are mainly induced by vibration components in the low-frequency range, causing large displacement over a long duration. Numerical results indicate that the normal frequency of the vertical elastic vibration mode is detected at approximately 310 Hz and that the rigid-body bounce mode of the ballast layer occurs at one-third of the elastic vibration mode frequency. They coincide substantially with values held by field measurements. Stress acting on the angular part of the ballast is more than 1000 times greater than the average loading stress under the sleeper bottom. The combined structure, which consists of the ballast layer and sleepers, vibrates easily in synchrony with resonance motions induced by the impulse waves. Improvement of the contact condition on the sleeper bottom is expected to decrease the displacement amplitude of ballast gravel, thereby reducing ballast degradation

Vertical natural modes of the gravel aggregate in the ballasted railway track

This research investigates the natural vibration characteristics of the ballast layer by using field measurement, full-scale experiments and large-scale finite element analysis. The results indicate that the natural frequency of the vertical elastic vibration of the ballast layer is numerically detected at around 310 Hz at which the whole ballast aggregate repeats the vertical expansion and shrinkage elastically, and that the rigid-body natural vibration numerically occurs approximately at 120 Hz at which the mass of the track structure vibrates simultaneously up and down as depending on the stiffness of the ballast layer. The stress acting on an angularity part of the ballast gravel is inferred to be about 1100 times greater than the average stress on the bottom surface of the sleepers

Vibration Attenuation at Rail Joints through under Sleeper Pads

Modern railway tracks require electrification to power the trains and signaling systems to detect near real-time location of trains on railway networks. Such systems require the rail to carry and return the residual electricity back to substation, while enable signals to transfer within a track circuit. This track circuit requires rail jo ints to divide and insulate each loop of the circuit. Such the rail joints often generate impact transient dynamics to track systems. This paper presents the filed investigation into the vibration attenuation characteristic of under sleeper pads (USPs), which are the component installed under the concrete sleepers generally to improve railway track resilience. The field trial is aimed at mitigating rail joint impacts in a heavy haul track under mixed traffics. \u27Big Data\u27, obtained from both the track inspection vehicle and the sensors installed on tracks, demonstrate that track surface quality (top) of the section was improved after the trac k reconstruction. Fourier analysis results showed that the track surface (or vertical deviation) tends to deform at larger dis placement amplitude and resonates at a lower wavelength of track roughness. Interestingly, the operational pass-by vibration measurements show that the USPs has resulted in an increased v ibration of both rail and sleeper with USPs. Although the studies have found that the sleepers with USPs tend to have lesser flexures, the field data also confirms that a railway track with USPs could experience a large amplitude vibration, especially when excited by a high-frequency impact force. These dynamic behaviours imply that the use of soft to moderate USP could p otentially induce dilation of ballast whilst the use of hard USP may reduce sleeper-ballast friction. In the end, these could then w eaken lateral track stability over time