Vibration Decay Rate Analysis and Test on Ballasted Railway Track

In the railway transportation industry, the rail is considered to be the dominant source ofrolling noise over the usual speed range (<160km/h). It has been well documented that the rate of decay of vibration along the rail is closely linked to the noise performance of the track. In this study, a finite element model of a periodic supported rail is developed in ABAQUS to study the acoustic performance of the rail. To compute the decay rates, acceleration responses along the rail are converted into the frequency domain and then the decay rates are obtained for each 1/3 octave band by processing the response levels. It is shown that the decay rate results obtained by FEM follow the same trend as the measured decay rate. Therefore the FEM decay rate can be used for generating comparisons between different tracks as an indicator of their acoustic performance. To test the vertical decay rate on a real track, a rail section at the Sadeghieh subway site is also tested and analyzed. To this end, the vertical responses of the rail are measured by two accelerometers. It is shown that at low frequencies (below the cut-on frequency), the decay rate resulting from the accelerometer on the sleeper place is 2dB less than the decay rate result from the accelerometer on the mid –point.However at high frequencies (above cut-on frequency), the decay rate results from bothaccelerometers correspond closely to each other.