Characteristics of elastic wave propagation and anomalous Doppler effect in the periodic structure of floating slab track

Abstract

Floating slab track is widely used in urban rail transit because of its proven vibration attenuation and isolation performance. To investigate the elastic wave propagation in floating slab structure, the characteristic equation for wave dispersion is obtained using generalized plane wave expansion. Double periodicities from unit slab and fastener spacing are considered simultaneously. The complex dispersion curve of the infinite periodic floating slab track is obtained. Eight band-gaps are found to exist in the range from 0 to 300 Hz, and the corresponding theoretical analysis on wave dispersion is provided. An impact test was conducted, which verifies the band-gaps blocking effect on elastic wave propagation. Based on the wave-mode properties, it is found that the band-gap formation mechanism of track structure with double periodicities is different from track structure with a single periodicity, i.e., the localized Bragg scattering or localized resonance modes cannot prevent the propagation of coupled elastic waves in the case of double periodicities. The results in the frequency-wave number domain demonstrate that anomalous Doppler effect occurs in the stopband range and the normal Doppler effect occurs in the passband range.