The spectral feature of the track irregularity has a great impact on the running stability of high-speed trains. This study assesses the service reliability of the high-speed rail (HSR) ballastless track structure considering the effect of wavelength distribution characteristics of the track irregularities. The serviceability limit state (SLS) function of the ballastless track is established with respect to the derailment coefficient and wheel-unloading rate. To overcome the problem of high computational cost in the iteration of reliability assessment for the vehicle-track system, this study proposes an improved response surface method (RSM) and the explicit solution of the SLS function of the ballastless track can be realized. Compared with the traditional RSM, the improved RSM can adaptively adjust the variable interpolation coefficient to increase the iterative convergence speed. To obtain the vertical and lateral wheel-rail forces, a 3-D vehicle-track coupling model is established based on multibody dynamics and the finite element method (FEM). To analyze the wavelength effect of the track irregularities, a binary wavelet-based inversion algorithm is proposed to generate time series of both the vertical and alignment irregularities from the track irregularity spectrum (TIS). By comparing it with the MCS method, it is found that by using the improved RSM method, the convergence condition of the reliability index can be satisfied only by tens of iterations and the total computation time is 1.92 x 10(4) shorter than using MCS. Finally, the effect of different wavelengths of the track irregularity on the service reliability of track structure is discussed. The results show that the wavelength of 32 to 64 m is the main unfavorable wavelength range affecting the track service reliability under the normal operation condition of HSR.
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