Random Track Irregularities On Long-span Bridges And Its Combination With Bridge’s Deflection

Since China’s first high-speed railway in 2008,it has developed rapidly.High smoothness and high stability of train operation have always been the high-speed railway’s goals.Countries customized strict codes to achieve it.In recent years,the design and construction of long-span railway bridges have brought new challenges to track irregularity management.We have only made corresponding trial regulations on the railway line’s management standards for track irregularities.The applicable management standards are still insufficient for long-span railway bridges,especially those of kilometers.This paper starts with the measured track irregularity data on the bridge.The track random irregularity spectrum of large-span railway bridges is explored.The combination relationship between it and the additional deformation of the bridge is given to consider the random irregularities when performing the track shape and position evaluation.The main contents are as follows:(1)Track irregularity is a random process,so it is an intuitive and efficient method to describe its characteristics using Power Spectral Density(PSD).PSD method is also tended to be used in codes to show the track irregularities Five types of track irregularities power spectrum such as height and gauge of 16 groups measured track irregularity on the high-speed railway are estimated by Welch-Method.Comparing the obtained measured spectrum to the quantile spectrum(line spectrum)of the track irregularity spectrum of the ballast track in China’s high-speed railway and getting the envelope.According to the results,it is found that the 90% quantile spectrum can envelope the measured spectrum.The frequency-domain solution of amplitude,and chord measurement amplitude for random irregularity in the wavelength range of 2-60 m and the frequency-domain solution of standard deviation in 1.5-42 m,are obtained by basing and combining the random vibration theory and the analytical formula of the irregularity power spectrum of China’s high-speed ballasted track.The amplitude,Chord-Method amplitude in 2-60 m,and Track Quality Index(TQI)in1.5-42 m of the 16 sets measured bridge’s track irregularity samples in the above wavelength range are lower than the 90% of their frequency-domain values,which demonstrates the feasibility of 90% quantile spectrum as an operational spectrum.(2)The combined relationship between bridge additional deformation and random irregularity is discussed in this paper and gives the distribution function of the combined track irregularity.By comparing the combined data in the spatial and frequency domains,we discover that the combined track irregularity amplitude can be approximated with their standard deviations in the frequency domain.Further,it’s found that there is an approximate linear relationship between A,σ and z,then the corresponding linear fitting formula is given.