Deformation Evaluation Method Of Railroad Bridge Based On Chord Measurement Method And Track Quality Index

High-speed railroad has formed network in China’s central and eastern plains and coastal areas,with the network expanding to the central and western China,the need to build a large number of long-span bridges to cross large rivers and canyons is in a hurry.The current standard for deformation control of long span bridge is too strict,which leads to excessive bridge stiffness and unreasonable technical and economic indicators.The additional deformation of long span bridges due to temperature change,shrinkage creep and environmental factors is large,resulting in initial track irregularities before the train travel on the bridge,which cannot meet the long-wave irregularities limits of the current code.Current study focuses on single specific bridges,which is not representative.This paper focuses on the study of reasonable chord length and amplitude limits of track irregularities control on long span bridges by the way of vehicle dynamics theory and dynamic simulation.Specific research content is introduced as followed:(1)Considering the dispersion nature of the factors that influence the train when crossing the bridge,the relationship between the amplitude of chord measurement and the maximum acceleration of vehicle for bridge deformation under different excitation is studied.The results show that for random track irregularities,there is a relatively strong correlation between the amplitude of the chord measurement and the maximum acceleration of the vehicle;for the additional deformation of the bridge,the chord measurement method with long chord length still has a relatively strong correlation with the vehicle vibration,and it is suggested to use the 40m-chord length chord measurement method to manage the long wave irregularities of the track,and the management limit is also listed in this paper.(2)Based on the random vibration theory,the transfer relationship between the long-wave height irregularities and vehicle acceleration is studied.By using this transfer relation,the standard deviation of random track irregularities under different excitations,the standard deviation of the measured values of different chord length chord measurement method and the standard deviation of vehicle acceleration can be calculated.The accuracy of the transfer relation is illustrated by comparing it with the standard deviation of the corresponding physical quantities calculated using the time domain ways,which in turn verifies the accuracy of the ratios counted in this paper.In addition,since the power spectrum of the random irregularities of the track in each country has been given in an analytical form,the standard deviation and amplitude of the random irregularities of the track in each country can be treated as constant values through this transfer relationship,which is same as to the acceleration of vehicle.In this way,the relationship between the vehicle acceleration caused by each of the three excitations: random track irregularities,bridge deflection and bridge deformation after the superposition of the first two is investigated.(3)Through example and theoretical derivation,the combined relationship of track quality index TQI for three kinds of deformations,namely,track random irregularities,bridge deflection and bridge deformation after the superposition of the first two,is studied.The results show that the combined relationship of vertical single standard deviation of the three kinds of track deformation mentioned above satisfies the square root of sum square(SRSS)combination.