| With the development of urban rail transit,vibration and noise problems also appear.Compared with ballastless track,ballasted track has better vibration and noise reduction performance,and lower maintenance costs in later period,so it is feasible to apply in the main subway line.At present,there are few studies on the corresponding relationship between ballasted track structure and vibration reduction effect.In this paper,for Beijing Metro Line 6,based on the analysis of vibration characteristics in time domain and frequency domain of ballasted track,according to the evaluation index of dynamic characteristics,vibration reduction effects and safety,study the mechanical characteristics and damping effects of ballasted track,and put forward to the design parameters of ballasted track to improve vibration and noise problems.The main research contents are as follows:(1)The dynamic model of the vehicle-track coupling system is established,and the accuracy of the model is verified by comparing the results of the model with those of literature and laboratory drop-weight test.By comparing the dynamic responses and vibration reduction effects of ballastless track and ballasted track structure,it can be concluded that compared with the ballastless track,the rail vibration acceleration of ballasted track decreases,while the displacement of rail and the vibration acceleration and displacement of track bed increase,and the increase of elasticity of ballasted track resulting in the increase of vibration acceleration of track bed;The rate of wheel load reduction and derailment coefficient of the both tracks are less than specification limits;By analyzing the 1/3 octave of vibration acceleration,it is found that the vibration acceleration level of rail and track bed decreases by 5.15 d B and 30.75 d B respectively,and the damping effect is obvious for ballasted track,compared with ballastless track.(2)By analyzing the dynamic responses and damping effects of the track,the reasonable value range of thickness track bed,stiffness of fastener and running speed is obtained.With the increase of the thickness of track bed,the vibration acceleration and displacement of rail increase,and vibration acceleration of track bed increase.In the low frequency range,the thickness of 35 cm～40 cm track bed has a better damping effect on rail and sleeper;The increase of fastener stiffness leads to the increase of vibration acceleration and displacement of sleeper and the vibration acceleration of track bed,fastener force.Compared with 40 k N/mm,the fastener with 80 k N/mm stiffness in the range of 6～32 Hz can reduce the vibration acceleration level of the rail by 7.86 d B,and the damping effect is the best;The increase of running speed leads to the increase of track dynamic responses.Compared with 140 km/h,the acceleration level of rail vibration can be reduced by 10.64 d B at 80 km/h in the range of 5-125 Hz.(3)By comparing the dynamic responses and vibration reduction effects of concrete sleeper,ladder sleeper and elastic sleeper,it can be concluded that the ladder sleeper reduces the vibration acceleration and displacement of the rail,but the elastic sleeper is the opposite,Both of them can reduce the vibration acceleration of the track bed and fastener force.Compared with ladder sleeper,the elastic sleeper can reduce the vibration acceleration level of the track bed by 20.03 d B in the range of 10～160 Hz.In the range of 160～1000 Hz,ladder sleeper has the best damping effect on track bed.The advantages and disadvantages of the two types of sleeper in engineering cost and maintenance work are compared to provide reference for sleeper selection.(4)By analyzing the influence of stiffness change of pad on dynamic responses of elastic sleeper and ladder sleeper track,it can be concluded that,the increase of sleeper pad stiffness can effectively reduce the displacement of rail and sleeper,but will increase the vibration acceleration of track bed,so it is recommended that the stiffness of the sleeper pad should be about 60 k N/mm.For elastic sleeper,sleeper pad can reduce the vibration of rail and track bed,but can increase the vibration acceleration level of track bed.The dynamic responses of track under multi-parameter combination of stiffness of fastener and sleeper pad is considered comprehensively,it is put forward that the optimal matching stiffness is 60～80 k N/mm for both the stiffness of pad and fastener combined with the sensitivity coefficient of dynamic parameters. |
