Research On Vibration And Structural-borne Noise Prediction Of U-beam Bridge In Urban Rail Transit And Its Key Parameters Influence Study

U beam bridge has been increasingly applied in urban rail transit lines in recent years.However,deep research about vibration and noise caused by this beam type under the load of the train is rare,especially for the field of dynamic response and structural noise under the specific track structure.Thus,in order to obtain comprehensive understanding of the U beam bridge,we carry out this research to study these issues.Firstly,we put a review about the structural characteristics of U beam bridge.Method that using multi-body dynamics and finite element method is studied to established a model predicting the dynamic response and the two noise of the U beam bridge system under typical working conditions.The results show that:1)The model established in our study is consistent with the calculation results in previous literatures;2)The dynamic structure responses of whether there is rubber pad under the track bed are both within the range of the specification.;3)The using of vibration isolation pad will increase the dynamic response of the track structure and reduce the dynamic response of the U beam bridge.Therefore,the vibration isolation pad can efficiently reduce the structural noise of the bridge;4)The bridge-structure-borne noise in both situations are mainly distributed in the low frequency range below 100 Hz,locating at the top of the bridge wing plate and under the beam body.Based on the results above,effect of key parameters on the system dynamic response and the two noise of the structure is further studied.The results show that :1)As the train accelerates,dynamic response of each component of the U beam bridge system and the bridgestructure-borne noise increase in varying degrees.Thus it can be reduced by controlling the vehicle speed.2)The deformation of the rail can be controlled by increasing the stiffness of the fastener,but the excessive increase will raise the vertical vibration acceleration of the rail,track bed and U beam sharply.Our study suggested a range of 20 MN/m ~50 MN/m of the rail fastener's vertical stiffness of in U beam bridge system;3)Increase of the vertical stiffness of the fastener will raise the bridge-structure-borne noise,especially when it is above 50MN/m;4)The response amplitude of the track structure above the vibration reducing pad will be increased by decreases of the stiffness of the rubber isolator,whereas vibration acceleration of the bridge decreases.That is,the increase of the stiffness of the vibration isolator will raise the bridge-structure-borne noise.So smaller stiffness of the vibration isolation pad should be considered to control the noise level of the U beam bridge.But stiffness can not be too small as the structural noise in the low frequency below 20 Hz would be amplified.