Research On Vibration Reduction Performance Of Metro Overhead Damping Monolithic Track Bed

While rail transportation is convenient for people to travel,it also causes certain environmental pressures and negative effects.The impact of rail transit vibration on the surrounding environment is particularly prominent.Viscoelastic constrained damping monolithic track bed（hereinafter referred to as damped monolithic track bed）is a new method of vibration damping of track bed based on constrained damping structure.The damped monolithic track bed was used for the first time on an elevated line of the Qingdao subway to reduce the impact of vibration on the structure.This paper first studies the conventional mechanical properties and dynamic mechanical properties of Qtech-T118 viscoelastic damping material（hereinafter referred to as Qtech-T118 material）on the damping monolithic track bed.Based on this,a field test was carried out with a subway elevated line as the engineering background.The vibration data of the damped monolithic track bed is analyzed,and the vibration reduction performance of the damped monolithic track bed is obtained.Finally,the reliability of the field test of the viscoelastically constrained damping monolithic track bed is verified by theoretical formula prediction.The main findings are as follows:The conventional performance test of Qtech-T118 material shows that the Qtech-T118 material applied to the viscoelastic constrained damping monolithic track bed is an environmentally-friendly,fast-curing,and damping material that meets engineering requirements.Analysis of dynamic mechanical properties shows that Qtech-T118 material has a wide glass transition temperature and obvious damping properties.It is feasible to apply Qtech-T118 material to the damping layer of the constrained damping monolithic track bed.On-site testing and analysis of the vibration damping performance of the monolithic track bed on the surface of the elevated beam,the results show that the vibration damping performance of the monolithic track bed increases with increasing temperature.Taking the human body Z vibration level(VL_max)as the evaluation index,the low temperature in winter（-13℃）and high temperature in summer（27℃）are against the ground;The vibration reduction performance of the earth（1^#）bridge pier（2^#）and U-shaped beam wall（3^#）was studied.The vibration measurement performances of the three measurement points at the ground measurement point,the bridge pier measurement point and the U-shaped beam were 6.95 d B and 5.09 d B,respectively.And 9.94 d B.At the measuring points,the vibration damping performance of the elevated ballast damping monolithic track bed is 13.76%,20%,and 29.95%,respectively.Taking the octave spectral interpolation loss as the evaluation index,the vibration damping performance of the elevated ballast damping monolithic track bed is affected by temperature.It is 5 ～ 6d B.The human body’s Z vibration level(VL_max)at three measurement points is affected by temperature changes of 7.9d B,11.4d B,and 7.8d B,respectively.By comparing the two evaluation indexes,the vibration test data of the surface-damped monolithic track bed in the summer and the winter test data show that the bridge pier and U-beam have good vibration damping performance.The z-vibration level changes are 9.44 d B 5.53 d B and 11.97 d B,respectively.The maximum amplitude is reduced by 11.72%,and the vibration reduction effect is significant.The field test and analysis of the vibration damping of the overall track bed at the elevated station show that when the train stops at the station,the changes in the human body’s Z vibration level(VL_max)of the damping of the overall track bed at the station platform and the hall are 6.04 d B and 5.92 d B,respectively,a reduction of 7.52% 7.59%;when the train leaves the station,the changes in the human body’s Z vibration level(VL_max)of the damping of the overall track bed at the station platform and hall are 2.51 d B and 6.13 d B,respectively,and the reductions are 3.28% and 7.81%.Taking the octave spectrum interpolation loss as the evaluation standard,the damping of the overall track bed is not affected by the stop and exit of the train.Elevated station damping the overall track bed is about 2 ～ 6d B,and the vibration damping performance is significant.The vibration prediction results of the damped monolithic track bed show that with the increase of the predicted distance,the vibration near the measuring point caused by the subway train gradually decreases.The vibration model is used to predict the vertical level of the ground in the range of 0 to 5 m,and it is compared with the field test.The results were compared with the Z-level VL_max of the field vibration-damped monolithic track bed body.The Z-level error of the field test was 2 to 3%,and the field test data was reliable.