Simulation Study On Urban Railway Train Induced Environmental Vibration And Secondary Noise In Over-track Buildings

With the rapid development of urbanization,urban land resources become scarce.If the upper space of urban railway yards and their adjacent areas is used to develop real estate,land resources will be utilized intensively and economically.The vibration caused by pass-by trains can transmit into over-track buildings through track and soil,which will cause pollution of environmental vibration and indoor secondary structure-borne noise.It has become an environmental constraint factors of real-estate development in the vicinity of railways.The previous model in railway industry could only predict the environmental vibration of the first floor of a building caused by railway,and there were no models predicting indoor secondary structure-borne noise of over-track buildings caused by railways'vibration.Therefore,it is necessary to study the influence of environmental vibration and indoor structure-borne noise caused by railway on over-track buildings,analyze and demonstrate feasible vibration isolation measures and their performances,develop models which can predict the influence of environmental vibration and indoor secondary structure-borne noise caused by railways on different floors of over-track buildings.This study was combined with the first planned project of over-track residential buildings above railways in China.Utilizing the data of vertical vibration acceleration sampled on steel rail in the field of the planned project,the vertical vibration load from trains?wheel-rail force?can be determined.On this basis,a simulation model was built in software and the reasonability of the method was verified by comparing simulation results with test results.The influences of thickness and height of over-track platform?a transfer floor?above ground and the influences of structure and height of buildings on environmental vibration and secondary structure-borne noise in over-track buildings were quantitatively studied.A model predicting environmental vibration and secondary structure-borne noise in over-track buildings were established.Besides,the vibration isolation effects of concrete piles and trenches were studied by simulation,respectively.Results of this study can provide a theoretical and technical basis for the prevention of environmental vibration and secondary structure-borne noise in over-track buildings.The main conclusions are shown as follows.?1?In over-track buildings,VL_Zmax,the maximum vertical Z-weighted vibration level at the center of different floor increases with the rise of building floor.In multi-storey,small high-rise and high-rise buildings of frame structure,the VL_Zmax of each floor is 0.1?4.4 dB,0.0?3.8 dB and 0.1?5.1 dB higher than that in the building of shear wall structure,respectively.When the thickness of over-track platform increases 0.5m,the VL_Zmax of each floor in multi-storey,small high-rise,high-rise buildings will decrease by 0.4?3.0 dB,1.3?3.3 dB and 0.1?3.4 dB,respectively.When the height of over-track platform above ground increases 4m,the VL_Zmax of each floor in multi-storey,small high-rise,high-rise buildings will increase by 0.1?0.5 dB,0.1?0.9 dB and 0.3?0.9 dB respectively.Combined with the simulation results in this study,the previous prediction model in railway industry was improved through introducing the modification of thickness and height of over-track platform,the modification of building structure and floor.The improved model can predict the VL_Zmax of different floor in buildings on a over-track platform.?2?In multi-storey,small high-rise and high-rise buildings of frame structure,?_Amax,the average of the maximum equivalent continuous A-weighted sound pressure level of secondary structure-borne noise at 1.2 m above the ground of each floor,is 4.4 dB,6.0 dB and 7.6 dB higher than that in the buildings of shear wall structure,respectively.When the thickness of over-track platform increases 0.5m,the?_Amax of multi-storey,small high-rise,high-rise buildings will decrease by 1.5?2.3 dB,2.2?2.8 dB and 1.8?3.6 dB,respectively.When the height of over-track platform above ground increases 4m,the?_Amax of multi-storey,small high-rise,high-rise buildings will increase by 0.4?1.9 dB,0.5?2.0 dB and0.2?1.5 dB,respectively.The VL_Zmax on the ground below over-track building could be predicted by the previous model in railway industry.In present study several modifications were introduced according to the difference between the vibration acceleration level in each1/3 octave band and the VL_Zmaxon the ground,the difference between the vibration velocity level and the vibration acceleration level in each 1/3 octave band on the ground,and the difference of_Amax of secondary structure-borne noise between each floor on an over-track platform and ground floor.Based on the VL_Zmax of ground floor and the modifications above,a model predicting the_Amax of secondary structure-borne noise of different floor in a building on a over-track platform is established.?3?When the distance between the center of over-track building and the centerline of railway is 16.5 m,concrete piles with a diameter of 0.5 m were arrayed with a same interval in the middle of an over-track building and a railway.On different floors in a multi-storey building,the insertion losses of VL_Zmax induced by single-row concrete piles of 6 m,12 m and 24 m depth were 0.1?1.9 dB,0.4?2.2 dB and 1.2?2.7 dB,respectively.Compared with that of single-row concrete piles,the insertion loss of VL_Zmax of double-row concrete piles with an interval of 0.5 m between two rows increased by 1.6?2.8 dB.When concrete piles are replaced by an open trench with a depth of 3m,4.5m or 6m,the insertion loss of VL_Zmaxwill be-1.1?0.7 dB,0.6?2.2 dB and 1.5?4.2 dB,respectively.When the open trench is further filled with concrete or foam plastic,the insertion loss of VL_Zmax will decrease by1.9?2.9 dB and 0.5?0.6 dB,respectively.