Study On Band Gap Characteristics And Vibration Reduction Effect Of Combined Periodic Row Piles

With the rapid development of rail transit in China,the issue of environmental vibration has become increasingly prominent.Due to the relative scarcity of urban soil resources,rail transit lines inevitably approach buildings,resulting in environmental vibration that has serious negative impacts on the safety of buildings,the use of precision instruments,and the physical and mental health of residents.The existing environmental vibration reduction measures include vibration source vibration reduction,propagation path vibration reduction,and vibration receiving body vibration reduction.Adopting vibration source vibration reduction and vibration receiving body vibration reduction requires a lot of manpower and material resources,and it is difficult to ensure its vibration reduction effect.However,propagation path vibration reduction is widely used due to its convenient construction and excellent vibration reduction effect.By periodically designing the damping barrier,its unique bandgap characteristics can be utilized to directionally reduce vibration in specific frequency bands.Based on the above background,this thesis first calculates the band gap characteristics of composite periodic pile arrays in ideal and detuned states using finite element method,and studies their vibration reduction performance by combining frequency domain analysis and time domain analysis.Based on this,a multi periodic composite pile array is proposed and its band gap characteristics and vibration reduction performance are calculated;Subsequently,the measured attenuation domain characteristics of the combined periodic row piles in the bandgap frequency band were verified through indoor model tests;Finally,a three-dimensional numerical model was established through vertical coupling of vehicle rail and finite element method,and applied research and comparative analysis were carried out on different arrangement forms of combined periodic row piles.The main research conclusions are as follows:(1)The mechanism of band gap generation in the combination of periodic pile rows was revealed,and the variation pattern and vibration reduction performance of the ideal combination of periodic pile rows under different influencing factors were systematically analyzed.The mechanism of band gap generation in scattering type periodic piles is the coupling effect of elastic waves,while the mechanism of band gap generation in local resonance type periodic piles is the natural vibration consumption of oscillators in periodic structures.The periodic constant,filling rate,wrapping thickness,density,and elastic modulus have a significant impact on the band gap and transmission loss of periodic row piles.The peak acceleration attenuation of scattering type periodic row piles and local resonance type periodic row piles within the band gap range are 99.1% and82.1%,respectively,and the peak acceleration attenuation outside the band gap range is68.0% and 51.0%,respectively,indicating that periodic row piles also have certain vibration reduction performance outside the band gap range.(2)Based on the study of the variation of the band gap of the detuned combined periodic pile array under different influencing factors,a multi periodic pile array was proposed and its band gap characteristics and vibration reduction performance were studied.The cut-off frequency of the first order bandgap of the scattering type periodic pile decreases with the decrease of the radius detuning rate,while the initial frequency of the first order bandgap of the local resonance type periodic pile increases with the decrease of the radius detuning rate and the thickness of the wrapping layer;When the embedded scattering periodic structure and the embedded local resonance periodic structure are used,the first bandgap frequency range is reduced from 62.9 Hz～159.8 Hz to 40.6 Hz～159.8 Hz and 5.8 Hz～11.4 Hz,respectively.The peak acceleration attenuation within the bandgap range is 98.5% and 96.1%,respectively,proving that the multi period combination pile has good bandgap adjustment and vibration reduction performance.(3)A roadbed vibration test bench was designed and built,and model tests on the vibration reduction performance of composite periodic row piles were conducted.The vibration waves in some frequency bands will diffract from both sides and bottom of the row piles to the surface,causing vibration amplification.However,the overall vibration acceleration amplitude of the row piles after vibration reduction is significantly lower than that of the case without row piles.Within the design band gap range,the maximum attenuation of vertical and lateral acceleration amplitudes is 99.7% and 99.0%,respectively,confirming the measured attenuation domain characteristics of periodic row piles.(4)The vibration reduction performance of composite periodic row piles under different arrangement forms was studied.For vertically arranged periodic piles,the insertion loss of surface vibration level increases with the increase of pile arrangement depth and number of rows;By changing the angle of pile arrangement,the maximum insertion loss of vertical and horizontal vibration levels can be increased by 6.0 d B and5.4 d B;For horizontally arranged periodic row piles,the insertion loss of surface vibration level increases with the increase of row and column numbers,and decreases with the increase of the distance between the pile body and the vibration source;For periodic row piles with vibration source induced vibration,the insertion loss of surface vibration level increases with the depth of row pile arrangement.When the depth of row pile arrangement is 24 meters,the maximum insertion losses of vertical and horizontal vibration levels are27.0 d B and 32.5 d B.(5)The attenuation domain performance of composite periodic row piles was studied,and the vibration reduction performance of composite periodic row piles under different layout forms was compared and analyzed.Vertical and horizontal periodic row piles have typical attenuation domain performance.When the row pile arrangement depth is 8 meters,within the band gap range of the periodic row piles,the vertical and horizontal vibration level insertion losses under the surface vibration source are 3.8 and 4.5 times that of the other frequency bands,while the vertical and horizontal vibration level insertion losses under the underground vibration source are 4.1 and 3 times that of the other frequency bands;The near-field vibration reduction performance of vibration source induced periodic row piles is superior,while the far-field vibration reduction performance of vertically arranged periodic row piles is superior.