Field Vibrations And Its Response Spectrum Analysis Around The Periodic Bridge Subjected To High-speed Trains

At present,32 m and 40 m standard span bridge structures have been widely used in high-speed railway construction,and have passed through the urban areas where the dwellings gather,which has caused a lot of environmental vibration problems.Therefore,this paper proposes an accurate and effective environmental vibration prediction calculation method,which has very important engineering practical significance for the evaluation of environmental vibration and pre-planning route selection.In this paper,on the basis of virtual excitation method,infinite-periodic structure theory,thin layer method-perfectly matched layer-volume method(TLM-PML-VM),the frequency domain model of the finite element of the periodic bridge structure,and the bridge foundation-site soil coupling model were established respectively.The dynamic response characteristics of the field soil around the bridge structure and the field vibration response spectrum under the action of high-speed trains are studied,which can provide a reference for the environmental impact assessment in practical engineering.The main contents of this article are:(1)Vertical stochastic dynamic analysis of vehicle-bridge time-varying systemBased on the structural dynamics and finite element theory,the 10-degree-offreedom vehicle-bridge vertical equation of motion is derived.According to the basic principle of the virtual excitation method that the track irregularity is equivalent to a series of simple harmonic loads,the virtual excitation input form of the axle-bridge timevarying system is constructed.The separation iteration method is used to solve the equations of motion of the vehicle-bridge time-varying system,and a vertical stochastic dynamic analysis program for the vehicle-bridge coupling system is compiled.Finally,the random vertical vibration characteristics of the vehicle-bridge time-varying system are analyzed based on the triple standard deviation principle.(2)Analysis of frequency-domain finite element model of periodic bridge structureThe theory of infinite periodic structure and the mechanical model of periodic bridge structure are introduced.Based on the infinite periodic structure theory and frequencydomain finite element method,the frequency-domain finite element dynamic equation and frequency-domain finite element characteristic equation of the bridge structure are derived,and the calculation method of the basic span load spectrum under train loading is proposed.Finally,by means of the compiled dynamic analysis program of the periodic bridge structure,the influence of spring stiffness and damping on the attenuation characteristics of the periodic bridge structure is studied.Furthermore the frequency dispersion characteristics of the periodic bridge structure and the frequency spectrum and time-history characteristics of the dynamic response induced by train loads are analyzed.(3)Dynamic interaction analysis of bridge foundation-soil coupling systemBased on the thin layer method-perfectly matched layer(TLM-PML),the field soil model is established and the dynamic responses of the site soil under dynamic loads are deduced and solved,and then the volume method(VM)is introduced to establish the foundation-site soil dynamic interaction model,and derived the foundation dynamic impedance function and the bridge foundation-site soil vibration frequency response function.Finally,the foundation soil dynamic analysis program is compiled to compare and analyze the vibration characteristics of the site soil under the conditions of the model dimensions and multi-piers.(4)On-site vibration test analysis of bridge-site systemThe evaluation indicators of ground vibration and China's control standards for environmental vibration are introduced.Daxi Passenger Dedicated Line as the engineering background with the bridge structure type,the arrangement of field test points and test conditions are introduced.The elimination of trend items,smoothing processing and the removal of background vibration are used to pre-process the original test data.Furthermore,the vibration characteristics at each measurement point under a specific vehicle speed are analyzed in the time domain,frequency domain and 1/3 octave spectrum.Finally,the total vibration acceleration level VAL and the total weighted vibration level VL are used to analyze the ground three-way vibration characteristics and attenuation propagation laws at different vehicle speeds,which provides a basis for the validity verification of the numerical prediction method.(5)Analysis of dynamic response and vibration response spectrum of site soilFirstly,the selection of allowable limits for environmental vibration is introduced.Taking a high-speed rail as the engineering background,three sub-structures are used for simulation,namely vehicle-bridge interaction subsystem model,periodic bridge structure subsystem model and foundation-site soil interaction subsystem model.The dynamic response of the site soil is solved,and the vibration response and propagation law of the site soil are analyzed in the time domain,frequency domain and one-third octave frequency spectrum,respectively.Moreover,the effectivenss of the prediction method from a qualitative perspective is verified.the prediction method from a qualitative perspective.Then,a variety of train speeds are used to simulate the dynamic response of soil for different sites to obtain a site vibration response spectrum,and also the influence of different factors on the characteristics of the site vibration response spectrum is analyzed.Finally,the site vibration response spectrum is analyzed according to the selected environmental vibration limits,and the environmental vibration thresholds for viaduct high-speed raiways is calculated and summarized.