Analysis Of Dynamic Response Of Underground Frame-structure Metro Station Under The Action Of Horizontal Earthquake

The continuous expansion and the growing population of the city is a serious challenge to the ground transportation.The development and vigorous construction of underground rail transit have eased the pressure of ground transportation.Many cities around the world have carried out subway construction.The frame structure is often used as the structure of subway stations because of its good integrity,flexible space division and strong seismic resistance.With the frequent occurrence of earthquake damage to underground structures,the seismic response and actual seismic performance of frame-structure subway stations need to be fully studied.The paper takes the frame-structure subway station,Fuxing Subway Station of Chongqing Rail Transit Line 6 as the engineering background.Based on the shaking table model test,with the help of the shaking table test system in Geotechnical Laboratory Building of Chongqing University.In this paper,a layered shear box that can better simulate the boundary conditions of the foundation is used to carry out the shaking table test of the frame structure subway station.Through various sensors arranged on the structure and the soil,the acceleration of the structure and the soil,the strain of the structure and the soil pressure at the structure-soil interface are measured to study the seismic response and regularity of the frame-structure subway station.And through the MIDAS-GTS NX finite element software,the dynamic responses such as the relative horizontal displacement,the strain and the acceleration of the frame-structure subway station under earthquake action are analyzed.The main research parts are listed as follows:(1)Based on the actual size of the frame-structure subway station,the size and the bearing range of the shaking table,combined with the Bockingham-π similarity ratio theorem,the three physical parameters of the elastic modulus E,geometric size l,and acceleration α are taken as the basic physical quantities.And other parameters are derived from the similarity ratio coefficients.Plexiglas is used as the material of the station structure,and the size of the model structure is determined according to the similarity ratio coefficient of the geometric size.The layered shear model box which can effectively reduce the effect of the seismic wave boundary reflection is adopted to bear the model and the soil.With reference to the ideal mix ratio test of the model soil proposed by the predecessors,a similar material of grade IV surrounding rock is formulated to simulate the soil.A real recorded seismic wave-Kobe wave,and a synthetic seismic wave-Chongqing artificial wave is selected as the input waves,and the loading modes of the seismic waves are designed,and use piezoelectric accelerometer,strain miniature earth pressure gauge and resistance strain gauge to measure the structure and soil layer Soil pressure,soil pressure at the structure-soil interface and structural strain.Piezoelectric accelerometers,strain-type miniature earth pressure gauges and resistance strain gauges are used to measure the acceleration of the structure and the soil,the earth pressure at the structure-soil interface,and the structural strain.(2)Seismic waves are inputted according to the experimental design.Time-history data records of various points under various loading conditions through sensors are obtained,and the experimental data are analyzed.The seismic responses of the frame-structure subway station system are analyzed from three aspects: the acceleration response of the station structure and the soil layer,the strain of the station structure,and the earth pressure on the interface between the side wall and the soil layer.The variation of the acceleration response of the station structure and the soil layer along the height direction is analyzed,and so is the difference of the acceleration response between the station structure and the soil layer;the strain changes and laws along the height of each floor slab,center column and side wall of the station are analyzed,and the parts with the largest strain response are found out;the law of earth pressure response of the side wall-soil layer contact surface along the height of the structure is analyzed,and the part of the largest earth pressure response is found.Through the analysis of acceleration,strain and earth pressure responses,the weak parts of the structure are determined.(3)In response to the seismic responses of the frame-structure subway station,finite element numerical simulation is carried out.Using the MIDAS-GTS NX finite element software,based on the original site geological survey data and the physical and mechanical parameters of the station structure materials,the 2D finite element model of the main structure and soil Layer is established.The appropriate constitutive relationship for the structure and soil layer is choose,and the appropriate boundary conditions for the soil layer to accurately simulate the original site soil layer are choose.Kobe Wave recorded in Kobe,Japan,and the artificial wave in Chongqing,which is artificially synthesized according to the specifications are selected.The acceleration time-history curves to simulate the action of the earthquake are inputted,and the appropriate time step is selected.The nonlinear time-history analysis method provided by the software is used to carry out the earthquake effect simulation of the subway station.(4)According to the two-dimensional finite element numerical simulation of the frame-structure subway station,the results are analyzed.From the cloud diagram of relative horizontal displacement of the main structure of the station,the displacement trend of the station structure in the height direction can be roughly seen.According to the specific data,the relative horizontal displacement of the station side wall and the center columns in the height direction is analyzed in detail.It’s found that the relative horizontal displacement of the side wall as well as the center columns,increases with the height;from the strain cloud diagram of the station structure,it is found that the strain response at the bottom of the side wall,the bottom and top of the column,the connection between each floor and the side wall is relatively larger,and the strain response law of these parts is specifically analyzed;finally,the acceleration response of the structure and the soil layer and the amplification effect along the height are analyzed,and the acceleration response law of the structure and the soil layer is obtained.From the three aspects of the response,the horizontal displacement of the station,the strain of the station structure,and the acceleration of the station structure and the soil layer,the unfavorable seismic location of the subway station is determined.