| For a long time,it is generally believed that the underground structure has good seismic performance.The traditional view is that the horizontal seismic force plays a decisive role in the damage of the structure and the vertical seismic force is insignificant.The investigation of the damages of the Hanshin Earthquake in Japan in1995 showed that the underground structure will also be destroyed under the action of strong earthquakes.This has caused domestic and foreign experts to study the vertical seismic force.Although column-free large-span subway stations can provide ample space,there are few studies on the seismic performance of such stations considering soil structure interaction,especially the dynamic response and seismic measures under horizontal vertical seismic coupling and adverse conditions such as vertical bias.Therefore,taking column-free large-span subway station in Metro Line 5 as the research object,the seismic performance of long-span column-free subway station structure under bidirectional seismic action considering soil structure interaction(SSI)were studied.The main research contents and results are as follows:(1)Combined with the actual engineering situation,the change law of dynamic stress-dynamic strain of the test soil was studied through GDS test,and the contact surface between soil and concrete surface was studied through the modified direct shear test,which was used as the theoretical basis on the design of the shaking table test and the finite element numerical simulation analysis.The G/Gmax～γ and D～γ curves of the engineering expansive silty clay were fitted,and the Davidenkov model parameters of the engineering soil and the reference values of A,B and γ0 were given.Based on the elastic wave theory,the method of combining sawdust and soil is used to prepare model soil to simulate the soil mass of the site.In order to obtain the best mix proportion,three different mix proportion model soils with the mass ratio of soil to sawdust of 1:3,1:5and 1:6 were designed though dynamic triaxial tests.The similar ratios for shaking table tests were designed.(2)Taking a column-free subway passenger station of line 5 as the research background,the shaking table test of the pillarless long-span subway station model considering the bidirectional seismic action was carried out.The general rules of the seismic response of the station model structure and the surrounding soil were studied.The acceleration components in vertical and horizontal directions respectively play a leading role in the depth of the foundation and on the surface of the soil layer.The deformation of the middle plate of the model structure is large under the vertical earthquake action.The peak acceleration of the model structure under the bidirectional earthquake actions is greater than that under the unidirectional earthquake action.Under the action of earthquakes,the damage of the model structure is mainly concentrated at the junction of the roof and the side wall where slight cracks occur along the loading direction,indicating that the connection between the roof and the side wall of the column-free subway station and the middle plate are structurally weak locations.Those sections should be strengthened.(3)The three-dimensional finite element analysis model of the soil-column-free long-span subway station was established and the corresponding finite element analysis was carried out.The comparison and analysis with the shaking table test results were carried out.The results are in good agreement with each other and the reliability of the finite element analysis results is verified.Through a large number of finite element analysis,the main law of stress distribution of this kind of structure under the horizontal and horizontal-vertical bidirectional seismic action is studied.The results show that under the action of horizontal vertical bidirectional earthquake,the horizontal acceleration response of soil and structure increases and with the increase of input acceleration peak,the acceleration increase of station structure is obvious,among which the stress of middle plate is increased significantly.Through the finite element analysis of single column and column-free subway station,it can be seen that the stress of the middle plate of the station is increased to about 2.5 times of the original stress in the event of a bidirectional earthquake.The stress of the plate in the station of the column subway station has been increased to about 1.4-1.5 times of the original stress.(4)According to the situation that the surface side of passenger station is empty,the shaking table test of the model structure under the vertical bias load is carried out.The analysis of the shaking table test under the bias load shows that the strain value of the left lower wall and the right upper wall of the structure is large because the model system is in the bias state.The earth pressure of the structure under bidirectional seismic action is higher than that under unidirectional seismic action,and its value is greater than the sum of simple superposition of horizontal seismic action and vertical seismic action.Under the earthquake,the inertial force on the left side of the structure is large,so the top of the model structure will be squeezed.The existence of end columns can effectively improve the spatial stability of the model structure and reduce the seismic response of the structure and the earth pressure.(5)The optimization method of seismic engineering for column-free subway station is discussed from the aspects of damage,buried depth and structural form.Though the finite element model analysis,it is considered that under the action of earthquake,increasing the buried depth in the project is conducive to reducing the horizontal displacement of the structure under the action of earthquake,but if the buried depth is too large,the structural stress value increases accordingly and there is a reasonable range value of the buried depth of the structure.Through the comparative analysis of the dynamic response of arch and rectangular section subway structures,it is considered that the peak stress in the horizontal loading direction in the middle span of the middle plate the arch structure can be reduced to about 1 / 3 of the original peak stress and the overall stress value is low,so the stress form of arch section subway structures is more reasonable. |
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