Seismic Response Analysis Of Subway Station Under Oblique Incidence Of SV Wave At Any Angle

In recent years,with the development of underground transit systems in China,the subway has become major transport of our lives.In addition,China is a country with frequent earthquakes.It has caused widespread concern about the safety of underground structures’ seismic performance such as subway stations.Many of the existing seismic studies on underground structures only consider that the seismic waves are incident vertically from the bedrock or the oblique incidence within the critical angle.In fact,as a main form of ground motion,SV waves have critical angle problems.SV waves exceed the critical angle.When the critical angle is incident,the soil layer will produce inhomogeneous waves,and the near-surface particles will move in the form of Rayleigh surface waves,accompanied by greater vertical seismic action.However,the author has not yet found a method to realize the supercritical angle incidence of SV waves,nor has it found that the SV wave supercritical angle oblique incidence is considered in the seismic analysis of subway stations.On the other hand,engineering structures are often affected by non-vertical incidence in earthquakes,and due to the construction of the station,the foundation environment of the adjacent ground buildings will change.At the same time,affected by the surrounding complex architectural environment,the foundation around the subway station is not the semi-infinite layered foundation in the design state.Conducting the study of the dynamic interaction between subway stations and adjacent above-ground structures under the action of earthquakes,as well as taking into account the oblique incidence of seismic wave,are of great significance to improving the seismic safety performance of underground structures.In this paper,based on the accurate dynamic stiffness matrix of the layered foundation in the frequency domain,the free-field vibration response of the SV wave under oblique incidence at any angle is derived,and the equivalent nodal force on the viscoelastic boundary node is obtained.The layered foundation is realized by the ABAQUS finite element software Seismic input of oblique incident SV waves at any angle.Compared with the results of the literature,it is verified that the method in this paper has high accuracy in simulating the input of obliquely incident SV waves at any angle.On this basis,the method is used to establish the finite element numerical analysis model of subway station,subway station-soil-ground frame structure under the action of obliquely incident SV wave at any angle in Category Ⅱ,Ⅲ,and Ⅳ sites,and to study the response law of the subway station ground motion under oblique incidence of SV wave at any angle,and the response law of the interaction of the above-ground frame structure-soil-metro station.Through the analysis of the results,the following conclusions are drawn:(1)The impact of SV wave supercritical angle incidence on the seismic response of the station is closely related to the site category,and it exhibits a significant amplification effect in the Category Ⅱ and Ⅲ sites.This kind of magnification is most obvious for the axial force.The axial force of the side wall of the station when the Kobe wave is incident at an angle of 35° in the Category Ⅱ site is 3.61 times that of the vertical incidence,and the axial force of the side wall of the station at the angle of 40° oblique incident on the Category Ⅲ site is 1.34 times that of the vertical incidence.However,the 45° oblique incidence of the El centro wave on the central column of the station in a Category Ⅳ site is 0.93 times that of the vertical incidence.(2)The oblique incidence of SV wave must be considered in the seismic analysis of the subway station-soil-ground structure,otherwise the seismic response of the station will be seriously underestimated.For example,under the vertical incidence of Kobe wave at the Category Ⅳ site,when the distance between the station and the above-ground frame is 0m,the subway station-soiloverground structure system of the bottom side wall of the station will be 71% larger than the axial force without the above-ground structure,while under the 30° oblique incidence,the axial force of the subway station-soil-ground structure system will be 146% larger than that of the non-ground structure condition.On the other hand,the subway station-soil-ground structure system is subjected to a 30°oblique incident earthquake.The axial force on the side wall of the station is 1.48 times that of the side wall when it is incident perpendicularly.Given the vertical incidence of SV waves only,it will undoubtedly greatly underestimate the axial force of the side walls of the station.Similar situations exist in Category Ⅱ and Ⅲ sites.(3)Compared with the station bending moment and shear force when there is no above-ground frame,in the subway station-soil-overground frame system,the distance between the station and the frame has a complicated influence on the station bending moment and shear force,and the bending moment and shear force will be affected by the distance.And the influence of the angle of incidence is sometimes greater than the moment shear force of the station without the above-ground frame,and sometimes it is smaller than the moment shear force of the station without the above-ground frame.However,the basic law of axial force for subway stations is that the station axial force of the subway station-soil-overground structure system is greater than that of the soil-metro station system.The existence of such an above-ground structure will increase the axial force of the subway station.The distance between the station and the ground frame increases and decreases.At the same time,this magnification will also decrease as the oblique incident angle of the seismic wave increases.(4)The influence of the subway station on the deformation of the above-ground frame structure is related to the site.When the distance between the frame and the station in a Category Ⅱ site is less than 10 m,the subway station has an amplifying effect on the deformation of the above-ground frame structure,up to 16.5%(compared to no subway station construction).When it exceeds 10 m,it will weaken the deformation of the ground frame.When the SV wave is incident at 0°,15°,40° oblique incidence,the subway station will magnify the deformation of the above-ground frame in the Category Ⅲ site.At 30°,50° oblique incidence,there will be magnification and weakening.The Category Ⅳ sites mainly magnify the deformation of the above-ground frame.The closer the distance between the station and the frame,the greater the magnification.