Seismic Response Analysis Of Underground Stations In Horizontally Layered Sites Under Oblique Incident Seismic Waves

Urban rail transit is an important choice for citizens to travel.China is a major country in urban rail transit.Underground stations serve as the hub of urban rail transit,and its seismic research is very important.Scholars at home and abroad have done a lot of research on the seismic response of underground structures,and most of them are based on the vertical incidence of seismic waves.But in reality,seismic waves are rarely incident vertically.The seismic response of the underground structure is mainly affected by the difference in site motion,and the seismic response of the free field caused by the oblique incidence of the seismic wave is different from that of the vertical incidence.Therefore,it is necessary to study the impact of obliquely incident seismic waves on the structure of the underground station.In order to discuss the seismic response of underground structures under the action of obliquely incident seismic waves,the linear seismic response analysis of the obliquely incident seismic waves at the site of the homogeneous soil layer overlying the bedrock is carried out first,and then the non-linear seismic response of the obliquely incident seismic waves at the horizontal layered site The analysis and the results of the nonlinear site analysis are used in the reaction displacement method to analyze the response of the underground station structure caused by oblique incident seismic waves.The results of this article are as follows:(1)The linear seismic response characteristics of the homogeneous soil layer on the bedrock under the action of oblique incident seismic waves are analyzed.From the perspective of frequency domain,the dynamic stiffness matrix of the entire soil layer is collected to solve the free-field linear seismic response of the homogeneous soil layer overlying the bedrock,and the calculation result is converted into the time domain in combination with the inverse Fourier transform.The calculation process is realized by Fortran programming.The conclusion is drawn by calculating the free field response of different seismic waves acting on the free field at different incident angles.The results show that different seismic waves have different responses to the free field when obliquely incident.When the SH and SV waves are obliquely incident,the peak displacement and peak acceleration response of the soil layer will be greater than that of normal incidence.The free field response caused by oblique incident seismic waves is different at different depths.(2)On the basis of the linear algorithm and the calculation method of equivalent linearity,the nonlinear site response under the action of obliquely incident seismic waves on a horizontally layered site is studied.The results show that under the action of obliquely incident seismic waves,the horizontally layered nonlinear free field agrees with the linear free field of homogeneous soil layers.The seismic response caused by obliquely incident seismic waves will be greater than when the seismic waves are perpendicularly incident.(3)Using the site analysis results of the horizontally layered nonlinear free field,the seismic response characteristics of the underground structure under oblique incident seismic waves are analyzed.Among them,the SV wave 82 °,72 ° and SH wave 55 are selected according to the site response analysis results °,35 ° and normal incidence,and consider the incident wave amplitudes of 0.2g and 0.4g and the seismic wave control points on the bedrock and free field surface.The calculation results show that the seismic response of underground structures caused by obliquely incident seismic waves will be greater than that caused by vertically incident seismic waves.The different control points of seismic waves cause the site response to be different under oblique incidence of seismic waves,thus affecting the seismic response of underground structures.When the incident wave amplitude is 0.2g,the control point is selected at the oblique incidence seismic wave of the bedrock,and the calculated internal force and interlayer displacement results are smaller than the control point selected at the free field surface.When the incident wave amplitude is 0.4g,the opposite is true.Therefore,when considering the oblique incidence of seismic waves,due to structural safety considerations,the seismic design and analysis of underground structures should comprehensively consider the amplitude of the incident wave and the choice of control points.