Research On Nonlinear Seismic Response Of Layered Sites

A large number of earthquake disaster data show that complex site conditions and local site effect have a significant influence on site seismic response.For the same earthquake,the difference of site conditions will cause different ground response,and the local site effect will have a significant influence on the intensity and spectrum characteristics of ground motion.The site seismic response analysis is essentially a complex three-dimensional numerical analysis,but the site seismic response is usually regarded as a one-dimensional problem,it cannot well simulate the real state of the layered site.In addition,the determination of bedrock ground motion time history is the key to engineering seismic design and site seismic response,but ground motion records are easy to obtain,while bedrock ground motion time history is relatively scarce.In the case of complex soil layers,the research on the seismic response of onedimensional to multi-dimensional sites,and the research on reliable bedrock ground motion time history obtained from the ground motion acceleration records of the site are the focus and difficulty of current research.Therefore,it is very necessary to carry out the research on the nonlinear seismic response of the site.In this thesis,the ground motion inversion analysis of different site types and different cutoff frequencies is carried out,and the ground motion time history at the bedrock is obtained,and the comparison law of one-dimensional frequency domain and time domain seismic response of different site types is discussed.Since the one-dimensional frequency domain analysis cannot truly reflect the nonlinearity of the soil,relying on the actual project in Sishui County,Jining City,the one-dimensional and two-dimensional nonlinear seismic responses of the site are further studied.The main contents and conclusions are as follows:(1)According to the nine surface ground motion records selected from the American PEER database,the influence of different ground motion cutoff frequencies on the site ground motion inversion under different site types was studied,and the input ground motion time history at the bedrock was obtained by using the deconvolution program of DEEPSOIL.The ground motion time history obtained by the forward modeling analysis of the soil layer is basically consistent with the actual record,it proves the correctness and reliability of the site seismic inversion analysis.(2)For nine different soil layer profiles under different site types of Class II,Class III and Class IV,the ground motion time history of the bedrock is taken as the input ground motion,and the one-dimensional site ground motion response is compared and analyzed by frequency domain equivalent linearization method and time domain nonlinear method.The research shows that when the peak acceleration of the input bedrock ground motion is small,the results of the frequency domain analysis and the time domain analysis results are consistent.Under different earthquakes,the one-dimensional site time domain analysis can better reflect the nonlinear characteristics of soil than the frequency domain analysis.When the input ground motion peak acceleration is different,different site types have different ground motion responses.(3)According to the actual project in Sishui County,Jining City,Shandong Province,four typical borehole sections with different soil parameters are selected.Considering the influence of local site effect,the one-dimensional and two-dimensional nonlinear ground motion responses of non-uniform soil layers are compared and discussed by using DEEPSOIL and FLAC3 D numerical analysis software.The research shows that with the difference of the peak acceleration of ground motion input to the bedrock,the two-dimensional nonlinear analysis and the one-dimensional nonlinear analysis have different peak accelerations at different depths.The amplification effect of two-dimensional nonlinear analysis on soil layer is more obvious than one-dimensional nonlinear analysis,and the two-dimensional numerical analysis results are closer to the actual ground motion records.