The Response Characteristics Evaluation Method Of Ground Motion Based On Model Test

Site effect has a direct impact on the severity of earthquake disasters.Nonlinear characteristic and amplification effect are two main form of seismic response characteristics,the research on seismic response characteristics in loess area has attracted more and more attention,and it became a hot topic in field of engineering application.The response characteristics evaluation method of ground motion not only lead a way to understanding of site's characteristics,but also provide theoretical significance and practical value for rapid assessment,eventually improving the defense ability of earthquake disaster in the loess area.Through ways of shaking table test and the numerical simulation technology,utilization ratio of strong-motion recording is improved,and the development in the field of strong-motion research is promoted,which make a good base for stadying seismic response characteristics.To obtain the response characteristics of ground motion in the loess site,based on the shaking table test,combined with the numerical simulation technology,the model of a homogeneous soil type loess site and a complexed soil structure loess site are established respectively.Two methods including Quasi-Transfer Spectra(Abbrev.HVSR method)and Transfer Function(Abbrev.TF method)are used,strong-motion recording from Tangyu and Wenxian strong motion station was input.As a result,it revealed the site nonlinear characteristic,and verified the amplification effect of loess site under earthquake load.By comparing the correlation between two methods,the application of HVSR method on the ground motion effect under strong ground motion have been discusseed.The main contents and results are concluded as follows:(1)Research on the response of different site conditions on seismic effect are reviewed,the development progress and principle of HVSR method and TF method are expounded,the comparison between the two methods is carried out,and the limitation of TF method on the field effect is theoretically analyzed.(2)Based on shaking table test,the seismic response characteristics of loess site are analysised.Results show that: PGA amplification coefficient decreases and the predominant frequency moving to low direction with the increasement of ground motion.The thickness has great influence for PGA amplification coefficient and the predominant frequency,PGA amplification coefficient increasement and the predominant frequency moving to low direction with the increasementt of the thickness of the cover layer of the loess site.PGA amplification coefficient and spectrum characteristics of two loess site is slightly different,but the overall trend is similar under the two component loads of different seismic waves.The trend of PGA and PGA amplification coefficient is similar with the increasement of thickness of the cover layer of the loess site.(3)Model parameters including material configuration,basic physical parameters and strength parameters are obtained,through shaking table test and laboratory experiment,on basis of above,two model of a homogeneous soil type loess site and a complexed soil structure loess site are established respectively.Then numerical simulation is calculated by FLAC 3D.Based on the numerical simulation,the contour of two model are analysised.Results show that: contour of stress and displacement of two site model are layered distribution,the vertical stress is largest at the bottom of the model,vertical displacement and vertical stress are the opposite,the maximum vertical displacement appears at the surface of the model.The maximum vertical stress of a complexed soil structure loess site is 300 kPa more than homogeneous soil type loess site,meanwhile,the vertical displacement increases 0.2m.Strong-motion recording from Tangyu strong motion station was input,the contour of displacement of two site model are layered distribution,the displacement is largest at the shallow layer of the loess site,its value is 2 times more than the lower,there is a clear transition zone between the two parts of the loess site,the displacement is not obvious at the bottom of the model.(4)Results of the shaking table test and the numerical simulation is similar,there is no obvious difference between HVSR curve and TF curve,both of which can accurately give the excellent frequency of the site and react the nonlinear characteristics.HVSR method is feasible to describe the site condition in earthquake engineering,especially in the aspect of description of soil layer's non-linearity characteristics.The research method can extend research and application of strong-motion recording,the results can explore the theory and method of shaking table test,enrich and develop the theory of loess dynamics,improve the evaluation method of site effect,provide the theoretical foundation for the selection and design of building site,so as to achieve the purpose of earthquake disaster prevention and reduction of earthquake loss.