Influence Of Magnitude And Epicenter Distance On Seismic Design Response Spectrum Of Loess Site

The seismic design response spectrum is derived from the seismic response spectrum or the site-related response spectrum,which is the basis for the seismic design of the structure.The research on the influencing factors of the response spectrum and its calibration method has always received extensive attention from the academic and engineering circles.Loess is a kind of special soil,it has the characteristics of water sensitivity and power vulnerability.It is widely distributed in my country.The Loess Plateau is an area crossed by the north-south seismic belt in my country.There are frequent seismic activities,high intensity,and serious earthquake disasters.Magnitude and epicenter distance are two important factors that affect the seismic design response spectrum.It has important theoretical significance and engineering application value to carry out research on the factors affecting the seismic design response spectrum and its calibration method in the loess area.On the basis of summarizing the existing research results,this paper uses a large number of strong earthquake records in the loess area to study the influence of the magnitude and epicenter distance on the seismic design response spectrum of the loess site,and obtains some meaningful research results;a new response spectrum calibration method is proposed,and take the actual project as examples to illustrate the feasibility and advantages of this method,and the following main research work has been completed.(1)Briefly summarize the related concepts and calculation methods of response spectrum,and comb the research process of response spectrum.The methods of calibrating design response spectrum such as Newmark three-parameter method,two-parameter method,and differential evolution algorithm are introduced in detail.Through comparative analysis,pointed out that the current calibration of response spectrum needs to be further resolved.(2)A new method to calibrate the seismic design response spectrum using the Nelder-Mead simplex algorithm is proposed.The principle of the Nelder-Mead simplex algorithm and its application in engineering are introduced in detail;the Newmark three-parameter method,the two-parameter method,the differential evolution algorithm and the Nelder-Mead simplex algorithm are used to calibrate and compare the acceleration records of 16 different sites.The results show that the error of the seismic design response spectrum calibrated by the Nelder-Mead simplex algorithm is smaller,which illustrates the feasibility and suitability of the algorithm for calibrating the seismic design response spectrum.(3)The influence of magnitude and epicenter distance on the seismic design response spectrum of loess site is statistically analyzed.Based on the collection of a large number of strong earthquake records on loess sites,the collected494 horizontal acceleration records on loess class II sites are grouped according to magnitude and epicenter distance,and use the Nelder-Mead simplex algorithm to calibrate.After statistical analysis,the variation characteristics of the magnification coefficient platform value and characteristic period of the seismic design response spectrum of the loess site with the magnitude and epicenter distance are summarized.With the increase of the magnitude,the platform value shows a gradually increasing trend,but the influence of epicenter distance on the platform value is not obvious;as the magnitude and epicenter distance increase,the characteristic period tends to increase.The study found that the seismic design response spectrum amplification coefficient platform value is between 2.6 and 3.22 under the action of large or small earthquakes,and its statistical value is higher than the 2.5 specified in the seismic code.The statistical value of the characteristic period is relatively close to the specified value.(4)Taking two projects as examples,the application of the Nelder-Mead simplex algorithm in actual projects is introduced.The advantages of this method are demonstrated by comparing with the parameters of the site-related spectrum given in the seismic safety evaluation report of the engineering site.Research indicates that the seismic design response spectrum curve calibrated based on the Nelder-Mead simplex algorithm can more truly reflect the spectral characteristics of ground motions.The calibration result has a smaller error with the actual seismic response spectrum,which is suitable for engineering seismic design.