Statistics Of Characteristic Parameters And Research On Fitting Method Of Design Response Spectrum

Earthquake response spectrum is strong ground motion information that is recorded and dealt with.The research of response spectrum under different sites is benificial to seismic design of structure.In the past 10 years,many strong motion observation stations with detailed site information are built in Sichuan,Yunnan,Gansu and Shanxi,which all in the north-south seismic belt of China,so abundant valuable strong seismic records are obtained.Based on the summarization of response spectrum calibration method,a new calibration method is given.Ultilizing the strong seismic records of Sichuan,Yunnan,Gansu and Shanxi,the characteristic parameters of response spectrum are obtained and analysed.The main research and achievement are as follows:1.The differential evolution is used to calibrate response spectrum,and a new calibration method is proposed.The principles of three parameters calibration method of Newmark,two parameters calibration method and least square fitting method are introduced.All the methods have advantage and shortcoming,and the main defect lied on the fitting accuracy.This thesis applys the differential evolution to the calibration of response spectrum,then it is used to deal with the strong ground motion records in Sichuan,Yunnan,Gansu and Shanxi.The calibration results are compared and analysed that are obtained from different calibration method to the same record.The results show that the response spectrum calibrated by differential evolution method approach the seismic response spectrum.It has the higher accuracy and fast computational efficiency,so this method is suitable to deal with substantial records.At last,the response spectrum of seismic records in Sichuan,Yunnan,Gansu and Shanxi are calibrated and the characteristic parameters of each records are gotten.2.The variety of peak platform value for response spectrum is analysed along with site category,earthquake magnitude and epicentral distance in Sichuan,Yunnan,Gansu and Shanxi.The results show that the distribution of peak platform value is approximately normal.On the same site category,The mean value of peak platform increases with earthquake magnitude in both the near fault and far field,but The mean value of peak platform on the second site category decreases with great earthquake magnitude.All the mean values of amplification coefficient spectrum are above2.5.The peak platform value of acceleration response spectrum is also analysed alongwith site category,earthquake magnitude,epicentral distance.It increases with site category and earthquake magnitude,but decreases with epicentral distance.At last,the site influence coefficients are calculated.3.The variability of characteristic periods are researched along with site category,earthquake magnitude and epicentral distance.The results show that characteristic periods of horizontal acceleration response spectrum increase with site category and earthquake magnitude.The characteristic periods of the second site category increase with epicentral distance.The characteristic periods of far fault is greater than it of the near field.The statistical results show that characteristic periods of design response spectrum of great earthquake in the far field is bigger than that of Chinese seismic design code.4.The vertical characteristic parameters are analysed along with site category,earthquake magnitude and epicentral distance in Sichuan,Yunnan,Gansu and Shanxi.The results show that that the distribution of vertical peak platform value is approximately normal,and it increases with earthquake magnitude.The effect of epicentral distance to vertical peak platform value is not obvious.This thesis shows that the peak platform value of vertical response spectrum is higher than the horizontal value on the base of the same site category,epicentral distance and earthquake magnitude.The characteristic periods of vertical response spectrum increase with site category for both small earthquake and great earthquake,so is for near field and far field.The vertical characteristic periods of the second site category increase with epicentral distance for great earthquake.The vertical characteristic periods on the same site category increase with earthquake magnitude.5.The ratio of vertical ground motion to horizontal motion is researched along with different site category,earthquake magnitude and epicentral distance.The ratio of vertical acceleration peak value to horizontal value increase with site category for small earthquake but decrease for great earthquake.The peak ratio increase with earthquake magnitude on the same kind of site category.The ratio first increase and then decrease with epicentral distance.The research results show the ratio of vertical ground motion to horizontal motion is different in the whole range of period.The ratio on first and second site category is above 0.65 when the period is under 0.1s and above 1.0s,but the ratio is under 0.65.This character is very obvious.The statistical results show that the vertical earthquake excitation is 0.65 of horizontal excitation by Chinese seismic design code is worth discussing,so it is suggested that the ratio should vary with therange of period.