Modification Of Code Response Spectum Considering Long-period Ground Motionsand Seismic Records Selectionfor Isolated Structure Dynamic Analysis

Unlike ordinary ground motion,long-period ground motion is rich in low-frequency components,with a longer duration,energy concentrated in the low-frequency areas and other characteristics,it's easy to cause long-term structural damage.However the early strong earthquake can get the earthquakes of the reliable cycle is usually not more than 3s ~ 4s,it is difficult to study the long-period characteristics of ground motion.At present,most of the country's design response spectrum does not take the impact of long-term ground motion into consideration,and the application cycle is not long enough to meet the long-period structure of the seismic design needs.At the same time,the ground motion can be very different according to different ground motion parameters,thus affecting the response to the structure.But there is not yet a seismic index for the seismic isolation structure and method for selecting record of ground motion.Therefore,this paper discusses the definition of long-period ground motion and the occurrence probability of long-period ground motion on various types of sites by collecting and analyzing the long-period ground motion data,and revises the long-period section of the normative response spectrum.Aiming at the long-period structure of isolated structure,the relationship between the characteristics of ordinary ground motion and long-period ground motion and the response of isolated structure is analyzed.And the ground motion parameters are selected according to the seismic parameters with the isolation structure response,the suggestions for selecting the ground motion records of the isolated structure dynamic analysis are given.The main contents and conclusions of this paper are as follows:(1)A new method for defining longperiod ground motion is given,the characteristic of earthquake wave power spectrum are used to choose long-period ground motions.The long-period ground motion is defined that the ratio of the area of ground motion power spectral density within 0.1-0.5 Hz to the total area is more than 30%.Analyzing about 20,000 earthquake waves from different regions in the world,we observe that long-period ground motion percentage roughly the total ground motions of 3%-5.5%,meanwhile,the probability of long-period ground motion on the soft site is more than on the hard site,because long-period ground motion on classification site II percentage roughly of 3% and those on classification site III and IV of 6.3%-8.3%.Discussing YJK's wave database and code for seismic design of isolated building on editing,we find that the proportion of long-period ground motions in YJK's wave database is less than 3% and the proportion on the soft site is much less than the actual probability,however,the Special verification earthquake waves for the class ? site given by code for seismic design of isolated buildings consider long-period ground motions effects.(2)The descending segment decay index,the first falling end time value and the long period segment spectral value of the standard response spectrum are corrected and designed.By collecting the seismic records of different fields,the average spectra of different fields and the average spectra of different damping ratios were calculated and compared with the recommended response spectra.The results show that the proposed spectrum can be well fitted with the average spectrum,indicating that the proposed spectrum is reasonable and feasible,and can be used as the basis for engineering design.(3)Four typical seismic isolation structures were combined by Latin hypercube sampling.Selecting 30 pieces of the general ground motions and the long-period ground motions,the time history analysis of four typical isolated structures is carried out respectively,we discuss the relationship between twenty ground motion parameters and six response parameters of isolated structures,the results show that: there is a difference in the correlation between ground motion parameters and different structural responses,the relationship between the general vibration and the long-period ground motion is not the same as the correlation of the same structural response.However,the three parameters,such as the peak velocity and the peak acceleration ratio,the seismic characteristic period and the earthquake moving time,are strongly related to the seismic response,and it is suggested that it can be used as isolation Structural selection of ground motion indicator..(4)Using the peak velocity and peak acceleration ratio of the ground motion parameters as the control index,seismic records of the time-history analysis of the isolated structure are selected and compared with the earthquakes obtained by using the ATC-63 time history analysis wave selection method and the seismic records obtained by time history analysis of wave selection method in China,comparisons can be get from the effective time,compared with the normative response spectral value of the error,the seismicity of seismic records and whether the selected seismic records include long-term ground motion and other aspects.The results show that the seismic records obtained by the proposed wave method are in accordance with the requirements of China's seismic code,but it is better than the seismicity of seismic records obtained by our seismic selection method,which may include long-period ground motion.The seismic record obtained by ATC-63 time-history analysis method is better,and it may include long-period ground motion,but the error of spectral spectrum can be larger and can not meet the requirements of China's seismic code for selected seismic waves.