Research On Intelligent Method For Extracting Perdominant Period Of The Site

The predominant period is a harmonic component of the seismic wave which resonates with the foundation soil layer,and it is the main parameter of site soil division and building seismic design.The methods to determine the predominant period of the site can be roughly divided into two categories: direct method and wave velocity method.No matter what kind of method is used to calculate the predominant period,it usually needs to input other control parameters besides the formation information.In order to get more reasonable results,some methods need to debug these parameters.A method of automatically extracting the predominant period of a site is proposed in this paper.When this method is used to calculate the predominant period of a site,it only needs to input the formation parameter information to get the predominant period of the site,and it doesn’t need to input any other control parameters besides the site information.In this paper,seismic waves are assumed to be plane waves which vertical upward propagation from bedrock.The site is simplified as horizontal stratigraphy.The site is treated as a geodetic filter acting on seismic waves.So The seismic response model of layered elastic half-space is established.The time history of seismic response of the model under the action of plane pulse wave is obtained by the above method,and then the period spectrum of seismic response is obtained by discrete Fourier transform of the time history of seismic response.The predominant period is the period corresponding to the maximum value of the periodic spectrum of the seismic response.This method is called the pulse response spectrum method in this paper.Pulse response spectrum method not only avoids the problems of simple model or complex calculation of traditional method,but also makes the calculation faster and more accurate,which is more conducive to the intelligent extraction of site predominant period.In order to get the purpose of automatically extracting the predominant period of the site,the value range of seismic wave holding time,time interval between sampling points,starting period,ending period and period interval in the pulse response spectrum method is summed up by using the single factor analysis method.The seismic response time history and its pulse response spectrum under the action of plane wave impulse are obtained by calculating,and the pulse response spectrum is obtained according to this value range.The spectrum searches the natural vibration period of the site until the maximum value of the seismic response period spectrum is found,.The site predominant period is determined by the corresponding period value.So as that can realize the intelligent extraction of the site predominant period.According to the above method,the corresponding MATLAB calculation program is compiled,and the engineering example calculation is carried out to verify the accuracy and effectiveness of this method.