Modeling Study On Power Spectrum Of Ground Motion Evolution

Seismic motion is a time and frequency non-stationary random process.The seismic motion power spectrum model can describe the frequency domain distribution of seismic motion energy,and is one of the important components of seismic motion random model.At present,most of the power spectrum models are based on the assumption of stationary random process.However,the real seismic motion is a non-stationary random process.During the seismic process,not only its amplitude changes,but also its frequency domain characteristics change,with the characteristics of intensity and frequency non-stationary.However,seismic motion is actually a non-stationary process.During the earthquake,not only the amplitude but also the frequency domain characteristics will change,and it has non-stationary characteristics of intensity and frequency.The non-stationary characteristics of seismic motion frequency and strength have an important effect on the response of the structure,and especially for the important structure after damage,which frequency characteristics will change,and the frequency characteristics of seismic motion will also change,so higher requirements are put forward for the seismic safety of important structures.In order to describe the time and frequency non-stationary characteristics of seismic motion more accurately,the research on the evolutionary power spectrum of seismic motion is started,which can reflect the energy distribution in frequency domain of seismic motion and the intensity's time-varying characteristics of each frequency component.This paper introduces the traditional evolutionary power spectrum method and the new evolutionary power spectrum method based on energy,and obtains the evolutionary power spectrum by using the seismic motion data(99)from the three directions of Wenchuan Earthquake in 2008,and makes a comparison between them.The specific work is as follows:Firstly,the power spectrum model of seismic ground motion was organized and summarized.Four kinds of typical intensity envelope function models were introduced,and the traditional evolution power spectrum was obtained by strength envelope function and power spectrum of stationary stochastic processes.In addition,based on the assumption thatthe seismic acceleration belongs to a wide-band random process,the evolutionary power spectrum is estimated by the statistical moment of energy generated by the small damped linear system in the random seismic process.On the basis of the above theoretical research,the calculation example is solved by using the seismic motion data(99)from the three directions of Wenchuan Earthquake in 2008.The intensity envelope function of Wenchuan Earthquake is calculated,and According to the traditional method of evolutionary power spectrum,the images of evolutionary power spectrum of three directions(EW,NS,UD)of Wenchuan Earthquake are obtained by strength envelope function and power spectrum of stationary stochastic processes.In addition,the velocity and displacement of SDOF system under the seismic motion are calculated by the Newmark? method,and the images of evolutionary power spectrum of Wenchuan Earthquake are obtained by the energy method.A comparative analysis on the images of evolutionary power spectrum by two methods reveals that the trend fitting is very close,although there is a slight gap.