【摘要】 首先对美国NGA数据库中的3551组地震记录按场地、震级、震中距进行了分组.采用一维连续小波变换得到每条记录的小波功率谱,给出任意时间处小波功率谱最大值所对应的主频率随时间变化的曲线,并对相同分组内的主频率取给定时间窗的均方根值,通过非线性最小二乘法拟合得到不同分组下便于工程应用的主频率时变曲线.此外,本文给出了不同分组下的强度包线,改进了现有的小波包变换,以主频率时变曲线和强度包线为目标,提出了对地震动主频和幅值进行调整的方法.算例分析表明,本文给出的调整方法能够模拟真实地震动频率和强度的非平稳特性.更多还原

【Abstract】 In this paper,3551 sets of earthquake records from the NGA database were grouped according to the site condition,the magnitude and the epicentral distance.Wavelet spectrum of each record is calculated by using one dimension continuous wavelet transform.The timedependent predominant frequencies corresponding to the maximum values of wavelet spectrum at every time were considered,and the root mean square(RMS) of the predominant frequencies within a short time window in every group of ground motion was computed.Furthermore,timevarying curves of predominant frequencies for engineering applications were obtained by fitting RMS values of frequency based on nonlinear least square method,in addition,amplitude envelope in every group of ground motion were also presented.Based on the wavelet packet transform improved,an approach adjusting predominant frequency and amplitude of ground motion time histories that according to time-varying curve of predominant frequency and amplitude envelope was proposed.Finally,an illustrate example showed that the adjusted record possess the same nonstationarity of frequency and amplitude as actual earthquake record.更多还原