中文摘要：

为了给长周期地震动的选取和评价提供依据及量化指标,利用Hilbert-Huang变换理论分析地震动能量特性,提出评价地震动周期特性的方法;并且对典型的常规地震动和近、远场长周期地震动的时域、频谱分布、地震动放大系数谱及周期特性进行了分析,得到了近远场长周期地震动的时频域特性及其与常规地震动的差异。在此基础上,提出用β谱曲线2到10s谱值和周期的平方加权平均值βl作为长周期地震动的界定参数;根据178条近场地震动和151条远场地震动的βl值的统计分析结果提出：βl〉0.4的地震动为长周期地震动,βl〈0.2的地震动为短周期地震动（即常规地震动）,0.2≤βl≤0.4的地震动为中长周期地震动。这将为柔性桥梁抗震分析时长周期地震动的选取提供依据。

英文摘要：

To provide the selection and evaluation of long-period earthquake ground motions with a quantitative criteria a new methodfor the evaluation of seismic periodical characteristics is proposed based on the energy characteristics of ground motions derived from Hilbert-Huang Transformation analysis.The difference of the time domain and frequency domain characteristics between the typical conventional ground motions and the near-field/far-field long-period ground motions are obtained through the analysis of the time domain,spectrum distribution,acceleration dynamic magnification factors spectra and periodical characteristics.As a consequence the parameterβl,which is defined as the weighted square average value of the periodicity of spectrum cureβbetween 2sand 10 s,is taken as the boundary parameter of ground motions.According to the results of statistical analysis of 178near-field records and 151far-field records,the ground motions are classified into long-period（βl〉0.4）,moderate period（0.2≤βl≤0.4）and short period（βl〈0.2）ground motion.This will provide the basis for the analysis of long-period ground motions of flexible bridges.