近场地震动频谱特征周期研究

Studyon the characteristic period of near field ground motions

基于999条具有完整信息的欧洲及其毗邻地区的近场强震动记录,对反映地震动频谱特性的不同特征周期参数(反应谱卓越周期T。、平滑化反应谱卓越周期T_o、傅氏幅值谱平均周期T_m)进行了研究,分析了场地条件、地震震级等因素对近场水平向及竖向地震动频谱特征周期的影响,并探讨了我国现行规范中设计反应谱特征周期T_g取值的合理性问题。统计结果表明:在近场区域场地和震中距仍是影响地震动频谱特征周期的重要因素,因为近场地震动的复杂性,震级对地震动频谱特征周期的影响不是很明显;近场区域竖向与水平向地震动的频谱特征周期有明显差别,且场地越软竖向与水平向地震动频谱特征周期的比值越小;我国现行抗震规范中设计反应谱的特征周期取值偏低,可能是偏于不安全的。

Three characteristic periods （i.e.,predominant period Tp ,smoothed spectral predominant period To and mean period Tm ）were calculated in this paper based on 999 records of near field ground motions from the earthquakes in Europe and its adjacent areas.Those characteristic periods were analyzed to study the impacts of site condition,earthquake magnitude and other factors on the frequency contents of vertical and horizontal ground motions in near field,and to discuss the reasonable value of characteristic periods in current seismic design code.The results show that site condition and epicentral distance are the important factors affecting the characteristic periods of ground motions in near field,but the influence of earthquake magnitude is not obvious for the complexity of the near field ground motions.The characteristic periods of vertical and horizontal ground motions are obviously different,the ratio of vertical and horizontal ground motions becomes smaller when the stiffness of site condition decreases.This study indicates the value of characteristic periods used in current seismic design code is probably unsafe.