近断层速度脉冲型地震动特征周期的估计与调整

Estimation and adjustment of eigenperiod of response spectrum of near-fault pulse-type ground motion

基于美国NGA数据库,在断层投影距小于25 km范围内挑选了1387条地震加速度记录,分别按照断层距和场地条件进行分组,对近断层速度脉冲型地震动的频谱特性、特征周期,及其与断层距、震级的相关性予以分析。结果显示:①出现速度脉冲型地震动的比例与断层投影距之间存在明显的线性相关关系,但其与震级的变化不相关;②地震动速度脉冲周期与震级之间存在强相关;③对于近断层速度脉冲型地震动,采用动态变化的加速度和速度反应谱峰值周期进行特征周期的计算,更加符合真实情况;④地震动速度脉冲有放大地震动特征周期的作用,水平向放大的比例与竖向相当,且放大作用与场地条件相关,在较硬场地上放大较多。本文基于上述近断层地震动的统计分析结果,对现行抗震设计规范中定义的特征周期提出了适合于工程应用的调整系数,并建立了速度脉冲周期与震级之间的关系模型,分析结果显示二者的拟合效果较好。

1387 acceleration recordings within 25 km of Joyner-Boore distance were selected from NGA database and grouped according to the Joyner-Boore distance and site condition.Then the characteristics of near-fault pulse-type ground motions were discussed by using different ways,including spectral characteristic,eigenperiod of response spectrum and the relationships with the Joyner-Boore distance and earthquake magnitude.The results show that:①The number of near-fault pulse-type ground motions is related to the Joyner-Boore distance,but not to the earthquake magnitude.(2)The period of velocity pulses is strongly related to the earthquake magnitude.(3)For near-fault pulse-type ground motion,it is more accordant with the reality to use dynamic peak period of pseudo-acceleration and pseudo-velocity response spectra of ground motion to calculate the eigenperiod of response spectrum.(4)The velocity pulses of ground motion has the effect of enlarging eigenperiod of response spectrum,and the enlargement scale of horizontal and vertical are the same.Moreover,the amplification is related to the site conditions,which amplifies more on the harder site.Based on the results of statistical analysis of near-fault ground motion mentioned above,the adjustment coefficient for eigenperiod of response spectrum in the current seismic design code is provided in this research,which is suitable for application in engineering.And the satisfied relationship between period of velocity pulses and earthquake magnitude is established based on the regression analysis.