在分析特殊型地震动如近场脉冲型地震动或远场类谐和地震动时,研究和设计人员更关注于地震动的时域特性.鉴于目前尚不具有一种成熟的用于分析地震动时域特性的方法,在研究中通常采用肉眼辨别地震动.但在肉眼辨别的过程中并没有定量的指标描述地震动的特性,因此这种方法容易引入人为的主观性误差.地震动的时域特性主要指地震动的振动周期和强度随时间的变化情况.如有一种定量描述这种变化的方法便能消除肉眼辨别中引入的主观性误差.为解决该问题,本文提出了一种简便、有效的分析地震动速度时程时域特性的速度零点法ZVPM(Zero Velocity Point Method).采用这种方法可以定量地分析地震动速度时程的振动周期和强弱程度随时间的变化情况,并可以通过定义的幅值参数、周期参数和相位参数获取等效的地震动速度时程.鉴于脉冲型地震动对结构具有特殊的破坏作用,本文采用速度零点法分析了24条典型的强脉冲型地震动,并基于速度零点法提出了一种简便的脉冲周期计算方法.为便于工程设计人员快速地获取本文所选脉冲型地震动的等效速度脉冲,文中给出了每一条地震动等效速度脉冲的数学表达式.
Long-period ground motion has become an important consideration because of the increasing number of large and long-period structures.Therefore,a thorough investigation on the formation and characteristics of longperiod ground motion is desirable for engineering applications.In this work,an analytical study is performed to examine the effect of several parameters and the combining mode for equivalent harmonic components on the dynamic response of systems.The results of the work show that the harmonic components in equivalent ground motion are evidently influenced by the intensity rise time,duration,phase and combining mode.Moreover,the long-period ground motions are simplified and simulated by separate harmonic components through proper combination.The findings of the work are believed to be useful in the selection of input ground motion in structural seismic analysis.
