强震地面运动的超随机特性研究

简述了几种常用的地震动平稳随机模型，这几种地震动平稳随机模型的功率谱是一组光滑的函数，相应的自相关函数基本上是指数衰减的振荡函数，且很快衰减到零；但是真实地震动的归一化自相关函数则有一较显著的随机噪声项，这个随机噪声的幅值为0．15左右，这就是本文中所说的超随机特性。目前常用的地震动平稳随机模型没有考虑这个随机噪声项及其对结构反应的影响。本文将真实地震动的自相关函数分解为一确定性函数和一随机噪声的叠加，并对自相关函数中的噪声部分进行了分析，得出两条重要性质。本文的研究结果表明地震动加速度时程的平方和(SS)比峰值加速度(PGA)更好地量度了地震地面运动强度。由于归一化自相关函数的随机噪声部分所对应的功率谱的随机波动成分对频率的积分为零，即归一化自相关函数的噪声部分对地震动总功率或平方和的贡献为零，因此自相关函数的随机噪声项对地震动的幅值影响不大，但自相关函数的随机噪声项明显改变了地震动功率谱在频域上的分布特征，因此会对结构反应产生一定的影响。由于篇幅所限详细内容将在下一篇文章中作进一步探讨。     

Seismic structural control using semi-active tuned mass dampers

This paper focuses on how to determine the instantaneous damping of the semi-active tuned mass damper (SATMD) with continuously variable damping. An off-and-towards-equilibrium (OTE) algorithm is employed to examine the control performance of the structure/SATMD system by considering the damping as an assumptive control action. The damping modification of the SATMD is carried out according to the proposed OTE algorithm, which is formulated based on analysis of the structural movement under external excitations, and the measured responses of the structure at every time instant. As examples two numerical simulations of a five-storey and a ten-storey shear structures with a SATMD on the roof are conducted. The effectiveness on vibration reduction of MDOF systems subjected to seismic excitations is discussed. Analysis results show that the behavior of the structure with a SATMD is significantly improved and the feasibility of applying the OTE algorithm to the structural control design of SATMD is also verified.     

An off-and-towards-equilibrium strategy for vibrational control of structures

Traditional control strategies have difficulty handling nonlinear behavior of structures, time variable features and parameter uncertainties of structural control systems under seismic excitation. An off-and-towardsequilibrium （OTE） strategy combined with fuzzy control is presented in this paper to overcome these difficulties. According to the OTE strategy, the control force is designed from the viewpoint of a mechanical relationship between the motions of the structure, the exciting force and the control force. The advantage of the OTE strategy is that it can be used for a variety of control systems. In order to evaluate the performance of the proposed strategy, the seismic performance of a three-story shear building with an Active Tendon System （ATS） using a Fuzzy Logic Controller （FLC） is studied. The main advantage of the fuzzy controller is its inherent robustness and ability to handle any nonlinear behavior of structures. However, there are no design guidelines to set up the corresponding control rule table for a FLC. Based on the proposed strategy for the FLC, a control rule table associated with the building under study is developed, which then allows formation of a detailed algorithm. The results obtained in this study show that the proposed strategy performs slightly better than the linear quadratic regulator （LQR） strategy, while possessing several advantages over the LQR controller. Consequently, the feasibility and validity of the proposed strategy are verified.     

强震记录频率非平稳特性的若干研究

本文将美国西部、中国台湾和其它地区在基岩场地上的156组地震记录按不同震级、震中距分组,分析了持续时间随震级、震中距的变化规律,在此基础上研究了强震记录的穿零率以及主频的时变特性,并用一直线来拟合穿零率随时间的变化规律,给出了此直线拟合参数在不同震中距、记录方向条件下的取值范围,以此来反映频率特性随时间变化的非平稳性,此外还通过运用峰点法在频率特性非平稳性中考虑涟波效应。所得结果与穿零率的相应结果进行了对比。文中的分析结果表明,穿零率方法是可以在一定程度上反映频率特性的非平稳性的。     

地震动不确定性及其影响因素的初步分析

选取欧洲强震记录数据库中,同一台站记录到的两次地震以及两个不同台站记录到的同一地震的强震记录,分析了它们的PGA比值、卓越频率和反应谱的不确定性以及不确定性对结构反应的影响,得出：影响地震动不确定性的因素主要有震源机制、地震波传播途径、场地类别等。在此基础上,进一步分析了地震动不确定性对结构反应的影响。