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为了识别结构模态参数及其时变特性,以HilbertHuang变换(HHT)方法为基础,结合传递函数的概念,定义了HHT边际谱、HHT边际谱频响函数及HHT边际移动谱。相比使用恒定频率和模态振幅而言,HHT方法可以更好地处理信号的非线性和非平稳性,它由经验模态分解和Hilbert谱分析组成。首先对信号进行经验模态分解,得到若干个固有模态函数(IMF),然后对IMF进行Hilbert变换得到信号的边际谱。相比Hilbert边际谱,边际谱频响函数能够识别高一阶模态参数,而边际移动谱可以识别结构模态参数的时变特性。对一个3层钢筋混凝土框架结构三线型退化模型在强震作用下的各层输出加速度响应进行HHT边际移动谱分析,识别出了结构在强震作用下刚度折减、自振频率随着地震加速度的增加而改变的过程,表明边际移动谱可以识别结构参数的时变特性。
In order to identify structural modal parameters and their time-varying characteristics, HHT marginal spectrum, HHT marginal spectral response function and HHT marginal moving spectrum are defined based on the Hilbert-Huang transform (HHT) method and the concept of transfer function. Compared with the use of constant frequency and modal amplitude, the HHT method can better handle the signal nonlinearity and non-stationary, which consists of empirical mode decomposition and Hilbert spectral analysis. First of all, the signal is decomposed empirically, and several intrinsic mode functions (IMFs) are obtained. Then the IMFs are Hilbert-transformed to obtain the marginal spectrum of the signal. Compared with the Hilbert marginal spectrum, the frequency response of the marginal spectrum can identify the first-order modal parameters, while the marginal moving spectrum can identify the time-varying characteristics of the structural modal parameters. HHT marginal displacement spectrum analysis of the output acceleration responses of each layer of a three-layer degenerated model of a three-story reinforced concrete frame structure under strong earthquakes shows that the stiffness of the structure is reduced under strong earthquakes. The process of changing with the increase of acceleration shows that the marginal moving spectrum can identify the time-varying characteristics of structural parameters.