Mode identification by eigensystem realization algorithm through virtual frequency response function

Abstract

Mode identification in civil engineering uses ambient excitation response, where the excitation is assumed to be stationary white noise. However, practical engineering conditions cannot satisfy this assumption of ideal excitation. This paper proposes an innovative method based on eigensystem realization algorithm and a proposed virtual frequency response function. The formulation of the virtual frequency response function is derived from the ratio of the cross-power and autopower spectral density functions of the measurement signals. The impulse responses are calculated by inverse Fourier transform of the product of the virtual frequency response function and the frequency response function of the reference point. After obtaining impulse responses, eigensystem realization algorithm is then performed to identify structural modes. The proposed virtual frequency response function and eigensystem realization algorithm are validated by a numerical example. The results show that the virtual frequency response function and eigensystem realization algorithm can give much a better impulse response than natural excitation technique and identify more precise mode parameters. Finally, the proposed method is applied to a practical engineering bridge, where the results by the virtual frequency response function and eigensystem realization algorithm can also give better results than those given by natural excitation technique and eigensystem realization algorithm.