Structural Damage Detection From Cross-correlation Function Analysis Of Stochastic Responses

Unexpected incidents always cause huge loss of life and property. The structural safety has aroused widespread concerns in recent years, which in turn promotes the development of the structural health monitoring system (SHMS). Dynamic based structural damage detection method is still a hot and difficult topic in the SHMS research. It is practically necessary to apply the dynamic responses induced by environment excitation in structural damage identification.In this study the damage detection method is investigated based on the cross-correlation functions of structural random vibration. The following topics are included:(1) The cross-correlation functions between the structural displacement, velocity and acceleration excited by the white noise are derived and then amended for the case of the bandlimited white noise. The amplitude vectors of the cross-correlation functions of adjacent measurement points are built and also proved satisfying the solid-shape principle. Theoretical foundations for damage detection method based on cross-correlation functions of dynamic responses are established.(2) Cross-correlation functions of dynamic responses based method for damage determination, locating and quantification is proposed. Several key issues including noise immunity, sample length and identification "blind area" in the application of the method are discussed. By numerical simulation of a continuous beam and an eight-story steel frame, the dynamic responses cross-correlation functions are verified feasible for the structural damage detection under environmental excitation.(3) By using wavelet package, dynamic responses are decomposed to several frequency bands and the "signal energy" of each band is used to build damage characteristic vector which is used as the input information of support vector machine. In this way, the damage is identified from the prospective of pattern classification. Based on the damage simulation of the frame structure where the acceleration responses are taken as input information of support vector machine, the comparative analysis between single-point and multi-point measurements indicates the deficiency of directly using the wavelet decomposed acceleration "band energy" as the damage characteristic quantity.(4) The analytical expressions are also derived indicating that the dynamic responses cross-correlation functions contain more damage information than the time-history response. It is proposed to combine support vector machine and dynamic response cross-correlation as the new method for damage detection. Taking ASCE-SHM benchmark model of phase IIe as example, accelerations, acceleration cross-correlation functions and the amplitude vector of cross-correlation functions are respectively used to extract the damage feature and build the support vector machine. By comparing their damage identification results, it is shown that the damage feature extracted from the cross-correlation functions is an excellent characterization.(5) For the aim of practical application in structural damage detection, two steps of identification technique based on cross-correlation functions and support vector machine are provided.