Condition assessment of structures under ambient white noise excitation

This paper proposes a damage detection method based on the wavelet packet energy of covariance of measured acceleration responses of structures under ambient excitation. It is a model-based method comparing the measured acceleration responses before and after damage occurrence. The ambient excitation is assumed to be white noise. A damage index based on the change of modal strain energy is used for damage localization. The damage quantification is performed using the sensitivity of the wavelet packet energy of the covariance function. A cantilever five-bay truss structure is used to demonstrate the efficiency of the method with three damage scenarios. The combined two-stage approach is shown capable of locating and accurately quantifying local damages in the presence of measurement noise. A nine-bay three-dimensional truss structure is also assessed in the laboratory with the proposed method, and the whole process of damage detection with incomplete and noisy measurement, initial model error, etc., is demonstrated to be successful for identifying, with good accuracy, local damages in members.