عنوان مقاله [English]
Identification of the modal parameters of the damaged structure by signal processing of vibration based on changes in dynamic properties such as frequency, stiffness, and mode shape of structures. Some of these approaches fail when applied to civill engineering structures, the main reasons are the low sensitivity of the structural response to the damage location, or the low accuracy of structural response obtained by installed sensors. However, due to the rigorous evaluation and low cost of signal processing methods, this method has made a great progress. Signal processing methods have been extensively employed to examine the measured system responses and determine system variations. These methods include Fourier analysis, wavelet transform and Hilbert-Huang transform.
During the last decades, the number of vibration-based damage detection methods has been greatly developed and has influenced much of the research. The purpose of these methods is to determine the resulting changes in the modal characteristics of the structure including its natural frequency, mode shape, and damping ratio. For example, the basis of the Fourier transform method is to determine the structural modal parameters from the random vibration data in the frequency range. However, time-frequency analysis is introduced to overcome the limitations of the Fourier method, the most important of which is not providing a frequency-time range of a signal. The first case of frequency-time analysis was the short-time Fourier transform method based on the Fourier transform of the data divided by the time window function. According to this method, the interaction between time and frequency is difficult due to the existence of the time window function. If the windows are smaller in the time segment, its accuracy increases, and in the frequency domain it becomes less accurate.
Several damage detection methods have been proposed based on the vibration signal of structures. In most of them, a damage index has been described as the difference between damage and undamaged structure. This paper intends to propose a damage detection method based on the amplitude coefficient correlation of damaged and undamaged responses of structures, while a signal decomposes to IMFs and the changes appear in the first IMF. Therefore, every change on the original signal can be revealed on IMFs, since the original signal depends on IMFs. Also, these changes have an effect on the analytical signal and the Hilbert transform. The instantaneous frequency is measured joints on the structure is calculated by the Hilbert transform of the first IMF of response. Then, by introducing the instantaneous frequency energy (EDI), the location of damages are detected. To assess the feasibility and reliability of the proposed method, the ASCE benchmark problem has been used. To consider the robustness of the proposed method, contamination of signals during the data acquisition process is investigated. The ASCE benchmark study is carried out by the International Association (IASC) ASCE Structural Health Monitoring Task Group. The dynamic responses of the structure have been obtained by numerical analysis under random vibration loading. To evaluate the HHT method, it is required to attain the damaged responses of the ASCE benchmark. The first five damage patterns of the ASCE benchmark building is used. Then the damage on the structure is detected with a comparison of damage and undamaged dynamic responses. According to the measured noise levels, dynamic responses to noise values have been contaminated and the results have been evaluated. According to the results, this method can trace the location of the damage by the energy of instantaneous frequency.
Therefore, the locations of damages in different scenarios were located with the EDI index and velocity vector. The results show that the proposed method determined the location of damage with the acceptable accuracy for low and moderate damage in damage scenarios.