Spectral-Based Damage Identification in Structures under Ambient Vibration

The motivation behind this paper is to develop a spectral-based damage detection and damage localization scheme using in-service ambient vibration in the context of non–model-based damage characterization. In this regard, a response parameter known as spectral moment is implemented for structural damage identification. The damage identification procedure starts with developing response power spectral density (PSD). The principal structural response features are then extracted from the frequency distribution of the spectrum using spectral moments. It is demonstrated that, although, spectral moment is a nonmodal characteristic of a process, it is related to modal parameters of a response signal since the spectral moment at each location is proportional to its corresponding modal vector. Hence, it is expected that due to damage occurrence spectral moment undergoes a variation. On this point, a damage sensitive feature is defined by comparing the spectral moments of two successive states of the structure. It is demonstrated that at a damage location there is a pronounced distinctive change in the indicative feature which is implemented for damage localization. The major advantages of the method include, first, the method works based on output-only measurement data, and second, it does not require any representative model of the structure and finally, unlike modal data that provides information at specific frequencies, the presented method is a broadband approach using information in a wide frequency range. The effectiveness and robustness of the proposed technique was validated by numerical simulations and an experimental case study. A series of numerical simulations with different damage scenarios was carried out on an Euler-Bernoulli beam subject to a band-limited random Gaussian excitation. Damage was simulated by reducing the flexural rigidity of elements at particular locations in single or multiple states. An experimental case study was also investigated utilizing a reinforced concrete jack arch which is one of the major structural components of the Sydney Harbor Bridge. Damage was introduced by creating a crack via applying gradual load using load cell. The numerical and experimental analyses indicated a promising sensitivity of the approach to detect and localize structural damage.