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Damage detection at an early stage is of great importance especially for infrastructures since the cost of repair is considerably less than that of reconstruction. The change in stiffness and frequency could obviously indicate the occurrence of damage and its severity. Wavelet transform is a powerful mathematical tool for signal processing which provides more details compared to Fourier transform. In this paper, a model-free output-only wavelet-based damage detection analysis has been performed in order to achieve perturbation of detailed function of acceleration response in bridge piers. First, a nonlinear time-history finite element analysis was performed using 9 consequent earthquake records; from which, time-history acceleration response was derived. Also pushover and hysteresis curves were drawn based on the results. Furthermore, applying wavelet transform to structural response, some irregularities appeared in decomposed detailed function which imply on damage presence in the models. Finally, peak values of details could lead us to time instants of damage.

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A new model-free output-only signal processing-based damage detection procedure was carried out in this paper. First of all, a finite element model as the representative of reinforced concrete (RC) frames was constructed and subjected to a specific loading protocol in OpenSees. The protocol consisted of 9 consequent different near-fault fling-step pulse-type earthquake records with low-amplitude white noises among them to simulate the collapse procedure. The analysis process was complemented in three levels: (a) the Fourier transform was utilized to extract the vibration frequency, (b) the time instants of damage occurrence were detected by using the discrete wavelet transform, and (c) accurate damage detection was made by using the extracted pulse components of the records as loading protocol for earthquake simulation and the discrete wavelet transform. The results revealed that the proposed combinatorial method could efficiently diagnose the damage in the RC frames. Also, applying a pulse component instead of an original record increases the accuracy of damage detection by 70%.