Damage-sensitive features from non-linear vibration response of reinforced concrete structures

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Reinforced concrete structures respond in non-linear manner under dynamic loads even at low levels of vibration. This causes softening in concrete which may result in the unstable vibration. By considering the non-linearity, the effects of amplitude of vibration on the modal characteristics can be used to extract damage-sensitive features. In this article, investigations carried out on the phenomena associated with non-linear vibration, which were observed during the vibration tests on damaged reinforced concrete structures, are discussed. For effectively identifying the non-linear damage features in reinforced concrete structures from the frequency spectral information, an appropriate vibration testing procedure is formulated in this study. Damage features are evaluated from the changes in vibration amplitude with frequency at different damage levels under various types of excitations and their force levels. Damage indicators based on basic signal statistics and non-linearity in vibration responses are evaluated. Using the phase-plane information obtained from various damage scenarios, non-linear damage indices have been formulated. Another significant non-linear damage feature has been identified by the occurrence of higher harmonics observed by analysing the spectral density functions obtained from the frequency domain decomposition. The results obtained from this study would pave the way for identifying the damage in heterogeneous and non-linear structures such as reinforced concrete.