This study investigates the possibility of using changes in the nonlinear vibration characteris-tics to detect damage in reinforced concrete beams. Two concrete beam specimens were gradually damaged by means of static loading tests. Following each loading step, the beams were unloaded and dynamic tests were carried out in suspended case. The nonlinear vibration characteristics of the specimens were studied by applying frequency domain methods and the presence of harmonics and amplitude dependency of resonant frequencies are identified. The non-linearity in dynamic behaviour of concrete beams are quantified by Hilbert transforms of the frequency response functions. The comparison of results of nonlinear techniques with visual progressive cracking of specimens indicates that the presence and also the degree of nonlinearity are capable of detecting levels of damage in concrete beams.

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