Damage detection of RC beams based on experiment and analysis of nonlinear dynamic characteristics

The experimental and analytical investigation on damage detection of reinforced concrete (RC) beams has been carried out using a testing RC beam. The correlations between the damage extent and the nonlinear dynamic characteristics (NDC) of the testing beam are presented in this paper. The NDC of the RC beam were obtained by means of time–frequency analysis (TFA) of displacement responses from the impulsive and harmonic vibration tests. The correlation between the displacement amplitude and the excitation frequency in the case of forced vibration was obtained. Combining the results from the TFA with the relationship of displacement amplitude and corresponding natural vibration frequency (DA-CNVF) from the harmonic vibration tests, a reasonable window width for TFA was suggested. It is observed that the window width of seven times of the fundamental period of the testing structure is a suitable option in the time–frequency analysis. Using the TFA with this appropriate moving window width, the relationship between DA-CNVF at different damage levels in the case of free vibration was used to depict and analyze the NDC of the damaged RC beam. The feasibility of using NDC of a damaged RC beam from either forced harmonic or free vibration tests to detect damage level is discussed. The NDC of the reinforced concrete beam can be used to detect its damage levels if the apparent damage is not significant. Therefore, this damage detection method may be suitable for structures with small damage invisible or hard to be found by naked eyes.

▸ We do impulsive vibration tests of reinforced concrete beam at several load levels. ▸ We do the sweep frequency tests of the beam at corresponding load level. ▸ We select a suitable window width based on comparison of the two kinds of test results. ▸ We do the nonlinear dynamic characteristics analysis using short time FFT based on the window width. ▸ We do the damage identification of the beam based on nonlinear dynamic characteristics.