Damage Identification of RC Beams from Changes in their Vibration Characteristics

Abstract

The work presented here investigates the possibility of using changes in the nonlinear vibration characteristics to detect damage in reinforced concrete members. The vibration characteristics were studied by conducting ambient excitation vibration tests on reinforced concrete beams. The damages were detected by examining the changes in the fundamental frequency of the RC beams found from recorded time series data. The tests demonstrated that there is a change in nonlinear vibration behavior with damage. After that frequency domain data of time series were further studied to know the extent of cracks in RC beams due to the loading and a change in nonlinear vibration behavior was observed with increasing damage. The change in frequency content and the area of normalized Fourier Spectrum is prominent for flexure control beams. For flexure control beams area of normalized Fourier Spectrum increased up to the theoretical capacity of the beam and decreased gradually to the state where it could not take any load. However, In case of shear control beams the propagation of crack cannot be identified from the change in frequency content and the area of normalized Fourier spectrum. For both Flexure and Shear control beams, with propagation of crack below a certain sensor showed a jump in normalized Fourier Spectrum plot of that sensor data. These results indicate that the method is useful in detecting high levels of damage in reinforced concrete beams.