Nonlinear vibration characteristics of damaged concrete beams

The work presented here investigates the possibility of using changes in the nonlinear vibration characteristics to detect damage in reinforced concrete elements. The nonlinear vibration characteristics were studied by conducting impact excitation vibration tests on reinforced concrete beams. The nonlinearities were detected by examining the changes in the fundamental frequency during the decay of an impulse response with time (and hence, with amplitude of vibration). The tests demonstrated that there is a change in nonlinear vibration behavior with damage. The change is greatest at low levels of damage. After the beam has been loaded to 27% of the failure load in three-point bending there is a reversal in the trend and a slight reduction in nonlinearity with further damage. These results indicate that the method is unlikely to be useful in detecting high levels of damage in reinforced concrete bridges, however, it is capable of detecting low levels of damage not visible to the naked eye, and so has potential for assessment of special structures where very high levels of structural integrity are required.