VIBRATION TESTING FOR NONDESTRUCTIVE EVALUATION OF BRIDGES .2. RESULTS

The waveform-recognition techniques introduced in Part I are used to detect the presence of simulated cracks in the girders of a laboratory-size bridge as well as a highway bridge. Bridge structure is excited by using a modal hammer. Vibration response is picked up by using an accelerometer. To study the effect of noise, digital noise is added to the vibration response of the laboratory bridge. The frequency-response function is used as the bridge signature. Each waveform-recognition method described in Part I, except for the cross signature assurance criterion, is used to compare bridge signatures, and the results are evaluated and compared. When no noise is added. all the methods are successful in detecting cracks in the laboratory bridge. When synthetic noise is added, smoothing is used to reduce the noise effect. In the presence of noise, all techniques, with the exception of the equivalent level of degradation system methods, perform well. Using a limited number of signatures from the highway bridge, the waveform chain code is capable of detecting a simulated crack.