Comparison studies of open and breathing crack detections of a beam-like bridge subjected to a moving vehicle

Abstract

In this paper, based on the comparison between open and breathing crack detections of a vehicle–bridge system subjected to a moving vehicle, a wavelet spectrum technique for detection of breathing crack phenomenon is presented. The stiffness of element with an open crack is calculated from fracture mechanics and the stiffness of element with a breathing crack is modeled as a time dependent stiffness matrix using the stiffness of the element with an open crack. When there is a breathing crack, the stiffness matrix of the structure at each moment depends on the curvature of the structure at the crack position. The simulation results show that when the crack “breaths” the amplitude of the vibration of the beam is smaller than in the case of an open crack. This is a warning for crack detection by using the amplitude of the dynamic response when there is a breathing crack in the structure. The open and breathing cracks can be distinguished by monitoring the instantaneous frequency (IF) of the system using the wavelet spectrum. While the IF in the case of open cracks remains unchanged during vibration, it is varying when there is a presence of breathing cracks. It is interesting that peaks in the wavelet transform of the response used to determine crack positions in case of breathing crack(s) are much larger in comparison with the case of open crack(s). The cracks can be detected with a noise level up to 10% for the case of breathing cracks while it is only 5% for the case of open cracks [28]. These imply that the wavelet-based method for crack detection is much more efficient when breathing crack(s) are present in comparison with the case of open crack(s).