Single and Multiple Crack Detection in Simply-Supported Beams Using SWT

Any crack in a beam-like structure creates a local reduction in the stiffness which in turn, affects the dynamics of the structure. This local reduction in stiffness generates small discontinuities in the modal displacements of the beam at the crack locations. However, these discontinuities cannot be visually observed in the modal displacement plots. Therefore, the identification of cracks is performed by decomposing the modal displacements using the stationary wavelet transform (SWT). This paper investigates identification of multiple cracks in simply-supported beams using the SWT. The SWT decomposes a signal into two components that are known as the detail and the approximate coefficients. These coefficients can be viewed as the results of passing the signal through low-pass and high-pass filters. The approximate coefficient gives the low frequency components of the signal which in this case is the overall shape of the signal (mode shapes) and the detail coefficient gives the high frequency components of the signal which in this case contains any high frequency noise or effects of small structural discontinuities present in the signal. The detail coefficients of the SWT detect the existence of cracks by showing high values at the crack locations. The method presented can detect both single and multiple symmetric and non-symmetric cracks with high accuracy in beam-like structures. The modal displacement data of the cracked simply supported beams used are obtained from the finite element method. The results are validated experimentally.