Numerical cases of the use of natural frequencies to identify crack location and crack depth in beams under noise-free conditions have been widely reported. However, the capability of natural frequencies to identify cracks in noisy conditions has not yet been systematically addressed. Unlike previous work stressing the merits of natural frequencies in depicting cracks, this study reports the performance assessment of natural frequencies in characterizing cracks in noisy conditions. In the performance assessment, a cracked cantilever Timoshenko beam, with the crack flexibility modeled by fracture mechanics principles, is considered. The results demonstrate quantitatively and exhaustively that natural frequencies, as global dynamic properties of a structure, are somewhat insensitive to local slight damage. The outcome of this study provides a guideline for rational use of natural frequencies to identify cracks in actual beam-type structures
