Abstract: A method for identification of multiple cracks in beam-type structures is presented. The changes in nature frequency of the structure with various crack locations and depths are accurately obtained by means of wavelet finite element methods, and then the surface-fitting technique is employed to plot the surfaces of nature frequency shifts. The global cracked beam is divided into coarse mesh and the expressions relating changes in natural frequency and damage index matrix are formulated via an influence matrix. Damage index matrix can be solved by the resulting system of linear algebraic equations. The elements corresponding to the damage indexes with positive values are predicted to contain the crack. In each damage element, the corresponding natural frequency shifts are used as input in multiple cracks detection process and the crack locations and depths can be identified through finding the points of intersection of three frequency contour lines. Numerical exam-ple is employed to demonstrate the effectiveness of the pre-sented method.

Key words: Detection, Fault diagnosis, Multiple cracks, Wavelet finite element method