Study On The Theory And Method Of Vibration Based Structure Damage Identification

The Structures are exposed to various external loads such as hurricanes and earthquakes during their lifetime. The damage accumulates, which may lead to catastrophic failures causing costly repair or heavy loss of human lives. Consequently, the structure damage identification using the changes of their vibration characteristics has become a hot research topic throughout the civil, mechanical and aerospace engineering communities.Various damage identification methods based on changes of vibration characteristics are summarized. These methods can be classified as two categories. One is the damage index method, the other is the inverse method based on the model updating technology. The basis ideas and feature of these methods are described, and their limitations are discussed.Considering the feature that natural frequencies of structures are easy to measure with relative high accuracy, a damage identification method of truss structures by Stubbs et al is improved. The damage ratio of the element stiffness matrix can be inversed by the changes of the frequencies. A progressive algorithm is presented to reduce the error when the damage is relatively large.Base on the method mentioned above, a two-step damage identification method of frame structures based on the changes of frequency is presented. First, the location of damage is estimated. Then, the stiffness matrix of the suspicious damaged elements is decomposed to the compressing stiffness matrix and the bending stiffness matrix, the damage ratios of them are calculated respectively. The damage ratio of the area and moment of inertia in the section of the damaged element can be quantified using this method.The structural damage identification based on the minimum rank method is studied. Three limitations of the minimum rank method are discussed. First, the stiffness perturbation matrix calculated by the minimum rank method does not preserve the symmetry. Second, the calculated stiffness matrix does not preserve thesame sparsity (the zero/nonzero pattern of the matrix) as the original stiffness matrix. Third, the rank of the perturbation matrix is always equal to the number of modes used in the computation of the modal force error. Some improvement is presented to solve these problems.Finally, the numerical simulation of the damage identification is given on an offshore platform using the method presented in this paper.