Research On Structural Damage Identification Method By The Wavelet Transform Of Modal Pramaters

In engineering structures, there is a variety of damage which will cause disastrous consequences, not only threatening people's lives and security, but bringing about enormous losses of social wealth. The wavelet analysis has unique advantages in feature extraction, the singularity of signal detection, and signal denoising. Therefore, it is great significant theoretically and practically to use wavelet analysis to identify structural damage.The problem we have outlined in this paper deals greatly with the systematic study of a structural damage Identification method based on the wavelet transform of the modal parameters. Taking a simple-supported beam and one-story plane frame for example, the method based on the finite element mode theory for solving their dynamical parameters is presented. Through using the wavelet to transform the eigenvector of damage structure by wavelet singularity's detection theory, the theory to identify the location of crack of the damage structure is established, the deformation compatibility condition and internal forces equilibrium equation is given, and the method that identifies the location of crack through structure's modal parameters is discussed.Based on the wavelet transform of the vibration mode, a method to identify the damage location of a simple-supported beam is introduced. The crack location of the damage beam is identified by the maximum of wavelet coefficients. Then the influence of the identification of crack location under the multiple scales, different wavelets and different vibration mode are discussed. The Lipschitz exponent which is solved by the relation between the maximum of wavelet coefficients and scales is used to judge the extent of structural damage, the regulation of Lipschitz exponent with the crack depth, the crack location, other cracks, different vibration modes and different materials is discussed and the formulas for calculating the Lipschitz exponent are proposed under different factors, laying the foundation for further study on the extent of structural damage.The crack identification of a simple-supported beam and one-story plane frame is studied through the wavelet transform of rotation mode. The crack location of the simple-supported beam and plane frame is identified by the maximum of wavelet coefficients. The results of simulation experiments show that the singularity caused by geometric shapes can be avoided by the method, and it is more effective for crack identification.Continuous Wavelet Transform(CWT) is applied to the strain mode of the structure for the first time. The crack identification method based on the strain mode of the structure is established. And the wavelet denoising methods is used to denoise the wavelet coefficients of strain mode for the first time. Comparing the identification results before and after denoising, it is suggested that the maximum of wavelet coefficients only appears in the crack location after denoising.Taking advantage of the characteristics of curvature mode, the method based on wavelet transform of curvature mode to identify structural damage is presented. The influence of the identification of crack location under different wavelets is discussed. Comparing it with the results of structural damage identification by the wavelet transform of strain mode, it is found that the structural damage identification results of the two methods perform almost the same.