Research On Structural Damage Diagnosis By Wavelet Analysis

Wavelet analysis is a new time-frequency analysis method which has raised a research upsurge internationally in recent years. It is regarded as a breakthrough of Fourier Analysis. Damage diagnosis technique is an active research domain in cunent structure engineering and has strong engineering background. The correlative theory and technology are developing continuously. This thesis is concentrated on the research of the damage detection method by wavelet transform. The main subjects are summarized as follows:A wavelet-based approach is proposed for crack identification in beam structure by the singularity's detection. The fundamental vibration mode of a cracked simple-supported beam and the displacement of the middle of the beam under mobile force are analyzed using continuous wavelet transform by Mexican Hat wavelet. The position of the crack is located by the maximum modulus of the wavelet coefficients. The Lipschitzs exponent estimated by the wavelet coefficients is used as a useful indicator of the crack depth, which decays with the increase of crack depth. The influence of the crack location, the sampling distance of the vibration mode and the velocity of moving load to lipschitzs exponent are discussed. It is testified that this method is also in effect to noisy data. The position of the stiffness decline caused by the damage is also detected by this method. The validity of the proposed method is investigated both by analysis and simulations.The component energy in different frequency bands gained by wavelet packet decomposing which is sensitive to damage is used as damage index. A series of vibration test on a reinforced concrete beam under different damage degree are finished. The damage degree is recognized by the wavelet packet decomposing of the response signal collected in vibration test.The transient parameters are distilled by the compound wavelet transform of the vibration signal. The impulse response of the linear and non-linear viscous damping system is analysed by Morlet wavelet. The transient frequencies and amplitude are obtained from the ridges of the wavelet transform. So the parameters of the system are identified. The method is illustrated by three simulated example.