Study On Damage Identification Method Of Bridge Structures Based On Wavelet Analysis And Fractal Theory

The damage of bridge structures will inevitably appear during the course of their lifetime due to the performance degradation and external factors. Once the damage occurs, it will lead to significant casualties, and have a very bad influence on the long-term stability of our society and country. In order to nip the damage in the bud, and to avoid bridge accidents, It is very necessary to further study the bridge damage detection method and explore a simple,easy and effective identification method to monitor the health of bridge structures. In addition, it has far-reaching research and engineering value.This paper mainly studies on the vibration-based damage identification of bridge structures(damage location). And the fractal theory and wavelet anslysis are used to process the signals. The contents are as follows:Firstly, A fractal theory-based index for damage localization is proposed for bridge structures. The presence of damage will inevitably lead to the increasing of irregularity degree of the vibration mode in the damage location. What's more, The irregularity degree can be quantitativley described by the Katz fractal dimension. By shifting the sliding window along the modal curve, the fractal dimensions of different points can be measured, Comparision the fractal dimensions of damaged and undamaged bridge structures, the damage location will be identified. Different damage locations?degrees and multi-cracks are considerd to provide the effectiveness of the index.Secondly, the wavelet analysis tool is introduced to the study. The structural responses under impact excitation are decomposed into different sub-bands with separation of different modal responses by the multi-resolution analysis of discrete wavelet transforms. Then two different damage indexs based on the basis vibration mode are defined and used to identify the damage location. An example of a simply supported beam bridge model is used to show that the proposed indexs can examine the damage location correctly and effectively, and the experiment results are well agreed with the numerical simulation results.Finally, Considering both wavelet energy and flexibility curvature are very sensitive to local structural damage. a new damage index based on discrete wavelet decomposition and modal flexibility analysis is presented. Through numerical analysis and experiments of a two-span continuous beam,and by compared with the the damage index of relative energy curvature difference, the results show that the method is more effective.