Research On Application Of Wavelet Method In Damage Identification Of Bridge Structures

Bridge is one of the vital parts of the traffic and transportation system. The healthy status of bridge structures is the premise for traffic and transportation system to operate normally. At present, some bridges appear aging, damage and crack, even breaking down collapses for some reasons, such as design, construction, management, natural disasters and so on. There are too many examples to cite individually. Thereby, it is of great significance in theory and practice to perform health monitoring for bridge structures.Structural damage identification techniques are the important components of health monitoring system of bridge structures. The vibration-based methods for the structural damage identification are the hot researches at home and abroad. Many theories and methods for damage identification have been presented, but the methods are inadequate, Considering the state-of-the-art and state-of-the-practice of the structural damage identification methods, the dissertation is devoted to the numerical simulation for the damage identification method of bridge structures by wavelet methods, and has obtained some useful suggestions.This dissertation includes six chapters as follows:In the first chapter, the background and significance of the dissertation are introduced firstly. Secondly, the development of damage identification and health monitoring for bridge structures is surveyed. And then the state-of-the-art of the structural damage identification methods at home and abroad based on vibration test is summarized in detail and reviewed briefly. Finally, the scope and major research work of this dissertation is expounded.The second chapter is related to the basic theories,some concepts and algorithm structures of wavelet methods, including multi-scale wavelet and wavelet packet.In the third chapter, a damage identification method for bridge structures based on wavelet packet analysis method is presented, and a series of identification index of structure damage are firstly proposed based-on wavelet packet node energy: 1) the square ratio index of energyδE_j~i(n) and curvature of square ratio index of energyδE_j~i(n)'' based-on WPCE. 2) the energy ratio indexα_j~i(n) and curvature of energy ratio indexα_j~i(n)'' based-on WPCE. The accuracy and feasibility of these index have been proved by numerical simulations and actual test made in laboratory both in sole damage and multi-damage identification. Meanwhile the quantity relation between these index and sole-damage level has been proved.In the fourth chapter, based on the multi-scale wavelet analysis, a early damage warning index is proposed which is suitable for the structural damage identification on-line, and a warning index is also firstly proposed based-on wavelet packet method and statistical concepts.In the fifth chapter, a new identification method of modal data based-on Morlet wavelet. For the inadequate accuracy of narrow frequencies, two methods to improve the accuracy of Morlet wavelet have been established. To delete or decrease the end effect of identification caused by time-frequency windows, a method of signal symmetrical extension is proposed, and effect of improvement is obviously observed by numerical examples.