Damage Detection Method For Bridges Based On The Wavelet Packet Energy Rate

The bridge structure could suffer inevitable damage during its service life. In order to detect damage more effectively and take prompt measures for the normal operation of the bridge, the structural damage identification technology is gaining more and more welcomed in the Civil Engineering, especially in the Bridge Engineering. The structural damage identification technology can locate the damage, make out the damage degree and estimate the residual life, which means great significance in ensuring the economic security and the safety of people's life and property. Thus, it's quite important to take steps to study the structural damage identification.The main content of the present work includes:1. The reason to select this title is introduced in the first part. The following part makes a summery of the application of various structural damage identification methods, especially the application of the wavelet analysis in civil engineering.2. Then the concept of the wavelet analysis is illustrated. Based on the wavelet analysis,the wavelet packet analysis is put out. The wavelet packet analysis performs better in that it could undergo decomposition of both the low frequency and high frequency of signals, thus it holds better time-frequency resolution. Then the sensitivity of the wavelet packet to structure damage is discussed. The wavelet packet energy is deduced and leads to the conclusion that the total energy of a signal can be attained by the summery of all the sub-band on a certain decomposition level. The wavelet packet energy ratio index is proposed, and the essential conditions and properties of wavelet basis functions is also listed.3. A simply supported beam is taken as object for damage identification. The process of proposed damage index method for damage identification is interpreted in detail, which includes a comparative analysis of the wavelet packet energy ratio index and a traditional index. The comentropy, adopted as cost function, together with the signal energy of some node to choose the best wavelet basis function and decomposition level. The unilateral confidence limit is adopted, combind with the values of damage indexes of each node. The result proves the wavelet packet energy ratio index to be more effective. The damage degree enveloping line and enveloping zone are put up to estimate the damage degree based on the numerical model. Then a tower structure is taken to carry out a damage experiment using the proposed damage index method, which validates the feasibility and applicability of the wavelet packet energy ratio index. Therefore, the damage degree is successfully estimated by combining the numerical model and the experimental model.4. The main girder of a cable-stayed bridge model is taken as object to undergo damage experiment. The wavelet packet energy ratio index is conducted by obtaining the signal energy of each node. It tells from the results that this damage index method performs not as well as in the simply supported beam test and the tower structure test, thus the feasibility of the damage index method is again discussed.At last,a summery is made on the main work this paper has done, and problems that need further study is put forward.