Research On Bridge Structure's Damage Detection And Assessment Based On Dynamic Testing

There are a great number of existing bridges with different degree of damages and defects which are becoming more and more serious. In order to ensure the safety of the bridges in service and decrease the total fee of maintenance and repair, detecting these bridge damages and assessing them in time becomes an important issue in bridge engineering field. Because of the convenience, fastness and being able to detect on line real time, bridge damage detection and assessment based on dynamic testing attracts much more attention. Based on the feature of bridge structures, some research work on dynamic damage detection and assessment has been done in the following:1. All kinds of damages of bridge structures are analyzed. The element damage parameterizing methods are discussed and the element modulus decreasing factor is selected as damage detection parameter in this thesis. The effects on natural vibration of bridge structure damage are analyzed by matrix perturbation theory. The first and second order perturbation formula of eigenvalue and eigenvector due to structure damage are directed. The changes of eigenvalue and eigenvector of typical structure as simply-supported beam, continuous beam and arch from typical damages are analyzed by numerical method. And the dynamic testing theory and methods commonly used in actural bridge testing is introduced. These analyses and introductions provide the experiential knowledge to dynamic damage detection and assessment.2. The boundary conditions of actural bridges are analyzed. The analytical formula and examples of actural bridge testing and calculation show that the change of boundary conditions has much more notable effects on natural vibration results than light structure damages. So that the change of boundary condition must be taken into account in dynamic bridge damage detection is put forward in this thesis. And the boundary condition parameters discernment method is established based on eigenvalue and eigenvector perturbation and least-square optimization theory. Then according to the damages of hanger in arch bridge, the hanger damage discernment method is put forward based on the boundary condition parameters discernment method. The discernment methods are both verified to be of well precision and less calculation effort through numerical examples. 3. According to the common bridge structure damages, after the beforehand detection of boundary condition parameters, the methods of firstly finding damage position then detecting damage degree and damage detection using parameters grouping are respectively set up. The former method adopts modal strain energy change ratio (MSECR) to detect the damage position to decrease the number of damage parameters, and the later decreases the number of damage parameters by parameter grouping and divides the parameter group into new small groups to realize the final damage detection. In both detection methods Marquardt form nonlinear least-square optimization algorithm or modified Powell direct optimization algorithm is used. According to the damage detection methods, the optimization arrangement of dynamic testing points is brought up. The program of the damage detection methods is developed based on Matlab program language, then author verifies that the methods are of fairly well precision with a continuous beam finite element modeling.4. As to the dynamic testing error of real bridge, the analytical method and the numerical calculation are respectively used to analyze the effects on damage detection results of dynamic testing error. The results show that the existing testing error decreases the damage detection precision, even causes wrong damage detection. So how to decrease the testing error in selecting dynamic testing facilities, testing methods and signal processing is introduced.5. The art of the state of bridge behavior assessment is introduced, and then the behavior assessment including safety, durability and practicality based on the damage detection methods are erected. And the direct performance assessment based on dynamic parameters is also tentatively discussed.6. At last, taking the 240m-span cable stayed bridge- Qianwei Minjiang Bridge as example, the dynamic testing results before and after the cable exchange engineering are used as damaged and undamaged dynamic parameters to detect and assess the cable damage. And the detection and assessment results of cable damage verify that the method can be initially applied to engineering practice.