Damage Identification Based On Dynamic Characteristics Of Structures Under Control

The research and the application of the diagnosing of the safety of structures have become the leading research problems in the constructional engineering. When a structure is damaged its mechanical strength will be reduced and the dynamic characteristics of the structure will be changed. Therefore, the damage of the structure can be detected by analyzing the variation of its dynamic properties.The paper aims on the modal parameter identification and the damage detection methods based on vibration data. Modal parameters of the structures are identified based on the input and output signals.Firstly, modal parameters and their identification methods are introduced. Theoretically, modal parameters can be obtained by solving the corresponding eigen equations. But, modal parameters of complex structures are usually identified by system identification theory in practice. The results of the two methods are compared in the paper. It shows that the lower orders modal parameters can be identified with high precision but the identification results of higher orders modal parameters are not satisfactory by the system identification method.Much work has been done in studying some new methods for the pole placement for the second order vibration system. The method using displacement and velocity feedback to assignment poles is general. But the method to assignment poles by acceleration feedback is more useful in practice. A lumped masses model and a cantilever beam are used to test the method. In the examples, the first benchmark model is founded by finite element method. Then the pole placement method is employed to place the poles of the structure so that the modal indictors are more sensitive to the damages than the corresponding uncontrolled structures.Modal parameters of the structure without control and under control are identified respectively for the assuming damage patterns. Two damage identification methods are used in the paper. In the first method model updating techniques are used to detect the damages in the lumped masses model with the frequency and mode data of the controlled and the uncontrolled structure. In the second method the linear estimation result of the sensitivity of the analytic solution is used. More frequency information from the controlled structure is used and the condition of the sensitivity matrix has been improved. So, the damaged position and the damaged degree can be detected more accurate.