Study On Structural Dynamic Model Updating And Damage Detecting Based On Sensitivity Analysis

Updating initial finite element model by model updating technology based on the measured modal parameters can make full use of theoretical modal analysis and experimental modal analysis. The updated finite element model can reflect the dynamic characteristics of the structures more accurately and predict the dynamic response of the structures more reliably than the initial model. Combined with the measured results, it also can detect the damage and evaluate the condition of the structures. So structural model updating and damage detection are becoming the frontier research issues in civil engineering field.The first thing is to know the structural dynamic characteristic in order to predict structural response, control vibration, evaluate the damage state and monitor the health state. Structural dynamic parameters depend on structural parameters. Their theoretical values can be obtained by finite element analysis(FEA) while their measured values can be achieved by experiment modal analysis. Due to the damage of the structures among other influences, the large difference of structural dynamic parameters exists between their theoretical values and their measured values. The arisen problem is how to update the initial model to make the theoretical values close to the measured values. Up to now, there are several finite element model updating methods are proposed, such as matrix optimization updating method, submatrix model updating method, matrix updating method based on sensitivity anlysis, finite model updating method based on frequency response functions and model updating method via design parameters. The corresponding advantages of these methods are briefly discussed. Then model updating method via design parameters is chosen to be used in this thesis for model updating and damage detection because this method has the obvious physical meaning for damage detection.The ambient vibration test on a arched vierendal truss of RC aqueduct is the engineering background in this thesis. The results show that the updated element model can reflect the dynamic characteristics of the arched vierendal truss properly and it can serve as a benchmark for assessing the structural condition further. The shaking table test on a 12-storey reinforced concrete frame model is the experimental background in this thesis. This frame model is taken as the research object for further research. Firstly, corresponding vibration modes and frequencies of the first eight modes are extracted through modal analysis by the large commercial software ANSYS. Then the initial finite element model is updated by model updating method via design parameters based on sensitivity analysis and the benchmark model is established. Finally take the frequencies to simulate the damage information and take elastic moduli of the components to mark damage level and assume the elastic modulus reduction of one component and two components as the single-damage and multi-damage cases. Furthermore, the modal frequencies under each case are taken as the measured frequencies of damaged structure. The elastic moduli of the components are obtained through updating the damaged structure based on the benchmark finite element model. Comparing the updated moduli with the assumed values, the applicability of model updating method to detect the damage is verified. Damage detecting for the experimental frame structure under a loading case and comparison with the experimental results also prove the practicality of the model updating method for damage detection.The results in this thesis show that model updating method via design parameters based on sensitivity analysis is effective to update the model and it provides rapid convergence rate. For damage detection, this method is also effective, especially for those components with high sensitivity.