Finite Element Modeling And Updating Of Girder Bridge With Application To Its Condition Assessment

Modal deflection method based on operational modal analysis (OMA) under traffic excitation, not only combines the advantages of dynamic testing and static load testing, but also avoids the disadvantages of the lack of reliable theories and methods of dynamic testing and high costs of static load testing. On Tongyang Canal Bridge (TYCB) and Zhangjiagang Bridge (ZJGB), two prestressed concrete continuous box-girder bridges, this dissertation studies a feasible, effective and reliable method, modal deflection method based on OMA under traffic excitation, to bridge condition assessment. Its main contents are as follows:Using MSC.Patran, a well known finite element modeling software, the 3-D finite element models (FEM) of TYCB and ZJGB were constructed. Modeling methods and processes of constructing their FEMs, which basically reflect the actual static and dynamic behavior of TYCB and ZJGB, were discussed. The effect of bridge overlays, main bridge pier height, lateral guardrails and element division on the dynamic characteristics were also discussed.The mathematical model of dynamic FEM updating is generalized and transformed into a single-objective or multi-objective optimization problem, so the real?coded genetic algorithm (RGA) can be applied to FEM updating. Using modal frequencies and mode shapes, four evaluation metrics, natural frequency, MAC, modal flexibility matrix and deflection, are defined to evaluate the updated FEM. Thus different objective functions are defined with four evaluation metrics for FEM updating. On the FEMs of TYCB and ZJGB, the feasibility and superiority of RGA to FEM updating, are discussed based on defined objective functions. The updated FEMs of TYCB and ZJGB basically reflect their actual static and dynamic behavior, so their accurate mass-normalized experimental mode shapes can be obtained with their updated FEMs.The ways of getting mass?normalized experimental mode shapes based on mass changes in different points on the bridge were developed. Their accuracy of calculating the scaling factor were studied. The effect of mass changes and their placements to the scaling factor also were studied. A way of getting mass-normalized experimental mode shapes based on FEM was proposed and its concrete steps was presented. On static load testing, this dissertation also proposed a way of getting mass-normalized experimental mode shapes. Its feasibility and superiority, and the effect of static load testing to the scaling factor were studied.Some key issues of modal deflection method based on OMA under traffic excitation and applied to bridge condition assessment were studied based on the FEMs of TYCB and ZJGB. They include accuracy and reliability of transforming modal deflection into static deflection, the effect of the number of modal parameters to modal deflection, modal parameters of different types of mode shape to modal deflection, and the effect of vehicular traffic to modal deflection. On TYCB and ZJGB, getting their mass-normalized experimental mode shapes, calculating modal deflection by experimental modal parameters, comparing modal deflection with measured static deflection, this dissertation discussed the feasibility, effectivity and reliability of modal deflection method based on OMA under traffic excitation to bridge condition assessment. The effect of random errors of the experimental mode shapes to the errors of the modal deflections was also studied.