A Study On The Finite Element Model Updating Method For Box-girder Bridges

The generic elements method can refine the finite element model not only at the model parameter level but also the model element pattern level by reversible transforming the element's eigenvalues directly,so that it can overcome the limitations of parameter correction and matrix element correction in the procedures of finite element model updating for the complex cross section structure models such as box girder bridges.The generic elements method can realize the conversion between different elements and maintain the element's degree of freedom,the symmetry of the element matrix,the positive definiteness of the mass matrix and the semi positive qualitative invariance of the stiffness matrix by correcting the parameters of the transformation matrix.In terms of damage identification,the generic elements method is used to identify structural damage degree through the change of the modified parameters.In view of the asymmetric damage of the box girder section,the generic elements method can realize the transition from the mechanical model of the bending torsional uncoupling to the mechanical model of the bending and torsion coupling during the correction process,so as to overcome the shortcomings of the stiffness reduction method,and can truly reflect the problem of the symmetry box section structure losing the symmetry of the section of the damaged part because of the damage.Thus,the experimental data can be fitted more reasonably.Based on the initial beam element model,the two stage model updating method is used to fit different types of damage of box girder members by modifying the parameters.The family element method has unique advantages for the box girder bridge model updating,and can be used for the calibration and damage identification of the box girder bridge finite element model.Based on the generic elements method,the following contents are mainly studied in this paper:(1)Based on beam element model,the finite element model updating of four degree of freedom and six degree of freedom non damage structural box girder is realized by generic element method,and the identification of complex section characteristics is realized.(2)Based on the generic element method,the two step model correction method is proposed for the damage box girder,and the finite element model of the box girder with different damage forms is corrected.At the same time,a method for identifying damage location of single position damage structure is proposed.(3)In this paper,some studies have done to analyze the relationship between the correction parameters and the damage degree and the location of the damage.From the study,a way to judge the degree of damage by modifying the parameters is provided.At the same time,the difference of the correction parameters between the two position damage and the single position damage is analyzed.(4)Considering the combination of the twisting mode and the bending mode of the structure which asymmetric damaged,This paper studies the method for the finite element model updating of the asymmetric damage structure by changing the eigenvector of the element matrix and modifying the specific parameters in the transformation matrix according to the generic elements method.The method is verified by finite element model updating for the box girder bridge with different damage forms.At the end of this paper,the number of elements needed to be corrected when the damage occurs at different position is studied for single span beam.