Structural-State-Assessment-Oriented Finite Element Modeling Of Long Span Bridge And Its Applications

The main purpose of this research is to study some basic problems in FE modeling and numerical simulation for structural state assessment of long span bridges. The strategies for an efficient state assessment oriented FE modeling are discussed, and the relative model updating theories and model verification method for developing the FE model is presented. The processes of simulation of structural dynamic response and fatigue damage in long span bridges are constructed. The main parts of the research are listed as follows:1. The properties of a structural-state-assessment-oriented FE model (SSAOM) is discussed, and the relative strategies for establishing the SSAOM is presented. To accurately compute the structural static response, the modal response and the dynamic response, an effective FE model of long span bridge for structural state assessment should nicely be developed. The SSAOM should be able to configure the structural arrangement, material properties and the connected conditions in a real bridge. An efficient method is adopted to simplify the FE model for improving calculation efficiency, in which the constructed geometrical anisotropic slab is simulated as material anisotropic plates, and the method of deciding the related material constants is devised. In order to reduce uncertainties in the process of establishing SSAOM, it also carefully simulates some important factors which include the initial configurations of the FE model, the initial stresses in main cables, hangers and the main girders, the connections between bridge tower and main girder, and the interaction between main girder and piers. As a case study, an FE model of the Tsing Ma Bridge (TMB) in Hong Kong is established for its state assessment.2. Some improvements on the traditional matrix and parameter updating method are obtained. With the aims of the general direct updating method, the perturbation factor of stiffness matrix is adopted into the updating process to preserve the symmetry and sparsity of the matrix and to keep the mechanical meanings of the updated model more expressly. Using the transformed matrix between the local vectors and the global ones, the correlation matrix of structural stiffness matrix with the updating parameters is given.Basing on the improved work, original research on multi-stage model updating method is presented. The kernel philosophy of the multi-stage model updating method is used to update a complicated FE model with multi steps, i.e. firstly localize the model errors and then update the error parameters. The structural model is meshed with substructures in which the member space configurations and the material properties could be simulated accurately. Correspondingly, the developed FE model is suitable to structural state assessment, and the computed D.O.F.s (Degree of freedoms) with the FE model could easily match with the measured ones. The perturbation matrix method and the local displacement correlation method are used to localize model errors. With the localized model errors, direct updating method, correlation matrix method and sensitivity analysis method are developedseparately to update the error parameters of the elements in substructure. Comparing with the computed results, it is shown that the error localization methods and the parameter updating methods developed here are fine. As a case study, the model of the Run Yang Nan-Cha suspension bridge tower is updated with the multi-stage model updating method. Comparing the updated FE model here with the updated model using traditional updating method, it could be concluded that the multi-stage updating method is more effective.3. Verification of the updated SSAOM of long span bridge is carried out. The FE model is validated with the measured and the corresponding processed information including static response (influence line), modal property data and dynamic response. As a case study, the SSAOM of the Tsing Ma Bridge is verified. The Results show that the developed Tsing Ma Bridge model could simulate the static response and dynamic response accurately.4. The dynamic responses of a long span bridge under traffic loadings are simulated with the established SSAOM, and the fatigue damage in the bridge is analyzed. The traffic loadings are applied to the FE model as moving loadings which vary with the traffic loading location, the loading magnitude and the loading velocity. As a case study, the dynamic responses of the Tsing Ma Bridge under railway loading and highway traffic loading are simulated. The simulated results illustrate that the dynamic stress in the bridge is linear and behaves locally, but the dynamic deflection is nonlinear and manifests wholly. With the damage equality principle, the innovative concept of effective traffic flow is set up, which could ascertain the loading cycles in the fatigue analysis of a real bridge under random traffic loadings. Using modified Miner's law with considering the effect of mean stress in the structure, the fatigue damage of the TMB is analyzed. The fatigue damage simulation results show that the stress magnitude in the members is reduced seriously during the accumulated wrecking in the bridge service time.