Finite Element Baseline Model For Structural Health Monitoring System Of Long-span Cable-stayed Bridge

With the continuous development of design and construction technology in, bridge engineering, several long-span cable-stayed bridges have emerged. As its stiffness become more and more flexible, they are more sensitive to dynamic loads such as wind loading and earthquake effect. Therefore, the demand for structural health monitoring and damage detection on cable-stayed bridges are ever increasing, a finite element model for long-span cable-stayed bridge must be established to accurately reflect its actual operating state. Thus it can be adopted for the effective assessment on the structural health state of the bridge. Based on the static and dynamic test data for the bridge, finite element model updating was conducted on its corresponding initial finite element model. To ensure that the numerical analyzed results from the finite element model could agree with those from field measurement effectively, a finite element baseline model could be constructed for the following structural health monitoring procedure.Taking the long-term structural health monitoring for the Guangzhou Hedong Bridge as an example, the acceleration responses for the pretension cables and bridge decks for this bridge were measured under different types of excitation simultaneously and continuously. The system identification methods in both time and frequency domain are developed to obtain the pretension cable force and dynamic characteristic of bridge system. The SAP2000 API for MATLAB environment is investigated to explore the following finite element model updating on the full bridge. The main content included in this thesis are described in the following:Firstly, the identification on the pretension force for cables and dynamic characteristic of bridge decks were conducted by analysis on the long-term structural health monitoring data for Guangzhou Hedong Bridge. A MATLAB-based toolbox for identifying the fundamental frequency of pretension cables was developed; the theories of auto- and cross-spectral estimation method, stochastic subspace identification method and the wireless monitoring system were introduced in this thesis. The estimation of pretension forces in measured cables and the identification of dynamic characteristic(including the natural frequencies, mode shapes and damping ratios) of the first few vibration modes were extracted for the whole bridge. The identified results obtained from both time and frequency method is compared with those identified results from the operating modal analysis software(ARTeMIS) to testify the effectives of the proposed algorithms.Based on the information about the section physical properties and the construction drawings of Guangzhou Hedong Bridge, an initial SAP2000 finite element model was established. By updating and adjusting the critical physical parameters, the agreement between the numerical analyzed and actual deformation shapes of bridge, the numerical analyzed cable forces and those from field measurement almost reach. Therefore the finite element baseline model was finally obtained for this bridge by adopting the pretension force test.Modal analysis on the bridge was then conducted for the established finite element model, the natural frequencies and modal shapes for the first 20 vibration modes were then obtained. The effect of the different physical parameters(the type of elements for modeling cables in the finite element model, the elastic modulus, the boundary conditions and side piers, etc.) on the dynamic characteristic of the bridge were investigated. Several key physical parameters affecting the dynamic characteristics of the bridge were identified. These parameters could be used to construct the objective function, the sensitivity analysis and finite element model updating procedures for the bridge.Finally the comparisons of measured results with the corresponding numerical analyzed results were conducted, thus a finite element baseline model could be established for the structural health monitoring of the bridge. Meanwhile the structural parameter identification system PARIS was adopted to demonstrate its analyzed results for the finite element model updating on the UFC Bridge. By taking UFC bridge as an example, the theories of sensitivity analysis and structural optimization were investigated. The potential application of these theories into the finite element model updating on the baseline model of Hedong Bridge was discussed in the final section of this thesis.