Study On Baseline Finite Element Modeling Of Long Span Cable-Stayed Railway Bridge With Three-Truss Main Girder

A precise finite element model (FEM) is important to facilitate the model-based tasks, including but not limited to seismic-and wind-resistant design, model validation and updating, damage identification and structural health monitoring. The initial finite element model, which fails to reflect the actual structure due to the ideal assumption and simplification, should be verified and updated. Using Anqing Yangtze River Railway Bridge, a triple truss four-line high speed cable-stayed railway bridge with its main span 580m, as the target, an initial FEM is constructed by using space modeling strategy, within which the sensitivity analysis of natural frequency to structural parameters is carried out. This thesis introduces the procedure of deck alignment test, cable tension test, and ambient vibration test. A baseline FEM is constructed by calibrating the initial FEM that is built based on blueprints. The constructed baseline FEM is the basis for obtaining static and dynamic responses and provides guidance for maintenance, safety assessment, structural health monitoring, and so on. This study has important theoretical significance and practical engineering value.The main conclusions are as follows:1. Methods and steps are detailed on determining the initial equilibrium configuration of long span cable-stayed bridge based on its blueprints. The result shows the initial equilibrium configuration can be obtained by defining the measured deck alignment as the main objective and the measured force the secondary objective.2. Sensitivity analysis of natural frequencies to structural parameters is carried out. Both elastic modulus and mass density of the structural components have an impact on the structural natural frequencies. For the first vertical natural frequency, elastic modulus of the cables is very sensitive. And for the first transverse natural frequency and the first torsional natural frequency, elastic modulus of the main truss is significantly sensitive.3. Initial deck alignment and cable force of this long span cable-stayed bridge are measured. Ambient vibration test is conducted. The modal parameters are identified by using both peak-picking (PP) method and stochastic subspace identification (SSI) method. The modal parameters identified independently by PP method and SSI method have an excellent agreement, which demonstrates that ambient vibration test can be able to efficiently extract the modal parameters of long span cable-stayed bridge.4. Some factors in finite element modeling of long span cable stayed bridge with three-truss main girder are discussed in detail, including the initial equilibrium configuration, cable sag, geometrical nonlinearities and simplifying orthotropic deck. The result shows the large deformation has a small effect on static analysis and the cable sag has a small effect on natural frequency but has larger effect on static analysis. The strategy that keeps the whole spatial configuration with orthotropic deck plate and simplifies U-rib and T-longitudinal beam enables to present a good performance to reflect the overall spatial behavior of orthotropic deck.5. The combination of the precise modeling strategy and measured data provides an effective way to construct a baseline FEM. With the aid of sensitivity analysis, adjusting some sensitive structural parameters leads to an excellent agreement between the model calculated and measured results. The updated FEM can be used as the baseline FEM of the Anqing Yangtze River Railway Bridge. This baseline FEM is the basis for obtaining static and dynamic responses and provides guidance for maintenance, safety assessment, structural health monitoring, and so on.