Study On Wind Stability Of Super Long-Span Cable-Stayed Bridge Under Construction

At present, With maturity and improvement of the bridge design theory, and the emergence of the new construction technology and new materials, the span of cable-stayed bridges becomes longer and longer, several cable-stayed bridge with span length beyond 1000 meters have been built, and also a few of super long-span cable-stayed bridges are being planned. With increasing of span length of cable-stayed bridges, structural stiffness and also stability are declined, and the construction time is also increased. During the construction period, the bridge structural system is constantly changed and the final state has not yet formed, less structural stiffness and larger structural displacements happen as compared to the bridge in completion, and the wind stability becomes worse. Therefore, the wind stability, which should be considered accurately in the design and construction process, is becoming an important factor affecting the development of cable-stayed bridges in future. To ensure the safety of bridge construction, the wind stability of the cable-stayed bridge under construction should be investigated comprehensively. In this dissertation, by taking the world's biggest long-span cable-stayed bridge-the Sutong Bridge over the Yangtze River as example, the wind stability of the whole process of its construction has been investigated numerically. The research results provide helpful guidance and valuable reference for the construction of the super long-span cable-stayed bridge.By using the computer programs including three-dimensional geometric nonlinear finite element analysis(GNFEA) based on the CR formulation, structural dynamic characteristic analysis(SDCA) based on the subspace iteration method, bridge structural nonlinear aerostatic analysis(BSNAA), and bridge structural flutter analysis(BSFA), structural dynamic characteristics, the aerostatic and aerodynamic stability for the bridge under construction and in completion are analyzed, and the evolutions of these mechanics properties during the whole construction period are also discussed. The results show that: with the progress of construction, (1) the natural frequencies decrease significantly in the early stages, and decrease slightly in the later stages. The vertical bending frequency increases remarkably as the temporary piers are set. In the later stages, there exists many lateral-torsional coupled modes; (2) the critical wind speed of aerostatic instability decreases monotonously, and the lowest critical wind speed appears at the maximum single cantilever stage; (3) the flutter critical wind speed decreases gradually, and the lowest flutter critical wind speed appears at the bridge in completion. The erection of the temporary piers in side spans and the completion of the side spans can improve the aerodynamic stability of the bridge under construction.