Mechanical Behaviors Of Asymmetric Extradosed Cable-stayed Bridge With Single Tower And Double Spans

The extradosed cable-stayed bridge, which is composed by the main girder, stay cable and tower, is a kind of composite structure. The girder is designed as a flexural element, while the stay cables act as the tension member and the tower bears compressive load. Most of the external loads on the deck is carried by girder, and the rest is carried by the stay cables, all of the loads is transferred to the ground through the tower and the pier. The loads carried by girder are partly reduced with the support of stay cables, which improves the bearing capacity and the safety of the structure. The analyses on mechanical behavior of this kind of bridges are very difficult due to the numerous combinations of construction members whose functions are quite different as well as it’s statically indeterminate structure. Besides, how to determine the stiffness of each structural member becomes another key issue for designers who have to face with. To solve this problem, a large amount of researches is done by scholars both at home and abroad. But most of the research works focuses on the numerical analysis of a specific bridge, which can only reach an individual conclusion that helps rarely for designers.In this paper, based on the assumption that the tension force in each cable is the same and it could be seemed as a filmy tension force, several analytical solutions are derived by using the Ritz Method, which include the equivalent membrane tension of the stay cable, the cable force ratio of long span and short span as well as the main girder deflection. The analytical solutions is validated by the finite element results via software MIDAS/CIVIL. Furthermore, the error analysis and error correction are done at the aim of meeting the requirement of precision. The analytical solutions can help designers to understand the cooperation mechanical behaviors of this kind of bridge.Secondly, the parametric investigation of single-tower asymmetric extradosed cable-stayed bridge is studied by using the derived formulations. The result can be applied to reveal the influence of different design parameters to the structural mechanical behaviors of the bridge, as well as to help designers draft reasonable structure parameters during the period of conceptual design. Besides, the effect of member stiffness on the structure is also discussed in this paper. By changing the stiffness of girder, cables and tower, we can know how the stiffness parameter of different components influences the internal force and the deflection of the girder. And the stiffness ratio of different members also has a effect on the whole structure, which is also studied to make us understand extradosed cable-stayed bridge better.In a word, the results of this thesis give an insight into mechanic essence of extradosed cable-stayed bridge, and can help designers draft design parameters conveniently and efficiently.