Static Behavior Analysis And Structural Improvemnt Of Expansion Device For Long-span Multi-pylon Cable-stayed Bridges

To deal with the excessive deformation caused by temperature, which beyond the reach of traditional expansion joint, engineers and experts, inspired by the operation principle of piston, conceived an idea of a new expansion device for long-span bridge. This expansion device, which composed mainly of small box-girder, a big box-sleeve, bearings and damping, can release a considerable axial displacement of main girder by the sliding bearing installed in one side of this device. The expansion device was initially designed and applied by T.Y.Lin International and soon adopted by a couple of foreign bridges. In the year of2013, the device was firstly and successfully installed in a domestic bridge named Jiashao Bridge.By taking the cable-stayed bridge with four towers, four cable planes and two bridge decks, which is a preliminary design for Qiongzhou Channel Bridge, as the research object, according to the design of the original expansion device adopted by Jiashao Bridge, this thesis assumed that an expansion device was installed in the main span of the bridge and analyzed the static behavior of the bridge under the temperature load via ANSYS, a kind of FEM software based on the theory of Finite Element Method, to verify the necessary of the device. There also was a study about the constrain form between the girder and the pylons. The best stiffness ratio of small box-girder to big box-sleeve had been discussed and the range of the ratio turned out to be about1/9to1/50.Besides, the improvement on the original expansion device was proposed in this thesis by identifying its transfer mechanism. The new structure resists moment and sharing force by support reaction instead of by the ribbed slab in the fixed end for connecting, which can ameliorate local stress concentration or a number of problems caused by it.The comparison research on working performance and structural performance of original and new expansion device concluded that the new one can release larger axial displacement of main girder and raise the distribution of stress to a more reasonable level from local stress concentration. In conclusion, the new structure of the expansion device could perfectly co-work with the main girder and keep itself from structure destruction and local buckling.