Study On The Design Technology For Externally Prestressed Continuous Rigid Frame Bridge

With a three-continuous-span of 75+130+75m, the Qijiang rigid-frame bridge, crossing over Qijiang River in Chongqing, is financially supported by the Ministry of Communications of China, for the first time, with the external prestessing technology in practice.Two 16.75m-wide bridges, symmetrizing the transverse direction, constitute the Qijiang Bridge. One is designed with internal and external prestressing, whereas the other is internal, the results of them have been compared between two breadth bridges to gain the differences. The external prestressing bridge is studied in this thesis. The external prestressing tendons are only for the stage after all internal prestressing tendons have been tensioned and grouted. The optimized aim for the internal and external is that all the internal prestressing only for the self-weight and the construction loads, while the external ones for all other loads. The prestressing alignment and the amount and the supererogatory tendons have been analyzed.The key location including turning zones, anchorage zones and the end of the sidespan for the external tendons replacement workplace have been designed and analyzed with finite element method, and the results have been introduced in. detail. After the optimized design and results estimated, the finial design and the achievement have been introduced.The internal prestressed bridge has three direction tendons: longitudinal, transverse and vertical while the external prestressed bridge no vertical one. They have a similar stress situation, for the optimized external prestressing could provid more effective shear resistance and flexural capacity, although the total weight of all the longitudinal prestressing tondons is smaller than the internal prestressing bridge. Being no vertical tendons, high quality concrete can be obtained and more tendons can be saved.The design results of this bridge prove that more labor and finance could be saved for the optimal external tendons with the special rate to internal tendons. More effective structure behaviors, less amount of tendons, higher quality concrete, and shorter construction time could be expected.