Study On Appropriate Layout Of Pre-stressing Strands In PC Continuous Rigid Frame

With the development of highway, many large span bridges, including pre-stressing concrete continuous rigid frame bridges, are built at home and abroad. Especially in the west of China where V-shaped gorge is of the main terrain feature, such bridges are very appropriate. A series of similar problems of this kind of bridge exist, such as serious excessive deflection at the span centre and some local cracks in sternum. Started with the program of layout of strands, the problems of reasonable layout of pre-stressing strands and optimization design of pre-stressing force are discussed in this thesis. Take the symmetric three-span Buliuhe Bridge in the surrounding area of Longtan Reservoir in Guangxi and asymmetric four-span Buermen Bridge in the west of Hunan for instance. The problem of deflection at the span centre is discussed from the point of view of reasonable inner force distribution. The solid model of Buermen Bridge of which strands are laid in three directions is established in order to carry out the research on the principal tensile stress of sternum. The main content of research in the thesis is as followers:1. Advantages and disadvantages of several different programs on how to lay bars at present are analyzed.The problem of vertical pre-stressing force design of continuous rigid frame bridge is analyzed according to concrete strength criterion.2. The optimization design of pre-stressing force of the PC continuous rigid frame bridge and the coefficient optimization of low bended bars are discussed.3. The special braced construction model is founded based on Poweranalysis program. The deflection of Buliuhe Bridge and Buermen Bridge is further studied. By adjusting the size of different pre-stressing force to control permanent load inner force distribution of the superstructure in the bridge, and further analyze the effect of aging elastic deflection influenced by this inner force distribution during the process of bridge service. Take Buliuhe Bridge for example analyze different economic design project of pre-stressing strands.4. Take Buermen Bridge in the west of Hunan of which strands are laid in three directions for example, the calculation method using solid elements to simulate the construction process of the continuous rigid frame bridge is proposed, and the whole construction process has been simulated and calculated. As an assistant method, its validity and superiority have been proved, compared with the result of the other method using spatial beam element. Finally, the principal tensile stress of the sternum and its sensitivity toward the loss of vertical pre-stressing force at the phrase of construction are studied.