Research On Nonlinear Performance And Design Method Of Partially Prestressed Concrete Cable-stayed Bridge

China has the largest number of cable-stayed bridges in the world. Based on the mechanical characteristics of cable-stayed bridge systems, the partially prestressed design method is used to design the concrete cable-stayed bridge to achieve more reasonable forced state and ensure the structural safety. After making a comprehensive review on research status of partially prestressed concrete (PPC) structure, a segmental model test is made by taking the concrete material nonlinearity into consideration. Parametric study is conducted and a simplified method for PPC cable-stayed bridge design is presented. The main work is:(1) Partially prestressed design idea on concrete cable-stayed bridge is presented. It is shown that partially prestressed design can overcome some weak points of fully prestressed design, which especially suits cable-stayed bridges. The partially prestressed design can effectively reduce cable-stayed bridge pressure and bring cost savings without affecting the normal use and security.(2) The method of layered beam element with rigid arms is proposed to simulate the microscopic crack propagation in concrete. Following this, the material nonlinearity is in included in the model. The entire failure progress analysis of two RC beams under different pressure are performed and compared. Model validation with experimental data for a PC beam demonstrates that the proposed method can accurately simulate the material nonlinear behavior of concrete beams under different axial force. The proposed model can also track the structural response in the near-collapse stage without numerical difficulties by using a new numerical algorithm.(3) A segmental test design method is proposed for the concrete cable-stayed bridge. Segments with the greatest plastic deformation in the main beam are selected to reflect the system mechanical characteristics of cable-stayed bridges. No-stayed cable segments are used to eliminate the influence of boundary condition. The segmental model is supported by elastic bearings at ends. After calculating the length of no-stayed cable segments and the stiffness of elastic bearings, the internal force of control section and control cable is close to that of the actual bridge. Thus, the test goal is achieved that a model with combination of limited cables and beams can reflect the overall performance of the cable-stayed bridge on the premise of test accuracy.(4) An indoor PPC cable-stayed bridge segmental model test is carried out. After completing the beam design and manufacturing, desired bridge shape is achieved. The test under cyclic load is carried out within elastic range and with different crack width. Cracks are found to be stable and can be completely closed after unloading. It is found that there is still large loading capacity in the cracked structure and the stiffness reduction is not significant. After comparison of measured data and theoretical results, the correctness of the nonlinear calculation method is verified.(5) The redistribution of internal forces and parametric study in PPC cable-stayed bridges are conducted. The nonlinear performance is analyzed such as the bending moment increment and deflection at mid-span of concrete cable-stayed bridge. The parameter of post-prestressed reinforcement and non-prestressed reinforcement ratio is investigated. The crack propagation, carrying capacity of the structure, the trend and distribution of crack width with load growth are studied in detail. Results show that cable-stayed bridge after cracking undergoes significant redistribution of internal forces. Post-prestressing reduction can effectively reduce the compressive stress of concrete without reducing the carrying capacity. The post-prestressing level imposes small effect on the crack width. Through nonlinear analysis on three PC cable-stayed bridges with different spans, it is found that the larger the redistribution of internal forces, the larger the span. The carrying capacity is mainly controlled by strength of cables.(6)A design of PPC cable-stayed bridges based on the cracking control and simplified design is proposed. According to normal stress controlling conditions on the top and bottom of beam sections, this thesis uses stress balanced method to decide the reasonable finished dead state of the main beam of PPC cable-stayed bridge. After discussing many formulas for crack width, the thesis proposes that the allowable tensile stress on beams can be defined by the crack width at 0.1mm. Estimation and arrangement method of prestressed reinforcement and design procedure of PPC cable-stayed bridge are proposed. Finally, a simplified design and a demonstration example of PPC stayed bridge are presented.