Calculating Method For Design Of Externally Prestressed Concrete Bridges

Externally prestressed concrete bridges are developing rapidly with advantages of reliability, maintainability, economy and etc in their life cycles. Depending on the Guide Specifications for Design of Highway Externally Prestressed Concrete Bridges ("Guide Specifications" for short) supported by the constitution project of highway engineering standards of the Ministry of Communications of China and other related research projects, a series of model tests have been carried out, and a whole process analysis approach and a simplified calculating method have been developed in accordance with the imperfection related to the existing calculating method for designing of externally prestressed concrete bridges.Based on the prototypes of highway prestressed concrete bridge types in China, 18 flexural tests and 27 shear tests of monolithic and segmental simply-supported externally prestressed concrete model beams, 3 flexural tests of monolithic and segmental concrete continuous model beams have been done. The flexural and shear behaviors as well as the failure modes of these beams are investigated. The flexural and shear mechanisms as well as their variations vs testing parameters, and the regular pattern of internal force distribution in continuous beams are revealed. These tests provides basis for studying the whole process analysis approach and the simplified calculating method of externally prestressed concrete bridges, and also enriches testing achievements of externally prestressed concrete beams, especially segmental concrete beams.A complete whole process analysis approach for externally prestressed concrete bridges can be divided as three parts, the linear elastic analysis from the first construction stage to the final shaping stage of superstructures, transforming the final shaping state of linear analysis to initial state for nonlinear elastic analysis and finally, the nonlinear analysis from the initial state to the ultimate state. Based on the testing results and other research achievements, the effects of cracking and opening at joints in segmental beams are simulated by using a reinforced concrete beam element with variable cross-sections. Based on the whole process analysis approach established in the thesis, a computer program is compiled and verified by the testing results. Compared with other approaches and programs, the whole process analysis approach and the computer program developed by the author can show the working characteristics of structures at different stages and throughout.Considering effects of segmental joints and other major factors on flexural bearing capacity of externally prestressed concrete bridge beams, the regression formulas for the ultimate stress increment and the effective height of external prestressing tendons are set up on the basis of the flexural testing results and the analysis aided with the computer program, thus the simplified calculating formula of flexural bearing capacity is given. According to the shear testing results and the different shear failure modes from the tests, the simplified calculating formulas of shear bearing capacity for oblique sections and joint sections are also established by using regression analysis and theoretical analysis. The imperfection in the simplified calculating formulas of shear bearing capacity, especially for sections at joints of externally prestressed concrete bridges is overcomed. The reliability and rationality as well as usability of the calculating methods have been validated by the testing results and comparative analyses.