Shrinkage, Creep And Prestress Losses Analysis Method Considering Time Variation And Uncertainty For Concrete Bridge

Because of the strong crossing ability, big global stiffness, nice appearance, comfortably driving and low price, the application prospect of PC concrete bridge is better than other long span bridges. According to the incomplete statistics, the bridges which have built at home and abroad, concrete bridges are the largest share in the different bridge structures: there are concrete bridges which are more than 70% in Europe and the United States, and more than 90% in China. But more than 70% of the concrete bridges shows that excessive mid-span deflection and web cracking about 1/4L appeared in many bridges after served for few years, and that is the key question for controlling bridge development.The scholars at home and abroad found by disease analysis:shrinkage, creep, and prestress losses on concrete bridge are the main reasons. But related shrinkage and creep, prestress losses calculation methods at the present is not perfect, for the differences between the different methods are up to 30%. With the development of transport infrastructure, there is an urgent need to find new shrinkage, creep and prestress losses methods to resolve the practical engineering problems.This paper starts from further improving shrinkage, creep, and prestress losses calculation methods for concrete bridges. The systemic and in-depth research such as considering time variability and uncertainty of shrinkage and creep for concrete bridge, the interaction between shrinkage, creep and stress relaxation effect for the long-term prestress losses, and light-weight concrete bridge structure applied in engineering, are carried out.The main research results and innovations are as follows:(1) Firstly, the theory significance, the present development, the application background and research results of shrinkage, creep and prestress losses have obtained. Main insufficient and disadvantages of shrinkage and creep, prestress losses analysis methods be applied widely in concrete bridge are analyzed. Then the research contents and work achievement are introduced.(2) Shrinkage and creep analysis method considering time variation and uncertainty for concrete bridge. For determining time variation and uncertainty, which is the properties of shrinkage and creep of long span concrete bridge, the age-adjusting effective modulus method is promoted for the former and Latin Hypercube Sampling stochastic finite method for the latter. This is the method to account time variation and uncertainty of concrete bridge shrinkage and creep simultaneous. This method could be applied in finite program according to APDL parameter technology, age adjusting function of concrete elastic modulus which applied in ANSYS program and PDS statistical analysis module. Result of test and calculation shows that, measured value of shrinkage and creep for tested beam, and moment of three-span continuous girder bridge under which, fall in the middle range of calculation of this method. All of these indicate that the shrinkage and creep analysis method here is available. The calculation range by shrinkage and creep analysis method in this paper can take into account the multiple stress state on bridge, so the results ensure bridge structure more safely.(3) Long-time prestress losses analysis method of a concrete structure by shrinkage, creep and stress relaxation. There are time variation, uncertainty and interaction among concrete shrinkage, creep and prestress relaxation. So the balance equation of tendons and concrete stress, and the coordination reconfigumtion condition is promoted to analysis the time variation, Latin Hypercube Sampling method is promoted to analysis the uncertainty, to form a long-time prestress losses analysis method of concrete structure based on shrinkage, creep and prestress relaxation. The analysis shows that the measures result more than one year of prestress girder experimental model are located in the middle of calculated confidence interval in prestress losses, and the prestress losses analysis method of concrete structure is accurate and reliable.(4) Continuous rigid-frame bridge with density gradient concrete. Focusing on common existing issues of long span continuous rigid-frame bridge—excessive mid-span deflection and box girder cracks, this paper proposes a new continuous rigid-frame bridge with density gradient concrete as following:reducing the structure weight and optimizing the structural mechanical performance. The continuous rigid-frame bridge with density gradient concrete is composed of three types of concrete materials with different density. Those concrete materials are high-strength normal concrete in pier-beam consolidation, fiber-reinforced cracking-resisted high-strength semi-lightweight concrete between mid-span and pier-beam consolidation (about 1/4L), and high-strength lightweight aggregate concrete in mid-span. All the researches show that it is reasonable and reliable for mechanics performance of continuous rigid-frame bridge with density gradient concrete.(5) Shrinkage and creep effect of a continuous rigid-frame bridge with density gradient concrete is analyzed by shrinkage and creep analysis method considering time variation and uncertainty for concrete bridge. The analysis shows the bridge stress and deflection increase significantly in the first 3 years, and become stable after 3 years. The deflection increment and internal forces for certainty values by shrinkage and creep analysis method in this paper, are equal with the result of the age-adjusting effective modulus method. In the 95% confidence limits and 30 years, shrinkage and creep range interval is smaller, and the confidence limits larger by shrinkage and creep analysis method in this paper. So there is a high assurance for bridge safety. It is feasible in engineering applications for Shrinkage and creep analysis method considering time variation and uncertainty for concrete bridge.The research provides a theoretical basis for resolving mid-span deflection and web cracking about 1/4L appeared in many bridges.