The Study On The Ultimate Strengrh Of Continous Girder Bridge Under Externally Prestressed Reinforcement

The technology of externally prestressed reinforcement is widely used in reinforcement for old bridge because of its convenient installation, safe structure and economical cost, after a few of service life there will be structure aging, reinforcement corrosion and low carrying capacity for large number of bridges, so we need to adopt external prestressed strengthening techniques. As we know, under the ultimate carrying capacity, a good performance of the bridge is very important, but most of exiting theoretical analysis and experimental researches are based on simple beam structure, and research for continuous beam bridge is very little, so there will be problem if model based on simple beam structure is applied to continuous beam bridge, a great deal of experimental analysis for which are also not practical. Therefore, under the ultimate carrying capacity adopting nonlinear FEA to analysis external prestressed strengthening technology is an effective method. This article is aimed to establish external prestressed strengthening model by commercial ANSYS and complete the study of the ultimate strength of structure.The study of external prestressing is different from internal bounded prestressing. Between the externally cable and the concrete points of contact only occur at deviators and anchorages, and anchorage point is incompatible with concrete strain, so hypothesis of plane sections can not be applied,and we need to analysis based on the overall balanceable condition. Our country introduced modifier formulas ruled by AASHTO-04,which is deduced from the directly proportional relationship of the the span centre deflection and limiting stress increment,and is also applied to continuous beams by the relationship between the number of the plastic hinge. This simplified method is partially rational, but the derivation process based on the simply supported beam model exits do not conform to the continuous girder bridge,so it can not be completely applied to continuous girder bridge calculation.First, this article analysis standard formula and find out the effect on the result in the simplified calculation in the derivation process of the formula,and gives an analysis on the loopholes when rormula is applied to the continuous beam bridge. Second, we will get differences of the calculation result between different formulas, so that we can verify the clarity, rationality and practicality of this article and get ready for the following content in the data.Third, finite element model is taken to analysis the different number of spans, contious beam with cross-section and variable cross-section and reinforcenment in different span to get the fitness of standard formula to the three condition,and put forward amendments according to the difference of solution to model and formula.At last, this article desigin 27 continous girder brider bridge under externally prestressed reinforcement, and use these ANSYS FEA modes to do the nonlinear analysis, we will study the effect on the the ultimate stress increment of externally prestressed tendons that ordinary steel reinforcement ratio, effective prestress and distance beween deviators and comparing with the formula solution to get the influence of the different parameter.. In the whole process, we systematically analysis the importance of the formula of ultimate stress to continuous beam bridge, and influence factors of limit stress of reinforced girder Bridges. So we know more about working performance of the external prestressed strengthening bridge, which give the reference for the improvement of external prestressed reinforcement design and the computing method of ultimate stress.