Analysis Of Crack Cause And Method Of Consolidation Maintenance Of Prestressed Concrete Continuous Box-girder

With the increasing mature of constructing bridge technology, such as the high strength concrete, the high tensile reinforced steel bar and the prestressed force and so on, the long-span prestressed concrete continuous box-girder develop rapidly day after day in the recently short several dozens years. Along with the development of transportation enterprise, the prestressed concrete continuous box-girder has obtained widespread application in modern kinds of bridges since 60's in our country, and had completed successively in large numbers long-span bridges with the world standard. These completed bridges basically are designed according to the entire prestressed concrete component, which should not appear crack reasonably in the beam body under the normal use limiting condition, but actually the practical situation is opposite for many continuous box-girders. Therefore, we analyze and research the cause of typical crack which appears to the prestressed concrete continuous box-girder and we propose the scientific effective method of preventive and control and the method of consolidation maintenance, which have the significant realistic significance.Based on investigating and summarizing the cause of typical crack which appears in many long-span prestressed concrete continuous box-girders and the methods of consolidation maintenance, this article thoroughly studies the theory of beam section stress in prestressed concrete continuous box-girder, and emphatically from theory to practices, it studies the cause of typical crack and the design of structural consolidation maintenance and the method of construct of the bridges in Xiangtan. The main contents are:(1) According to the reports about the crack examination before consolidation maintenance and the static and dynamic load experiments about second Xiangjiang river bridges, the article discussed briefly the main quality problem of this bridge.(2) From the seven aspects(such as the stress characteristic of the box beam section, the dead load stress(stagnates effect including the box beam's shear hysteretic effect), the prestressed force, the temperature stress, the concrete shrinkage creep stress, the live load stress(including reverse, distortion), the calculation analysis of principal stress and so on), this article studies the calculation theory of the prestressed concrete continuous box beam section stress.(3) Then using the plane finite element method GQJS8.9, this article calculate and analyze the cause of typical crack of second Xiangjiang river bridge, specially for the longitudinal crack on down-deck of box beam, taking the solo directional board calculation theory as the foundation, establishes"the plane frame" model, induced the quite practical calculation formula for deck transverse direct stress, which proposes one simple and practical analysis method for the cause of box beam deck longitudinal crack. In this foundation, considering the faultiness of the criterion, the design theory and the constructing craft of continuous box-girder, it proposes the efficiency method to preventive and control crack.(4) Based on the stress mechanism, design calculation methods, construction craft, it discusses thoroughly several typical consolidation maintenance methods(fracture grouting method, external pre-stressed cable reinforcement method, glue steel reinforcement method, carbon fiber reinforcement method) of the second Xiangjiang River bridge, then pointes out its success and its deficiency.(5) Finally evaluates objectively consolidation effect according to the results contrast with static load and dynamic load experiments before and after consolidation construction, which indicates this consolidation methods are as a whole scientific and effective methods, it's one of typical models which synthetically use existing old bridge's consolidation technologies achievement, it has successful aspect and also has insufficiency aspect, and has widespread representation, has reality and the significance of using for reference undoubtedly for the consolidation maintenance of other same type bridges.