Research On Factors Of Long-term Deflection For Long-span PC Continuous Box-girder Bridge

According to the survey, the existing continuous girder bridges usually appear long-term midspan continued deflection and cracks on the box girders during the service period. And this phenomenon is more prominent in the long span continuous girder bridge. It not only affects the security and service life of the bridge during operation but also seriously restricts the pace towards long-span. At present, the causes of continued downwarp aren’t well understood, the effective measures for controlling deflection are still relatively little. So it is necessary to continue studying this respect at this stage.In this paper, based on the length orientation of Guangdong transportation hall"The Design and Construction Technique of Long-span Prestressing Concrete Continuous Bridge for Serviceability", the causes of long-term midspan continued deflection of long-span prestressed concrete continuous girder bridge are studied from three major respects which are theoretical analysis, numerical simulation analysis and the actual value contrastive analysis. The major contents and results are as follows:(1) This paper introduces the development and general damage of long-span prestressed concrete continuous girder bridge, and also the development, enhance mechanism and application to bridge of steel fiber concrete, describes the current situation of deflection of continuous beam (rigid frame) bridge at home and abroad, and also points out the problems that would be studied in the future.(2) Taking the Fushan Huayang Bridge as a research object, the finite element models are formatted, deformation factors are analysised about sensitive extent. The effect of concrete shrinkage and creep, prestressed effect, dead weight of structure, shear effect, the closure jacking force, conventional bars on deflection of main girder are investigated.(3) The study analyzes concrete strength and volume ratio of steel fiber on the short-term and long-term deformation of continuous girder bridge. Besides, it studies out four projects and analyzes deflection deformation properties of continuous girder bridge when different length ranges are added steel fibre. (4) By choosing related parameters, such as material properties and loading parameters which are obtained from the construction site, a finite element model is established to accurately simulate construction process. The variable regularity of the girder’s stress and deformation in different construction stages are getted. Then through the comparison of numerical results and monitoring measurement results, their changing tendency is in agreement qualitatively.The innovation of this paper lies in:①Selecting the second long-span continuous girder bridge that its span is168m, these factors, including shear effect, the closure jacking force, conventional bars, are introduced, and its affection on deflection is analyzed.②The study analyzes the affection on the short-term and long-term deformation which is brought by concrete strength and volume ratio of steel fiber. Besides, in order to compare deflection deformation properties and economic properties, four different plans are studyed out, and by comparison, the optimal is offered.This study conducts sensitivity analysis to these factors, which are very important to predict flexibility deformation during its construction and its service phase. Bsides, it discusses the effect of deformation properties by adding steel fiber. The research results can provide references for this kind of bridge system design and construction.