Technology Research Of Reducing The Down Deflection Of Long Span Concrete Beam Bridge

Continuous rigid frame bridge have strong span ability, short construction period, structural lightweight and low construction cost advantages, much of the world architect’s good graces of all worlds. But after a dozen years or decades of operation, found a serious phenomenon of deflection across the large span prestressed concrete beam bridge, affect the use of bridge performance and structural safety, become a large span prestressed the development of concrete beam bridge a huge obstacle.In this paper, relay on Luo tian le bridge, the current creep as basis, innovatively explore the box girder cross section parameters, prestress degree and other factors with relationship between mid span long-term creep deflection, obtain structure long-term lower deflection decreased with the pivot beam height increased; with increasing degree of prestress, the control of the change of the pivot beam height to mid span lower deflection in more and more insignificant. Mid span lower deflection increase with the middle beam height decrease, increasing prestressed each beam corresponding mid span lower deflection is reduced, and may appear upper deflection phenomenon. Changes middle beam height impact structure long-term deflection is small, bottom thickness increases can reduce mid span long-term deflection, but the effect was not as good as increasing the fulcrum beam height, the fulcrum of the smaller floor by increasing the thickness of beam compete with to control the cross in the long-term deflection is not feasible, and the need to ensure that compete with the larger increase of the pivot beam floor thickness. Beam cross section in the vicinity of the increase of web thickness thinning area, cross the long-term deflection can be effectively reduced, and away from the beam cross-section of the web thickness after thinning is not too sensitive (eg, greater than60m later), and thus meet the requirements, and prestressed construction layout requirements under the premise of cross-section beams in the vicinity should try to reduce the web thickness, thinning region in the span of about60～80m or so. While the "zero moment theory" applied to reduce the prestressed concrete box girder rigid frame bridge span deflection of long-term, expand the "zero moment theory" application, but also for reducing prestressed concrete box girder rigid frame bridge mid span long-term deflection to find a new way.In reducing the large post-span prestressed concrete bridge span deflection after construction studies that:temporary cable-stayed bridge in process on the long-term deflection into little effect on the reduction of inter-and long-term no significant effect on deflection. Using technology to reduce long-term deflection of top temporary construction measures apply only to pier, the consolidation of the rigid frame bridge beams and piers greater resistance to push the stiffness, the effect is more obvious. And the main beam can effectively influence the shrinkage and creep, reducing concrete shrinkage and creep under the main beam due to torsion. If the main beam during the operational phase of principal stress to allow a further condition to balance the tendons caused by shrinkage and creep internal forces, the reduction would be more effective bridge deflection.Results of this study has reference for the prevention of long span prestressed concrete girder bridge main beam deflection.