Analysis On Oversize Deflection In The Girder For Long-span PC Bridges

With the development of pre-stress technology, the PC continuous rigid frame bridges with box-girders have been applied extensively in our country in the last years. However, many promblems have appeared during most construction or operational course of PC bridges with box-girders, especially oversize deflection in the girder and cracks in the webs. The appearances of these diseases exert extremely negative effect on the safety, endurance and normal using of the structure.Through analyzing the main girder's oversize deflection reason of large span prestressed concrete girder bridges both domestic and abroad, we know that the factors of the main girder's oversize deflection mainly relates to shrinkage and creep of concrete,effective prestress,longitudinal prestress efficiency of the main girders and etc. Beacause of shrinkage and creep deformation of concrete could also cause prestress loss, that, it can be considered that the main reason of the main girder's oversize deflection of large span prestressed concrete girder bridge is prestress loss.In this paper, based on referencing lots of documentation, the oversize deflection in the girder in the webs of the wide span bridges were analyzed in detail in view of prestress losses,shrinkage and creep of concrete,the variation of beam rigidity and temperature variation. And were simulated with three-dimensional finite element soft MIDAS under longitudinal and vertical prestress loss,shrinkage and creep of concrete,the variation of beam rigidity and temperature variation. By analying we knew that, the main factor that affacted oversize deflection in the girder was prestress loss. Construction stage's shrinkage and creep of concrete was the factor that affected oversize deflection in the girder after prestress loss, and the variation of beam rigidity and temperature variation were the less effect than prestress loss and shrinkage and creep of concrete. So prestress loss and shrinkage and creep of concrete were the main factors that affected oversize deflection in the girder.Theoretical calculation of pre-stress loss becomes more and more prefect with the prestress loss theory continually developing. But it is very difficult to be achieved precise result in actual calculations ,because pre-stress loss was affected by many factors, for example, the prestress loss because of shrinkage and creep of concrete related with not only the time but also each other, which were mutual restraints and interactive. So the real time monitoring and improving longstanding deformation prediction accuracy becomes particularly important.