Research On Shrinkage And Creep Effects Of Continuous Concrete Box Girder Bridge Transformming From Simply-supported Bridge

The construction method of transforming simply-supported bridge into continuous girders bridge has been developed from span of 20～30m at earlier time to 50～70m, and the length of span is still increasing are becoming longer. In the past,the massive concrete used in irrigation works has been applied in structural engineering field and be used much more often in bridge engineering. Since shrinkage and creep are inherent material properties of concrete, the accurate estimation of the effect of shrinkage and creep on bridge construction is important for design, construction and monitoring of bridges.Based on the 70m box girder of Hangzhou Bay Trans-ocean Bridge and 60m box girder of Xiangshan Harbor highway Bridge, the thesis studied the necessity and timing of low strength tensioning, the influence of secondary tensioning as well as the effect of secondary tensioning on shrinkage and creep. And then it studied the effect of shrinkage and creep on linear shape and internal force of the bridge as both simply supported system and continuous system. Besides, it studied the cracks in the wet-joint concrete due to concrete shrinkage and creep.Then, this thesis has researched on the variation of temperature and stress of box girder from initial setting to final setting stage. In this process, it is found that tensile stress exceeds the tensile strength of concrete. According to the stress, elastic modulus and strength development, the tensioning timing and value of tensioning force are recommended to avoid the incident of exceeding tensile stress.Then it studied the bridges under different structural system during construction through the finite element analysis.It is found that the secondary tensioning doesn't influence the alignment and internal force of the box bridge. In addition, the stress and displacement will be changed under the effects of shrinkage and creep. The box girder's stress has been changed much less in simply supported system than in continuous system. Both of the stress and alignment variation are large in continuous system under the effects of shrinkage and creep.At last, it studied the stress of wet connector used for the transformation from simply-supported into continuous girders bridge. The significant tensile stress appeared at the inside of the wet-connector which exceeds the concrete tensile strength and will result in the crack.