Key Construction Techniques Of Cast-in-situ Box Girders And Precast Box Girders

With advantages such as good integrality, large stiffness, comfortable driving condition and complex structures easy to make, pre-stressed concrete continuous box girders cast-in-place has been widely used in overpass bridges, interchange bridges and curved bridges. Precast box girders also have many advantages like standard production, saving formwork cost, accelerating the construction speed and reducing influence on structures by shrinkage and creep. In the flourishing development period of transportation cause, it must receive good economic and social profits to popularize this type of structure.However, there are problems and insufficiencies in the constructions and using of the two types of bridges aforesaid. In order to solve part of the problems in the construction of both the box girders cast-in-situ and constructed by simple and continuous support which were widely used for the small and medium span bridge at home and abroad, the key techniques both in the construction of cast-in-situ box and in the process of precasting box girder were summarized on the background of two bridges. The main contents were as follows:(1) Combined with the construction of the cast-in-situ box girder in south of Liu-he interchange overpass, research on key techniques about the plan of foundation treatment for full space support, the design and construction of the supporting system were carried out.(2) Combined with the construction process of cast-in-situ box girder, and the construction technology of pres-tress system, key steps causing quality descending of concrete were analyzed. And Countermeasures to control quality of box girders were put forward.(3) According to the characteristics of the box girder constructed by simple and continuous support, the theory and regulations of the inverted pre-camber for the precast box girder were summarized, and the method of setting the construction inverted pre-camber which was applicable to the structure system of the precast box girder was given. Meanwhile, in order to find out the reasons for the phenomenon that there was large difference between the actual arch camber and the designed arch camber, the key factors influencing cambers of precast box girders were analyzed, through the contrast of theoretical calculations and the actual situation of the construction. And corresponding Countermeasures were proposed.(4) According to the phenomenon that the precast box girder might has "three legs" during storage, lifting and other process, analysis was made by using 3-D finite element model, and the torsion on the impact of the structural performance was studied to ensure the safety of the precast box girders during construction process. The key construction techniques of continuous cast-in-situ prestressed concrete box girders and the precast box girders were introduced in this paper, and they were better applied in practical projects, also can serve as certain reference for projects of the same kind.