Cast in situ construction of prestressed concrete continuous box girder
Content Introduction Urban overpasses, viaducts and approaches to large bridges are generally in dry land, and cast-in-situ casting with supports is widely used. The cast-in-situ casting of prestressed concrete continuous box girders is relatively simple, and most construction teams can widely use it. 1、 Construction method 1. Foundation treatment The foundation treatment method is determined according to the requirements of the box girder section size and the support type on the foundation. If the support span is large, the requirements on the foundation are high, and the foundation treatment form should be strengthened, otherwise it can be relatively weakened. Foundation treatment forms include ① foundation replacement and compaction; ② Concrete strip foundation; ③ Pile foundation plus concrete beam, etc. During foundation treatment, the drainage of the foundation shall be well done to prevent the impact of rainwater or water dripping during concrete pouring and curing on the foundation. 2. The supports used for the construction of concrete box girders are mainly ① assembled with universal rods; ② Composite system of strong strut, truss and I-beam; ③ Bailey piece assembly; ④ Light portal support; ⑤ Other steel wood composite structures. The type of support used must be determined according to the existing material and equipment conditions and engineering characteristics. At present, light door supports are widely used. The layout of the support shall be determined according to the beam section size and through calculation to ensure that the strength, stiffness and stability meet the requirements. In addition to the weight of the beam concrete, the weight of the formwork and support, the construction load (people, materials, machines, etc.), the wind force acting on the formwork and support, and other possible loads (such as snow load, guarantee facility load) shall also be considered during the calculation. The support shall be preloaded according to the requirements of the technical specifications to collect the deformation data of the support and foundation as the basis for setting the camber. When setting the camber, the influence of tensioning on the camber shall be considered. The camber is generally set as a quadratic parabola. Wooden wedges, sand cylinders, jacks, U-shaped jacking, etc. can be used as the unloading equipment of the support according to the support form, and the unloading equipment shall have sufficient strength.