Prestressed tendon installation of cast-in-place concrete box girder with movable formwork
The cast-in-situ simple beam adopts spiral corrugated pipe to make holes. In order to prevent the corrugated pipe from being damaged during concrete pouring and vibrating, a polyethylene liner is placed inside the corrugated pipe. After the concrete is initially set, the polyethylene liner is taken out and then pre-prepared. Stress steel strands pass through the tube.
The spiral steel belt corrugated pipe is produced in batches by the coiling machine at the site. Each section is 10m long and the joint is connected by φ95 bellows. In order to prevent the joint from leaking when the concrete is poured, the joint is tightly wrapped with waterproof tape. After each batch of steel strands enters the construction site, they are routinely tested and their elastic modulus is determined. The steel wire cutting machine adopts a grinding wheel cutting machine, and it is strictly forbidden to use electric welding and gas cutting. After the length of the steel strands is designed according to the design (including the working length of the tension at both ends), the strands are first bundled into bundles. When the single root number is used, the ends of each steel strand are marked with different colors or different numbers. The spacing of the wire used for braiding is not more than 2m, so that the strands are straight, to prevent misalignment when the top tension is pulled, so that the strands are Winding in the tunnel, resulting in inaccurate prestress. When you put on the bundle, wrap the steel bundle in a round shape, pull it at one end, and feed it at one end.
According to the "prestressed tendon positioning net sitting table" provided by the design drawing, the coordinate system whose coordinate origin is set at the center of the beam bottom plate is converted into the coordinate system whose coordinate origin is set at the edge of the bottom plate, which is convenient to be along the bottom of the template. The side seam measures the position of the prestressing tendon in the vertical plane, and the position of the horizontal plane of the prestressing tendon is converted into the distance from the outer mould of the web.
The linear control of the bellows generally adopts beam end, mid-span, vertical starting point (horizontal starting point), and other five-section control. The control section is first welded to the steel frame by Φ16 threaded steel, then put on the bellows and steel strands, and then reinforced with positioning ribs at other locations. The spacing of the positioning ribs of the bellows shall not be greater than 1 m, and the positioning steel bars shall not be smaller than the Φ12 rebar, and the steel bars of the main frame are welded firmly. During the welding operation, the bellows below the solder joints are covered with wood to prevent the high temperature from burning the bellows.