1. If a corrugated pipe is used to form a hole, a thick plastic pipe should be inserted into the corrugated pipe before pouring (the outer diameter of the plastic pipe is slightly smaller than the inner diameter of the corrugated pipe). After pouring, the plastic pipe should be pulled out after the initial setting of concrete.

2. If a hole is made with a glue stick, pay attention to the sealing of the joint of the glue stick, and also grasp the time of pulling out.

Box girder construction scheme:

Take the standard construction of 20-meter box girder as an example

1 Processing of bottom plate and web reinforcement

1), storage and inspection of reinforcement

Steel bars are stored on special scaffolding and covered on the support above 0.5m from the ground. All kinds of steel

Ribs shall be marked and stored according to manufacturer, batch and type, and shall not be mixed.

2), steel processing:

Steel bar production is completed in the steel bar processing shed. Before steel bar setting-out, pay-off is carried out first, and then pay-off is carried out after being reviewed by technicians. The quantity, specification, length and quantity of reinforcement shall be indicated in the blanking sheet. Steel products and semi-finished products are stacked separately with complete marks. Cushions are stored in welded steel frames with a ground clearance of 750px. See Annex 2 for inspection methods and frequency of reinforcement processing and installation.

3), steel welding

When arc welding is used, the overlapping parts of two steel bars should be bent in advance to make the axes of the two steel bars consistent. The weld length of double-sided welding shall not be less than 5d+50px, and that of single-sided welding shall not be less than 10d+50px. The weld should be full to ensure the welding quality.

Do not cut off the steel bars that interfere with bellows, and make special-shaped steel bars according to the cross section of the beam.

The height and spacing of the diaphragm reinforcement shall be consistent, meet the design requirements, and ensure accurate alignment after installation.

4) Installation of bottom plate and web reinforcement

When box girder reinforcement is constructed, the bottom plate and web reinforcement shall be bound first. Before the bottom plate reinforcement is bound, tire molds shall be set at both ends of the bottom mold to control the position of the main reinforcement of the bottom plate. The main reinforcement spacing is 70mm, 70mm, 123mm and 100mm from outside to inside respectively. The welded joints of bottom reinforcement shall be staggered at the maximum bending moment of each hole as far as possible, and the joints of adjacent reinforcement shall be staggered for 35d.

After the installation of floor reinforcement is completed, vent holes are set according to the drawings, and PVC pipes with a diameter of 50mm are bound on the reinforcement skeleton. Both ends of PVC pipe are sealed, and the distance from the beam end is 6000px and 12250px respectively. The vent holes at both ends are symmetrically arranged, and each beam plate has four vent holes. PVC pipes are firmly bound on the low-plate steel bars, and the positions are correct. The pipes are filled with fine sand to avoid pipeline leakage and blockage when pouring concrete.

When binding the web reinforcement skeleton, the self-made fixture should be used to ensure the accurate spacing of reinforcement, and the stirrup joints should be staggered. All steel bar intersections should be firmly bound by tie wire, and the bound skeleton should have sufficient rigidity and stability to ensure that the position of reinforcement is not affected when concrete is vibrated. Every 1500px, a set of bottom plate sleeve reinforcement, and every 1500px, a set of web plate sleeve reinforcement.

Installation sequence of steel bars: first bind the bottom plate steel bar, then bind the web plate steel bar, set the prestressed pipe positioning steel bar, and wear corrugated pipe. Erect the side formwork and internal formwork of box girder, bind the roof steel bar after the acceptance of the supervision engineer, hang the roof steel bar for construction to ensure the steel bar is neat and consistent, and spot weld the roof shear bar on the roof sleeve steel bar in advance to ensure the same number and spacing.

5), the installation of the block

The cushion block adopts customized precast concrete cushion block, and the thickness of the cushion block is customized according to the drawing design, and the wire is embedded during prefabrication. The bottom cushion blocks are arranged in 6 quincunx shapes per square meter, and the bottom protective layer cushion blocks are arranged in two layers, one between the steel bar and the bottom die, and the other between the steel bar and the core die. The cushion blocks of the web protection layer shall be arranged in a quincunx shape with four blocks /m2, and the cushion blocks of the web protection layer shall also be arranged in two layers, one layer is arranged between the steel bar and the mandrel, and the other layer is arranged between the steel bar and the side formwork, all of which are firmly bound. The protective layer cushion block is supported on the outer steel bar of steel mesh, and the cushion block is firmly bound with the steel bar to prevent the concrete from falling off during vibrating. The thickness of the protective layer is set in strict accordance with the requirements of the design drawings. Net protective layer of top plate 100px, web plate 50px and bottom plate 75px.

2 Install bellows and reserve vent holes.

After the steel bar binding of the bottom plate and the web structure is completed, φ 8 steel bars shall be welded with bellows, and the steel bar grid shall be positioned according to the design requirements, and the steel bar grid shall be welded into a "well" shape. Strictly control the position of steel skeleton, set a curve segment every 1250px and a straight segment at 2500px, with accurate vertical and horizontal coordinates. The positioning steel tic-tac-toe frame is welded and fixed with the steel skeleton to prevent displacement during concrete pouring.

After the positioning tic-tac-toe frame is set, install bellows. Before installation, check the bellows one by one to ensure that there are no cracks and sundries in the pipeline. High-density polyethylene plastic corrugated pipe with an inner diameter of 50mm is adopted, and the pipe joint is connected with a larger corrugated pipe. The corrugated pipe joint is hammered flat at the corrugated pipe joint to prevent the corrugated pipe from turning over when passing through the steel strand, which will lead to pipe blockage in severe cases and make it difficult to pass through the steel bar. The connection length of the joint is 875px, and both ends are screwed symmetrically. Joints should be sealed to prevent cement slurry from entering the pipeline. Circular curve transition is adopted at the corner of corrugated pipe. In order to ensure the smooth flow of the pipeline and the accurate and firm position of the corrugated pipe, plastic pipes are added to the corrugated pipe and twitched during concrete pouring.

After the corrugated pipe is installed and positioned, the full-time quality inspector will conduct a comprehensive inspection in conjunction with the steel bars, and check the size of the steel skeleton of the bottom plate and the web plate, the spacing between the steel bars and the thickness of the protective layer; Check the bellows for holes, disconnection and deformation, and make adjustments at any time. After passing the inspection, report to the supervision engineer for inspection, and the formwork can be erected only after passing the inspection.

3. Install the mandrel and side form.

All prefabricated box girder formwork in this contract section adopts the shaped steel formwork specially made by the manufacturer according to the design drawings (the external formwork panel is the original flat plate with 6mm thickness). After the new template comes into play, try to assemble and remove rust, and then formally assemble the template. And ensure the correct sequence when splicing in the future. After the formal splicing is completed, the staggered joints of the formwork shall be polished and leveled to make the joints of the formwork transition smoothly. All formwork of box girder shall be painted with formwork paint before installation for demoulding.

Rubber pads consistent with the dental plate should be placed in the dental plate to prevent pulp leakage between the teeth.

The core mould is assembled by steel plates, and the inside is connected by angle steel ribbed bolts. Each joint is sealed with pull-back tape to prevent slurry leakage. After the installation is completed, adjust the elevation and size of the mandrel, and set a pressure bar at the top of the mandrel every 2 meters along the beam length direction to prevent the mandrel from floating up and moving, which will cause the inaccurate size of the bottom web. The compression bar consists of channel steel and fasteners. After pouring the roof concrete, dismantle the pressure bar and vibrate for the second time.

Adjustable legs are arranged below the side formwork to adjust the height of the side formwork. The top and bottom of the side formwork are supported by bolt holes along the beam length direction, and the bolt holes at the bottom correspond to the reserved holes of the bottom formwork support one by one. During installation, the left and right side forms are fixed with tie rod bolts through the reserved holes in the base, and a sponge strip slurry stop belt is inserted between the side forms and the bottom form to prevent slurry leakage. At the top, use φ 16 tie rod to pass through the steel pipe, and pull out and fasten the inner top. When demoulding, releasing the leg side form will automatically demould due to its own weight. According to the needs of construction, an attached vibrator is set on the side formwork to ensure the beam concrete is vibrated compactly.

After the formwork is installed, check the plane position, top elevation, node connection and vertical and horizontal stability to ensure that the formwork is not deformed, displaced or leaked during concrete pouring. When there is deviation beyond the allowable range, it should be adjusted in time. The joint between precast box girder and hollow slab core mould shall be sealed with pull-back adhesive tape. Effective measures should be taken to prevent the spindle from floating. The pressure bar to prevent the mandrel from floating should be tightened by the ground anchor and should not be directly fixed on the formwork.

Before installing the anchor pad, check whether its size is correct. The anchor pad shall be firmly installed on the end formwork, and the bolts of the positioning holes shall be tightened. The gasket should be strictly aligned with the channel and perpendicular to the end of the channel. Grouting holes of anchor pads shall be sealed with wooden plugs. The exposed part of the anchor pad outside the beam body should be sealed to prevent water, mud and other sundries from corroding the bellows.

4. Tie the roof reinforcement, and install negative bending moment, corrugated pipe and anchorage.

After the installation of side formwork and core formwork is completed, the top plate reinforcement shall be bound, and the top plate reinforcement and web reinforcement shall be bound one by one. The binding requirements are the same as those of the bottom plate and web reinforcement. The exposed steel bars of the wing plate are evenly spaced and the length meets the design requirements of the drawings. At the same time, negative bending moment bellows and anchors have constraints, and their requirements are the same as those of positive bending moment bellows and anchors. Install negative bending moment tensioning reserved groove template, the upper longitudinal main reinforcement at the reserved groove template is disconnected and bent upward, after negative bending moment tensioning grouting, adjust the reinforcement and weld it, and the reserved groove is tensioned and poured together with the wet joint.

The corrugated pipe with negative bending moment is spot-welded on the main reinforcement of the roof with U-shaped reinforcement to ensure the height accuracy of the corrugated pipe. The negative bending moment pipe penetrates into the PVC protection pipe to prevent the pipe from being deformed or blocked, and the two ends are exposed 250px. Before the initial setting of concrete, it shall be pulled out by special personnel to prevent pipe plugging. After the binding of roof reinforcement is completed, set the roof protective layer pad, and the thickness of the protective layer shall be controlled according to the drawing requirements, that is, 100px.

Check whether the position and quantity of embedded steel bars in bridge deck pavement are accurate. Check whether the corrugated pipe is straight, whether the anchorage is closely connected with the corrugated pipe, whether the grouting hole of the anchor pad is plugged with a cork, and whether the position of the reserved groove is accurate.

After the anchorage comes into play, check its factory certificate and quality certificate, and take samples for appearance, hardness and static load anchorage performance test. Only after passing the inspection and being confirmed by the supervision engineer can it be used.

Before installing the anchorage, check whether its size is correct, whether the anchorage model is consistent with the drawing, and whether the bell mouth of the anchor plate is blocked. During installation, the corrugated pipe is inserted into the anchor plate and sealed to prevent cement slurry from entering and blocking the pipeline. The position of spiral rib is accurate, the center is concentric with corrugated pipe, and the end is close to anchorage. The reinforcement under the anchor should be attached to the corrugated pipe and anchorage, and tied firmly.