Construction Method of Prefabricated Beams in Houses

The construction method of prefabricated beams in houses is mainly divided into two major processes: on-site installation and in-factory production of prefabricated box girders. The specific steps are as follows:

I. On-site Installation Process

1. Surveying and Setting Out
   Mark the control line for the length of the prefabricated beam placement on the top of the prefabricated column, with an error strictly controlled within 10 millimeters to ensure precise positioning of the beam.

2. Erection of Support Frames

• Lay a 20-millimeter-thick wooden pad at the bottom of the support frame and use an adjustable base to adjust the height.
• The main material of the frame is 48-millimeter-diameter steel pipes, connected by couplings to form a stable structure; the main ledger uses steel pipes of the same specification, and the secondary ledger uses 50×100-millimeter square timbers to form a layered support system.
• The frame must have sufficient bearing capacity and undergo preloading tests to eliminate non-elastic deformation.

3. Lifting of Prefabricated Beams

• Use a lifting beam spreader as the lifting device and fix the hook to the preset lifting points on the prefabricated beam to ensure uniform force distribution.
• During lifting, slowly lower the hook and detach it after the beam is steadily placed on the support frame to avoid structural damage caused by impact.

4. Elevation Re-measurement and Adjustment

• Use a level gauge to re-measure the elevation of the prefabricated beam, allowing an error of ≤5 millimeters. If the error exceeds this range, adjust it using an adjustable base or shims.
• Install other beams sequentially and re-measure each one after installation to ensure overall elevation consistency.

II. In-factory Production Process of Prefabricated Box Girders

1. Preparation of Pedestals and Bottom Molds

• The pedestal is cast with reinforced concrete, and the bottom mold is made of stainless steel plates, with a preset camber according to design requirements (usually L/1000~L/3000, where L is the beam length).
• The pedestal is provided with tie rod reserved holes every 5 centimeters for template reinforcement.

2. Reinforcement and Template Construction

• The bottom and web reinforcements are bound and formed on a dedicated jig, and the corrugated pipes are fixed simultaneously with the reinforcements to ensure accurate positioning of the prestressed ducts.
• After the reinforcements are lifted to the template, use high-strength mortar blocks to control the thickness of the protective layer; the side and core templates are installed using a gantry crane, and adhesive tapes are pasted at the joints to prevent grout leakage.
• The top reinforcement is installed last, and the positioning of the anchor slot templates and embedded parts (such as expansion joint reinforcements and anti-collision guardrail reinforcements) is completed simultaneously.

3. Concrete Pouring and Curing

• Pour the concrete layer by layer from one end to the other, with a layer thickness of ≤30 centimeters. Use an external vibrator for the bottom and web, and an internal vibrator for the top and areas above the corrugated pipes.
• Immediately after pouring, activate the automatic spray curing system for a curing period of ≥7 days, and spray unique identification information on the surface of the beam.

4. Prestressing and Anchor Sealing

• After the concrete strength reaches 75% of the design strength and the age is ≥7 days, use intelligent tensioning equipment to symmetrically tension the prestressed steel strands in strict accordance with the design sequence.
• Immediately after tensioning, perform duct grouting (using a dedicated grouting material) and then seal the anchor and pour the end concrete.

5. Beam Removal and Storage

• The beam can be removed and transported only after the grout strength in the duct reaches ≥30 MPa. Use a dedicated beam transport vehicle for transportation, place wooden pads during stacking, with a stacking height of ≤2 layers, and a storage time of ≤3 months to avoid structural deformation caused by long-term stacking.