Reinforcement of Old Prefabricated Slab Houses
The reinforcement of old prefabricated slab houses requires selecting scientific solutions based on the degree of floor slab damage and functional requirements. Common reinforcement methods are as follows:
1. Carbon Fiber Sheet Bonding at the Bottom of the Slab
Suitable for residential or office buildings with fine cracks, slightly insufficient load-bearing capacity, and sensitivity to headroom. High-strength carbon fiber sheets are bonded along the span direction at the bottom of the slab to enhance flexural load-bearing capacity and inhibit crack development. Advantages: Convenient construction, no increase in self-weight; Disadvantages: Limited improvement in stiffness, requiring attention to fire protection (carbon fiber has poor fire resistance). If there are large concentrated loads, anti-shear U-shaped hoop sheets should be used as supplementary reinforcement.
2. Steel Plate Bonding at the Bottom of the Slab
Thin steel plates 3-6mm thick are bonded to the bottom of the slab using structural adhesive, sharing the load with the original floor slab. Steel plates have a high modulus of elasticity, significantly improving slab stiffness, reducing vibration and deflection, and are suitable for places with high performance requirements such as libraries and computer rooms. Construction Points: Rust removal and drilling of the steel plates (also serving as adhesive injection and air exhaust holes) are required, along with proper anti-corrosion and fire-resistant coatings.
3. Adding Steel Beam Supports
When the floor slab is severely damaged or requires a substantial increase in load-bearing capacity, H-shaped or I-shaped steel beams can be added beneath the slab, fixed to walls or columns using chemical anchors or rebar planting. This method causes minimal disturbance to the original structure, is suitable for decorated houses where construction from above is not possible, and can be flexibly arranged in local heavy-load areas. Construction Preparation: A temporary support system needs to be erected, with steel pipe supports placed every 1.2 meters along the length of the prefabricated slab. Key nodes should use H-shaped steel beams for support, with beam sections not less than 200*200mm.
4. Overlay Reinforcement Layer (Post-Cast Layer) on the Slab Surface
Remove the original slab surface leveling layer, roughen the concrete surface, and apply an interface agent. Then, lay a bidirectional steel mesh and pour 40-80mm thick high-strength fine aggregate concrete or polymer mortar. This method can simultaneously improve load-bearing capacity and stiffness, solve waterproofing and pipeline embedding issues, but will reduce indoor headroom. The impact of the added self-weight on the lower structure needs to be evaluated.
5. Crack Repair and Local Strengthening
Non-structural cracks (width <0.3mm) should be sealed using epoxy resin pressure grouting; areas with local concrete spalling or exposed rebar should be derusted, coated with rust inhibitors, and then restored with high-strength repair mortar. This is an auxiliary measure often used in conjunction with other reinforcement methods.
6. Enhancing the Integrity of Prefabricated Slabs
For prefabricated hollow slabs, the following measures can be taken to improve integrity and seismic resistance: chiseling grooves at slab joints, implanting tie bars, and pouring fine aggregate concrete to form a "post-cast strip"; adding angle steel or concrete edge beams at slab ends to prevent slippage and detachment; uniformly casting a steel mesh fine aggregate concrete layer on the slab surface to connect all slabs into a whole.
A comprehensive structural safety assessment must be conducted before reinforcement, focusing on checking the crack width at the production area of the prefabricated slabs (special treatment is required if exceeding 0.3mm) and the connection status between the prefabricated slabs and the ring beams (bolts with a rust rate exceeding 30% need to be replaced).
