Reinforcement of Prefabricated Slab Roof in Old Houses
The reinforcement of the prefabricated slab roof in old houses requires a combination of structural assessment and targeted measures. The specific methods are as follows:
1. Structural Safety Assessment and Foundation Treatment
First, a comprehensive structural safety assessment of the old house is necessary, with a focus on checking the crack width at the production site of the prefabricated slabs. If the crack width exceeds 0.3 millimeters, pressure grouting or structural adhesive repair should be used. At the same time, the connection status between the prefabricated slabs and the ring beams should be inspected. If the bolt corrosion rate exceeds 30%, they should be replaced with stainless steel or galvanized bolts to ensure connection reliability. This step is a prerequisite for reinforcement and can prevent reinforcement failure due to hidden defects.
2. Local Reinforcement with a Small Increase in Load
When the roof load increase is relatively small, carbon fiber sheets can be directly pasted on the bottom of the hollow slabs. Carbon fiber has the characteristics of high strength and light weight. By bonding with epoxy resin to form a composite structure, it can effectively improve the flexural bearing capacity of the slabs. During construction, ensure that the bottom of the slabs is clean and dry. The carbon fiber sheets should be fully laid along the slab span direction, with a lap length of not less than 200 millimeters, and a protective coating should be applied to prevent aging.
3. Adding Steel Beams to Change the Force System
If the load increase is relatively large or there is sufficient space at the bottom of the slabs, steel beams can be added at the bottom of the slabs. The newly added steel beams are connected to the walls through supports, converting the uniformly distributed load of the original slabs into concentrated loads and significantly reducing the mid-span bending moment of the slabs. H-section steel is recommended for the steel beams, and the section height should be determined according to the span calculation, generally not less than 200 millimeters. The recommended spacing between steel beams is 1.2 - 1.5 meters, aligned with the joints of the prefabricated slabs to avoid local stress concentration.
4. Slab Joint Treatment and Structural Strengthening
For the slab joint positions detected during the structural inspection, the original filling materials should be removed, and No. 6 deformed steel bars should be implanted (with a spacing of 150 - 200 millimeters), and then C30 fine aggregate concrete should be poured. This method can restore the load-transfer performance of the slab joints and prevent overall damage due to joint failure. In addition, constructional columns should be added at the four corners of the house, with a section size of 240×240 millimeters. No. 6 and No. 8 steel bars should be used for reinforcement, and they should be reliably connected to the floor slabs to form a space frame structure and enhance the lateral stiffness of the house.
5. Construction Preparation and Temporary Support
Before reinforcement construction, a temporary support system should be erected, with steel pipe supports set every 1.2 meters along the length of the prefabricated slabs. H-section steel beams should be used for support replacement at key nodes. The section of the steel beams should be not less than 200×200 millimeters, and they should be fixed to the walls through chemical anchors or expansion bolts to ensure the structural safety of the roof during construction. Before removing the supports, the load transfer of the newly added components should be completed to avoid secondary damage caused by improper unloading sequence.
