Creation of Openings in Prefabricated Floor Slabs of Houses

The creation of openings in prefabricated floor slabs of houses requires careful evaluation and the adoption of standardized measures, which should be comprehensively judged based on the floor slab type, opening location, size, and reinforcement methods.

1. Floor Slab Type and Adaptability to Opening Creation

Prefabricated slabs, due to the presence of slab joints and prestressed tendons, are prone to stress concentration when openings are created, necessitating a rigorous risk assessment. Prestressed multi-holed slabs, being thin-walled components, experience a significant reduction in load-bearing capacity when openings are made. If the requirements (such as opening location and size) are not met, a separate cast-in-place slab strip should be installed for pipeline installation. Arbitrary chiseling of through-holes from top to bottom is strictly prohibited.

2. Requirements for Opening Location and Size

1. Location Selection: Priority should be given to areas near beams, columns, or load-bearing walls, where the stress is relatively low, ensuring higher safety for opening creation. The central part of the floor slab or areas with larger spans are subject to concentrated stress, and opening creation in these areas may weaken the structural strength and should be avoided or strictly restricted.
2. Size Limitations:
   • Small-sized circular or square openings (e.g., with a diameter ≤ 300mm) have a relatively minor impact on the structure.
   • Large-sized or irregularly shaped openings are prone to causing stress concentration or insufficient stiffness of the floor slab and should be handled with caution.
   • The creation of openings in prestressed multi-holed slabs should comply with local technical guidelines (e.g., 2018 Yong DX-12), and arbitrary enlargement is prohibited.

3. Reinforcement Methods and Standard Requirements

1. For openings with a size ≤ 300mm and cut reinforcement ≤ 5%: No special reinforcement may be required, but it is essential to ensure that the reinforcement is not cut by the main tendons.
2. For openings with a size > 300mm and ≤ 1000mm and cut reinforcement ≤ 20%: It is recommended to adopt steel plate bonding or carbon fiber reinforcement, enhancing the local load-bearing capacity to compensate for structural losses.
3. For openings with a size > 1000mm or cut reinforcement > 20%: Section steel beams (such as H-section steel or I-beams) should be added at the edge of the opening. After being wedged tightly, adhesive or high-strength cement grout should be injected, and reliable anchoring with the supporting structure should be ensured to maintain overall stability.
4. Reinforcement of prestressed multi-holed slabs: Reference can be made to local technical guidelines, adopting methods such as reinforcement with configured steel bars, reinforcement with wire mesh followed by cement mortar coating to restore structural performance.

4. Construction Precautions

1. Before creating an opening, a reinforcement detector should be used to confirm the location of the reinforcement and avoid cutting the main tendons. The thickness of the floor slab should be measured, and existing damage (such as cracks or corrosion) should be inspected.
2. Arbitrary bonding or welding of section steel to the bottom of the slab is strictly prohibited due to mismatched stress mechanisms, difficult anchoring, and uncontrollable construction quality.
3. After reinforcement, the opening should be kept flat to avoid affecting usability, and professional personnel should operate to ensure safety.

5. Professional Evaluation and Load Re-calculation

Before creating an opening, a qualified structural engineer must conduct an evaluation, complying with standards such as the Code for Design of Building Structures (GB 50010). After opening creation, the load distribution of the floor slab should be re-calculated to ensure that the load-bearing capacity meets the design requirements.