Steel Bar Layout for Prefabricated Houses

The steel bar layout of prefabricated slabs in prefabricated houses is typically designed based on the type of slab and its stress characteristics. The core principle is to arrange the steel bars in the tensile zone to enhance tensile capacity while meeting requirements for load-bearing, crack resistance, and durability.

1. Principle of Steel Bar Arrangement
   Concrete has high compressive strength but low tensile strength. The addition of steel bars significantly improves the structure's tensile performance. According to structural mechanics, a simply supported slab experiences maximum bending moment at the midspan under uniform load, with the bottom in tension. Therefore, steel bars are usually arranged at the bottom of the slab. For two-way slabs (with a length-to-width ratio close to 1:1), a two-way steel bar mesh needs to be arranged at the bottom to withstand bending moments in both directions.

2. Steel Bar Layout for Different Types of Prefabricated Slabs

   • Ordinary Prefabricated Slabs: Suitable for scenarios with smaller spans and lighter loads, steel bars are arranged in a single layer at the bottom, with a spacing generally ranging from 100 to 200 mm and a diameter of 6 to 12 mm.
   • Two-Way Slabs: When the length-to-width ratio is close to 1:1, a two-way steel bar mesh is configured at the bottom. The spacing and diameter of the steel bars need to be determined based on the design load.
   • Prestressed Prefabricated Slabs: By pre-applying tension to the steel bars, the crack resistance and load-bearing capacity are improved. The steel bars are still arranged in the tensile zone (bottom), with a spacing usually not exceeding 100 mm.
   • Prestressed Hollow Slabs: Only longitudinal load-bearing steel bars are configured, located at the bottom within the hollow section. The spacing is not greater than 100 mm, and there are no steel bars in the hollow area.

3. Construction Considerations

   • Cover Thickness: An adequate thickness of concrete cover is required around the steel bars, usually not less than 15 mm, to prevent steel bar corrosion.
   • Negative Bending Moment Steel Bars: At the slab ends and supports, additional steel bars may be required to resist negative bending moments (such as the tensile force when the slab corner curls upward).
   • Steel Bar Connection: The overlapping or welding of steel bars must comply with specifications to ensure reliable force transmission.

4. Material Selection

   • Steel Bars: Priority should be given to HRB400 or HRB500 hot-rolled ribbed steel bars, which have high yield strength and good ductility, enabling better adaptation to deformation.
   • Concrete: The strength grade should usually not be lower than C30 to ensure compressive capacity and bonding performance with the steel bars, avoiding debonding that could lead to structural failure.

The steel bar layout of prefabricated slabs must comprehensively consider structural type, load conditions, and material properties. Through scientific calculations, the diameter, spacing, and position of the steel bars are determined to ensure structural safety, durability, and cost-effectiveness.