Rebar Design for Prefabricated Slab Houses

The rebar design for prefabricated slab houses should be comprehensively determined based on slab type, load, span, and relevant codes, with the core principles being to meet the requirements for load-bearing capacity, minimum rebar ratio, and structural details. The specific design points are as follows:

1. Design Principles

• Load-Bearing Capacity Requirements: The quantity of rebar should ensure that the prefabricated slab does not fail under tensile, shear, and bending forces. For example, a prefabricated slab with a span of 5.2 meters requires double-layer bidirectional rebar. The main rebar should be HRB400-grade deformed steel bars (diameter 10-12 mm, spacing 100-150 mm), and the distribution rebar should be 8-10 mm steel bars (spacing 150-200 mm).
• Minimum Rebar Ratio: The minimum rebar ratio for ordinary load-bearing rebar is usually 0.2%-0.45%, depending on the type of member and the concrete strength. For example, for a prefabricated slab in a rural self-built house that is 50 cm wide and 12 cm thick, the rebar ratio of the main rebar should meet the lower limit specified in the code.
• Structural Requirements: Distribution rebar, temperature rebar, and other structural rebar should be provided. For example, roofs or large-area floor slabs require temperature rebar to cover areas without negative rebar to resist thermal expansion and contraction stresses.

2. Typical Rebar Configurations for Prefabricated Slabs

• Prefabricated Hollow Slabs:
  • Load-Bearing Main Rebar: Located in the tensile zone at the bottom of the slab, usually consisting of 4-8 bars with a diameter of 6-12 mm (such as HPB300 or HRB400). For example, a hollow slab that is 1200 mm wide and has a span of 4 meters may be configured with 6 main rebar with a diameter of 8 mm.
  • Distribution Rebar: With a diameter of 6-8 mm and a spacing of 150-300 mm, arranged along the width of the slab.
  • Prestressed Rebar: If prestressing technology is used, 2-4 high-strength steel strands (diameter 9.5-15.2 mm) may be used to partially replace the load-bearing main rebar.
• Prefabricated Solid Slabs:
  • Bidirectional Load-Bearing Rebar: Arranged longitudinally and transversely, usually consisting of 6-10 bars per meter with a diameter of 8-12 mm. For example, for a standard residential slab (span ≤ 2 meters), the short-span slab uses 8 mm rebar with a spacing of 200 mm; when the span exceeds 2 meters, it is upgraded to 10 mm rebar with a spacing reduced to 180 mm.
  • Structural Rebar: With a diameter of 6-8 mm and a spacing of 200-300 mm, used to control cracks.

3. Rebar Configurations for Special Scenarios

• Seismic Design: Bidirectional crack-resistant rebar is added on the upper part of the composite layer, with a rebar ratio ≥ 0.1% and a spacing ≤ 200 mm.
• Opening Reinforcement: When the opening is > 300 mm, additional rebar should be added on each side of the opening, with a cross-sectional area ≥ 1/3 of the cut-off rebar. For example, around the reserved openings for air-conditioning pipes, ≥ 2 rebar with a diameter of 8 mm are often embedded, with an extension length exceeding 25 times the diameter.

4. Construction Precautions

• The rebar cover should be ≥ 15 mm to prevent corrosion; at the connection between the prefabricated slab and the beam, an anchorage length (≥ 30 times the rebar diameter) should be reserved.
• The acceptance criteria should refer to the "Code for Design of Concrete Structures" (GB50010) for load tests to ensure design safety.