What is #4 Rebar?
Rebar (reinforcing steel) designated as #4 refers to its size in the U.S. numbering system, where the number corresponds to the diameter in 1/8-inch increments.
- Diameter: 4/8 inch = 0.5 inches (12.7 mm).
- Cross-sectional Area: 0.20 in² (129 mm²).
- Weight: ~0.668 lbs per foot (0.996 kg/m).
Key Grades for #4 Rebar
Rebar grades indicate yield strength (measured in ksi or MPa):
- Grade 40 (ASTM A615):
- Yield strength: 40 ksi (275 MPa).
- Low strength, used in light-duty applications.
- Grade 60 (ASTM A615/A706):
- Yield strength: 60 ksi (415 MPa).
- Most common for structural concrete (beams, slabs, columns).
- Grade 75 (ASTM A615):
- Yield strength: 75 ksi (520 MPa).
- High-strength applications (e.g., foundations, bridges).
Typical Uses in High-Rise Buildings
#4 rebar is versatile but best suited for light to moderate loads:
- Slabs and Flooring:
- Reinforcing thin concrete slabs or topping slabs.
- Walls:
- Non-load-bearing walls, partition walls, or shear walls with lighter reinforcement needs.
- Beams and Columns:
- Secondary reinforcement (stirrups, ties) to hold larger bars in place.
- Stairs and Ramps:
- Light reinforcement for curved or stepped sections.
- Seismic Zones:
- If using ASTM A706 (weldable, ductile), #4 bars may serve in lateral ties for earthquake resistance.
Advantages of #4 Rebar
- Ease of Handling: Smaller diameter allows easy bending and cutting.
- Cost-Effective: Lower material cost compared to larger bars.
- Tighter Spacing: Useful in confined spaces (e.g., thin walls or slabs).
Limitations in High-Rise Construction
- Lower Load Capacity: Not suitable for primary reinforcement in heavily loaded columns or transfer beams.
- Higher Quantities Needed: May require more bars to achieve required strength, increasing labor costs.
Design Considerations
- Code Compliance:
- Follow ACI 318 (U.S.) or local codes for spacing, cover, and lap splice lengths.
- Environmental Exposure:
- Use epoxy-coated or stainless steel #4 rebar in corrosive environments (e.g., coastal areas).
- Seismic Requirements:
- Opt for ASTM A706 Grade 60 in ductile detailing for earthquake-prone regions.
Example Applications in High-Rises
| Structural Element | Typical Grade | Purpose |
|---|---|---|
| Slab Reinforcement | Grade 60 | Crack control, thermal expansion |
| Shear Wall Ties | Grade 60/75 | Lateral stability |
| Staircase Reinforcement | Grade 40/60 | Lightweight support |
When to Avoid #4 Rebar
- Heavy Load-Bearing Elements: Use larger bars (e.g., #6, #8) for columns, transfer beams, or deep foundations.
- High-Stress Zones: Areas with tension or shear demands may require higher-grade or larger bars.
Summary
#4 rebar is a practical choice for secondary reinforcement in high-rise buildings but should be paired with larger bars for primary structural elements. Always prioritize:
- Compliance with engineer specifications and local codes.
- Grade selection based on load requirements (Grade 60 is standard for most uses).
- Corrosion protection in harsh environments.