Concrete Column Design Calculator
Design reinforced concrete columns per ACI 318: calculate gross area, steel area, steel ratio, and axial load capacity.
Inputs
ACI 318: residential 21–28 MPa; structural columns 28–55 MPa; high-rise 55–83 MPa
ASTM A615: Grade 40=280 MPa; Grade 60=420 MPa (most common); Grade 80=550 MPa
ACI 318: minimum 4 bars rectangular, 6 bars circular; steel ratio 1–8% of gross area
Results
Axial Load Capacity (φPn)
2,958,571 N
Adequate Steel Ratio?
1 (1=yes, 0=no)
How to Use This Calculator
- Enter the factored axial load (Pu) and factored moment (Mu) in kN and kN-m.
- Set the concrete compressive strength (f'c) and steel yield strength (fy).
- Input the column cross-section dimensions in mm.
- Review the Required Steel Ratio, Reinforcing Bar Count, and Slenderness Check.
- Ensure the Steel Ratio falls between 1% and 8% per ACI 318 requirements.
How the result changes with Column Width
| Column Width | Axial Load Capacity (φPn) | Adequate Steel Ratio? |
|---|---|---|
| 380 | 2,852,491 N | 1 (1=yes, 0=no) |
| 830 | 5,239,291 N | 1 (1=yes, 0=no) |
| 1,370 | 8,103,451 N | 0 (1=yes, 0=no) |
| 1,820 | 10,490,251 N | 0 (1=yes, 0=no) |
What each input means
- Concrete Strength (f'c)
- Specified compressive strength of concrete at 28 days per ACI 318 Table 19.2.1.1. Minimum strength varies by exposure class; structural columns typically 28–55 MPa (4,000–8,000 psi).
- Steel Yield Strength (fy)
- Yield strength of reinforcing steel per ASTM A615 or A706. ACI 318 §20.2.2.4 permits fy up to 550 MPa for ties; columns commonly use Grade 60 (420 MPa) or Grade 80 (550 MPa) per ACI 318.
- Column Width
- Width of the rectangular column cross-section.
- Column Depth
- Depth of the rectangular column cross-section.
- Number of Rebars
- Total number of longitudinal reinforcing bars. ACI 318 §10.7.3.1 requires minimum 4 bars for rectangular columns and 6 bars for circular columns. Maximum steel ratio is 8% of gross area.
- Rebar Size (diameter)
- Nominal diameter of each rebar. Common sizes: 16, 19, 22, 25, 29, 32 mm.
- Confinement Type
- Select 1 for tied column (φ=0.65) or 2 for spiral column (φ=0.75).
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersConcrete Strength (f'c) = 30, Steel Yield Strength (fy) = 420, Column Width = 400, Column Depth = 400 = 7 input(s) provided
- Calculate Axial Load CapacityAxial Load Capacity2958571 = 2958571
- Calculate Adequate Steel Ratio?Adequate Steel Ratio?1 = 1
- Calculate Gross AreaGross Area160000 = 160000
- Calculate Steel AreaSteel Area4080 = 4080
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