RC Column Design Calculator
N-M Interaction Diagram
All 6 checks pass
N-M InteractionPASS
Utilization
48.9%
Utilization48.9%
SlendernessPASS
λ
15.2
λlim
26.2
Utilization57.9%
ReinforcementPASS
As,prov
2513mm²
As,min
345mm²
Utilization13.7%
Link DesignPASS
Spacing
200mm
s,max
400mm
Utilization50.0%
Summary
| Check | Required | Provided | Util. | Status |
|---|---|---|---|---|
| Slenderness λ | ≤ 26.2 | 15.2 | 57.9% | PASS |
| Min eccentricity | 30.00 kN·m | 120.00 kN·m | 0.0% | PASS |
| N-M Interaction | ≤ 1.0 | 0.49 | 48.9% | PASS |
| As,min | 345 mm² | 2513 mm² | 13.7% | PASS |
| As,max | ≤ 6400 mm² | 2513 mm² | 39.3% | PASS |
| Link spacing | ≤ 400 mm | 200 mm | 50.0% | PASS |
Related calculators
⧉Column Interaction Diagram
Full strain-compatibility P-M interaction envelope for rectangular and circular RC columns, with a direct axial load / moment design-point check.
▦Foundation Design
Isolated, combined, strip, mat and pile-cap footing design — bearing, flexure, one-way and punching shear, and development length.
⦿Rebar Calculator
Calculate rebar areas, number of bars and spacing for any diameter. Supports EC and ACI bar designations.
RC Column Design v1.0Learn: What is reinforcement ratio, and why does it have min/max limits? →Learn: Development length and anchorage: why rebar needs to "grip" the concrete →Learn: Effective depth (d) vs overall depth (h): why the distinction matters →Learn: Understanding punching shear in slabs and footings →Learn: Load paths: how a load actually gets from a slab to the foundation →
Min Eccentricity [EC2 §6.1(4)]▼
Minimum Eccentricity
EC2 §6.1(4)Minimum eccentricity
e0 = max(h/30, 20mm)
e0 = max(13.3, 20)
e0 = 20.0 mm → MEd,min = 30.00 kN·m
EC2 §6.1(4)Design moment
MEd = max(|MEd|, MEd,min)
max(120.00, 30.00)
MEd = 120.00 kN·m
Slenderness [EC2 §5.8.3]▼
Slenderness Check
EC2 §5.8.3.2Radius of gyration
i = √(Ic/Ac) = √(b·h³/12 / (b·h))
Ic = 2133333333 mm⁴, Ac = 160000 mm²
i = 115.5 mm
EC2 §5.8.3.2Slenderness ratio
λ = leff / i
λ = 1750 / 115.5
λ = 15.2
EC2 §5.8.3.1Limiting slenderness parameters
A = 1/(1+0.2φef), B = √(1+2ω), C = 1.7 − rm
A = 0.70, ω = 0.402, B = 1.34, rm = 0.67, C = 1.03, n = 0.551
λlim = 20×0.70×1.34×1.03/√0.551 = 26.2
EC2 §5.8.3.1Slenderness classification
λ ≤ λlim → Short column; λ > λlim → Slender column
15.2 ≤ 26.2
✓ SHORT COLUMN — no second order effects
N-M Interaction [EC2 §6.1]▼
Interaction Diagram
EC2 §6.1Section properties
Ac = b×h, As = Σ(area of each bar)
Ac = 160000 mm², As = Σ over 8 bars
As = 2513 mm²
EC2 §6.1Maximum axial capacity
Nmax = fcd·Ac + fyd·As
Nmax = 17.00×160000 + 434.8×2513
Nmax = 3812.7 kN
EC2 §6.1N-M interaction check
Design point must lie within interaction curve
(NEd, MEd) = (1500.0, 120.00) kN, kN·m
Utilization = 48.9% — ✓ PASS
Reinforcement [EC2 §9.5.2]▼
Reinforcement Limits
EC2 §9.5.2(2)Minimum reinforcement
As,min = max(0.1·NEd/fyd, 0.002·Ac)
max(0.1×1500000/434.8, 0.002×160000)
As,min = 345 mm²
EC2 §9.5.2(3)Maximum reinforcement
As,max = 0.04·Ac (outside laps)
As,max = 0.04 × 160000
As,max = 6400 mm²
EC2 §9.5.2Check
As,min ≤ As ≤ As,max
345 ≤ 2513 ≤ 6400
ρ = 1.57% — ✓ PASS
Links [EC2 §9.5.3]▼
Link Design
EC2 §9.5.3(1)Minimum link diameter
φlink,min = max(6mm, φbar/4)
max(6, 20/4)
φlink,min = 6 mm — ✓
EC2 §9.5.3(3)Maximum link spacing
scl,max = min(20φbar, b, h, 400mm)
min(400, 400, 400, 400)
scl,max = 400 mm — ✓
EC2 §9.5.3(4)Critical zone
lc = max(h, b, l0/6, 450mm)
max(400, 400, 583, 450)
lc = 583 mm — spacing in zone = 0.6×400 = 240 mm