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Column Interaction Diagram Calculator

Outer ring

Bars distributed around the perimeter — one per corner, remainder split between faces. Additional rings are inset progressively inward at real clear-spacing offsets.

b=400h=400d=342d'=59c=408T25As=3927 mm²NEd=500kN
N-M Interaction Diagram
01k2k3k4k5k-1k0100200300400BalMu(500, 150)M (kN·m)N (kN)
Key Interaction Points
PointN (kN)M (kN·m)
Pure Compression4907.40.0
Balanced Point1353.5333.1
Pure Bending0.0252.9
Pure Tension-1707.40.0
Design Point (Pu, Mu)500.0150.0
  • Short-column check only — no slenderness or second-order moment magnification is applied; use RC Column Design for slender columns.
  • Uniaxial bending about one axis only.
  • Circular sections are assumed spiral-tied and rectangular sections tied (governs the ACI φ transition floor and the axial capacity cap factor) — verify this matches your actual detailing.
  • Checks a single user-supplied load point (Pu, Mu) against the section’s interaction envelope — this tool doesn’t generate load combinations for you.
  • Verify all provisions against the governing code edition and applicable National Annex before use.
Related calculators
▥RC Column Design

Axial and biaxial bending design with interaction diagram per EC2 and ACI.

▦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.

Column Interaction Diagram v1.0Validated against 20 benchmark cases →
Interaction CheckPASS
Utilization
50.3%
Utilization50.3%
Calculation
EC2 §6.1Section properties
Ac = b×h, As = Σ(area of each bar)
Ac = 160000 mm², As = Σ over 8 bars
As = 3927 mm²
EC2 §6.1Maximum axial capacity
Nmax = fcd·Ac + fyd·As
Nmax = 20.00×160000 + 434.8×3927
Nmax = 4907.4 kN
EC2 §6.1N-M interaction check
Design point must lie within interaction curve
(NEd, MEd) = (500.0, 150.00) kN, kN·m
Utilization = 50.3% — ✓ PASS