Combined axial compression + bi-axial bending per EN 1993-1-1 §6.3.3. Interaction equations 6.61 and 6.62 with k-factors from Annex A (alternative) or Annex B (general). Full step-by-step: χy, χz, χLT, Cm, all four k-factors.
| Npl,Rd | — |
| Nb,Rd,y | — |
| λ̄y | — |
| Curvey | — |
| χy | — |
| Nb,Rd,z | — |
| λ̄z | — |
| Curvez | — |
| χz | — |
| Mcr | — |
| λ̄LT | — |
| χLT | — |
| Mb,Rd | — |
| Cmy (Annex B Table B.3) | — |
| Cmz | — |
| CmLT | — |
| kyy | — |
| kyz | — |
| kzy | — |
| kzz | — |
| Mpl,Rd,y | — |
| Mpl,Rd,z | — |
| Wpl,y | — |
| Wpl,z | — |
| Section class | — |
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EN 1993-1-1:2005+A1:2014 §6.3.3 — Two interaction equations govern beam-column design:
Eq 6.61: NEd/(χy·NRk/γM1) + kyy·My,Ed/(χLT·My,Rk/γM1) + kyz·Mz,Ed/(Mz,Rk/γM1) ≤ 1
Eq 6.62: NEd/(χz·NRk/γM1) + kzy·My,Ed/(χLT·My,Rk/γM1) + kzz·Mz,Ed/(Mz,Rk/γM1) ≤ 1
χy, χz — Flexural buckling (§6.3.1): Ncr = π²·E·I/Lcr², λ̄ = √(A·fy/Ncr), χ from Eq 6.49. Buckling curves per Table 6.2 (rolled I: h/b>1.2, tf≤40mm → y=a, z=b).
χLT — LTB (§6.3.2.2): Mcr from Annex F (simplified fork BC), λ̄LT = √(Wpl·fy/Mcr). LTB curve: Table 6.4 (h/b≤2.0 → curve b, else curve c). Plateau λ̄LT,0 = 0.4, β = 0.75.
Cm — Equivalent moment factors (Annex B Table B.3): Cm = 0.6 + 0.4·ψ ≥ 0.4. CmLT = max(Cmy², 0.9).
Annex B (general): kyy, kzz from Table B.1. kyz = 0.6·kzz. kzy from Table B.2 using CmLT.
Annex A (alternative): Auxiliary C-factors Cyy, Czz from Table A.2. kyy = Cmy²·(1/μy)·Cyy/χy etc. More accurate for stocky members with high axial ratio.
Cross-verify χy, χz independently: /tools/steel-column-buckling (§6.3.1).
For LTB verification: /tools/lateral-torsional-buckling-en (§6.3.2).
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