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CivilKits/Calculators/Structural/Design/Eurocode/EN 1993-1-1 / flexural buckling

structural / design / eurocode 3

Eurocode 3 column flexural buckling.

Calculate non-dimensional slenderness, reduction factors, and design buckling resistance about both principal axes without hiding the effective lengths or imperfection curves.

Curve selection is an engineering input

CivilKits does not infer a curve from section dimensions. Select each curve from the applicable EN 1993-1-1 table using section type, fabrication route, grade, thickness, and buckling axis.

declared calculation basis

Two axes, two explicit stability checks.

The calculation follows first-generation EN 1993-1-1:2005 + AC:2009 + A1:2014 §6.3.1 for a uniform prismatic Class 1–3 member under axial compression.

Elastic critical load and slenderness

FLEXURAL MODENcr = π²EI/Lcr²  ·  λ̄ = √(Afy/Ncr) = Lcr/(iλ1)  ·  λ1 = π√(E/fy)

The page evaluates y and z independently from the entered radius of gyration and effective-length factor. The effective length is kL; selecting k is part of the structural model, not a result produced by this page.

European design buckling curves

EN 1993-1-1 §6.3.1.2Φ = 0.5[1 + α(λ̄ − 0.2) + λ̄²]  ·  χ = min{1, 1/[Φ + √(Φ² − λ̄²)]}
MEMBER RESISTANCENb,Rd = χAfy/γM1

The listed a0, a, b, c, and d curves correspond to α = 0.13, 0.21, 0.34, 0.49, and 0.76. The governing displayed resistance is the lower y- or z-axis result.

What this page does not check

  • Section classification or Class 4 effective area; use verified gross Class 1–3 properties only.
  • Torsional or flexural-torsional buckling, which can govern open sections even when both flexural-axis checks pass.
  • Combined axial force and bending, lateral-torsional buckling, second-order frame analysis, system instability, built-up members, or restraints.
  • Connections, imperfections outside the selected curve model, fire, fatigue, seismic design, execution, or robustness.