Eurocode 3 lateral-torsional buckling screen.

Estimate the major-axis buckling resistance of a Class 1, 2, or 3 steel section using the first-generation EN 1993-1-1 general case and a user-supplied elastic critical moment M_cr.

Declared scope: preliminary member screen

This page implements the general method in EN 1993-1-1 §6.3.2.2. It does not calculate M_cr, select a section, or provide a complete steel member design.

first-generation Eurocode basis

Separate the buckling model from the resistance reduction.

The calculation follows EN 1993-1-1:2005 with AC:2009 and A1:2014, using the general lateral-torsional buckling method in clause 6.3.2.2. M_cr is deliberately an input so the designer can document the actual restraints, moment diagram, load application, and section properties used to obtain it.

Equations used

NON-DIMENSIONAL SLENDERNESSλ_LT = √(W_yf_y/M_cr)

REDUCTION FACTORΦ_LT = 0.5[1 + α_LT(λ_LT - 0.2) + λ_LT²]

BUCKLING RESISTANCEχ_LT = 1/[Φ_LT + √(Φ_LT² - λ_LT²)] · M_b,Rd = χ_LTW_yf_y/γ_M1

The declared section class controls the modulus convention. The result is compared with M_Ed as a utilisation screen.

Assumptions and limits

First-generation EN 1993-1-1 general case, clause 6.3.2.2, under major-axis bending.
User-supplied M_cr and imperfection factor α_LT; CivilKits does not perform the elastic critical-moment analysis.
No Class 4 effective properties, modified rolled-section method in clause 6.3.2.3, axial-force interaction, shear/torsion interaction, fire, fatigue, connections, or restraints design.
Confirm section classification, buckling curve, γ_M1, load combination, and National Annex before project use.

official sources

Use the national publication with the general method.

The applicable national publication and National Annex remain normative. The JRC material below provides Eurocode implementation context and a worked NCCI for lateral-torsional buckling.