Buckling Verification of an Angle Section

by Thibaut Frette
Product technical specialist


In this article, we will design an Angle section in pure compression, considering its principal axes (u-u & v-v).  

Keywords: Advance Design, Angle, Eurocode 3, EN 1993-1-1


ke most steel structural members, angle sections are designed not in their geometrical axes (y-y & z-z, parallel to the legs) but in their principal axes (u-u & v-v).

2.    Theory

The Eurocode 3 convention for member axes refers to the axes about which the moment acts.

For most sections, that would be the geometrical axes (y-y & z-z):

  • y-y is the cross-section axis parallel to the flanges
  • z-z is the cross-section axis perpendicular to the flanges

Yet, this convention is not suitable to angle sections, for which bending occurs about the principal axes (u-u & v-v).

Therefore, the u-u & v-v axes should be used instead:

  • u-u major principal axis
  • v-v major principal axis

3. Application

Assume a L 90×9 equal leg angle, subjected to a NEd = 80 kN compressive axial force.

Steel grade is S275.

The effective slenderness (λeff) refers to annex G from EN1993-3-1:

EN1993-3-1 (Annex G)

The effective slenderness involves a k parameter, which depends on the type of restraint, as per Table G.2 from EN 1993-3-1.

For buckling about the v-v axis though, the k formula is unchanged.

Table G.2 from EN1993-3-1

The angle section under consideration is properly designed.

4.     Conclusion

Angle sections should be designed about their principal axes, especially in pure compression situations, where buckling typically arises about the v-v axis.

The upcoming update of Advance Design (version 2023.1) will enable this option, while letting the user consider the effective slenderness ratio.

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