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).
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
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:
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.
The angle section under consideration is properly designed.
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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