Lateral Torsional Buckling Curves

LTB Curves - General case

The General case as defined in EN 1993-1-1 art. 6.3.2.2 uses a limit slenderness of 0,2.

For deciding if the LTB check should or should not be executed art. 6.3.2.2(4) refers to the Alternative case which uses a limit slenderness of 0,4.

It is clear that this is an inconsistency within the code. In case for example the slenderness has a value just below 0,4 this would erroneously lead to the conclusion that no LTB check should be done. In this case however the Chi reduction value for curve d for example is 0,85 which indicates a 15% reduction of the bending capacity.

Therefore, conform the theory, for the General case the limit slenderness used in art. 6.3.2.2(4) is set to 0,2.

LTB Curves - Alternative case

For the 'Rolled & Equivalent welded case'  given in art. 6.3.2.3 the theory in Ref.[9] clearly specifies that it is valid only for I-sections or sections with comparable shape.

Therefore this article is applied only in case of the following form-codes:

- Symmetric I-sections (Formcode 1)

- Asymmetric I-sections (Formcode 101)

A specific National Annex can overrule this condition and use this article also for other sections. For more information reference is made to the Theoretical Background of National Annexes to EN 1993.