The "general method" for assessing the out-of-plane stability of structural members and frames and the comparison with alternative rules in EN 1993 - Eurocode 3 - Part 1-1

The key to harmonizing the rules for the assessment of in-plane and out-of-plane stability of structural steel members is a common definition of equivalent geometric imperfections. The nature of these is given by the elastic-critical buckling mode and their amplitudes are obtained from the evaluation of test results for member resistance according to EN 1990 — Annex D — Basis of structural design.

EN 1993 — Part 1-1 — Design of steel structures — contains a set of alternative rules for stability checks. Of these, the "general method" could potentially function as a consistent and reliable set of rules for assessing both flexural and lateral-torsional buckling for any loading and support conditions, and also cover the case of combined compression, biaxial bending and torsion. This report describes the basis of the "general method" and its extension to the treatment of any stability problems in bar structures.
The reliability of the method is verified by test evaluations. This means it can be used as reference method for checking the accuracy of the other alternative stability rules in EN 1993-1-1. A comparison shows that the other alternative rules meet the requirements on the whole, with deviations of about ±10 %, which define their modelling uncertainty.