A consistent approach for flexural and lateral torsional buckling as basis for a general buckling curve

Abstract

ABSTRACTChapter 6.3.4 of EN 1993‐1‐1 (1) deals with the General Method for the verification of stability problems of in‐plane loaded frames or beams. For the general case of having combined moment and normal force the method provides two different approaches to determine the reduction factor for out‐of‐plane buckling. They accord to the special case of lateral torsional buckling (“LTB” – i.e. with moment only) and flexural buckling (“FB” – i.e. with normal force only) on the other hand. However, in general cases this produces inconsistencies leading to conflicts with the intended generality of the formulation and finally to incorrect results. Because the individually combined effect of the in‐plane actions My and N are the reason for the out‐of‐plane instability. This requires a reduction considering the individual load combination. To find a solution for this, the in‐plane‐ and out‐of‐plane effects can be put together in a general formulation to obtain a buckling curve for combined moment and normal force ensuring consistency with the buckling curves of the special cases. By this the choice of buckling curves in Eurocode 3 clause 6.3.4 (1) can be improved.