Buckling curves for lateral torsional buckling of unrestrained beams

In Eurocode 3 two methods to determine the ultimate lateral torsional buckling load of steel beams in bending are presented: the General and the Specific Methods. Both methods make use of buckling curves, but the curves to be used are different for both methods. The ultimate lateral torsional buckling load can also be calculated using the Finite Element Method (FEM) by means of a geometrical and material non-linear analysis on a beam including imperfections (GMNIA). This paper compares the ultimate loads based on the design rules in Eurocode 3 for lateral torsional buckling of unrestrained beams in bending to the ultimate loads obtained with Finite Element simulations on the basis of a parameter study. It is concluded that the Specific Method gives a large over-estimation of the ultimate load found with FEM simulations, while the General Method gives good results. Therefore, Nationally Determined Parameters in the Specific Method should be chosen with care in the National Annexes