Statistical evaluation of the lateral-torsional buckling resistance of steel I-beams, Part 1: variability of the Eurocode 3 resistance model

Abstract

The EN version of part 1-1 of EC3 introduces significant changes in the evaluation of the lateral torsional buckling resistance of unrestrained beams, as well as alternative design procedures. Simultaneously, as a part of the preparation of the National Annexes of EC3 part 1-1 and the establishment of the corresponding NDP's (Nationally Determined Parameters) it becomes necessary to define the partial safety coefficients for the bending resistance of beams when lateral-torsional buckling is a potential failure mode. In this paper the methodology for the resistance evaluation of beams subjected to instability is briefly described and the results are compared with FEM numerical results for the same elements. Subsequently, to assess the accuracy of the alternative design formulae, a statistical analysis of the results is performed on the basis of EN 1990-Annex D. A methodology is proposed for the evaluation of the design procedures allowing for the uncertainties in the resistance model. Results are presented for a wide set of beam geometries and loading cases and a proposal for the definition of the partial safety factor is presented for the various methods, in line with the target failure probability of EN 1990.