Proposition of a modified formulation to predict the lateral-torsional buckling resistance of steel beams: meta-analysis of test data

Abstract

Abstract Lateral-Torsional Buckling (LTB) is an important limit state that must be considered in the design of steel members subjected to bending. During the process of revising of the Brazilian Standard ABNT NBR 8800:2008, it was questioned whether the present formulation would really lead to good results vis-à-vis the experimental tests. To this end, a comprehensive review of the technical literature was carried out, looking for test results that could be compared with the ones using the equations provided in the Brazilian Standard. Then, a meta-analysis was performed by comparing the test results with the ones of the ABNT NBR 8800:2008 methodology. It was observed that, for beams subjected to uniform bending moments and simple supports, the formulation proved to be adequate. However, for the case of beams with variable bending moments, for which the factor Cb (modification factor for non-uniform bending moment diagram) is used, it was realized that the formulation could lead to unsafe results, especially for high values of Cb. A modified formulation was then proposed, with the introduction of Cb only in the elastic range of the equations (only in the buckling moment equation) and in the equation for the slenderness parameter corresponding to the beginning of yielding, λΓ. The proposed modified formulation, as well as the EN 1993-1-1:2022 methodology, were subsequently included in the meta-analysis. Structural reliability analyses were also carried out for both the ABNT NBR 8800:2008 and the modified methodologies. The analyses showed that the reliability indexes of the modified formulation were higher than those of the ABNT NBR 8800:2008 one and closer to the recommended "target value".

Keywords

• lateral torsional buckling
• experimental analysis
• steel beams
• meta-data analysis
• LTB