Reduction in the Critical Moment for Lateral Torsional Buckling of Coped Beams

Abstract

The paper presents a computational analysis of the effect constructional details of coped connections, assumed to be a fork support in calculations, on the critical LTB moment values. On the basis of analytical formulas by Lindner [1], a formula, having a simple form, was derived for the reduction factor rn for the critical LTB moment. The parameters for the formula were presented in a tabular form, taking into account the beam section (IPE/HEA), the type of beam to end-plate connection (Types 1-3), the load type (q / P) and the way the load is applied (top / bottom flange). The correctness of the derived formula was validated on the basis of the analytical results and the Finite Element Method results obtained with the Abaqus/CAE software. In the program, the beam geometric dimensions and connections were represented as volumetric finite elements. Additionally, the dimensions of the end-plate for IPE and HEA section series were arranged in a systematic manner following the British catalogue.

Lateral Torsional Buckling of Steel Beams Elastically Restrained at the Support Nodes

“…The literature on different issues related to lateral torsional buckling (LTB) of beams is vast, yet in a majority of cases it focuses on the determination of critical moments with the assumption that fork support is used. For such idealised support conditions, among others, the impact of the following was investigated: (a) distribution of the bending moment [2][3][4][5][6][7], (b) points at which various transverse loads are applied over the section height [2,[8][9][10][11], (c) elastic restraint against torsion over the beam length [11][12][13][14][15][16][17], (d) geometric ratios of monosymmetric sections [3,5,9], (e) coped beams and "incomplete" end plates [14,[18][19][20][21][22][23], and (f) point lateral bracings [16,17,[24][25][26][27].…”

“…In addition to the elastic restraint against rotation about the major axis of the section (i.e., in the plane of the beam greater stiffness), a restraint of warping and rotation with respect to the minor axis in the support sections is also found. Theoretical, e.g., [14,18,19,21,22,[28][29][30][31][32][33][34], and also experimental investigations [20,23,30] indicate that taking into account the actual conditions of beam support at the structure nodes can significantly affect the value of the elastic critical moment.…”

“…Computations for different cases of beams were done analytically and validated using the Finite Element Method (Abaqus). In studies [18,22], the influence of reduced connection of beams ("incomplete" end plate welded only to the web and coped flanges of the section) on the critical moment was analysed. It was confirmed that such a structural design options lower the value of the critical load compared with the fork support.…”