The Influence of Constructional Detail to Lateral-Torsional Buckling of Beams

Abstract

The resistance of steel members in bending can be influenced by the lateral-torsional stability phenomenon. This paper investigates the influence of end plates in beam to column joint on the value of elastic buckling moment Mcr. The investigated beam is considered as simply supported in bending about horizontal and vertical axis. The rotation about its longitudinal axis is prevented. The warping is partially restrained by the use of a constructional detail which is represented by warping restraints on both ends of the beam. The investigated beam is loaded with equal and opposite end moments, which deduce the constant bending moment diagram, the worst one in the theory of LTB. The National Annex to STN EN 1993-1-1 [1] recommends for the design of steel members to LTB to use for the buckling length factor for torsion 1.0 for a simple support and for warping fixity of both ends 0.5. Both assumptions are very frequently used in design practice, but the real behaviour of steel joints is different. The parametric study considering only the influence of end plates on LTB was presented in [2,3]. The presented parametric study takes into account the end plates together with the torsional stiffness of columns. The results are in the form of ratios Mcr,approx/Mcr,exact. Both values of Mcr were calculated with the influence of constructional detail, but each value with a different manner. The Mcr,approx is approximative value calculated via the proposed two steps procedure and Mcr,exact is calculated with the computer program [1P]. The buckling length factors in torsion kw which are inputs for the two steps analysis of Mcr,approx proposed in this paper are also presented.