Critical Lateral-Torsional Buckling Moments of Steel Web-Tapered I-beams

Ioannis G. Raftoyiannis, Theodore Adamakos
Department of Civil Engineering, National Technical University of Athens, Athens 15780, Greece.

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This paper deals with the stability of steel web-tapered I-beams subjected to bending loads. Tapered beams can carry a maximum bending moment at a single location while in the rest of the member the moment carrying capacity is considerably lower. This results in appreciable savings in materials as well as in construction. Numerous researchers have focused on the investigation of the elastic behavior of tapered I-beams and many theoretical findings have been incorporated into the current specifications. According to Eurocode 3, the elastic critical moment is used for determining the design strength against lateral-torsional buckling (LTB) of I-beams with uniform cross-section and a number of coefficients is employed accounting for the boundary conditions, the cross-sectional geometry and the type of transverse loading, while no detailed information is given regarding non-uniform members. In this work a simple numerical approach is presented for determining the critical lateral-torsional buckling loads of web-tapered I-beams. Modification factors of the elastic critical moment with reference to the mean cross-section are given for various taper ratios. The results presented in graphical form are compared with those of previous investigations. The approach presented herein can be very easily applied for the design of tapered beams against lateral-torsional buckling.