Lateral bracing requirements for cantilever steel I-beams

In the design of hot rolled steel structures, stability is one of the most important considerations. In terms of flexural members, e.g., a steel I-section beam, bent about the major principal axis, lateral buckling about the minor principal axis in combination with torsional buckling is the main stability concern. To prevent lateral-torsional buckling from occurring, lateral braces are typically installed perpendicular to the longitudinal axis of the flexural member, either on the top and/or bottom flange or near the shear-centre of the beam. Nethercot developed an equation to predict the critical elastic lateral-torsional moment resistance of cantilever beams, which involves a series of effective length factors, which are dependent on the brace configuration, type and position of loading, as well as cantilever system. This effective length factor approach has become widely used as a simplified method to calculate the elastic lateral-torsional buckling moment resistance of cantilever steel beams. However, no specific guidelines for the design of the lateral braces are available in design standards.This thesis will include background information on elastic beam buckling theories, an introduction to the development of research on lateral brace requirements, and a discussion on the currently used lateral bracing requirements in North American and British Standards. Details of a study concerning the lateral bracing design requirements for cantilever I-beams, carried out with the use of the finite element software Buckling Analysis of Stiffened Plates (BASP), are provided. Concerning the required brace stiffness, the results from the numerical parametric study are compared with the results from the Canadian Steel Design Standard CSA-S 16 and the SSRC (Structural Stability Research Council) method of the United States.It is shown that the current code methods are generally conservative for top flange loaded cantilever beam cases in terms of the predicted elastic lateral-torsional buckling capacity. Furthermore, the current bracing design requirements provide adequate results in most cases, except for the prop cantilever scenario without a tip brace