Improved stiffness and strength requirements for point lateral bracing in beams

Abstract

Point lateral braces are essential for economical steel beam design by preventing out-of-plane deformations during construction. While previous studies have focused mainly on a single midspan brace, the behavior of beams with multiple braces under lateral–torsional buckling remains unclear. This study develops a unified framework for assessing the stiffness and strength requirements for beams with multiple braces. A modified stiffness coefficient, N_i, is proposed to more accurately define ideal brace stiffness varying brace numbers, load positions, and moment gradients, leading to a generalized stiffness requirement applicable to both single and multiple braces. The results indicate that, contrary to AISC provisions—which tend to overdesign as brace numbers increases—additional braces reduce both the required stiffness and bracing force, enabling more efficient designs. The buckling load equivalence model (BEM), originally formulated for columns, is adapted for beam bracing and, when combined with initial imperfections and threshold deflections, yields conservative and reliable predictions regardless of brace quantity. The proposed method offers a more rational approach to brace design compared with current AISC criteria.