Cross Stiffeners for Beams in Torsion

Abstract

Systems for torsional stiffening, including longitudinal plate, transverse plate, box, and cross stiffeners of I-beams are reviewed. Different configurations for cross stiffeners are presented, including crosses fully formed on both sides of the beam, formed on one side only, or split with half of the cross on one side of the web and the other half of the cross on the other side of the web. The split-cross configuration is particularly desirable, being easy to fabricate but almost as effective as the full-cross configuration. Multiple butting and multiple overlapping cross stiffeners allow torsional stiffening along the entire length of a beam. Relationships for the mechanics of single butting, multiple butting, and multiple overlapping cross stiffeners are developed, and equivalent St. Venant's torsion constant are derived. Design parameters for cross stiffeners are reviewed and a stiffener slope of 45° is recommended. The effect of cross stiffeners on lateral torsional flexural buckling of I-beams is shown to significantly increase the beam capacity.