Stiffness Requirements for Diaphragm Bracing of Beams

Abstract

Light gauge metal sheeting is commonly used in the building and bridge industry for concrete formwork. The metal forms, if properly attached to the beam or girder, often behave like a shear diaphragm and restrain the lateral displacement of the top flange, therefore improving the lateral-torsional buckling capacity prior to placement and hardening of the concrete. This paper presents the results of a computational study on the stiffness requirements for shear diaphragms used for beam bracing. Doubly and singly symmetric cross sections were studied. The parameters that were investigated included diaphragm stiffness, load type, load position, cross-sectional shape, and web slenderness. The type of loading has a significant effect on the bracing behavior of the shear diaphragm. Current solutions in the literature are based upon uniform moment solutions and often overestimate the capacity of diaphragm-braced beams. Solutions are presented that can be used to determine diaphragm stiffness requirements to prevent lateral-torsional buckling for general load applications.