Stiffness requirements for diaphragm bracing of beams

Light gauge metal sheeting is commonly used in the building and bridge indu stry for concrete formwork. The metal forms, if properly attached to the be am or girder, often behave like a shear diaphragm and restrain the lateral displacement of the top flange, therefore improving the lateral-torsional b uckling capacity prior to placement and hardening of the concrete. This pap er presents the results of a computational study on the stiffness requireme nts for shear diaphragms used for beam bracing. Doubly and singly symmetric cross sections were studied. The parameters that were investigated include d diaphragm stiffness, load type, load position, cross-sectional shape, and web slenderness. The type of loading has a significant effect on the braci ng 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 determ ine diaphragm stiffness requirements to prevent lateral-torsional buckling for general load applications.