Torsional stiffness requirements for diaphragm bracing of discretely braced I-girders

I-section girders are laterally interconnected by Torsional bracings that are discretely installed to increase resistance to lateral-torsional buckling. However, there are confusing discrepancies in the current design specifications for the stiffness of diaphragm-type bracings. The mathematical formula for determining the required torsional stiffness is still unclear. In this study, rigorous examinations were carried out to clarify the effects of the web distortional stiffness and the number of diaphragm bracings. To achieve the purpose of this study, the theoretical derivation of the stiffness equations was thoroughly examined. Three-dimensional finite-element analysis was used for the parametric numerical analyses of a series of feasible two-girder system models, and enhanced equations are proposed for achieving sufficient stiffness in the torsional bracings. The practical validity of the proposed equations are verified by statistical correlation analyses, which clearly prove their superiority compared to current design guidelines.