Stability Design of Cross-Bracing Systems for Frames

In this study, the inelastic load-carrying capacity of the compression diagonal of a typical cross-bracing system used in concentrically braced frames under gravity and wind loads is investigated, taking into consideration its interaction effect with the tension diagonal. Depending on the lateral stiffness of the tension diagonal, the compression diagonal can be fully or partially braced by the tension diagonal at their intersection point. An expression for the transition lateral stiffness, kst, that demarcates the fully and partially braced conditions is derived. When the compression diagonal is fully braced, its maximum load-carrying capacity is a function of its member slenderness, L/r, only. However, when the compression diagonal is partially braced, its load capacity is dependent upon both its member slenderness, L/r, and the lateral stiffness, ks, of the tension diagonal. Once the equations for the maximum load-carrying capacity of the compression diagonal are established, design guidelines are proposed and design examples are given to demonstrate how the proposed guidelines can be used for the design of cross-bracing systems in steel frames. The consideration of the lateral bracing effect will result in a more economical and logical design for such bracing systems.