Effective Length Factor for the Design of X-bracing Systems

Abstract

X-bracing systems made with single angles are quite common in steel structures. In current practice, the design of X-bracing members may be performed in one of two ways. The first method is to ignore the strength of the compression diagonal in resisting the imposed loads. Conversely, the second method recognizes the contribution of the compression diagonal. This method requires overall buckling of the full diagonal in the out-of-plane direction as well as buckling of one half diagonal about the weak principal axis to be investigated in calculating the effective slenderness ratio. However, for all the hot-rolled single equal leg angles (listed in Ref. 4), the radius of gyration about the weak axis, Z-axis, is greater than half of that in the out-of-plane direction. Accordingly, buckling of full diagonal in the outof- plane direction governs the strength of single-angle compression diagonals. The purpose of this paper is to provide designers with some recommendations regarding the effective length factor to be considered in the design of X-bracing systems. The recommendations were drawn from experimental and theoretical study of full-scale X-bracing specimens. For more details, refer to the original report by the authors.