Out-of-plane buckling and design of X-bracing systems with discontinuous diagonals

Several analytical studies have been conducted on the out-of-plane buckling of X-bracing systems. Most of these studies do not consider effects of the mid-span (center) connection and inelastic behaviors of X-bracing system. Usually, one diagonal is interrupted at the center and a gusset plate connects it to the other continuous diagonal and the discontinuous diagonal is modeled as partly pinned. In this study, simple approximated solutions are obtained for the direct evaluation of the elastic buckling loads of X-bracing systems with discontinuous diagonals. The effective length factors are suggested for the general case, i.e., tension and compression diagonals have different section properties, lengths, and axial loads. Inelastic buckling loads of X-bracing systems with discontinuous diagonals are also studied. Inelastic buckling loads are determined using column buckling curves with the suggested effective length factor, and are compared with those from FEM analyses. It is found that inelastic buckling loads of X-bracing systems with discontinuous diagonals from the column buckling curves are over-predicted when the stress level of a tension diagonal is high.