Comparison of chevron and suspended zipper braced steel frames

Chevron braced steel frames require large beams to redistribute the unbalanced vertical forces exerted on the beams after brace buckling. A new frame configuration similar to chevron brace was proposed in the literature, where zipper columns were attached between mid-spans of the beams from second to top story. During severe ground motion, the unbalanced vertical forces caused by buckling of lower story braces are in this case redistributed to the upper story braces by these zipper columns. Consequently, all story braces buckle successively from first to top story brace instead of concentration of inelastic action in one story. This system has been improved recently by adding an elastic hat truss between the top two stories to prevent the formation of a full zipper mechanism and to prevent collapse. A two-phase numerical study is undertaken in this study to evaluate the response of chevron and suspended zipper braced frames.