Comparison of chevron and suspended-zipper braced steel frames

• SZBF and IVBF provide quite similar performances for low-rise buildings.
• Huge sections at top braces & zipper struts of SZBF are a potential design challenge.
• IVBF is the better choice than SZBF as building height increases.
• SZBF is more prone to stability problems and second order effects than IVBF.

Suspended-zipper braced frame is a modified configuration of chevron braced frame in which zipper columns are added between story beams and a hat truss is attached between top two stories in order to redistribute the unbalanced vertical forces emerging following the brace buckling to avoid the use of deep beams. In this study, three- and nine-story chevron and suspended-zipper braced frames are analyzed to compare their seismic performances. The beams, columns, braces and zipper columns are modeled using nonlinear force-formulation frame elements and nonlinear geometric effects are included by utilizing corotational transformation. Nonlinear static analyses are performed until reaching a roof drift ratio of 3% and a set of twenty ground motion records scaled to match a 10% probability of exceedance in 50 years is used for nonlinear time-history analysis. The results appear to indicate that the lateral load capacity and drift demands for both low-rise chevron and suspended-zipper braced frames are very similar; however, the mid-rise chevron braced frame has a better performance compared to the mid-rise suspended-zipper braced frame.