Evaluation of the seismic performance of suspended zipper column concentrically braced steel frames

The performance of the most common type of concentric braced configuration, i.e. Chevron braces, is governed by buckling of first story braces in compression, resulting in a localization of the failure. To improve the performance of chevron concentric braced frames, zipper columns were introduced to transfer the unbalanced forces; over-strength braces were further introduced to avoid the complete collapse of the frame. Such concentric braced frames are called suspended zipper concentric braced frames. The objective of this study is to evaluate the seismic performance of suspended zipper concentric braced frames designed according to Eurocode 8 and to compare their performance with conventional concentric braced configurations. It is important to highlight that this study introduces a novel design methodology to size braces, zipper columns, beams and columns in suspended zipper frames. For this purpose, two concentric braced frame structures from each suspended zipper configuration and stud-to-ground configuration are designed and analysed for a ground motion with a probability of exceedance equal to 10% in 50 years, i.e. a return period of 475 years, with peak ground acceleration of 0.3 g. Based on the comparison of results, it can be concluded that the performance of suspended zipper frame is better than that of conventional concentrically braced frames in medium-rise buildings, but not in low-rise buildings. Furthermore, the novel design methodology is proven to be satisfactory in sizing the structural elements of suspended zipper concentric braced frames when considering the inelastic time history analyses results.