Concentrically braced frame (CBF) structures provide high stiffness and moderate ductility, while they are prone to damage concentrated within a single floor. To overcome this drawback, researchers have proposed to add a vertical member to the CBF system, labeled a “zipper column”, with the aim to involve the buckling and/or yielding of several braces. Thus, the zipper column members are designed to transfer the unbalanced forces caused by buckling of braces in chevron configuration along the building height. By employing the zipper braced frame system (ZBF), the damage is more uniformly distributed over the height. However structures taller than 8-storey are prone to lateral drift amplification due to the higher mode effects. In this study, in order to control the lateral drift, it is proposed to add a set of outrigger trusses over one floor, at the roof level, and if necessary at another floor among those located at the mid-height.
Accordingly, the purpose of this study is two-fold: i) to investigate the inelastic be-havior of the 12- and 16-storey ZBF building structures with elastic zippers located in a high risk seismic zone and ii) to study the behavior of ZBF structures when outrigger trusses are added.
Nonlinear time-history analyses conducted in Drain-2DX software are considered in this study to analyze the behavior of the 12- and 16-storey buildings without and with outrigger trusses that are subjected to 21 ground motions equally divided in three ensembles: crustal, subduction and near-field. Outcomes of the study show that buildings located in a high risk seismic zone (Victoria, B.C.) exhibit less seismic damage when outrigger trusses are added to the ZBF system.