The influence of lateral load patterns on the seismic design of zipper braced frames

Concentrically braced frames are prone to excessive interstorey drift concentrated within a single floor, have a limited ability to redistribute damage across the structure height and experience lateral strength degradation after braces have buckled. To overcome these drawbacks, an innovative system labeled zipper braced frames with elastic zipper columns (E-ZBFs) is analyzed and a method for zipper column design is proposed based on the use of invariant load patterns. Thus, the purpose of this study is twofold: (i) to validate the suitable static method for zipper column design through nonlinear time-history analyses and; (ii) to investigate the inelastic behavior of the 4-, 8- and 12-storey E-ZBF buildings located in a high risk seismic zone (Victoria, BC) under crustal, subduction, and near-field ground motion ensembles. Accordingly, the potential performance of E-ZBF buildings subjected to a giant Cascadia subduction earthquake was investigated. It was found that the long-period shaking from the megathrust Tohoku earthquake (2011) may cause severe structural damage in the 12-storey building and even collapse. In addition, findings of the present study are significant for the development of displacement loading protocols.