Evaluation of hysteretic behavior of eccentrically braced frames with zipper-strut upgrade

This paper describes the seismic behavior of Eccentrically Braced Frames (EBF) upgraded using zipper-struts which connect the mid-point of shear links in all stories.The numerical modeling of the zipper-strut-equipped model is conducted using finite-element method software under cyclic load, with the goal of evaluating the behavior of shear links. The interaction of shear links and zipper-struts is also studied. Furthermore, the prototypes are subjected to nonlinear static (Pushover) analysis in two configurations; one with moment-resisting connections and one with pinned connections. Finally, the increase of ductility coefficient for the prototypes with zipper-strut is studied. The prototypes are also subjected to time-history analysis using scaled earthquake records, with the purpose of studying the energy parameters of the models.The unbalanced shear force is distributed among all stories due to the added continuity among shear links. This results in the extension of structural displacement capacity according to acceptance criteria. Moreover, a noticeable delay occurs until shear links experience enough rotation to meet Collapse Prevention acceptance criteria. By imposing acceleration on the structure and conducting time history analysis, it is observed that the zipper-strut-equipped system shows a stronger tendency to form shear links, leading to greater dissipation capacity in plastic zone.

► The paper introduces a new upgrade to the regular Eccentrically Braced Frames.
► Vertical elements (zipper-struts) connect the midpoint of shear links.
► FEM, pushover and time-history analyses are conducted.
► The results show better behavior in controlling lateral force and story drifts.
► The new system is more ductile is more economical than most active systems.