Investigation of seismic response of asymmetric buckling restrained braced frames equipped with zipper struts

Abstract

One of the most important deficiency of buckling restrained braced frames is the concentration of lateral drifts in some specific stories and the soft story mechanism, under moderate to severe earthquakes. In this paper, in order to prevent the development of soft story mechanism in buckling restrained braced frames, asymmetric configuration along with a zipper strut is proposed for chevron type ordinary buckling restrained braced frame.The zipper strut connects the midpoints of beams at the brace intersections in all stories and carry the unbalanced axial force developed at the intersection. In addition, it causes the BRBs to uniformly yield over the height of structure. For this purpose, 4, 10, and 14 story buckling restrained braced frames were designed according to Iranian seismic code, and the nonlinear time history analyses were performed in Opensees, subsequently. The analysis results showed that the asymmetric buckling restrained braced frames possess more uniform lateral drift demands in comparison to ordinary symmetric buckling restrained braced frames, is less prone to the formation of soft story mechanism. The zipper elements were found to carry a significant axial forces during analyses, and were responsible for distribution of unbalanced forces among BRBs over the height of braced frames.

Keywords

• buckling restrained brace
• zipper strut
• time history analysis
• peak drift
• peak residual drift