A Comparative Study on Seismic Performance of Zipper and Special Chevron Braced Frames

Zipper braced frames are an innovative bracing system for steel structures. Conventional inverted-V-braced frames exhibit a design problem arising from the unbalanced vertical force generated by the lower story braces when one of them buckles. This adverse effect can be mitigated by adding zipper columns or vertical members connecting the intersection points of the braces above the first floor. In this paper anumerical study has been performed to estimate and to compare seismic performance of zipper braced and special chevron braced frames. For this purpose nonlinear pushover static analysis and nonlinear dynamic time history analysis have been performed on typical building structures with different number of stories under several earthquake ground motions. According to the analysis results، the ductility and response modification factors of chevron braced frames computed from nonlinear static analysis were generally smaller than the values obtained for zipper braced frames and the distribution of inter-story drifts ratio and maximum story drifts obtained from nonlinear time history analysis، demonstrates the efficiency of the zipper struts in achieving a more uniform damage distribution over the height of the structure، and generally satisfies allowable inter-story drift ratio limits.