Design and behavior of zipper-braced frames

This paper proposes a design methodology for zipper-braced frames aimed at achieving ductile behavior. Three zipper-braced models were designed on the basis of the proposed design procedure to carry the same masses as the 3-, 9-, 20-story SAC model buildings with moment-resisting frames designed for the Los Angeles area. Pushover analyses of the models were performed to estimate the overstrength, inelastic strength and deformation capacities for the entire structures, and assess the sequence of yielding and buckling in the members. The performance of the models was also evaluated using nonlinear dynamic analyses under an ensemble of 2%-in-50-year pulse-type near-fault ground motions. The analyses indicate that the design procedure produces safe designs, with the design becoming more conservative as the number of stories increases. The distribution of interstory drifts demonstrates the efficiency of the zipper struts in achieving uniform damage over the height of the structure, and generally satisfies allowable interstory drift ratio limits.