On the development of zipper frames by pushover testing

This paper presents the results from an experimental program on the behavior of special inverted-V braced frames with suspended zipper struts subjected to pushover loading. The model tested was a one-third-scale frame designed on the basis of a procedure proposed by the authors. The frame was designed to carry similar loading as the 3-story frames designed for the Los Angeles area for the SAC project. The displacement histories applied to the floor levels by three actuators were obtained from nonlinear pushover analyses of the model subjected to an invariant lateral force profile with the model pushed to the target roof drift ratio of 3.58% and then pulled to the roof drift ratio of —2.59%. The experimental results validated the partial-height zipper mechanism envisioned in the design procedure. Once the lower story braces begin to buckle, the suspended zipper will act as a tension hat truss to mobilize the other braces to buckle. The top-story braces were designed strong enough to prevent the overall collapse mechanism. The reduced-scale suspended zipper frame exhibited great strength and ductility and remained stable when the target roof drift was reached.