Results of early collaborative research on behavior of braced steel frames with innovative bracing schemes (zipper frames)

The new Network for Earthquake Engineering Simulation (NEES), which was inaugurated in late 2004 in the USA, intends to transform the way earthquake engineering research is conducted. In this paper, the initial collaborative experiences with an early NEES project will be described and some early technical results reported. The vehicle used for the collaboration is the development of design provisions and analytical tools for zipper frames. Zipper frames are intended to improve on the behavior of conventional inverted-V-braced frames, which exhibit poor performance arising from the early buckling of the lower story braces. A zipper frame provides better performance by forcing simultaneous buckling of all braces. In this project, that behavior is tied to the use of an elastic hat truss at the top of the building, which prevents the formation of an overall collapse mechanism. The collaborative nature of the project arises from the need to test prototype and small scale model structures under both quasi-static and dynamic loading, and by the need to supplement such tests with much more economical subassemblage ones.