The Applicability of the Zipper Strut to Seismic Rehabilitation of Steel Structures

Chevron frames (Inverted-V-braced frames or Vbraced frames) have seismic disadvantages, such as not good exhibit force redistribution capability and compression brace buckles immediately. Researchers developed new design provisions on increasing both the ductility and lateral resistance of these structures in seismic areas. One of these new methods is adding zipper columns, as proposed by Khatib et al. (1988) [2]. Zipper columns are vertical members connecting the intersection points of the braces above the first floor. In this paper applicability of the suspended zipper system to Seismic Rehabilitation of Steel Structures is investigated. The models are 3-, 6-, 9-, and 12-story Inverted-V-braced frames. In this case, it is assumed that the structures must be rehabilitated. For rehabilitation of structures, zipper column is used. The result of researches showed that the suspended zipper system is effective in case of 3-, 6-, and 9-story Inverted-V-braced frames and it would increase lateral resistance of structure up to life safety level. But in case of high-rise buildings (such as 12 story frame), it doesn-t show good performance. For solving this problem, the braced bay can consist of small “units" over the height of the entire structure, which each of them is a zipper-braced bay with a few stories. By using this method the lateral resistance of 12 story Inverted-V-braced frames is increased up to safety life level.

Authors:

• G. R. Nouri
• H. Imani Kalesar
• Zahra Ameli

Keywords:

• chevron-braced frames
• suspended zipper frames
• zipper frames
• zipper columns

References:

[1] "ASCE 7-05: Minimum Design Loads for Buildings and Other
Structures", 2005, American Society of Civil Engineers, Reston, VA.
[2] I.F. Khatib, S.A. Mahin and K.S., Pister, "Seismic Behavior of
Concentrically Braced Steel Frames", 1988, Report No. UCB/EERC-
88/01. Berkeley, Earthquake Engineering Research Center, University of
California
[3] R. Tremblay, L. Trica, "Behavior and Design of Multi-Story Zipper
Concentrically Braced Steel Frames for the Mitigation of Soft-Story
Response", 2004, Proceedings of the 13th world conference on
earthquake engineering.
[4] Ch. Yang, "Analytical and Experimental Study of Concentrically Braced
Frames with Zipper Struts", 2006, PhD thesis, Georgia Institute of
Technology.
[5] "AISC. Manual of Steel Construction, Load and Resistance Factor
Design", 2005, American Institute of Steel Construction.
[6] "OpenSees: Open Systems for Earthquake Engineering Simulation",
http://opensees.berkeley.edu.
[7] Federal Emergency Management Agency. NEHRP guidelines for the
seismic rehabilitation of buildings, Rep. FEMA 273 (Guidelines) and
274 (Commentary), 1997,Washington, DC.