Current World Environment Vol. 10(Special Issue 1), 106-110 (2015) An Overview of Pros and Cons of Zipper Braced Frames A. MIRZA GOL TABAR ROSHAN 1 and R. NODEH FARAHONI* 2 1 Civil Engineering Faculty, Babol Noshirvani University of Technology, Babol, Iran. 2 Structural Engineering, Babol Noshirvani University of Technology, Babol, Iran. http://dx.doi.org/10.12944/CWE.10.Special-Issue1.15 (Received: November, 2014; Accepted: April, 2015) ABSTRACT The chevron bracing system provides the highest level of stiffness and average ductility by using the yield or buckling of braces. This system demonstrates weak post-buckling behavior while other structural members such as beams, columns and joints show elastic behavior. As a result of bracing buckling at a story, the unbalancing force acts perpendicular on the middle of the beam span and results in the concentration of damage on that story. Consequently, the affected story becomes prone to the soft story mechanism and the structure collapses eventually. In order to prevent this problem, it is possible to place vertical elements (zippers) between beams so that the head of bracings are connected at height and the resulting unbalancing force in the story is transferred to upper stories. Such a frame is known as the zipper frame. With a proper zipper configuration, it is possible to address the problems and weaknesses of the chevron bracing frame. Therefore, zipper frames can become proper substitutes for this type of bracing systems. By using the chevron element in the chevron bracing and turning it into a zipper frame, it is possible to increase the strength, ductility and energy absorption capacity of such frames. Key-words: Chevron, zipper frame, ductility, energy absorption, bracing INTRODUCTION Lateral load-bearing systems should have the level of stiffness and strength required for preserving and controlling the lateral deformations of buildings. The increase in lateral deformations of buildings not only leads to an increase in the damage caused to structural elements, but also threatens the stability and story mechanism. The concentrically braced frame system is one of the most common lateral load-bearing systems. There are two types of this system depending on their resistance to lateral loads: Concentrically braced frame (CBF) systems and special concentrically braced frame (SCBF) systems. The major advantage of SCBF systems over CBF systems is their ability to absorb large nonlinear deformations and attenuation. Special concentrically braced frames (zippers) shown in (Figure 1) demonstrate a better seismic performance compared to chevron frames (Figure 2). In order to reduce the chance of formation of soft story and obtain stable non-elastic seismic responses with chevron frames (figure 3) it is recommended to add a zipper column to the junction between braces and the beam. The zipper column is added to chevron bracing frames to cause simultaneous buckling of all compressive braces and yielding of all tensile braces. As a result, a large amount of energy is wasted. An Introduction to Zipper Braced Frames In 1988, in order to address the seismic defect of chevron braces (inverse V) and prevent formation of soft story, Khatib et al 1 recommended to use zipper columns (figure 4) Zipper columns are attached vertically and lie perpendicular (90 degrees) to floor beams. These columns can transfer