EXPERIMENTAL AND ANALYTICAL STUDY OF THE CYCLIC PERFOR-\MANCE OF SPECIAL CONCENTRIC BRACED FRAMES

The special concentrically braced frame (SCBF) is a common type of steel structural system for resisting lateral loading. This type of system provides the required stiness and strength at relatively low cost. Design codes, based on past research, have recommended some details for connections and braces, in order to ensure suf- cient ductility and energy dissipation capacity in this system for their application in seismic design. In this paper, the behavior of four SCBF specimens with dierent details of connections is studied using experimental and numerical models. They are single story single bay sub-assemblages of frames with a single brace that are subjected to lateral cyclic loads. In the rst specimen, a 2tp straight line clearance at the end of the brace was observed, but, in the second specimen, an 8tp elliptical clearance was provided. In the third and fourth specimens, stieners were installed to provide enough sti- ness for gusset plates, so that they can act as xed ends for braces. The dimensions of the gusset plates in these specimens were naturally dierent. Measures such as stiness, strength, ductility, energy dissipation capacity and equivalent plastic strain are used to compare the behavior of specimens in experiments and nite element analysis. The results show that all specimens satisfy code expectations with regard to seismic performance. For unstiened gusset plates, the accumulation of plastic strain at the corners of the gusset plates and in the middle of the brace results in crack initiation and fracture in specimens in the nal stages of cyclic loading. In stiened specimens, although gussets are smaller, plastic hinges are formed in the middle and at the end of the brace element, but nal cracking and fracture occurs in the middle of the element. In these specimens, higher buckling resistance and lower out of plane displacement of braces are observed.