Development of centrically fused braced frame (CFBF) for seismic regions

Abstract

This research presents an experimental study to develop a novel structural fuse for concentrically braced frame (CBF) system using ductile mid-height gusset plate by proposing the specified innovative detailing. This concept leads to concentrated inelastic deformation and the largest stress demand on a very thin mid-height gusset plate as an intentional weak point. Since other structural steel members including corner gusset plates, braces, beam and columns remain within the elastic range of steel material; this concept protects structural elements from damages and improves seismic performance of CBF. To demonstrate the efficacy of the improved CBF system, which is so called “Centrically Fused Braced Frame (CFBF)”, cyclic lateral test are conducted on four three-fourth scale braced frame test specimens using the proposed detailing of mid-height gusset plates. The results of experimental study indicate that CFBF can meet the criteria as desired by AISC codes for CBF; Also it is shown that increasing the thickness of mid-height gusset plate within a very limited range between 2 to 5 mm decreases the strength degradation by up to 40% however increases the relative out-of-plane displacement of the braces approximately by up to 5 times. Finally a design method is suggested to enhance the cyclic behavior of CFBF system.