Experimental investigation of steel frames with single bays of symmetrical y-shaped concentric bracings

Abstract

To obtain wider openings than those provided by Chevron bracing, the braces are cranked and connected to the frame corner by an additional brace to form double y-shaped bracings. However, y-bracings are prone to instability and out of plane buckling, accompanied by low hysteretic energy absorption. An experimental research program, focused on y-bracing, was conducted at the BHRC structural engineering laboratory. Specimens presented in this paper include three full-scale single bay frames, with symmetric y-bracing of different cross sections and connection types. In addition, one specimen with Chevron bracing was tested as a reference. A quasi-static cyclic loading was applied increasingly until yielding and failure occurred in the specimens. The results show that out-of-plane buckling is the governing mode of behavior, despite differences in the detailing of cross sections and connections. Hysteretic energy dissipation and damping of y-bracing are remarkably improved due to the flexural deformation of brace members. The seismic performance of the three y-braced frame specimens and a reference Chevron-braced frame was assessed using the capacity spectrum method. The results show that the y-braced frame, with double gusset plates, can carry almost 60% more weight than y-braced frames with single gusset plates.