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

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.