Sliding corner gusset connections for improved buckling-restrained braced steel frame seismic performance: Subassemblage tests

Although brace-type hysteretic dampers have been widely adopted to mitigate structural damage under severe earthquakes, their performance was often limited by premature rupture of the welded corner gusset connection or its surrounding framing members due to additional frame action. Such a frame-gusset interaction was found more detrimental for buckling-restrained braced frames (BRBFs). A sliding corner gusset connection, which is connected to beam and column flanges by bolted end plates, but allows sliding deformations at the frame-gusset interfaces via employment of butyl rubber layers, is proposed to minimize such an interaction. Cyclic tests of three steel BRBF subassemblages, two with the proposed sliding configuration and another with the traditional welded one, were conducted to verify effectiveness of the proposed connection. Test results show that significant plastic damages were observed on the welded gusset connection and its surrounding beam. Seismic performance of this specimen was limited by significant out-of-plane and local buckling of the beam prior to brace rupture. Such an undesirable failure could be avoided by the proposed connection, in which the specimen with beam flange reinforcing plates exhibited satisfactory performance up to 4% drift, followed by additional 3% drift with 11 more cycles until brace rupture. The proposed connection is effective in reducing the seismic shear and flexural responses on the framing members, as well as the stress responses at the gusset interfaces. Structural behavior of the two types of gusset connection is compared and future research needs for design of these connections are provided.