Experimental research and cyclic behavior of buckling-restrained braced composite frame

• The boundary members of BRBCF are concrete-filled steel tube columns and steel beams.
• The BRBCF joints are welded splices beam–column–BRB connections.
• The failure modes of joints due to frame and brace action forces are analyzed.
• The BRBCF shows good cyclic behavior and energy dissipation capacity.
• The performance of composite frame is increased evidently while installed with BRBs.

The pseudo-static tests (PSTs) of one 1/3 scale 2-story 1-bay buckling-restrained braced composite frame (BRBCF) system consisting of concrete-filled circular hollow section (CHS) steel columns, steel beams and BRBs were tested in Harbin Institute of Technology, a same bare composite frame (CF) was tested to compare with BRBCF. The test BRBCF exhibited excellent performance and sustained no strength or stiffness degradation during the significant drift demands imposed by the subsequent quasi-static cyclic test, which possessed good ductility and energy dissipation capacity. Compared with CF system, the stiffness, load-bearing capacity and energy dissipation capacity of BRBCF system increased evidently. The welded splices beam–column-BRB connections are cheap joints and are convenient to install BRBs in construction site, the experiment demonstrated their ability to withstand major ductility demands. The BRBs didn't show global buckling, local buckling and fracture of inner cores. Test also found the damage in beam–column–BRB connections region, including fractures of the gusset and beam welds, local buckling of flanges and webs of beams and enforced loops due to frame and brace action forces, which should be considered in the design of BRBCF. For frames using the proposed gusset connection, the maximum frame drift prior to failure will be governed by the rotational capacity of the beam-to-column connection, not the axial deformation of the BRB. The fracture and buckle of CHS steel tubes at the first story base indicated the thickness of CHS steel tube of composite columns in BRBCF should be enlarged to avoid the early failure of composite columns.