Seismic performance of buckling-restrained braces using welded end and rectangular steel casing

Most of the buckling-restrained braces (BRBs) are constructed from a doubly-symmetrical steel core encased in the mortar-infilled square or circular steel casing. The bolt-spliced connection details are found most common for the brace-to-gusset connections. While the horizontal width of a large-capacity BRB using the square or circular steel casing could substantially reduce the usable floor area in a building, the bolted end connections would reduce the end stability and the yield region length. In this study, a BRB with a thin profile is developed which could sufficiently prevent the buckling restrainer from the possible global flexural buckling and local failure. The welded end-slot connection shortens the entire BRB joint region length, allows a more stable end condition and a longer yield region length than those in the BRB using the bolted end details. Cyclic loading tests are conducted in the Taiwan National Center for Research on Earthquake Engineering on five BRB specimens with two different cross-sectional configurations. A maximum core strain of 3.0% is reached during each test. Test results confirm the satisfactory performance with a very stable hysteretic response and very predictable axial stiffness. All specimens sustain a cumulative plastic deformation significantly greater than 200 times the yield deformation. The effects of the BRB yield region length ratio on the effective axial stiffness, the frame yield story drift and the core strain level are illustrated through a simplified approach.