Seismic performance of buckling-restrained braces using welded end and rectangular steel casing
Journal
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering
Date Issued
2014
Author(s)
Abstract
The buckling-restrained braced frame has been evolved into a very effective system for buildings in seismic areas. Most of the buckling-restrained braces (BRBs) are fabricated by using a doubly-symmetrical steel core, encased in the square or circular mortar-infilled 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 BRB end connections would reduce the length of the energy dissipation segment. The BRBs using a single flat core plate as the energy dissipation segment could be fabricated with a rectangular steel casing to minimize the intervention in the usable floor area. However, the high mode buckling of the flat core plate is likely to introduce significant outward bulging forces and cause local failure of the thin-profile steel casing. In this study, a novel BRB with a thin profile is developed to prevent the BRB restrainer from possible local failure. The core member of the proposed BRB primarily consists of at least two parallel flat plates connected by the additional perpendicular flat plate. The parallel plates develop most of the brace axial force and the high mode buckling of these plates is constrained by the perpendicular plate. The parallel plates are oriented perpendicular to the gusset and slotted at both ends. Thus, the welded end-slot connection allows a longer BRB energy dissipation segment than that in the BRB using the bolted end details. Cyclic loading tests are conducted in the National Center for Research on Earthquake Engineering on five BRB specimens with two different cross-sectional configurations. A maximum core strain of 0.04 is reached during each test. Test results confirm the satisfactory BRB 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. Tests also confirm that the exterior dimension of the steel casing can be no larger than 600„e400mm for a thin-profile BRB of 10m long with a yield capacity of 12,000kN. The hysteretic responses are satisfactorily predicated by the finite element model analysis. This paper concludes with the recommendation for seismic design of the proposed thin-profile BRBs.
Type
conference paper