Subassemblage Testing of CoreBrace Buckling-Resistant Braces (NZ Series)

Two BRB specimens (NZ1 and NZ2) was cyclically tested to support the design and construction of New Zealand International Convention Center in Auckland, New Zealand. A36 steel core plate was used, which was encased in a grout-filled round HSS casing of A500 Gr. B steel. The braces had a bolted connection at one end and an eccentric pin connection at the other end. The cyclic loading protocol was composed of three stages. The first stage loading was the same as that specified in the AISC Seismic Provisions. The second stage loading was developed to impose a greater deformation demand to the BRB specimens to demonstrate that the specimens could achieve a cumulative inelastic axial deformation of at least 200 times the yield deformation. The third stage loading was intended to evaluate the ultimate cumulative deformation and energy dissipation capacities; the amplitudes used for Specimen NZ1 were much larger than that for Specimen NZ2. Axial and transverse displacements were imposed in phase to the specimens in the horizontal plane to simulate the frame action effect at the gusset connections. In addition, a cyclic out-of-plane displacement in the vertical direction was imposed to Specimen NZ2. As a reference to evaluating this effect, Specimen NZ1 was not subjected to this component of displacement.
Both specimens performed well during the Stages 1 and 2 testing. Specimens NZ1 provided stable hysteretic response for two cycles at 18by displacement in Stage 3 testing. Core plate then fractured during the third cycle of the stage 3 protocol (at 20Δby). Specimen NZ2 experienced necking of the core plate during the 25th cycle of the stage 3 protocol (at 8Δby) before the test was stopped. Both specimens met the AISC Acceptance Criteria, showing stable and repeatable behavior with positive incremental stiffness and a cumulative inelastic axial deformation significantly greater than 200 times the brace yield deformation. The compression strength adjustment factors, β, was less than 1.3. The presence of an out-of-plane displacement reduced the values of both  and  factors somewhat. But the dissipated energy was about the same up to the Stage 2 loading. Specimen NZ2 showed a much larger energy dissipation capacity in Stage 3 testing because the imposed deformations were smaller.