What Is a Buckling-Restrained Braced Frame (BRBF)?
A buckling-restrained braced frame uses special braces with a steel core that yields in both tension and compression — the core is encased in concrete or mortar inside a steel tube that prevents it from buckling. Unlike conventional braces (which buckle in compression and lose capacity), BRBs yield symmetrically, dissipating enormous earthquake energy. BRBFs are the premium seismic system for buildings where performance matters.
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How BRBs work
The steel core carries the axial load; the encasing restrains buckling but is debonded from the core so it carries no axial load itself. In an earthquake, the core yields in tension on one cycle and in compression on the next — stable, symmetric hysteresis that absorbs energy far beyond what a buckling brace manages. The brace behaves like a structural fuse: it yields to protect the rest of the frame.
Advantages over conventional braced frames
Higher ductility (R=8, matching special moment frames), no buckling means no strength degradation, smaller braces for the same force (the full cross-section works in compression), and predictable performance that simplifies capacity design of the connections and columns. The trade-off: BRBs are proprietary manufactured elements ($5,000-$20,000+ each) with submittal and testing requirements — AISC 341 requires prototype testing of the brace design.
Design and construction
The structural engineer sizes the steel core area from the seismic forces, designs the connections for the brace's maximum (overstrength) capacity — the gussets and beams must survive the brace's full yielded strength — and details the frame for the brace deformations. BRBs arrive from the manufacturer with test certifications; the special inspector verifies the model, installation, and connections. Used in hospitals, high-rises, and essential facilities where the seismic performance justifies the premium.
The bottom line
BRBs yield in tension and compression without buckling — the premium seismic brace (R=8) for high-performance buildings. Design connections for the brace's overstrength; require manufacturer test certifications.
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