Hybrid buckling-restrained braced frames

• Novel enhancement of the buckling restrained brace (BRB) system.
• Use of low, medium strength, and high strength steel within the core of the braces.
• Use of the FEMA P-695 procedure to develop collapse fragility.
• Reduction of residual drift compared to traditional BRBs.
• Reduction in collapse probability compared to traditional BRBs.

Structural systems that are available in building codes are calibrated for good performance at severe performance objectives (like life safety) under high earthquake hazard levels. However, building performance under low earthquake hazards is uncertain. The optimum seismic structural performance depends directly on the ability of stable hysteretic energy dissipation of ductile systems. This paper introduces a new structural steel system called hybrid buckling-restrained braced frame (BRBF). The “hybrid” term for the BRBF system comes from the use of different steel materials, including carbon steel (A36), high-performance steel (HPS) and low yield point (LYP) steel in the core of the brace. Nonlinear static pushover and nonlinear incremental dynamic analyses were conducted on a variety of BRBF models to compare the seismic behavior of standard and hybrid BRBF systems. Hybrid BRBF systems are shown to have a significant improvement over standard BRBF systems in terms of various damage measures including a significant reduction in the problematic residual displacements of the standard BRBFs.