Buckling-Restrained Braces (BRB) are becoming more popular in modern designs and retrofits of existing buildings due to their ductile, symmetric and full hysteretic characteristics. They also have the ability to be tailored for both strength and stiffness to meet specific design requirements. Analysis has shown that there may be a discrepancy between the predicted ductility demand on BRBs determined from a nonlinear dynamic analysis and that determined from a code-based, elastic response spectrum analysis. Recent code changes have updated the drift requirements imposed on Buckling-Restrained Braced Frames (BRBF) in order to more accurately meet the ductility requirements for the BRB element. This paper will consider the code-conforming ELF designs of both 3-story and 6-story BRBF buildings, through non-linear dynamic analysis to recorded and synthetic strong-motion time histories and compare the resulting ductility, strain, and story drift demands to the code-required ELF 2% story drift demands. The potential negative effects of varying the yielding core lengths of BRBs to tailor the frame stiffness versus increasing the cross-sectional area of the BRB to achieve similar effect will be discussed. The resulting analysis-based overstrength factors will be compared with those resulting from the amplified elastic analysis. The ground motions used in this study encompass near-field and far-field motions for two different seismic hazards each at an importance level of 1.0 and 1.5. The research will suggest deformation ductility requirements that could be used for BRBF design and will comment on the applicability of the 2% story drift requirement in the current seismic provisions.
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