Energy-based seismic design of buckling-restrained braced frames using hysteretic energy spectrum

An energy-based seismic design procedure for framed structures with buckling-restrained braces is proposed using hysteretic energy spectra and accumulated ductility spectra. The procedure is based on the premise that the gravity load-resisting elements, such as beams and columns, are designed to remain elastic during earthquake, and all the seismic input energy is dissipated by the buckling-restrained braces. The proposed design procedure requires hysteretic energy spectra and accumulated ductility spectra corresponding to various target ductility ratios. The cross-sectional area of braces required to meet a given target displacement is obtained by equating the hysteretic energy demand to the accumulated plastic energy dissipated by braces. The design procedure was applied to three- and eight-story framed structures with buckling-restrained braces. Twenty earthquake records were utilized to construct the spectra and to verify the validity of the design procedure. According to analysis results, the mean values for the top story displacement correspond well with the given performance target displacements. Also, the inter-story drifts turned out to be relatively uniform over the structure height, which is desirable because uniform inter-story drifts indicate uniform damage distribution.