Seismic response of steel multi-tiered eccentrically braced frames: Fid-Bau Portal

Seismic response of steel multi-tiered eccentrically braced frames

Ashrafi, Abolfazl / Imanpour, Ali

Abstract Steel eccentrically braced frames (EBFs) are commonly used as a lateral load-resisting system, in particular in high seismic regions, due to their high ductility, stable and reliable yielding mechanism, and architectural versatility as compared to concentrically braced frames. This article presents the use of EBFs in tall single-storey structures where multiple braced panels with intermediate links are stacked along the frame height, which is referred to as multi-tiered eccentrically braced frames (MT-EBFs). A set of nine frames having different heights, number of tiers, relative tier heights, and brace-to-beam connections are designed in accordance with the Canadian steel design standard. The seismic performance of the frames is then examined using nonlinear response history analysis (NLRHA) with an emphasis on the stability of intermediate links and columns as well as in-plane tier drift and column moment demands. As potential solutions to this problem, alternative intermediate link designs are examined and their seismic performance is presented. The results show that lateral frame deformations tend to non-uniformly distribute between tiers due to uneven link shear yielding, which impose large moments on outer beams and in-plane and out-of-plane bending demands on the columns, which in some cases leads to column buckling. The unbraced intermediate links are found to be prone to lateral out-of-plane buckling. Alternative design strategies except MT-EBFs with laterally-braced links did not appreciably improve link and column stability. Intermediate link stability and column flexural demands shall be considered in seismic design of MT-EBFs.

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Highlights • The nonlinear numerical model of the steel multi-tiered eccentrically braced frame (MT-EBF) is developed. • Seismic response of MT-EBFs is examined using a numerical parametric study. • Lateral frame deformations tend to non-uniformly distribute between tiers due to uneven shear yielding of links. • Unbraced intermediate links are found to be prone to lateral out-of-plane buckling. • Large in-plane and out-of-plane moments are induced in columns due to progressive yielding of links and link buckling.