Seismic Performance Assessment of Multitiered Steel Concentrically Braced Frames Designed in Accordance with the 2010 AISC Seismic Provisions

Multitiered steel concentrically braced frames (CBFs) are commonly used to provide lateral resistance for tall single-story commercial, performing arts, sports, and industrial buildings. The seismic response of these frames is studied in this paper. A set of seven special concentrically braced frames (SCBFs), ranging from 9 to 30m tall with two to six tiers, located in a high seismic area was designed according to the 2010 AISC Seismic Provisions. Fundamental behavior of the two- and four-tiered frames was investigated using three-dimensional (3D) finite element models with shell elements, with particular focus on the buckling response of the columns. The seismic frame response and column stability were then studied more broadly for all frames using more computationally efficient 3D finite element models with fiber-based beam-column elements, which were validated against the shell element models. Multitiered CBFs designed according to current multistory CBF procedures are shown to develop drift concentration in a single tier and high in-plane column bending demand, which in some cases leads to flexural yielding and column instability. As potential solutions to this problem, alternate design strategies were studied and their seismic performance is also presented. Designing for higher seismic forces did not appreciably improve column stability, but use of fixed column bases or buckling-restrained braces provided improved distribution of drift over multiple tiers and reduced the occurrence of column instability. Unlike multistory braced frame seismic design, column flexural demands are more important in multitiered braced frames and must be considered in seismic design.