Analysis Methods for the Design of Special Concentrically Braced Frames with Three or More Tiers for In-Plane Seismic Demand

Abstract

This paper presents two analysis methods for the in-plane seismic response of steel multitiered braced frames (MT-BFs) with three or more tiers: (1) a substructuring technique; and (2) a stiffness analysis method. Both methods are consistent with the 2010 AISC Seismic Provisions and have been developed to estimate column flexural demands and tier drifts to prevent column instability and to mitigate concentration of tier drifts as well as premature brace failure under seismic loading. Both methods account for the progression of brace tension yielding along the frame height as observed in MT-BFs. The substructuring technique is simpler and is limited to regular frames, as it assumes a predefined yielding sequence. The stiffness analysis–based method is more rigorous and can predict the actual frame nonlinear response. It can be applied to both regular and irregular MT-BF configurations. The application of the methods is illustrated for two five-tiered special concentrically braced frame examples. Nonlinear response history analysis is performed to validate the proposed methods for the frames studied.