Numerical Investigation of Code-Designed Ductile Eccentrically Braced Frames

Nonlinear seismic analysis procedures can accurately estimate structural responses but are computationally intensive, making them impractical for engineering design. This study provides the first comprehensive evaluation of N2 and modal pushover analysis for eccentrically braced frames (EBFs), revealing their strengths and limitations in predicting link rotations, shear demands, and drift distribution under Canadian seismic hazards. Analyzed were four-, eight-, and 14-storey chevron EBFs under real and artificial ground motions compatible with the response spectrum of Vancouver, Canada. The findings indicate that inelastic link rotations for all EBFs remain below the design limit of 0.08 rad, except for the upper two floors of the 14-storey EBFs. Seismic analysis reveals that maximum inelastic link shear forces often exceed design recommendations. It is also observed that both the N2 method and MPA procedure could reasonably predict the peak roof displacements for low-rise EBF buildings. In addition, while the MPA procedure provides better predictions of maximum inter-storey drifts over all storeys for medium-to-taller EBFs, inter-storey drifts are not predicted well in the N2 method. Additionally, the current code formula for estimating the fundamental period of EBFs predicts shorter periods than those obtained from analysis. An improved formula for estimating EBF periods is proposed.