Proposed seismic design parameters for the moment-resisting knee-braced frame system

Abstract

This paper proposes and verifies the seismic design parameters, including overstrength-related force modification factor, ductility-related force modification factor, deflection amplification factor, and design period, for the steel Moment-resisting Knee-braced Frame (MKF) system. The building selected in this study is an office located in Vancouver, British Columbia, Canada, in which MKFs act as the lateral load-resisting system. 14 prototype frames spanning a wide range of geometrical configurations are designed following the requirements of the 2015 National Building Code (2015 NBC) of Canada. Nonlinear static analyses are carried out on the prototype frames to determine the preliminary ductility and overstrength factors. Six new MKFs (assessment frames) are designed using the proposed overstrength and ductility factors, and their seismic and collapse performances are examined by comprehensive numerical analyses, considering the effects of the potential sources of ground motion expected on the Canadian west coast, namely subduction intraslab, subduction interface and shallow crustal events. The results of this study suggest that the MKF system shall be designed as a moderately ductile system using overstrength and ductility factors of 1.60 and 3.0, respectively, with a height not exceeding 40 m in regions of high seismicity.