Estimating Seismic Performance Factors for a Dual System Comprising Buckling Restrained Brace Frames and Intermediate Moment Frames

Dual structural system is referred when two different lateral systems are combined together to provide the lateral force resisting system for a building structure. For different structural and architectural reasons, dual systems are used in building structures. The most common types of dual systems include special moment resisting frames (SMRF) combined with eccentric braced frames (EBF) or buckling restrained braced frames (BRBF) in steel buildings and special reinforced concrete moment frames combined with special reinforced concrete shear walls in reinforced concrete buildings. Buckling restrained braced frame is a lateral framing system that are being used in high seismic zones. According to American Society of Civil Engineers (ASCE), a dual system is permitted between buckling restrained braced frames (BRBF) and special moment resisting frames (SMRF) where SMRFs must be capable of resisting at least 25% of prescribed seismic force. Conventionally, dual systems are utilized at high seismic zones. For moderate seismic zones intermediate moment resisting frames (IMF) can be used instead of SMRF. But, ASCE does not provide any guideline to assess the structural responses when a dual system combining BRBF and IMRF are used in buildings located at moderate seismic zones. This research, shows a methodology to calculate the seismic parameters like Response Modification Coefficient (R), Over - strength Factor (Ωo) and Deflection Amplification Factor (Cd) which are not described by ASCE or FEMA guideline. Several archetypes of building structures are designed following FEMA guidelines with modified R as trial values for different seismic zones. To validate the trial values for R, system over - strength and period - based ductility, nonlinear 3D static (pushover) analyses were performed .