QUANTIFYING GLOBAL SEISMIC PERFORMANCE FACTORS IN DUAL SYSTEMS WITH BUCKLING RESTRAINED BRACED FRAMES

Abstract

Dual structural systems are commonly used in high rise buildings for various architectural reasons. Buckling Restrained Braced Frame (BRBF) is an emerging seismic force-resisting system that is currently being permitted by American Society of Civil Engineers (ASCE) to be used either as a single seismic force-resisting system or in combination with other seismic force resisting systems. In conventional practice, ASCE suggests that while using BRBF in conjunction with other lateral force resisting systems in a dual configuration, the lowest Response Modification Factor (R) pertaining to the softer system shall be used. This may result in significant overdesigning of structures as higher contribution from the BRBF system are often remain unutilized. This research aims at developing a methodology for calculating modified Response Modification Factor, R for structures where dual system occurs horizontally. This research investigates the effect of using the newly suggested Response Modification Factor (R) for dual systems, where a BRBF system is combined with an Intermediate Moment Frame (IMF). The study aims at proposing an innovative way of calculating Response Modification Coefficient (R), Over-strength Factor (Ωo) and Deflection Amplification Factor (Cd) pertaining to the dual system. A wide variety of archetype sets 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. The nonlinear models directly simulate essential deterioration modes that contribute to collapse behavior. Afterwards, for collapse assessment, nonlinear incremental dynamic analyses are conducted.