QUANTIFICATION OF SEISMIC PERFORMANCE FACTORS FOR CIRCULAR CONCRETE-FILLED STEEL TUBE DIAGRID STRUCTURES

Abstract

In 21st century, diagrid structures become more popular lateral force-resisting systems for high-rise buildings world-wide. It consists of several grids of diagonal members on building perimeter serving as both lateral bracing and vertical-load carrying members. Since the diagrid structure is a relatively new type of lateral force-resisting system, current building codes do not explicitly provide the seismic performance factors (SPFs) for this system to use in design process. This thesis aims to determine appropriate SPFs for the diagrid structure incorporating circular concrete-filled steel tube to enable structural engineers to design this system according to seismic performance expected in building codes. This research follows FEMA P695 procedure to evaluate SPFs by examining collapse performance of buildings based on nonlinear response history analysis considering various sources of uncertainties. The verified SPFs ensure an acceptably low likelihood of structural collapse under extremely rare earthquake ground motions or maximum considered earthquake. Sample buildings in this thesis are 18, 24 and 36-story buildings using circular concrete-filled steel tube diagrid as lateral force-resisting system. The buildings were assumed to locate in downtown Bangkok. Each sample building was subjected to 12 ground motion records based on its periods of vibration. The sample buildings designed with response modification coefficient equal to 5 meet the acceptance criteria of FEMA P695. A deflection amplification factor can be used as 5, and a system overstrength factor can be used as 3.