Seismic behavior and design of composite SMRFs with concrete filled steel tubular columns and steel wide flange beams

The use of composite structures has become more common for buildings in moderate to high seismic zones because of their cost-effective alternative compared to steel structures. A composite structure constructed of concrete filled tubular (CFT) columns is one of them. Due to lack of information related to the seismic behavior of composite structures, current design code provisions treat the composite structures as an extension of traditional steel or reinforced concrete structures.; This research presents an analytical study on the seismic behavior of a six-story prototype building utilizing a composite special moment resisting frame system constructed of CFT columns and WF beams (CFT-SMRF system). The prototype building was designed considered the code requirements for strength and stiffness using the International Building Code 2000 (IBC 2000) Provisions as well as the member inelastic deformation limits established in this research. The member sizes were controlled by the drift requirement and providing a strong-column/weak-beam configuration.; Analytical models of the members were developed for nonlinear analyses. The models were calibrated with available experimental test data. The effects of steel yielding and local buckling as well as concrete confinement, concrete cracking and concrete crushing that result in stiffness and strength degradation were incorporated into the models.; Static pushover analyses were performed. Time-history analyses were also performed using several earthquake records scaled to two hazard levels to evaluate and compare the seismic performance of the CFT-SMRF system with performance levels of Life Safety and Collapse Prevention. The limit states and inelastic response from analyses were used to evaluate the building performance. A reliability analysis was performed to investigate the possibility of failure in members.; The analysis indicated that the prototype building had a significant system overstrength because the design was controlled by drift requirement. The prototype building performed adequately under both hazard levels. Based on the observation from the analysis, some recommendations are made for improving current seismic design. These recommendations were applied to the prototype building without any change in the sizes of the structural members because the design was controlled by drift requirement.