ABSTRACT
As the application of performance-based seismic design begins to take root, it is clear that new structural concepts need to be developed to meet the demand performance for low and moderate levels of seismic loading. These demands can be met through the development of entirely new structural systems or the combination of existing structural elements that exploit their synergistic behavior in conventional systems. This paper describes an example of the latter, where the robustness and structural efficiency of concrete-filled tube (CFT) columns are combined with the ductility and recentering capabilities of a partially restrained (PR) connection utilizing a mix of materials (Fig. 4.1). This type of system is applicable in moment-resisting buildings from 3 to 10 stories, and combines a number of the advantages associated with composite systems (Mao & Xiao, 2006; Wu et al., 2006). The advantages for CFT columns include the fact that the concrete prevents local buckling of the steel tube wall and that the confinement action of the steel tube extends the usable strain of the concrete after ultimate compressive strength. These advantages result in stronger and stiffer columns with superior cyclic performance (Choi et al., 2010; Hu et al., 2010). In particular, concrete-filled tubes show enhanced ductility and reduced rates of degradation under cycling at large drifts when compared to conventional steel or RC columns (Mao & Xiao, 2006; Wu et al., 2006; Choi et al., 2010).
