Innovative Self-Centering Connection for CCFT Composite Columns

Abstract

Concrete filled steel tubes are regarded as ideal frame members in seismic resisting systems, as they combine large axial and flexural capacity with ductility. The combination of the two materials increases the strength of the confined concrete and avoids premature local buckling of the steel tube. These benefits are more prominent for circular than for rectangular concrete filled steel tubes. However, most common connection configurations for circular concrete filled tubes are not economic in the US market due to (a) the desire of designers to use only fully restrained connections and its associated (b) high cost of fabrication and field welding. Research indicates that well designed partially restrained connections can supply equal or even better cyclic behavior. Partially restrained connections also possess potential capability to develop self-centering system, which has many merits in seismic design.

The goal of this research is to develop a new connection configuration between circular concrete filled steel columns and conventional W steel beams. The new connection configuration is intended to provide another option for rapid assembling on site with low erection costs. The proposed connection is based on an extended stiffened end plate that utilizes through rods. The rods are a combination of conventional steel and shape memory alloy that provide both energy dissipation and self-centering capacity. The new connection configuration should be workable for large beam sizes and can be easily expanded to a biaxial bending moment connection.