Foundation connections for circular concrete-filled tubes

Concrete filled steel tubes (CFTs) promote economical and rapid construction. They offer increased strength and stiffness relative to structural steel and reinforced concrete. The steel tube serves as formwork and reinforcement to the concrete fill, thereby reducing the labor requirements. CFT components encourage the optimal behavior of each material (concrete and steel) while providing a symbiotic relationship between the two to mitigate undesirable failure modes. The fill increases the compressive strength and stiffness, delays and restrains local buckling of the tube, and enhances ductility and resistance if composite action is achieved. Both rectangular and circular CFT have been employed, but circular CFT provide better performance, because they provide increased confinement of the concrete and composite action. A missing component for circular CFT construction is reliable and ductile connections. The research described herein that investigated and develops design procedures for simple and economical connections of circular CFT piers or columns to reinforced concrete foundations, pile caps and wide cap beams (bridge construction) is presented and evaluated. The connection requires no dowels or internal reinforcement connecting the tube to the footing or cap beam. Experiments and analytical studies evaluate the inelastic seismic performance and establish design criteria for the connection. The seismic performance of a CFT column and connection assembly is compared to a conventional reinforced concrete column. The research shows that the proposed connection develops the full capacity of the composite column. The assembly provides excellent ductility and inelastic deformation capacity under seismic loading while mitigating damage even at larger drift demands. (C) 2012 Elsevier Ltd. All rights reserved.