An Economical and Efficient Foundation Connection for Concrete Filled Steel Tube Piers and Columns Charles W. Roeder Dept. of Civil Engineering, University of Washington 233B More Hall, Seattle, WA 98195-2700) croeder@u.washington.edu Dawn E. Lehman Dept. of Civil Engineering, University of Washington 233B More Hall, Seattle, WA 98195-2700) delehman@u.washington.edu ABSTRACT Concrete filled steel tubes (CFT) are economical and result in rapid construction. The steel tube serves as formwork and reinforcement to the concrete fill, and the fill increases the compressive strength and stiffness of the tube. The fill delays and restrains local buckling, and enhances ductility and resistance if composite action is achieved. Circular CFT provides better performance because the circular tube provides greater confinement of the concrete and composite interaction between the two materials. However, circular CFT is more difficult to connect to other structural elements, and recent research has provided a simple and economical connection to connect circular CFT piers or columns to reinforced concrete foundations, beams and pier caps. The connection does not require any reinforcement or dowels connecting the tube to the footing. A second variation of this connection permits sequencing of steel and concrete construction trades and connecting to precast concrete elements. A series of experiments have been completed to evaluate the inelastic seismic performance and establish design criteria for the connection. This work shows that the connection can develop the full capacity of the composite column, and provide great ductility and inelastic deformation capacity under seismic loading. INTRODUCTION Concrete filled steel tubes (CFT) permit economical structures that result in rapid construction. The steel tube serves as formwork and reinforcement to the concrete fill, and the fill provides increased compressive strength and stiffness to the steel tube. The fill delays and restrains local buckling, and enhances ductility and resistance if composite action is achieved. Both circular and rectangular CFT have been employed in construction. In general. circular CFT provides better performance than rectangular CFT, because the circular tube provides: • greater confinement of the concrete, • increased bond stress and composite interaction between the two materials, and • reduced susceptibility to local buckling