Seismic Behavior of Composite Concrete Filled Steel Tube Column-Wide Flange Beam Moment Connections

The results of an experimental research study involving the testing of ten full-scale moment resisting connections under simulated seismic loading conditions are presented. Each test specimen modeled the interior joint of a moment resisting frame consisting of square concrete filled steel tube columns and wide flange steel girders, where energy dissipation was designed to occur either primarily in the beams or in the connection panel zone during a severe earthquake. The results of the study indicate that moment resisting connection details can be economically designed that enable more than 0.045 rad of inelastic story drift to develop under cyclic loading. These details include split-tee connections without a shear tab, weak panel zone connections, and extended tee connections. Panel zone shear yielding and local buckling are shown to be a ductile mode of response, with minimal strength deterioration occurring in the connection. The use of interior diaphragms in the column is shown to locally stiffen the joint, but also lead to strain concentrations and fracture of the beam flanges at their weld access holes. Furthermore, strain concentrations develop at connection details that lack a gradual transition in geometry and result in a reduction in connection ductility.