Seismic behavior for connections of concrete-filled steel tubular column, H-shaped steel beam and steel bracing

Keywords：concrete-filled steel tube, beam-column connection, seismic behavior

     The properties of steel and concrete are fully utilized in the concrete-filled steel tube structures so that the strength, stiffness and ductility of the structure can be enhanced simultaneously. The construction of concrete becomes more efficient because the form-work for concrete is provided by the steel tube. Since longitudinal reinforcement and confinement are provided by the steel tube, the traditional longitudinal and transverse reinforcement may be eliminated. Continuous confinement provided by the steel tube prevents excessive spalling of concrete and the concrete filled inside the steel tube prohibits local buckling of the steel tube wall. Even though many advantages are exhibited by the concrete-filled steel tube structure, the application is limited because of the complicated beam-column connection and the lack of construction experience.

     The connections of the steel beam to the concrete-filled steel tube column can be divided into two main categories. The steel beam connected to the skin of the steel tube with or without diaphragms is one category. Another category is that the steel beam is connected to the concrete core by embedding connection components or extending the steel beam itself through the column. In the first category, the steel tube sustains the connection loads exclusively. Consequently, the steel tube is subject to high local distortion. The steel tube may be torn to failure before plastic bending strength of the beam can be developed. Therefore, it is not favorable to seismic resistant design. In the second category, both the steel tube and the concrete core sustain the connection loads so that better seismic behavior can be achieved. However, the connection detail becomes more complicated and the construction becomes more difficult especially when the beams are connected to the column from two horizontal directions.

     Moment resisting frame and braced frame may exist simultaneously in the structural system of buildings. For a particular column, one side is moment resisting frame and the other side is braced frame. In the joint research between Taiwan and USA, an experimental study on a full-scale frame will be carried out next year. The frame is three-story three-bay with concrete-filled tubular column and H-shaped steel beam. The central bay is a braced frame and the other two bays are moment resisting frame. For the interior column, one side is moment resisting frame and the other side is braced frame. In this project, the seismic behavior of the hybrid beam-column connection is studied and the design criteria of the connections are developed.