Concrete filled tube (CFT) columns combine steel and concrete in one member, which results in a member that has the beneficial qualities of both materials. Although CFT columns are suitable for tall buildings in high seismic regions, their use has been limited due to lack of information about the true strength and the inelastic behavior of a CFT member. In addition, no guidelines are available for selecting and designing the connection between the steel beam and the CFT column. The objectives of this research were to determine the strength of a CFT column and to develop a connection detail for connecting steel beams to CFT columns. Focus of this study was placed on moment resisting connections to circular columns.; The strength and ductility demand of the connection were investigated through the design and nonlinear dynamic analysis of a ten-story theme building utilizing CFT columns. The results of these analyses also provided information on typical member sizes and were used to decide on the geometry of the test specimens. In order to assess the strength and stiffness of a CFT column, six CFT beam-column specimens were tested. The tested columns exhibited very high levels of energy dissipation and ductility. The information gained from this experimental study was used to develop an analytical model to predict the capacity of a CFT column.; Based on the review of previous studies, it was concluded that the through beam connection detail is the most appropriate detail to achieve the strength, stiffness, and ductility required for a moment resisting connection. In this detail, the beam runs continuous through the column. The behavior of this connection detail was investigated through testing eight two-thirds scale cruciform connection specimens. The connection behavior was also investigated analytically using a three-dimensional nonlinear finite element model. Experimental and analytical results demonstrated the ability of this detail to develop the full flexural capacity of the beam. Design recommendations for the proposed detail were introduced based on the results of this investigation.
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