Concrete filled tubes (CFTs) consist of a steel tube with concrete infill. CFT columns offer an efficient and economical alternative to conventional reinforced concrete bridge columns, in that CFT columns can offer larger strength and stiffness and facilitate rapid construction. This report is the second in a series. The prior report focused on engineering methods for CFT components and seismically resilient CFT column-to-foundation connections. This report focuses on CFT column-to-cap beam connections. In contrast to column-to-footing connections the cap-beam connection has unique design considerations including inverted construction and geometric limitations. The research project uses experimental methods to develop design procedures for various CFT column-to-cap beam connections. Three connections were studied,namely: (1) an embedded flange connection in which the CFT is embedded in the cap beam, (2) a welded dowel connection in which a series of headed dowels is welded inside the tube and embedded into the cap beam (both fully bonded and partially deboned conditions were studied), and (3) a dowel connection in which an independent cage of headed dowels and transverse reinforcing is developed into the CFT and embedded into the cap beam. All specimens were constructed using precast cap-beam components to demonstrate the feasibility of using these connections for accelerated bridge construction (ABC). The experimental program included specimens that simulated either the transverse or longitudinal direction of the bridge. Results showed that the three connection types provide excellent ductility under reversed-cyclic loading while all superstructure elements remained essentially elastic. The report provides design expressions, a design example and proposed codified language to facilitate immediate implementation of the research results into practice.
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