Behavior of Reinforced Concrete Column–Steel Beam Roof Level T-Connections under Displacement Reversals

Results from an experimental study on the seismic response of two hybrid RC column-to-steel (S) beam (RCS) roof level Tconnection subassemblies are presented. The primary variables investigated were: (1) anchorage requirements in column longitudinal bars; and (2) confinement requirements in RCS roof level T-connections. In the first subassembly the column bars were anchored by providing a development length of 12 bar diameters and an end mechanical anchor with twice the diameter of the bar, while connection confinement was provided by steel band plates wrapping around the column regions just above and below the steel beam. This specimen exhibited a stable response up to 4.0% drift, the displacement at which a column bar anchorage failure occurred, which led to excessive bar slip through the connection with the associated decay in stiffness and strength. In the second specimen the development length for the column longitudinal bars was increased to 20 bar diameters and a larger bearing area for the mechanical anchors was provided through steel channel sections running transversely above the top flange of the steel beam. The behavior of the second specimen was characterized by large column inelastic rotations, good stiffness retention and energy dissipation capacity, and limited joint damage. Thus, experimental results indicate that properly designed RCS roof level T-connections exhibit a stable behavior under large inelastic deformation reversals, such as those induced by strong earthquakes.