An experimental investigation was conducted to investigate the behavior of composite columns subjected to simulated seismic loading conditions. Eight two-thirds-scale specimens were tested, each consisting of a structural steel shape encased in reinforced concrete. The parameters studied in the test program included the degree of concrete confinement required to achieve adequate ductility under cyclic loading, effectiveness of flange shear studs for enhancing flexural stiffness and strength, concrete compressive strength, and the shear resistance mechanism of the composite column. The results of the test program indicate that encased composite columns possess exceptional cyclic strength and ductility if buckling of the longitudinal reinforcement is inhibited. The encased steel shape was found to provide the primary resistance to transverse shear during overloading, with the shear studs not effective in enhancing the flexural resistance to lateral loading. The specimen flexural capacity under combined axial and lateral loading was found to be accurately predicted by analytical models based on full composite action, with ACI and AISC LRFD criteria providing conservative results.
