SEISMIC PERFORMANCE OF STEEL-ENCASED COMPOSITE COLUMNS

An experimental investigation was conducted to investigate the behavio r of composite columns subjected to simulated seismic loading conditio ns. 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 confineme nt required to achieve adequate ductility under cyclic loading, effect iveness of flange shear studs for enhancing flexural stiffness and str ength, concrete compressive strength, and the shear resistance mechani sm of the composite column. The results of the test program indicate t hat 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 effecti ve in enhancing the flexural resistance to lateral loading. The specim en flexural capacity under combined axial and lateral loading was foun d to be accurately predicted by analytical models based on full compos ite action, with ACI and AISC LRFD criteria providing conservative res ults.