BEHAVIOR AND DESIGN OF CONFINED HIGH-STRENGTH CONCRETE COLUMNS

Large scale high-strength concrete columns were tested under simulated seismic loading. The columns had either a square or a circular cross-section with 104 MPa or 90 MPa concretes, respectively. The test parameters considered included the volumetric ratio, grade and arrangement of transverse reinforcement. The columns were subjected to constant axial compression and incrementally increasing lateral deformation reversals. The results are presented in the form moment-displacement hysteretic relationships and indicate that high-strength concrete columns can be confined to possess inelastic deformabilities usually expected of normal-strength concrete columns. However, high-strength concrete columns do require higher lateral pressure, provided either by increased volumetric ratio or higher grade of transverse reinforcement. The effectiveness of high-strength transverse reinforcement depends on the efficiency of confinement reinforcement and the level of axial compression. Circular columns and square columns with closely spaced transverse and longitudinal reinforcement show superior performance when high-strength steel is used to confine concrete. The use of higher grade transverse steel in these columns permit a reduction in the volumetric ratio, without reducing column deformability.