Influence of Concrete Strength and Transverse Reinforcement Yield Strength on Behavior of High-Strength Concrete Columns

Eight large-scale high-strength concrete (HSC) square columns were constructed and tested under simulated earthquake loading. The concrete strength varied from 80 to 120 MPa. The columns were subjected to constant axial loads corresponding to 40 and 52% of the columns’ axial load capacity and to a cyclic horizontal load-inducing reversed bending moment. It is shown that, at constant volumetric ratio of confinement reinforcement and constant level of axial compression, concrete strength significantly influences the flexural behavior of HSC columns. It is also shown that, in some cases, high-yield-strength reinforcement may be used to effectively confine HSC while reducing the volumetric ratio of lateral transverse reinforcement. This highlights the need for a reliable index to account for high-yield-strength transverse reinforcement. The test results from this research program and others indicate that the confinement reinforcement requirements of the ACI and New Zealand Codes are not directly applicable to columns confined with high-yield-strength steel.