Behavior and design of high-strength circular reinforced concrete columns subjected to axial compression

High-strength concrete (HSC) can be of great interest for the construction of lower-stories reinforced-concrete (RC) columns in high-rise buildings. This superior material can reduce the dimensions of the columns, and therefore, can be considered as a more advantageous material than normal-strength concrete (NSC). To compensate for its higher brittleness nature, the confinement reinforcement ratio required for HSC has to be larger than that required for NSC. The aim of this study is to examine the confinement transverse steel reinforcement amounts required for HSC circular columns part of high-rise buildings. The study first compares the confinement reinforcement requirements given by leading standards. Following the comparative research, an experimental study on six HSC columns subjected to axial loading was performed. The results show that in terms of axial capacity, it is recommended to further examine the concrete strength reduction factor and that it is more reasonable to consider a value lower than 0.85 for the design of HSC columns. Moreover, in terms of confinement and ductility, the recommended volumetric transverse steel reinforcement ratio for HSC circular columns not considered as part of the seismic-force-resisting system (SFRS), can be based on the ACI standard requirement and equal to half of the maximum specified volumetric transverse steel reinforcement ratio required for HSC columns considered as part of the SFRS.