Axial compressive behavior of concrete columns with grade 600 MPa reinforcing bars

An experimental study was performed to investigate the axial compressive behavior of concrete columns with Grade 600 MPa reinforcing bars. Nine large-scale concrete square columns were constructed and tested under pure axial loading. The effects of Grade 600 MPa transverse reinforcement with two different configurations (Type A and B) and amounts were evaluated. The behavior of columns was characterized by sudden spalling of concrete cover and ductility failure for well-confined columns, which was dominated by effective confinement index (keρshfyh/fc′). Columns confined by Grade 600 MPa transverse reinforcement exhibited the better performance in terms of strength, post-peak deformability, and toughness when compared with columns reinforced with conventional steel. The benefit of using Grade 600 MPa longitudinal bars on the axial load capacity of columns is limited, but it is beneficial to improve the post-peak deformability and toughness of columns with Type B configuration. A design expression is proposed for the amount of seismic confinement to ensure ductility behavior for columns, based on the effective confinement index.