Effectiveness of adding confinement for ductility improvement of high-strength concrete columns

The use of high-strength concrete (HSC) can reduce the size of columns in tall buildings and save space. However, this will also reduce the flexural ductility of the columns. To restore the flexural ductility after using HSC, additional confinement has been recommended. In this paper, the effect of adding confinement on the flexural ductility of HSC columns is studied by nonlinear moment–curvature analysis taking into account the stress-path dependence of the steel reinforcement. The analytical results reveal that the addition of confinement would enhance the flexural ductility of columns by increasing the balanced steel ratio and balanced axial load level. However, the effectiveness of adding confinement to improve the flexural ductility of columns decreases as the axial load level or concrete strength increases. Finally, to evaluate the effectiveness of adding confinement, two previously derived formulas correlating the flexural ductility to various structural parameters are extended to incorporate the effect of the confining pressure.