Confinement reinforcement design for plain and fibre reinforced high strength concrete columns

A theoretical study was undertaken to propose the procedure and guidelines for the design of transverse steel confinement for the potential plastic hinge regions of plain (non-fibre) and steel fibre reinforced high strength concrete columns. To achieve this, confinement reinforcement for a few selected square and circular concrete column cross sections were designed for varying concrete compressive strengths (70-100 Mpa) and axial load levels (0.15 - 0.5). Theoretical moment curvature relations were found and curvature ductility factors were computed for all the columns. An attempt has also been made to evaluate the relevant confinement requirements of the Indian Standard Code IS-13920: 1993. The results indicate that the design equations of the Code are inadequate to provide satisfactory ductility for high strength concrete columns especially at high axial load levels. However, it has been shown that the use of steel fibre reinforced concrete results in a significant improvement in the structural response of such column cross sections. A new set of refined equations have been proposed in the present study to design the confining steel of non-fibre and steel fibre reinforced high strength concrete columns, which take into account the effects of high concrete strengths and axial load levels also. The confinement reinforcement design has been made performance based by relating the required quantity of reinforcement with the ductility demand.