Flexural ductility design of confined high-strength concrete columns: Theoretical modelling

• Design equation to estimate flexural ductility of HSC columns confined with steel straps.
• Design and analysis by limiting neutral axis depth.
• Design and analysis by limiting normalised axial force.

Since the past few decades, high-strength concrete (HSC) has found increasingly wide applications in civil and structural engineering. Its utilisation is needed for the construction of buildings where reductions in self-weight and size of structural members are important. However, it was consistently reported that HSC exhibits undesirably lower ductility with the increase of concrete compressive strength. To restore the ductility, additional confinement has been recommended. This paper investigates the effectiveness of using Steel-Strapping Tensioning Technique (SSTT) to increase the flexural ductility of HSC columns. The effects of SSTT-confinement on the flexural ductility of HSC columns is studied by non-linear moment–curvature analysis. Based on such analysis, a parametric study was conducted to investigate the effects of various parameters, such as normalised axial force, normalised neutral axis depth, concrete compressive strength and confining volumetric ratio, on the flexural ductility of such columns. The results revealed that the flexural ductility of HSC columns is highly dependent on normalised axial force and neutral depth axis of the columns. It was found that the flexural ductility design of SSTT-confined HSC columns can be simplified by controlling the maximum allowable values of these parameters. Finally, two design equations were proposed for the flexural ductility design of such columns.