Stress - Strain behaviour of high-strength concrete columns confined by low-volumetric ratio rectangular ties

Available test results and stress - strain models for poorly confined high-strength columns, more specifically for columns with a tie volumetric ratio smaller than 2·0%, are scarce. This paper presents test results loaded in the axial direction for square reinforced concrete (RC) columns confined by various volumetric ratio lateral ties including low volumetric ratio. Test variables include concrete compressive strength, tie yield strength, tie arrangement type and tie volumetric ratio. Local strains are measured using strain gauges bonded to an acryl rod. For square RC columns confined by lateral ties, the confinement effect was improved by changing tie arrangement type from type A to type B. A method to compute the stress in lateral ties at the concrete peak strength is proposed, as well as a new stress - strain model for the confined concrete. The model shows good agreement with stress - strain relationships established experimentally over a wide range of confinement parameters.