Modelling triaxial compression using the Microplane formulation for low confinement

A numerical model is developed to examine the effect of low confinement on the behaviour of high strength concrete columns. A 3-D model using the Microplane-M4 formulation with second order effects included using a total Lagrangian formulation is developed. A cylinder under uniaxial and triaxial stress states is modelled. Adjustments in the M4 model are proposed for the particular case of concrete columns under low confinement. Comparisons with empirical formulas for uniaxial and triaxially confined concrete show excellent agreement.