Plasticity constitutive model for stress-strain relationship of confined concrete

This paper presents a plasticity constitutive formulation for concrete under uniaxial compression and confinement in triaxial and biaxial compression. The failure surface is derived from a three-parameter loading surface. A new frictional driver is introduced in the loading function to control the failure surface at the peak and residual stress under confinement. In biaxial loading, a procedure to calibrate the out-of-roundness eccentricity is proposed that affects the shape of the failure surface. Both the hardening and softening functions are based on the continuous plastic volumetric strain. The softening function parameter is defined in terms of the plastic volumetric strain at the inflection point of the softening curve. A new flow rule is proposed that is dependent on the plastic dilation rate. Both a constant or nonconstant plastic dilation rate can be used. In this paper, only a constant plastic dilation rate is examined. The accuracy of the proposed approach is validated through comparisons with a number of available experimental results in uniaxial, biaxial, and triaxial loading.