A constitutive theory for the inelastic behavior of concrete

Abstract

A general theory for the inelasticity of concrete is proposed, the main constituents being a new, rate independent model of distributed damage for mortar and the application of mixture theories to account for the composite nature of concrete. The proposed theory of damage is capable of accommodating fully anisotropic elastic degradation, both in tension and in compression, in a manner which is ideally suited for computation. Mixture theories, on the other hand, are found to provide a simple yet effective tool for characterizing the values of the phase stresses that act on mortar and aggregate and which drive damage and plastic flow. This uneven distribution of stresses between mortar and aggregate is seen to lie at the foundation of effects such as the characteristic splitting failure modes in uniaxial compression and the unloading hysteretic loops that arise during cyclic loading. Further to furnishing useful insights into the physical mechanisms underlying the inelastic behavior of concrete, the proposed model provides a simple means of quantifying such behavior in a way which can be readily implemented in any standard finite element code. Possible generalizations of the theory are suggested. In particular, it is noted how rate and rheological effects can be incorporated into the proposed framework by extending it into the viscoplastic range and through the use of Eyring's theory of thermal activation.