Compressive failure, large-strain ductility and size effect in concrete: Microplane model

The paper presents applications of the microplane model for concrete in finite element analyses performed to investigate two aspects of the compressive behavior of concrete. The first aspect is the ductile response, observed under extreme pressures, and the second aspect is the quasibrittle response, exhibited under normal pressures. Pressures high enough to induce ductile response are developed, for instance in impact events, and the ductile properties of concrete at high pressures can be observed in the .tube-squash. test, conceived at Northwestern University, in which concrete is cast inside a thick steel tube. In such a test the confinement provided by the steel tube allows concrete to achieve very large deviatoric strains (with shear angles up to 70?), retaining integrity, without visible damage. The axial compression of the tube filled with concrete is reproduced with a finite strain, finite element analysis, proving the capability of the microplane model for concrete to capture accurately the behavior of concrete under extreme pressures. In conditions of normal confinement, concrete exhibits quasibrittle behavior in compression, resulting in a significant size effect in the compressive failure of concrete structures. Finite element simulations of the compressive failure of reduced-size columns show good agreement with the structural response observed experimentally. For the latter analysis, the microplane constitutive law is employed adopting the crack band model.