Size effect in concrete columns: Finite-element analysis with microplane model

Failure of concrete structures due to concrete failing in compression was recently shown to exhibit a size effect. This is not taken into account by current design codes based on failure criteria expressed in terms of strength or plasticity. But compressive failure of concrete cannot be described by strength criteria, since it is brittle and is caused by release of elastic strain energy stored in the structure. In this sense, it is similar to tensile failure governed by fracture mechanics. The paper presents a finite-element study of the size effect of compressive failure of geometrically similar concrete columns of different sizes. The test columns considered here are reduced-scale specimens made with micro-concrete of maximum aggregate size 3.35 mm and are loaded eccentrically. The analysis employs the microplane model for concrete. It is based on the crack-band concept and is shown to capture with good approximation the size effect observed experimentally.