Rate dependent fracture of notched plain concrete beams

Abstract

Three different effects control the influence of the loading rate on the structural response: creep of bulk material, rate dependency of growing microcracks and inertia forces. The first effect is important only at extremely slow loading rates whereas the second and the third effects dominate at higher loading rates. The rate sensitive model, which is based on the energy activation theory of bond rupture, is implemented into the microplane model for concrete. The creep of concrete is modelled by the rate type creep law, which is coupled in series with the microplane model for concrete. The rate sensitive microplane model is then used in a 3D static and dynamic FE analysis of notched plain concrete beams in order to investigate the influence of the loading rate on the resistance of the beams and on the size effect. The results of the study show that with increase of the loading rate the beam resistance increases. For very slow loading rates the creep-fracture interaction controls the behaviour of beams whereas at moderately high loading rates the rate of the growing microcracks dominates. However, for very higr loading rates the inertia forces control the response and all other effects can be neglected. It is shown that there is a critical loading rate for which the size effect on the nominal strength of the beam is minimal.