Numerical models for coupling creep and fracture of concrete structures

Numerical formulations to analyse basic creep and stress relaxation of concrete are presented in this paper, with a view to the computer implementation of the models. The numerical models are calibrated so that they fit experimental data. Then, coupling with time independent non local damage is discussed. The paper underlines the different approaches that can be envisioned in order to incorporate damage into the time dependent creep functions: the effective stress approach, and a second one where material damage acts on the time independent part of the creep functional. Some computer simulations have been carried out in order to judge the performance of the numerical models. Results show that using the effective stress approach, the kinetics of creep in bending beams is strongly correlated with the internal length when damage occurs. Also, the global behaviour of bending beams subjected to relaxation prior to failure is strongly influenced by the internal length variation and the loading rate effect. Results confirm the influence of the damage behaviour on creep or relaxation of concrete measured in the field of non-linear visco-elasticity associated to concrete fracture.