Numerical modelling of fracture of concrete

It is possible to determine fracture energy and tensile strain softening of concrete with a displacement controlled test on CT-specimens. The experimentally observed behaviour can be reasonably simulated numerically by means of the fictitious crack model after parameters have been determined by a computer module called SOFTFIT. The experimental findings show a marked size effect. This is in agreement with findings of other authors. A numerical model has been developed to distinguish between real fracture energy used for crack formation and damage energy dissipated in highly stressed zones. The numerical model explains the influence of the state of stress and the local variability of a material on fracture energy and this explains the size effect. The model can be further elaborated to take the heterogeneous structure of concrete into consideration. (orig.)