Abstract：Gradient-dependent damage model is widely used in the simulation of mechanical behaviours of concrete structures，which have localization phenomena. With the principle of nonlocal energy dissipation，the characteristic length of a gradient-dependent damage model should be the distance of two material points whose damage evolution processes can affect each other. Numerical simulations were performed on the evolution of damage process zone of concrete structures，and the size and evolution of damage process zone were studied. The adopted geometrical model is four-point-shearing beam，and ABAQUS/EXPLICIT software are taken as the numerical tools. The main results include：(1) The length of a complete damage process zone is between 0.042 1 and 0.061 2 m for the given double-notched beam，which is 0.15 m in width and 0.40 m in length. Variation of size of damage process zone is caused by variation of strain states，which are shearing dominated at beginning of deformation and tension dominated at the end of deformation. (2) Secondary damage process zone appeared at the end of deformation，and its size is about 0.036 7 m for the given structure. (3) For the single-notched beam with four-point shearing loads，which is 0.10 m in width and 0.44 m in length，the size of damage process zone is 0.047 3 m during deformation process. These results can be referred as the value of the characteristic length of a gradient-dependent damage model.
