Numerical investigation of factors influencing the experimental determination of concrete fracture energy

The fracture energy is one of the most crucial parameters for the numerical investigation of damage propagation and failure in reinforced concrete members. The correct characterization of concrete fracture properties can be compromised by different laboratory limitations, such as specimens size, mode of control, loading rate and the test apparatus. Nowadays limited recommendations exist concerning the experimental evaluation of fracture energy for normal and high strength concrete. In order to investigate the differences between different specimen sizes, evaluate the effect of mode of control and analyze the influence of different set-up on the fracture test, a numerical analysis supported by an experimental campaign is presented. The Lattice Discrete Particle Model (LDPM) has been used to simulate concrete and to provide realistic crack patterns and crack widths. In the first part of the study the position of the traveling crack tip is identified with two approaches and then used to investigate the strain rate distribution along the ligament. It is well-known that concrete is a visco-elastic material with strain-rate dependent fracture properties. For this reason in the second part of the study the potential influence of differences in loading rate on the effective fracture energy determined by the work of fracture method is investigated with simulated three-point bending tests of differently sized specimens and two notch depths