Assessment of the fracture of three-point bending concrete specimens

In structural concrete elements opening up of structural and non-structural cracks can lead to irreversible damage of the structure. A more precise prediction of the process of fracture would help us to avoid this occurring and the terrible consequences of an accident arising from it. Methods of assessing concrete fracture are not sufficient in order to determine the mechanical behaviour of concrete in case defects appear in it. The available analytical methods not always allow us to calculate all parameters of fracture while the experimental methods are expensive and sometimes their application is infeasible. In the work, along with analytical and experimental methods, digital methods are suggested. Here it was aimed at calculating the critical crack opening and fracture energy of concrete prisms being bent. In accordance with three-point bending scheme concrete specimens with cut cracks inside were bent. Concrete specimens have been formed from different mix. Bending force was added at deformation speed of 0.4 mm/min. At the same times the changing deflection of concrete specimen and lower opening of the crack were recorded. Stress intensity factor K-I was calculated by the ANSYS computer program because the traditional analytical equation was found to be inappropriate due to the distance between the supports (250 mm) and measurements (100 X 100 X 400 mm). With the aid of the stress intensity factor KI derived by the computer program and crack mouth opening displacement (CMOD) the determined experimentally critical crack opening were calculated. Also calculation of fracture energy was made.