Numerical Analysis of RC beam with High Strength Steel Reinforcement using CDP model

The article is based on preliminary research on use of high strength steel for RC elements. A reinforced concrete beam with a span length of 5700 mm has been subjected to four-point bending test. The bottom reinforcement of the beam was made of SAS670/800 high strength steel. This type of steel has no specific yield point. The yield limit declared by the manufacturer is specified as 670 MPa and the ultimate strength is equal to 800 MPa. The aim of the research was to establish a numerical model that would render properly the real beam behaviour. The model was created in the ABAQUS software using the CDP (Concrete Damage Plasticity) material model for concrete. The paper analyses the influence of several parameters on the results of numerical computations. The author's aim is to define values of the dilation angle that should be implemented in the model. Generally, the value of this parameter is established a priori, without any justification. The analysis reveals that in a situation when the dilation angle is greater than or equal to 25 deg, the numerical model predicts properly the damage obtained in the experiment. For lower values of the dilation angle, the failure mode is not consistent with the actual beam behaviour in the experiment. Another issue is whether and how the results from the model are influenced by the choice of specified concrete tensile behaviour. In the CDP model, this property may be set in three ways: by giving the stress displacement relation, stress - cracking strain relation or determining the fracture energy. All three alternatives are analysed and compared. Another aspect described in the paper, is the difference in load application through force control and displacement control as well as the influence of the amount of shear reinforcement. In order to analyse mesh size sensitivity, the results obtained for models with various mesh densities were compared.