Parameter identification of the concrete damaged plasticity model

The article is devoted to the development of methods for identification and validation of the parameters of the "Concrete Damage Plasticity" material model based on experimental studies. During the experiments, prismatic samples were tested for sign-constant cyclic load after preliminary heat treatment at various temperatures. According to the test results, the temperature dependences of the mechanical properties were established: the conditional proportionality limit, the ultimate strength, Young's modulus, and the scalar damage variable. Piecewise analytical envelopes were used to plot the stress-strain curves, which describe linear, inelastic, and descending parts. Accumulated concrete scalar damage variable during compression is determined based on the elastic modulus degradation analysis at each loading cycle. Parameters of analytical approximations are determined directly through experimental data or using numerical identification method based on an iterative process of searching for the minimum functional. The structure of the minimized functional contains auxiliary subfunctions due to well-known statistical indicators: the standard deviation of the compared values, the linear correlation coefficient, and the area under the compared dependencies. The search for the minimum of the desired value is carried out using the gradient descent method according to the criterion of the minimum contribution of the sum of three subfunctions. At the last step of the study, the obtained model is validated based on the calculation for uniaxial and cyclic loading of a single-element prismatic sample in the ABAQUS FEA. The developed calculation method makes it possible to complete the loading cycle at any axial force value, including zero, as well as to continue the next loading cycle from the current stress state. The considered method for validating the inelastic deformation model for concrete is characterized by its consistency and versatility. The results demonstrate sufficient accuracy in approximating uniaxial and cyclic stress-strain curves, and the proposed approximation relationships are free from ambiguity when converting the inelastic part of strain to plastic one.