Numerical Simulation of Concrete Exposed to High Temperature – Damage and Explosive Spalling

In the present paper a fully coupled three-dimensional thermo-hygro-mechanical model for concrete is discussed and used in the numerical studies. The model is formulated in the framework of continuum mechanics based on the principles of irreversible thermodynamics. Distribution of moisture, pore pressure, temperature, stresses and strains are calculated by employing a three-dimensional transient finite element analysis of implicit type. The mechanical strain, which is due to loading, temperature induced stresses and pore pressure, is calculated by using temperature dependent microplane model for concrete. The application of the model is demonstrated on three numerical examples. In the first degradation of bending resistance of plain concrete beams is studied as a function of temperature, the second demonstrates the influence of high temperature on bending resistance of reinforced concrete beams. It is shown that the model realistically predicts degradation of concrete resistance. Finally, due to the fact that explosive spalling is a local failure phenomenon, the influence of different kind of inhomogeneities is discussed. The local instead global (average) properties govern the explosive spalling. This explains the reason for relative large scatter of experimental results that are related to explosive spalling. The influence of inhomogeneities is illustrated on several numerical examples.