An energy-based elastoplastic damage model for concrete at high temperatures

Although structural concrete is widely used in civil engineering, the proper modeling of its thermo-mechanical behavior remains a challenging issue for the academic and engineering communities due to the complexity involved in the underlying micro-cracking process. In this work, the previous thermodynamically consistent energy-based elastoplastic damage model is extended to concrete at high temperatures, with the aim to describe the material nonlinear behavior and provide numerical predictions of concrete structures. Both the thermal expansion and transient creep strain are incorporated in the kinematics. Within the framework of continuum damage mechanics, two mechanical damage variables that lead to a fourth-order damage tensor are introduced to describe stiffness degradation of concrete under predominant tension and compression, respectively. Moreover, temperature-dependent mechanical properties are adopted to describe the thermal degradation and the thermo-mechanically coupled behavior of concrete at high temperatures. The plastic flow is described by the effective stress space plasticity and the evolution laws for the mechanical damage variables are driven by the conjugate elastoplastic damage energy release rates. The proposed model is validated by several benchmark experiments of plain concrete and then applied to reinforced concrete (RC) structures. The well agreement between the numerical predictions and experimental results indicates that the proposed model is promising in quantifying the global responses and assessing the safety of plain concrete and RC structures at high temperatures.