Modelagem computacional do concreto: implementação de um modelo termo-dano acoplado para fissuração e uma proposta de estratégia de homogeneização

Abstract

Concrete is a highly heterogeneous multiphase material and so its nonlinear behavior is directly linked to its micro and macrostructural features. In addition, it is known that its mechanical properties are degraded when the material is subjected to high temperatures, which can lead to the appearance and propagation of microcracks and, in extreme cases, to the complete failure of the structural element. Therefore, knowing the performance of concrete under thermomechanical loads is of great importance to assessing structural security after fire events, for example. However, carrying out experimental tests may not be an easy task for physical and financial reasons. Thus, the development of computational models that simulate these problems emerges as a flexible and economically viable alternative. On the other hand, in addition to the intrinsic complexity of the material, thermomechanical phenomena are naturally difficult due to their multiphysics characteristics. The temperature influences the mechanical response through the development of additional thermal stress and thermo-dependency of the properties and the mechanical phenomena impact on the temperature field due to called Thermal Crack Resistance. Coupling strategies have been proposed to solve this type of problem, each with its advantages and disadvantages. Regarding cracking modeling, continuous and discrete approaches have been shown to be adequate to describe the concrete failure process subjected to mechanical, thermal and mixed loadings. That way, this Ph.D. Thesis shows the implementation of a thermaldamage model based on interface elements with a high aspect ratio and on a traction damage law for concrete, using the framework of the Finite Element Method. One expression proposal to represent the Thermal Crack Resistance as well a homogenization strategy are presented. Several computacional tests are made and confronted with reference datas to prove the proposal methodology confiability. Results captured the nonlinear response arising from the reduction in stiffness due to the damage variable, as well as such as the influence of temperature on load capacity due to bidirectional coupling between the fields.