Modelos constitutivos para análise dinâmica não linear de pórticos planos de concreto armado

Abstract

The study of the behavior of reinforced concrete structures is of great importance for Civil Engineering. Thecnological and constructive methods advancements are responsible for the possibility of increasingly slender structures. With these advancements, concern about material and geometric nonlinear effects and about dynamic effects is growing. In order to contribute to the study of the behavior of reinforced concrete structures, this work aims to develop computational tools capable of correct modeling the nonlinear and dynamic effects in 2D reinforced concrete frames. This work focuses on the implementation of one-dimensional constitutive models based on the Theory of Plasticity and the Continuum Damage Mechanics. Two one-dimensional concrete constitutive models are implemented. The first model is based on the classical isotropic Mazars’ damage model and the second one is based on the plasticdamage model developed by Lee and Fenves. The implementation of the second constitutive model is done through the development of a return mapping algorithm using a Newton-Raphson method. Furthermore the contribution in the nonlinear material behavior of reinforced concrete, a numerical integration algorithm for nonlinear dynamic analysis is also implemented, the Generalized- method. This algorithm is able to reduce numerical instability problems (common in nonlinear problems) through the introduction of numerical damping in the higher vibration modes. With this property, the Generalized-a method becomes more attractive for nonlinear analysis than classical methods, as well the Newmark’s family of methods. The constitutive models are implemented in the academic software FAST (Finite Element Analysis Tool), developed at Laboratory of Computational Mechanics and Visualization (LMCV) from the Federal University of Ceará (UFC). FAST already owns geometrically nonlinear analysis of finite elements under large displacements through a corotational formulation, as well nonlinear elastic constitutive models for concrete and reinforced steel. The validation and verification examples showed that the implemented tools are able to capture some of the main nonlinear effects present in reinforced concrete structures, such as the stiffness degradation and the appearance of plastic strains.