Estudo do colapso progressivo de pórticos planos de concreto armado via análise não linear

Abstract

Safety is one of the major concerns of structural engineering. Therefore, in the design of building structures may be necessary not only to consider the dead load and live loads, but also special situations, as earthquakes, fire and explosions. In this sense, progressive collapse is a failure mechanism that has attracted the interest of designers and researchers in the last fifteen years, especially after the collapse of the Word Trade Center in 2001. Progressive collapse may be defined as a phenomenon where an initially localized damage causes a disproportionate effect on the structure, including its partial or total collapse. The goal of this work is to contribute to the study of this phenomenon developing a computational tool capable of modeling the progressive collapse of reinforced concrete structures. This tool is based on Finite Element Method and uses plane frame elements based on the Euler-Bernoulli theory of beams. Both geometric and material nonlinearity are modeled. The co-rotational kinematic description is used in order to allow adequate representation of the behavior of the structure when subjected to large displacements and rotations. Inelastic constitutive models based on plasticity theory and damage mechanics are used to model the mechanical behavior of reinforced concrete. The integration of sectional forces and the tangent matrix is carried out using the Gauss quadrature or the fiber method. The mathematical formulations presented in this work were implemented in the open source program FAST (Finite Element Analysis Tool) that has been developed in the Laboratory of Computational Mechanics and Visualization (LMCV) of the Federal University of Ceará (UFC). Initially, the tool was tested using classical examples of beams and frames with the geometric and material nonlinearity, and very good results were obtained. After verification, the program was used to analyze reinforced concrete frames tested in laboratory to study progressive collapse. Good agreement was obtained considering the complexity of the problem and the lack of knowledge of some important data required by the computational simulation. Therefore, the computational tool developed in this work was able to model the physical and geometric behavior of concrete structures subjected to progressive collapse, including the initial failure and the recovery of strength due to the catenary effect. The parametric studies performed showed that the reinforcement ratio is the most important parameter for resistance to progressive collapse, while the compressive strength has little influence. In addition, the cover for reinforcement has a significant effect on the initial response and peak load, but loses importance for large deformations where the response is dominated by the catenary effect.