Banca de QUALIFICAÇÃO: RAFAEL NUNES DA CUNHA

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : RAFAEL NUNES DA CUNHA
DATE: 19/06/2023
TIME: 08:00
LOCAL: meet.google.com/zgp-czgr-pdf
TITLE:

Lumped damage mechanics to analyze thin plates and slabs

KEY WORDS:

Thin plates; Slabs; Lumped damage mechanics; Strain localization; Nonlinear damage law; Fracture energy.

PAGES: 118
BIG AREA: Engenharias
AREA: Engenharia Civil
SUBÁREA: Estruturas
SPECIALTY: Mecânica das Estruturas
SUMMARY:

The research for a better understanding and description of structures is of fundamental importance in the field of structural engineering. For a perfect description it is necessary that the mathematical models allow the consideration of the physical nonlinear behaviour of materials. The main theories that allow nonlinear effects to be taken into account in structural analysis are plasticity theory, fracture mechanics, and damage mechanics. The first theory allows important results to be obtained in engineering, specifically to plastic collapse problems. The second theory allows describing the evolution and interaction between discrete cracks, starting from a predefined initial crack. The third theory proposes the incorporation of an internal variable to the problem, called damage, which describes the material deterioration at meso-scale. All these theories presented great contributions to structural engineering, however these theories also fall into limitations of the nonlinear solutions, such as the description of the nonlinear behaviour in the post-peak or by presenting infinite solutions, when analysing the strain localization problem. This phenomenon occurs in all materials and can be defined as a physical problem, in which materials exhibit narrow strain bands, drastically accelerating the ruin, or as a mathematical problem, with the loss of ellipticity of the equations that govern the problem. Lumped damage mechanics (LDM), which was initially proposed for frame elements and was later formulated for two-dimensional problems has been shown to be capable of developing nonlinear analyses, avoiding the problem of strain localization without the need for any regularization technique. Therefore, the present research aims to contribute to the evolution of nonlinear analyses, with the development of a finite element for the analysis of thin plates and reinforced concrete slabs, based on LDM. The classical DKT finite element was chosen, due to the good results provided by this element in linear elastic analyses. The DKT element was redesigned to incorporate the assumptions of LDC, being tested on generic examples with elastic and physical nonlinear analyses, using a nonlinear damage law (LDNL) for damage evolution. A good response of the proposed element was observed, in terms of the Force vs. Displacement curves, which have solution objectivity, as well as the collapse mechanism of the analysed plates, with the obtaining of inelastic or damage hinge lines, which are consistent with the positions predicted in the technical literature for plastic hinge lines. Moreover, an experimental campaign was also initiated, aiming to obtain own examples of steel fibre reinforced plates, in order to model them with the proposed finite element, besides relating the fracture energy of the material with the LDNL parameter. Furthermore, this research aims, based on the proposed plate element, to develop a finite element capable of modelling slabs. For this, new formulations for the damage evolution law are going to be studied and evaluated, together with laws for plastic strains. In this case, damage variables quantify concrete cracking, while plastic strains describe reinforcement yielding. Thus, with the development proposals of this thesis, it will be possible to implement the new equations and apply them to experimental examples, available in the literature, and, eventually, to real engineering cases.

BANKING MEMBERS:
Presidente - 072.485.254-99 - DAVID LEONARDO NASCIMENTO DE FIGUEIREDO AMORIM - UFS
Interno(a) - 1120064 - SEVERINO PEREIRA CAVALCANTI MARQUES
Externo(a) à Instituição - RODRIGO BARROS - UFRN