Cálculo orgânico de secções quaisquer em flexão desviada segundo o Eurocódigo 2

Neste trabalho são apresentados os resultados do desenvolvimento de um código computacional destinado à resolução de problemas de verificação e dimensionamento de secções compósitas genéricas, sujeitas a flexão composta desviada, de acordo com o Eurocódigo 2. É efectuada a sintetização da informação relativa ao comportamento dos materiais correntemente utilizados em secções compósitas. Foram estudados modelos estruturais do comportamento de vigas sujeitas a esforços normais e de flexão, incluindo modelos propostos pela regulamentação existente. A informação recolhida permitiu estabelecer um modelo de cálculo baseado num sistema de equações não lineares correspondente ao equilíbrio estático da peça. Para evitar a manipulação de expressões demasiado complexas e para que o modelo possa ser aplicado a qualquer caso, foi concebido um algoritmo simplificado que avalia o erro associado a cada equação do sistema. Este procedimento é utilizado pelo método de Newton Raphson, que constitui um processo iterativo destinado a calcular a solução do problema. O modelo de cálculo e a interface gráfica foram desenvolvidos com recurso à linguagem de programação C++ e à biblioteca Microsoft Foundation Classes (MFC), tendo toda a implementação sido efectuada com base em objectos. Como resultado obteve se um programa de utilização simples, em que a quase totalidade dos dados pode ser introduzida pela interface gráfica, e pode em seguida ser guardada em ficheiro. As fases de cálculo e de visualização dos resultados encontram se também integradas na interface gráfica. Os resultados obtidos foram validados com base em tabelas e ábacos de situações correntes, bem como em alguns resultados publicados que correspondem a casos de flexão composta desviada em secções não correntes

Modelo de análise não linear material de pórticos de betão armado : calibração das relações constitutivas

No presente trabalho é sumariamente descrito um modelo de análise não linear material destinado à simulação do comportamento de pórticos de betão armado. As barras podem ter secção qualquer, variável ao longo do seu eixo, sendo discretizadas por elementos de Timoshenko 3D. As secções transversais são discretizadas em quadriláteros, dando origem a um modelo de fibras. A influência na resposta de alguns parâmetros das leis constitutivas dos materiais foi avaliada com base na comparação com resultados experimentais

Elasto-plastic multi-fixed smeared crack model for concrete

Relatório 04-DEC/E-0

Comportamento de vigas de betão armado de secção oca submetidas a flexão, corte e torção

Neste trabalho são descritos ensaios de vigas de betão armado submetidas a flexão, corte e torção. Estes ensaios fazem parte de um trabalho de investigação experimental e numérico relativo ao comportamento não linear material de estruturas de betão armado. Os resultados obtidos são apresentados e discutidos. Para determinar as principais características do betão e do aço foram também realizados ensaios de compressão uniaxial em provetes cilíndricos de betão simples, ensaios de flexão sob três pontos de carga em vigas entalhadas de betão simples e ensaios de tracção em varões de aço

Crack constitutive model for the prediction of punching failure modes of fiber reinforced concrete laminar structures

The capability of a multi-directional fixed smeared crack constitutive model to simulate the flexural/punching failure modes of fiber reinforced concrete (FRC) laminar structures is discussed. The constitutive model is implemented in a computer program based on the finite element method, where the FRC laminar structures were simulated according to the Reissner-Mindlin shell theory. The shell is discretized into layers for the simulation of the membrane, bending and out-of-plane shear nonlinear behavior. A stress-strain softening diagram is proposed to reproduce, after crack initiation, the evolution of the normal crack component. The in-plane shear crack component is obtained using the concept of shear retention factor, defined by a crack-strain dependent law. To capture the punching failure mode, a softening diagram is proposed to simulate the decrease of the out-of-plane shear stress components with the increase of the corresponding shear strain components, after crack initiation. With this relatively simple approach, accurate predictions of the behavior of FRC structures failing in bending and in shear can be obtained. To assess the predictive performance of the model, a punching experimental test of a module of a façade panel fabricated with steel fiber reinforced self-compacting concrete is numerically simulated. The influence of some parameters defining the softening diagrams is discussed.The authors wish to acknowledge the support provided by the Portuguese Science and Technology Foundation (FCT) by means of the project PTDC/ECM/73099/2006 "CUTINEMO-Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures". The first author acknowledges the financial support of FCT, PhD Grant number SFRH/BD/23326/2005

Modelação de vigas reforçadas com laminados de CFRP inseridos no betão de recobrimento

São descritas as principais características do modelo numérico desenvolvido, que no âmbito do presente trabalho é aplicado na análise de estruturas de betão reforçadas com laminados de CFRP inseridos no betão de recobrimento. O desempenho do modelo é avaliado por intermédio da simulação do comportamento registado em ensaios experimentais

Bond behavior of near-surface mounted CFRP laminate strips under monotonic and cyclic loading

Near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminate strips are used to increase the load-carrying capacity of concrete structures by inserting them into slits made in the concrete cover of the elements to be strengthened and gluing them to the concrete with an epoxy adhesive. In several cases the NSM technique has substantial advantages when compared with externally bonded laminates. In order to assess the bond behavior between the CFRP and concrete under monotonic and cyclic loading, an experimental program, based on a series of pullout bending tests, was carried out. The influence of the bond length and loading history on the bond behavior was investigated. In this work the details of the tests are described, and the obtained results are discussed. Using the experimental data and an analytical-numerical strategy, a local bond stress-slip relationship was determined. A finite element analysis was performed to evaluate the influence of the adhesive on the global response observed in the pullout bending tests.The first author wishes to acknowledge the grant SFRH/BD/3259/2000 provided by FCT (Portuguese Foundation for Science and Technology) and FSE (European Social Fund). The tests were performed at the Structural Technology Laboratory of the Technical University of Catalonia, Spain, with the help of Miguel Angel Martín and Ernesto Diaz. The authors wish to acknowledge the support provided by S&P and Bettor MBT who supplied the material used in the study

Object oriented programming : data preparation and visualization of FEM models

In this paper two object oriented applications are described. The former is intended to generate data associated with the finite element method (FEM) and the later is a three-dimensional visualization tool named 3DMesh. Both are based on the principles of object oriented programming, namely encapsulation, inheritance and polymorphism. To support the preparation of FEM data, a language named 3DO was developed. Its syntax is similar to a subset of the C++ programming language. 3DO is based on object construction and modification by methods that require a small number of arguments. With this tool, mesh generation, definition of properties and loads and mesh refinement can be performed with limited user effort, even when the model is complex. All the generated information can be visualized with the program 3DMesh. This application is based on the OpenGL library and uses the Microsoft Foundation Classes to simplify its integration in the MS-Windows environment. 3DMesh implements an interactive navigation technique that allows the visualization of the model interior, preserving its integrity. Model attributes and the results of the FEM analysis can also be visualized

Near surface mounted CFRP strips for the flexural strengthening of RC columns: experimental and numerical research

In the present work, a strengthening technique based on near surface mounted (NSM) carbon fibre laminate strips bonded into slits opened on the concrete cover is used to improve the flexural capacity of columns subjected to bending and compression. This technique avoids the occurrence of the peeling phenomenon, is able to mobilize the full strengthening capacity of the strips, and provides higher protection against fire and vandalism acts. The present paper describes the adopted strengthening technique and reports the experimental characterization of the materials involved in the strengthening process. The results obtained in two series of reinforced concrete columns, subjected to axial compression and lateral cyclic loading, show that a significant increase on the load carrying capacity can be achieved by using the NSM technique. Cyclic material constitutive laws were implemented in a finite element program and the tests with reinforced concrete columns strengthened with the NSM technique were numerically simulated under cyclic loading. These numerical simulations reproduce the experimental load-displacement diagrams satisfactorily.The study reported in this paper is included in the research program "CUTINSHEAR-Performance assessment of an innovative Structural FRP strengthening technique using an integrated system based oil optical fiber sensors" Supported by FCT, POCTI/ECM/59033/2004. The second author acknowledges the support provided by the grant in the ambit of this research project