1,381 research outputs found
Simulação do comportamento à compressão uniaxial do betão reforçado com fibras de aço
Ensaios de compressão uniaxial efectuados com provetes cilíndricos reforçados com diferente percentagem de fibras de aço são descritos no presente trabalho. Os ensaios foram realizados sob controlo de deslocamento, de forma a obter-se a resposta até ao completo esgotamento da capacidade de carga dos provetes. Os resultados obtidos são apresentados e analisados.
Duas expressões tensão-extensão foram definidas com base nos resultados experimentais. Estas expressões podem ser utilizadas em modelos numéricos de simulação do comportamento não linear material destes compósitos. Uma das expressões adequa-se a modelos formulados em extensões totais, enquanto a outra expressão é apropriada a modelos elasto-plásticos. O desempenho destas expressões é avaliado
Memória descritiva e justificativa do projecto de estabilidade do edifício do Centro de Solidariedade de Braga
A presente memória descritiva e justificativa refere-se ao edifício do Centro de Solidariedade de Braga, construído no Monte do Picoto em Braga. Este complexo é constituído por um polivalente e um edifício central (ver Figuras 1 e 2). O edifício central é formado por seis blocos ligados entre si por uma laje de cobertura com duas grandes aberturas, uma oval e outra quadrada. Existem uns passadiços suspensos a ligar alguns destes blocos. O polivalente encontra-se enterrado, com uma camada de solo sobre a sua cobertura. No dimensionamento foram consideradas as recomendações da regulamentação em vigor, Nacional e Estrangeira. Os casos não devidamente tratados pela regulamentação disponível foram analisados tendo-se em conta resultados obtidos em investigação recente. O edifício é todo em betão aparente. A construção do edifício iniciou-se em 2001 e terminou em 2004
Centro de Solidariedade de Braga
O presente trabalho descreve os procedimentos que mais interessam do ponto de vista do dimensionamento estrutural de um edifício constituído por estruturas laminares, algumas delas de dimensão e geometria invulgar. A elevada complexidade estrutural de alguns dos módulos que constituem a estrutura exigiu a utilização de sofisticados modelos de cálculo, alguns deles
desenvolvidos para o efeito
Modelos constitutivos para a análise não linear material de estruturas de betão incluindo efeitos diferidos
Tese de doutoramento Estruturas /Engenharia CivilIn recent years concrete technology has been improved significantly due, mainly, to the
development of self-compacting concrete, ultra-fluid cement based materials, high
performance fiber reinforced concrete and engineered cement composites. These
developments have their main applicability in the pre-casting industry, where the earliest
demoulding of the pre-cast elements is an important aim for economic reasons. Due to the
relatively high cost of these advanced cement based materials, optimization of the behavior
of structural elements made with these materials is a fundamental issue for their
competitiveness. As a consequence, these materials are, in general, applied to relatively
thin elements that require special attention in terms of shear and punching resistance. With
the aim of studying these types of structures, a multi-directional fixed smeared crack model
for plane shells has been developed. This model implements an innovative approach for
capturing the behavior of laminar structures failing in punching, which is based on the
adoption of a softening diagram to simulate the behavior of the out-of-plane shear stress
components. Since most advanced cement based materials have relatively high binder content, the risk
of cracking at an early age should be evaluated using models that can estimate the heat
generated by the hydration of pozolanic components and the induced stress fields. For this
purpose, a FEM-based heat transfer model has been developed and integrated into a
mechanical model that can simulate the crack initiation and propagation in structures
discretized with solid finite elements. The mechanical model is a 3D multi-directional
smeared crack model with the capability of simulating the behavior of structures failing in
punching and shear. Shrinkage and creep are also a concern mainly for service limit states
due to crack opening limits. In the last two decades fiber reinforced polymer composite materials have also been used
for the structural rehabilitation of concrete structures, mainly for the flexural and shear
strengthening of reinforced concrete beams. The prediction of the behavior of the shear
viii Abstract
strengthened beams requires the use of crack constitutive models to simulate the decrease
of the shear stress degradation with the crack opening evolution, in agreement. Two
numerical approaches are proposed to simulate this phenomenon. One is based on the use
of a softening crack shear stress versus crack shear strain diagram to model the fracture
mode II, while in the other the total crack shear stress is obtained from the total crack shear
strain adopting a crack shear modulus that decreases with the crack normal strain. Fiber reinforcement mechanisms are more effectively mobilized when support redundancy
of a structure is high, since the stress redistribution capacity provides to this type of
structure an ultimate load that is much higher than the load at crack initiation. However,
the supporting conditions of a structure can change during the loading process, and even a
loss of contact can occur. To simulate accurately these situations, linear, nonlinear and
unilateral support conditions are numerically implemented.
To increase the robustness of the developed numerical models, innovative numerical
strategies are implemented in the stress update phase of the nonlinear finite element
analysis process. Furthermore, to improve the convergence performance of the finite
element nonlinear analyses an arc-length algorithm is implemented.
All the numerical models are implemented in the FEMIX 4.0 FEM package, using the
ANSI-C computer language.Fiber reinforcement mechanisms are more effectively mobilized when support redundancy
of a structure is high, since the stress redistribution capacity provides to this type of
structure an ultimate load that is much higher than the load at crack initiation. However,
the supporting conditions of a structure can change during the loading process, and even a
loss of contact can occur. To simulate accurately these situations, linear, nonlinear and
unilateral support conditions are numerically implemented.
To increase the robustness of the developed numerical models, innovative numerical
strategies are implemented in the stress update phase of the nonlinear finite element
analysis process. Furthermore, to improve the convergence performance of the finite
element nonlinear analyses an arc-length algorithm is implemented.
All the numerical models are implemented in the FEMIX 4.0 FEM package, using the
ANSI-C computer language. Estes materiais avançados de matriz cimentícia têm uma quantidade de ligante
relativamente elevado, pelo que a possibilidade de ocorrência de fendilhação nas primeiras
idades deve ser avaliada usando modelos que permitam estimar o calor gerado pela
hidratação do ligante durante o seu processo de cura, bem como a determinação das
correspondentes tensões. Para o efeito, no presente trabalho é desenvolvido um modelo de
transferência de calor baseado no método dos elementos finitos, o qual é integrado num
modelo mecânico que permite simular o início de fendilhação e a sua propagação em
estruturas discretizadas por elementos finitos de volume. Este modelo de fendilhação 3D
tem a possibilidade de simular a ocorrência de múltiplas fendas fixas distribuídas, bem
como o comportamento de estruturas cujo modo de ruptura é condicionado pelas
componentes de corte. A retracção e a fluência também são fenómenos de relevância em
estruturas constituídas por estes tipos de materiais, principalmente em estados limites de serviço por abertura de fenda, pelo que a sua modelação foi também integrada no modelo
termo-mecânico.
Nas últimas duas décadas, materiais de matriz polimérica reforçados com fibras contínuas
têm sido utilizados na reabilitação estrutural de estruturas de betão, principalmente para o
reforço à flexão e ao corte de vigas de betão armado. A previsão do comportamento das
vigas reforçadas ao corte requer o uso de modelos constitutivos capazes de simular a
diminuição da capacidade de transferência de tensão de corte com a evolução da abertura
de fenda. Duas abordagens numéricas são propostas para este fim. Uma delas baseia-se na
utilização de um diagrama de amolecimento para a modelação do modo II de fractura. A
outra suporta-se numa formulação total para a relação entre a tensão e a extensão de corte
na fenda, adoptando um módulo de rigidez correspondente ao modo II de fractura que
diminui com a extensão normal à fenda. De forma a aumentar a robustez dos modelos numéricos desenvolvidos, foram
implementadas algumas estratégias de actualização do estado de tensão no material durante
o processo de análise não linear. Com o objectivo de melhorar as características de
convergência dos métodos numéricos utilizados foram introduzidos algoritmos baseados
na técnica arc-length. Condições de apoio com comportamento linear, não linear e
unilateral também foram numericamente implementadas.
Todos os modelos numéricos foram implementados no software de elementos finitos
FEMIX usando a linguagem de programação ANSI-C
Plastic-damage smeared crack model to simulate the behaviour of structures made by cement based materials
This work proposes a constitutive model to simulate nonlinear behaviour of cement based materials subjected to
different loading paths. The model incorporates a multidirectional fixed smeared crack approach to simulate crack
initiation and propagation, whereas the inelastic behaviour of material between cracks is treated by a numerical strategy
that combines plasticity and damage theories. For capturing more realistically the shear stress transfer between the crack
surfaces, a softening diagram is assumed for modelling the crack shear stress versus crack shear strain. The plastic
damage model is based on the yield function, flow rule and evolution law for hardening variable, and includes an
explicit isotropic damage law to simulate the stiffness degradation and the softening behaviour of cement based
materials in compression. This model was implemented into the FEMIX computer program, and experimental tests at
material scale were simulated to appraise the predictive performance of this constitutive model. The applicability of the
model for simulating the behaviour of reinforced concrete shear wall panels submitted to biaxial loading conditions, and
RC beams failing in shear is investigated.The authors wish to acknowledge the FCT financial support provided by the Portuguese Foundation for Science and Technology in the scope of the SlabSys-HFRC research project, with reference PTDC/ECM/120394/2010
Shear strengthening of reinforced concrete beams with hybrid composite plates
The effectiveness of Hybrid Composite Plates (HCPs) for the shear strengthening of the Reinforced Concrete (RC)
beams was assessed by an experimental program. HCP is a thin plate of Strain Hardening Cementitious Composite
(SHCC) reinforced with Carbon Fiber Reinforced Polymer (CFRP) laminates. Due to the excellent bond conditions
between SHCC and CFRP laminates, these reinforcements provide the necessary tensile strength capacity to the
HCP. Two HCPs with different inclination of CFRP laminates (45º and 90º) were adopted for the shear
strengthening of RC beams by bonding these HCPs to the lateral faces of the beam with an epoxy adhesive. The
results showed that these HCPs have assured a significant increase in terms of load carrying capacity, mainly those
with inclined laminates. The SHCC surrounding the CFRP laminates in the HCP has offered effective resistance to
the degeneration of micro-cracks on macro-cracks, which has avoided the occurrence of premature mixed shallow
semi-pyramid-plus-debonding failure modes registered currently when using the NSM-CFRP technique. Advanced
numerical simulations were performed by using a FEM-based computer program, whose predictive performance
was demonstrated by simulating the experimental tests carried out. In this context a parametric study was executed
to evaluate the shear strengthening efficiency of the arrangement and percentage of CFRP laminates in HCPs, as
well as the influence of using mechanical anchors to avoid premature detachment of the HCPs.“PrePam –Pre-fabricated thin panels by using 17 advanced materials for structural rehabilitation” with reference number of PTDC/ECM/114511/200
Assessing the applicability of a smeared crack approach for simulating the behaviour of concrete beams flexurally reinforced with GFRP bars and failing in shear
Numerical simulation of beams failing in shear is still a challenge. With the scope of verifying the applicability of
smeared crack approaches to simulate the behavior of reinforced concrete (RC) beams failing in shear, a set of
concrete beams reinforced with longitudinal glass fiber reinforced polymer (GFRP) bars, experimentally tested
up to their failure, and comprehensibly monitored, are numerically simulated. The simulations are carried out
with a multi-directional fixed smeared crack model available in the FEMIX computer program that has several
options for modeling the crack shear stress transfer, which is a critical aspect when simulating RC elements
failing in shear. The predictive performance of the numerical simulations is assessed in term of load vs deflection, crack pattern at failure, concrete strains in critical shear regions, and moment–curvature relationship. The influence on the predictive performance of the following modeling aspects is also investigated: finite element mesh refinement; simulation of the crack shear stress transfer by using the classical shear retention factor and a crack shear-softening diagram; bond conditions between flexural reinforcement and surrounding concrete. The simulations carried out demonstrate that small dependence of the results on the finite element mesh refinement and adequate crack patterns can be obtained with refinement levels suitable for design purposes and taking into account the actual computer performances, as long as a crack shear-softening diagram is used. However, the predictive performance of the simulations depends significantly on the values adopted for the parameters that define this diagram, as demonstrated by the performed parametric studies.The first author aims to acknowledge the support provided by FCT
through the research project ICoSyTec -Innovative construction system
for a new generation of high performance buildings, with reference:
POCI-01-0145-FEDER-027990
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
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
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