Nuno Azevedo - Academia.edu (original) (raw)

Papers by Nuno Azevedo

Os modelos de partículas têm vindo a ser utilizados no estudo do comportamento de materiais quase... more Os modelos de partículas têm vindo a ser utilizados no estudo do comportamento de materiais quasefrágeis, em particular do betão. Este tipo de modelos permite a consideração da distribuição, quantidade e forma dos agregados no interior de um determinado provete de betão e a obtenção da resposta estrutural para diferentes condições de ensaio (compressão, tração, corte, curta duração, longa duração, entre outros).

Geotecnia, 2018

Os modelos de partículas, ao terem em conta a estrutura granular da rocha, consideram de forma ex... more Os modelos de partículas, ao terem em conta a estrutura granular da rocha, consideram de forma explícita a variabilidade associada ao material, razão pela qual têm sido aplicados com sucesso no estudo da fratura em rocha. Neste trabalho é apresentado um modelo de partículas 3D com base nos diagramas de Laguerre-Voronoi da estrutura granular, que permite ter em conta de forma aproximada uma geometria do tipo poliédrica mantendo a simplicidade e o reduzido esforço computacional característico dos modelos de partículas esféricas. Propõe-se então um modelo de contacto múltiplo no qual a superfície de contacto é definida com base nas facetas dos diagramas de Voronoi. O modelo de partículas é validado com base em ensaios experimentais em rocha (triaxiais, uniaxiais e ensaio Brasileiro). Apresentam-se vários estudos paramétricos que evidenciam a influência dos parâmetros do modelo de partículas nas propriedades macroscópicas elásticas e resistentes obtidas numericamente. É ainda analisada ...

Geotecnia, 2013

Modelos detalhados de partículas têm sido adotados na modelação da fratura em materiais quase frá... more Modelos detalhados de partículas têm sido adotados na modelação da fratura em materiais quase frágeis. Neste artigo é adotado um modelo de partículas 2D que tem sido desenvolvido tendo em vista o estudo da fratura em rocha. Os sistemas de partículas são gerados com base num algoritmo de geração de partículas poligonais baseado nos Voronois de Laguerre da triangulação de Delaunay dos centros de gravidade das partículas circulares. O modelo de partículas poligonais, aproximado através de partículas circulares que interagem entre si através de um esquema de contacto múltiplo, é validado em ensaios biaxiais, e em ensaios do tipo Brasileiro, em rocha. São apresentados vários estudos paramétricos que permitem identificar a influên cia dos parâmetros micromecânicos nas propriedades macroscópicas, elásticas e resistentes. É por fim analisada a relevância de um modelo de contacto com leis de enfraquecimento bilinear em tração e corte de modo a obter valores coerentes de tração última nos ens...

Geotecnia, 2021

Neste artigo apresenta-se a formulação e resultados da aplicação de dois modelos descontínuos tri... more Neste artigo apresenta-se a formulação e resultados da aplicação de dois modelos descontínuos tridimensionais que simulam a interação hidromecânica. Nestes modelos o comportamento mecânico é simulado de forma idêntica mas o comportamento hidráulico é simulado com duas abordagens diferentes. O primeiro modelo baseia-se numa formulação que admite o escoamento através de elementos planos de interface. O segundo modelo, que se propõe neste artigo, baseia-se numa discretização unidimensional, ocorrendo o escoamento através de elementos de canais. Os modelos hidromecânicos implementados no módulo computacional Parmac3D-Fflow são verificados e validados através de exemplos simples, e o modelo proposto é calibrado de modo a serem obtidos, com os dois modelos, os mesmos valores de pressão e de caudal.Foi desenvolvido um modelo hidromecânico de um conjunto barragem/fundação, tendo em consideração a existência de cortina de impermeabilização e de sistema de drenagem na fundação. Salientam-se a...

International Journal for Numerical and Analytical Methods in Geomechanics, 2005

ROS: The Research Output Service. ROS Home ROS Home. Advanced Search Advanced Search. ROS Quick F... more ROS: The Research Output Service. ROS Home ROS Home. Advanced Search Advanced Search. ROS Quick Finder. ...

Computer Methods in Applied Mechanics and Engineering, 2006

Structural Engineering and Mechanics

ABSTRACT The Discrete Element Method, DEM, is increasingly used in fracture studies of non-homoge... more ABSTRACT The Discrete Element Method, DEM, is increasingly used in fracture studies of non-homogeneous continuous media, such as rock and concrete. A 2D circular rigid DEM formulation, developed to model concrete, has been adopted. A procedure developed to generate aggregate particles with a given aspect ratio and shape is presented. The aggregate particles are modelled with macroparticles formed by a group of circular particles that behave as a rigid body. Uniaxial tensile and compression tests performed with circular and non-circular aggregates, with a given aspect ratio, have shown similar values of fracture toughness when adopting uniform strength and elastic properties for all the contacts. Non-circular aggregate assemblies are shown to have higher fracture toughness when different strength and elastic properties are set for the matrix and for the aggregate/matrix contacts.

Structural Engineering and Mechanics

ABSTRACT The Discrete Element Method adopting particles for the domain discretization has recentl... more ABSTRACT The Discrete Element Method adopting particles for the domain discretization has recently been adopted in fracture studies of non-homogeneous continuous media such as concrete and rock. A model is proposed in which the reinforcement is modelled by 1D rigid-spring discrete elements. The rigid bars interact with the rigid circular particles that simulate the concrete through contact interfaces. The DEM enhanced model with reinforcement capabilities is evaluated using three point bending and four point bending tests on reinforced concrete beams without stirrups. Under three point bending, the model is shown to reproduce the expected final crack pattern, the crack propagation and the load displacement diagram. Under four point bending, the model is shown to match the experimental ultimate load, the size effect and the crack propagation and localization.

III European Conference on Computational Mechanics, 2006

ABSTRACT The Discrete Element Method was initially applied to the analysis of discontinuous media... more ABSTRACT The Discrete Element Method was initially applied to the analysis of discontinuous media, e.g. in rock mechanics and soil mechanics. Recently the DEM has been used in fracture studies of non-homogeneous continuous media such as concrete and rock. A 2D circular rigid discrete element formulation based on the DEM that has been further developed to model concrete is adopted [1]. To simulate the concrete at the meso-level, random assemblies of particles based on a given sieve analysis have to be generated. The DEM model micro-properties also have to be previously calibrated through uniaxial tension and compression tests. The formulation of a 1D rigid discrete element that interacts with the discrete rigid particles through contact interfaces is presented. The DEM enhanced model with reinforcement capabilities is evaluated in a three point bending [2] and in a four point bending [3] tests experiments of reinforced concrete beams without stirrups. Under flexure loading conditions the model is shown to predict the expected final crack pattern, the crack propagation and the load displacement diagram. Under shear loading conditions the model is shown to predict the size effect behaviour that occurs on beams without stirrups failing under diagonal shear and also the expected crack propagation and final crack patterns.

Detailed rigid particle models have been proposed for modelling fracture in quasi-brittle materia... more Detailed rigid particle models have been proposed for modelling fracture in quasi-brittle materials. In the present study, a 2D rigid particle model that has been developed to study fracture phenomena in rock is adopted. The particle assemblies are created using a particle generation algorithm that generates polygonal shape particles based on the Laguerre Voronois of the circular particle gravity centres of an initial circular particle assembly. The particles are considered to interact through a multiple contact point model where the contact width and the contact location are defined given the Voronoi tessellation. The particle model is validated against known triaxial and Brazilian test results of a granite rock. Several parametric studies are presented showing the influence of the elastic and strength micromechanical parameters on both the macroscopic elastic and strength properties. Finally, a reference is made to the relevance of adopting a bilinear tensile/shear softening conta...

Rock Mechanics and Rock Engineering, 2014

ABSTRACT It is known that rigid circular particle models proposed in the literature do not proper... more ABSTRACT It is known that rigid circular particle models proposed in the literature do not properly reproduce the rock friction angle and the rock tensile strength to compressive strength ratio. A 2D rigid particle model is here presented which tries to overcome these issues while keeping the simplicity and the reduced computational costs characteristic of circular particle models. A particle generation algorithm is adopted which generates polygonal shape particles based on the Laguerre–Voronoi diagrams of the circular particle gravity centres. Several parametric studies are presented to show the influence of the micromechanical properties on both the macroscopic elastic and strength properties. It is shown that a good agreement with the known rock direct tensile to indirect tensile test ratio requires the incorporation of bilinear softening contact laws under tension and shear. Finally, the proposed model is validated against known triaxial and Brazilian tests of a granite rock.

Engineering Fracture Mechanics, 2008

The discrete element method, DEM, has been used in fracture studies of non-homogeneous continuous... more The discrete element method, DEM, has been used in fracture studies of non-homogeneous continuous media adopting circular or spherical particles. A 2D circular rigid DEM formulation developed with the purpose of modelling concrete is described and evaluated in uniaxial tensile and compression tests. According to this model, the aggregate can be modelled either as a rigid macro-particle or as a deformable group of particles. The inter-particle contacts can either be assumed as brittle or follow a given bilinear softening curve. It is shown that aggregate deformability, together with the consideration of pure friction contacts working under compression, increases the fracture energy in compression, leading to a better agreement with concrete tests. The softening contact model, by adding a higher capability of load redistribution, is shown to give a better agreement than the brittle model under tensile loading. The recognized crack mechanisms of the brittle model (tensile splitting, branching, bridging) are also present with softening.

Proceedings of 10th World Congress on Computational Mechanics, 2014

In the framework of the Portuguese National Programme for Dams with High Hydroelectric Potential ... more In the framework of the Portuguese National Programme for Dams with High Hydroelectric Potential (PNBEPH), a set of large concrete dams is currently under design or construction, including several 100 m high arch dams. Earthquake loading is one of the important aspects to be considered in the design of these structures. A variety of numerical methods have been developed over the years by various researchers and are presently available for seismic analysis of concrete dams. The methods in use by the dam engineering community have different approaches, for example, in the representation of the seismic action, the dam-water interaction or the structural nonlinear behavior. In the paper, the models applied in the study of new Portuguese dams are presented, and their fundamental assumptions discussed. In particular, the analysis of the response of arch dams to the Maximum Design Earthquake is examined, considering the non-elastic behavior of the contraction joints and the dam foundation. An explicit time integration algorithm was used in these simulations, allowing a detailed representation of the slip and separation events along the discontinuities. The boundary conditions appropriate for seismic analysis are discussed, namely the type of free-field boundaries employed. In the paper, the application of this modeling methodology to two new dams is presented and discussed. Foz Tua dam, that is already under construction, is a concrete arch dam, 108 m high and 275 m long at the crest. Fridão dam is also a concrete arch dam, 98 m high and with a crest length of 300 m. Design criteria and the results of the numerical analyses are discussed.

Os modelos de partículas têm vindo a ser utilizados no estudo do comportamento de materiais quase... more Os modelos de partículas têm vindo a ser utilizados no estudo do comportamento de materiais quasefrágeis, em particular do betão. Este tipo de modelos permite a consideração da distribuição, quantidade e forma dos agregados no interior de um determinado provete de betão e a obtenção da resposta estrutural para diferentes condições de ensaio (compressão, tração, corte, curta duração, longa duração, entre outros).

Geotecnia, 2018

Os modelos de partículas, ao terem em conta a estrutura granular da rocha, consideram de forma ex... more Os modelos de partículas, ao terem em conta a estrutura granular da rocha, consideram de forma explícita a variabilidade associada ao material, razão pela qual têm sido aplicados com sucesso no estudo da fratura em rocha. Neste trabalho é apresentado um modelo de partículas 3D com base nos diagramas de Laguerre-Voronoi da estrutura granular, que permite ter em conta de forma aproximada uma geometria do tipo poliédrica mantendo a simplicidade e o reduzido esforço computacional característico dos modelos de partículas esféricas. Propõe-se então um modelo de contacto múltiplo no qual a superfície de contacto é definida com base nas facetas dos diagramas de Voronoi. O modelo de partículas é validado com base em ensaios experimentais em rocha (triaxiais, uniaxiais e ensaio Brasileiro). Apresentam-se vários estudos paramétricos que evidenciam a influência dos parâmetros do modelo de partículas nas propriedades macroscópicas elásticas e resistentes obtidas numericamente. É ainda analisada ...

Geotecnia, 2013

Modelos detalhados de partículas têm sido adotados na modelação da fratura em materiais quase frá... more Modelos detalhados de partículas têm sido adotados na modelação da fratura em materiais quase frágeis. Neste artigo é adotado um modelo de partículas 2D que tem sido desenvolvido tendo em vista o estudo da fratura em rocha. Os sistemas de partículas são gerados com base num algoritmo de geração de partículas poligonais baseado nos Voronois de Laguerre da triangulação de Delaunay dos centros de gravidade das partículas circulares. O modelo de partículas poligonais, aproximado através de partículas circulares que interagem entre si através de um esquema de contacto múltiplo, é validado em ensaios biaxiais, e em ensaios do tipo Brasileiro, em rocha. São apresentados vários estudos paramétricos que permitem identificar a influên cia dos parâmetros micromecânicos nas propriedades macroscópicas, elásticas e resistentes. É por fim analisada a relevância de um modelo de contacto com leis de enfraquecimento bilinear em tração e corte de modo a obter valores coerentes de tração última nos ens...

Geotecnia, 2021

Neste artigo apresenta-se a formulação e resultados da aplicação de dois modelos descontínuos tri... more Neste artigo apresenta-se a formulação e resultados da aplicação de dois modelos descontínuos tridimensionais que simulam a interação hidromecânica. Nestes modelos o comportamento mecânico é simulado de forma idêntica mas o comportamento hidráulico é simulado com duas abordagens diferentes. O primeiro modelo baseia-se numa formulação que admite o escoamento através de elementos planos de interface. O segundo modelo, que se propõe neste artigo, baseia-se numa discretização unidimensional, ocorrendo o escoamento através de elementos de canais. Os modelos hidromecânicos implementados no módulo computacional Parmac3D-Fflow são verificados e validados através de exemplos simples, e o modelo proposto é calibrado de modo a serem obtidos, com os dois modelos, os mesmos valores de pressão e de caudal.Foi desenvolvido um modelo hidromecânico de um conjunto barragem/fundação, tendo em consideração a existência de cortina de impermeabilização e de sistema de drenagem na fundação. Salientam-se a...

International Journal for Numerical and Analytical Methods in Geomechanics, 2005

ROS: The Research Output Service. ROS Home ROS Home. Advanced Search Advanced Search. ROS Quick F... more ROS: The Research Output Service. ROS Home ROS Home. Advanced Search Advanced Search. ROS Quick Finder. ...

Computer Methods in Applied Mechanics and Engineering, 2006

Structural Engineering and Mechanics

ABSTRACT The Discrete Element Method, DEM, is increasingly used in fracture studies of non-homoge... more ABSTRACT The Discrete Element Method, DEM, is increasingly used in fracture studies of non-homogeneous continuous media, such as rock and concrete. A 2D circular rigid DEM formulation, developed to model concrete, has been adopted. A procedure developed to generate aggregate particles with a given aspect ratio and shape is presented. The aggregate particles are modelled with macroparticles formed by a group of circular particles that behave as a rigid body. Uniaxial tensile and compression tests performed with circular and non-circular aggregates, with a given aspect ratio, have shown similar values of fracture toughness when adopting uniform strength and elastic properties for all the contacts. Non-circular aggregate assemblies are shown to have higher fracture toughness when different strength and elastic properties are set for the matrix and for the aggregate/matrix contacts.

Structural Engineering and Mechanics

ABSTRACT The Discrete Element Method adopting particles for the domain discretization has recentl... more ABSTRACT The Discrete Element Method adopting particles for the domain discretization has recently been adopted in fracture studies of non-homogeneous continuous media such as concrete and rock. A model is proposed in which the reinforcement is modelled by 1D rigid-spring discrete elements. The rigid bars interact with the rigid circular particles that simulate the concrete through contact interfaces. The DEM enhanced model with reinforcement capabilities is evaluated using three point bending and four point bending tests on reinforced concrete beams without stirrups. Under three point bending, the model is shown to reproduce the expected final crack pattern, the crack propagation and the load displacement diagram. Under four point bending, the model is shown to match the experimental ultimate load, the size effect and the crack propagation and localization.

III European Conference on Computational Mechanics, 2006

ABSTRACT The Discrete Element Method was initially applied to the analysis of discontinuous media... more ABSTRACT The Discrete Element Method was initially applied to the analysis of discontinuous media, e.g. in rock mechanics and soil mechanics. Recently the DEM has been used in fracture studies of non-homogeneous continuous media such as concrete and rock. A 2D circular rigid discrete element formulation based on the DEM that has been further developed to model concrete is adopted [1]. To simulate the concrete at the meso-level, random assemblies of particles based on a given sieve analysis have to be generated. The DEM model micro-properties also have to be previously calibrated through uniaxial tension and compression tests. The formulation of a 1D rigid discrete element that interacts with the discrete rigid particles through contact interfaces is presented. The DEM enhanced model with reinforcement capabilities is evaluated in a three point bending [2] and in a four point bending [3] tests experiments of reinforced concrete beams without stirrups. Under flexure loading conditions the model is shown to predict the expected final crack pattern, the crack propagation and the load displacement diagram. Under shear loading conditions the model is shown to predict the size effect behaviour that occurs on beams without stirrups failing under diagonal shear and also the expected crack propagation and final crack patterns.

Detailed rigid particle models have been proposed for modelling fracture in quasi-brittle materia... more Detailed rigid particle models have been proposed for modelling fracture in quasi-brittle materials. In the present study, a 2D rigid particle model that has been developed to study fracture phenomena in rock is adopted. The particle assemblies are created using a particle generation algorithm that generates polygonal shape particles based on the Laguerre Voronois of the circular particle gravity centres of an initial circular particle assembly. The particles are considered to interact through a multiple contact point model where the contact width and the contact location are defined given the Voronoi tessellation. The particle model is validated against known triaxial and Brazilian test results of a granite rock. Several parametric studies are presented showing the influence of the elastic and strength micromechanical parameters on both the macroscopic elastic and strength properties. Finally, a reference is made to the relevance of adopting a bilinear tensile/shear softening conta...

Rock Mechanics and Rock Engineering, 2014

ABSTRACT It is known that rigid circular particle models proposed in the literature do not proper... more ABSTRACT It is known that rigid circular particle models proposed in the literature do not properly reproduce the rock friction angle and the rock tensile strength to compressive strength ratio. A 2D rigid particle model is here presented which tries to overcome these issues while keeping the simplicity and the reduced computational costs characteristic of circular particle models. A particle generation algorithm is adopted which generates polygonal shape particles based on the Laguerre–Voronoi diagrams of the circular particle gravity centres. Several parametric studies are presented to show the influence of the micromechanical properties on both the macroscopic elastic and strength properties. It is shown that a good agreement with the known rock direct tensile to indirect tensile test ratio requires the incorporation of bilinear softening contact laws under tension and shear. Finally, the proposed model is validated against known triaxial and Brazilian tests of a granite rock.

Engineering Fracture Mechanics, 2008

The discrete element method, DEM, has been used in fracture studies of non-homogeneous continuous... more The discrete element method, DEM, has been used in fracture studies of non-homogeneous continuous media adopting circular or spherical particles. A 2D circular rigid DEM formulation developed with the purpose of modelling concrete is described and evaluated in uniaxial tensile and compression tests. According to this model, the aggregate can be modelled either as a rigid macro-particle or as a deformable group of particles. The inter-particle contacts can either be assumed as brittle or follow a given bilinear softening curve. It is shown that aggregate deformability, together with the consideration of pure friction contacts working under compression, increases the fracture energy in compression, leading to a better agreement with concrete tests. The softening contact model, by adding a higher capability of load redistribution, is shown to give a better agreement than the brittle model under tensile loading. The recognized crack mechanisms of the brittle model (tensile splitting, branching, bridging) are also present with softening.

Proceedings of 10th World Congress on Computational Mechanics, 2014

In the framework of the Portuguese National Programme for Dams with High Hydroelectric Potential ... more In the framework of the Portuguese National Programme for Dams with High Hydroelectric Potential (PNBEPH), a set of large concrete dams is currently under design or construction, including several 100 m high arch dams. Earthquake loading is one of the important aspects to be considered in the design of these structures. A variety of numerical methods have been developed over the years by various researchers and are presently available for seismic analysis of concrete dams. The methods in use by the dam engineering community have different approaches, for example, in the representation of the seismic action, the dam-water interaction or the structural nonlinear behavior. In the paper, the models applied in the study of new Portuguese dams are presented, and their fundamental assumptions discussed. In particular, the analysis of the response of arch dams to the Maximum Design Earthquake is examined, considering the non-elastic behavior of the contraction joints and the dam foundation. An explicit time integration algorithm was used in these simulations, allowing a detailed representation of the slip and separation events along the discontinuities. The boundary conditions appropriate for seismic analysis are discussed, namely the type of free-field boundaries employed. In the paper, the application of this modeling methodology to two new dams is presented and discussed. Foz Tua dam, that is already under construction, is a concrete arch dam, 108 m high and 275 m long at the crest. Fridão dam is also a concrete arch dam, 98 m high and with a crest length of 300 m. Design criteria and the results of the numerical analyses are discussed.