Papers
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Um modelo discreto de partículas 2D para simulação da fratura em rocha: Formulação e Calibração
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 influência 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 ensaios diretos e nos ensaios Brasileiros.
Year: 2013
Number Pages:
97-101.
Author(s): Azevedo, N.
: Geotecnia
Volume:
129.
Keywords: Fratura em rocha; Modelo partículas
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3D stability analysis of gravity dams on sloped rock foundations using the limit equilibrium method
A convenient approach to performing stability analysis of concrete gravity dams is the so-called twodimensional
Year: 2012
Number Pages:
147-156pp.
Author(s): Bretas, E. M.; Leger , P.; Lemos, J. V.
: Computers and Geotechnics
Editor: Elsevier
Volume:
44.
Keywords: Sloped rock foundation; Limit equilibrium; Sliding; Concrete gravity dam
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Comparison of different techniques of tilt testing and basic friction angle assessment
A relevant parameter for estimating discontinuity shear strength is the basic friction angle, usually derived from different types of tilt tests. However, the tilt tests described in the literature produce varying basic friction angle values. From a large number of different types of tilt tests on different kinds of rocks, it was possible to conclude that the mechanisms of sliding along cylinder generatrixes and planar surfaces are quite different, andthat tests based on sliding along generatrixes are not appropriate for determining reliable basic friction anglevalues for discontinuity planes. Tests on small specimens are also not recommended, for geometry reasons and because ensuring reliable stress conditions is difficult. Toquantify the natural variability in tilt testing, large specimens of the same granite were tested. The results revealed coefficients of variation for the basic friction angle in the range of 5
Year: 2012
Number Pages:
1023
Author(s): Alejano, L.; González, J.; Muralha, J.
: Rock Mechanics and Rock Engineering
Editor: Springer
Volume:
Vol 45; Nr 6.
Keywords: Joint strength; Variability assessment; Tilt testing; Basic friction angle
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Masonry dams: Analysis of the historical profiles of Sazilly, Delocre, and Rankine
The significant advances in masonry dam design that took place in the second half of the19th century are analyzed and discussed within the context of the historical developmentof dam construction. Particular reference is made to the gravity dam profiles proposed bySazilly, Delocre, and Rankine, who pioneered the application of engineering concepts to damdesign, basing the dam profile on the allowable stresses for the conditions of empty and fullreservoir. These historical profiles are analyzed taking into consideration the present safetyassessment procedures, by means of a numerical application developed for this purpose,based on limit analysis equilibrium methods, which considers the sliding failure mechanisms,the most critical for these structures. The study underlines the key role of upliftpressures, that was only addressed by Lévy after the accident of Bouzey Dam, and providesa critical understanding of the original design concepts, which is essential for therehabilitation of these historical structures.
Year: 2012
Number Pages:
19-45pp.
Author(s): Bretas, E. M.; Lemos, J. V.; Lourenço, P.
: International Journal of Architectural Heritage
Editor: Taylor & Francis
Volume:
6.
Keywords: Safety assessment; Masonry dam
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Response by the Authors to S. R. Hencher
N/A
Year: 2012
Number Pages:
3p.
Author(s): Alejano, L.; González, J.; Nahon, A.
: Rock Mechanics and Rock Engineering
Editor: Springer
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Strain localization, strong discontinuities and material fracture: Matches and mismatches
The work focuses on the connections of strain localization modeling of material failure and discrete fracture mechanics. It is an attempt to give an answer to the old question of whether the finite element solutions of material failure problems based on strain localization techniques, using standard continuum stress
Year: 2012
Number Pages:
323-336pp.
Author(s): Oliver, J.; Huespe, A.E.; Dias, I. F.
: Computer Methods in Applied Mechanics and Engineering
Editor: ELSEVIER
Volume:
241-244.
Keywords: Fracture mechanics; Strong discontinuities; Strain localization; Computational material failure
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Modelling of arch dam foundation failure scenarios - case studies of Baixo Sabor and Alto Ceira dams
In concrete arch dam foundations, potential failure mechanisms are typically defined by natural rock discontinuities or the concrete-rock interface. Discrete element models are particularly adequate for the safety assessment of these failure scenarios, given their ability to represent the geologic structure of the rock mass, as well as the concrete cantilevers. Application of these procedures to 2 large dams presently under construction in Portugal, Baixo Sabor and Alto Ceira arch dams, is presented. The numerical models represent the foundation rock mass as a system of deformable blocks defined by the main faults and joint sets identified at the site. The safety analysis is performed by progressive reduction of strength along the discontinuities until the failure condition is reached.
Year: 2011
Number Pages:
299-312pp.
Author(s): Lemos, J. V.; Antunes , N.
: Dam Engineering
Editor: Global Trade Media
Volume:
vol. 21, no. 4.
Keywords: Discrete elements; Discrete elements; Failure analysis; Rock foundations; Arch dams
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Micromechanical Modelling of Stress Waves in Rock and Rock Fractures
The goal of this paper is to simulate the interaction of stress waves and rock fractures in a particle micromechanical model. Stress waves travelling in fractured rock masses are slowed down and attenuated by natural heterogeneities, voids, microcracks and, above all, by faults and fractures. Considerable laboratory and theoretical investigation have uncovered the major aspects of this phenomenon, but models that cover the core mechanisms of the wave propagation in rock masses are necessary to investigate aspects of wave
Year: 2010
Number Pages:
741-761pp.
Author(s): Resende, R.; Lamas, L.; Lemos, J. V.; Calçada, R.
: Rock Mechanics and Rock Engineering
Editor: Springer-Verlag
Volume:
43.
Keywords: Micromechanical model; Discrete element method; Stress wave; Rock dynamics; Rock joint
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Um modelo discreto de partículas para análise da fractura em betão armado
O método dos elementos discretos adoptando partículas para discretização dodomínio tem sido utilizado no estudo do fenómeno da fractura em meios nãohomogéneos, como o betão e a rocha. Neste artigo, é proposto um modelo de análisepara o betão armado no qual as armaduras são modeladas com elementos rígidosunidimensionais ligados por molas. Os elementos rígidos interagem com o betão,modelado por partículas circulares, através de uma interface de contacto. O modelo évalidado com base em ensaios de flexão em viga a três pontos e a quatro pontos,sem armaduras de esforço transverso. No ensaio de flexão a 3 pontos o modelo dáuma boa aproximação do comportamento real em termos do processo de evolução dafractura e da relação carga-deslocamento. No ensaio de flexão a 4 pontos, verifica-seuma boa correlação com os resultados experimentais, nomeadamente o valor dacarga última, o efeito de escala e a evolução do processo de fractura.
Year: 2010
Author(s): Azevedo, N.
: Revista Portuguesa de Engenharia de Estruturas
Editor: RPEE
Keywords: Fractura; Betão armado; Elementos discretos
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Numerical modelling for interpretation of stress measurements by overcoring
The overcoring method for measuring in situ stresses is frequently used in rock engineering projects. Most models for its interpretation assume that the rock is homogeneous, linear elastic and isotropic. The elastic constants are determined by various methods, namely by biaxial tests on the recovered core.A three-dimensional finite element model was developed, which allows to compute the stress state from the strain measurements obtained during overcoring, assuming a transversely-isotropic behaviour of the rock mass. Different testing methodologies for elastic constants determination of anisotropic rocks are introduced and discussed. Several numerical tests were performed to analyse the influence of the weakness planes that sometimes occur in the rock core owing to the tensile strains that are generated during the biaxial test. To avoid the tensile strains in the biaxial test, a new triaxial testing procedure of the overcored rock sample with the cell was developed. The effect of the degree of rock anisotropy on in situ stress determination and the error involved in neglecting rock anisotropy are analysed. Differences on the principal stresses and principal directions calculated considering the usual isotropic model and the developed numerical model for a real case of anisotropic rock are presented.
Year: 2009
Number Pages:
6.
Author(s): Figueiredo, B.; Muralha, J.; Lamas, L.
Keywords: Monitoring; Flat jack tests; Overcoring tests; Undergound cavern; In situ stresses
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Comunicação
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Modelo tridimensional do estado de tensão in situ num maciço rochoso. Geotecnia nas Infraestruturas
Os ensaios de medição de tensões in situ são necessariamente executados num número limitado de locais e a representatividade dos resultados obtidos é questionável quando se pretende conhecer o estado de tensão existente num grande volume de maciço rochoso. Assim, é importante utilizar modelos interpretativos globais, que possam integrar os resultados de todos os ensaios, realizados em diferentes locais, de preferência utilizando mais de um método de ensaio, para estimar o estado de tensão instalado no maciço rochoso interessado pelas obras de engenharia a construir. Neste trabalho apresenta-se o modelo numérico tridimensional do maciço rochoso desenvolvido, bem como a metodologia inversa utilizada para avaliar o estado de tensão na zona da nova caverna da central subterrânea do reforço de potência de Salamonde, no rio Cávado, com base nos resultados dos ensaios de sobrecarotagem e de almofadas planas de pequena área realizados. Com o objetivo de avaliar a influência dos efeitos diferidos ao longo do tempo no estado de tensão in situ, foi também realizada uma análise gravitacional visco-elástica utilizando o mesmo modelo numérico.
Year: 2014
Number Pages:
13p..
Author(s): Espada, M.; Lamas, L.
Editor: Sociedade Portuguesa de Geotecnia - SPG
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Modulação de cenários de rotura em barragens de gravidade de betão com um modelo discreto de partículas
A análise de cenários de rotura em barragens de gravidade em betão requer ferramentas computacionais que sejam capazes de lidar com o fenómeno da fendilhação. Neste trabalho adota-se um modelo detalhado de partículas (MP) nas zonas em que se espera que esta ocorra. É proposto um modelo MP híbrido, no qual, a rigidez de cada elemento finito onde se prevê que ocorra um comportamento não linear é substituída pela rigidez do sistema de partículas adotado na discretização do seu interior. Por razões computacionais, o tamanho adotado para as partículas é superior ao tamanho máximo do agregado incorporado no betão de barragens. Os resultados obtidos, estáticos e dinâmicos, com o modelo MP proposto são comparados com os resultados obtidos com um modelo de dano de duas variáveis e com um modelo MP global.
Year: 2014
Number Pages:
16pp.
Author(s): Azevedo, N.
Keywords: Cenários de rotura; Modelo de partículas; Betão; Barragem de gravidade
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Numerical modelling of masonry gravity dams considering the internal structure of the material
Frequently, numerical models of masonry dams disregard the discontinuous nature of the material. In some cases, those discontinuities control the structural and hydraulic behaviour of the masonry dam. The masonry proprieties are influenced by the quality of the material and the laying scheme of the stones on the external faces as well as in the inner material. The Discrete Element Method (DEM) has been used on analyses of gravity masonry dams. The capacity to model the discontinuities explicitly and the ability to perform coupled analyses are two significant benefits of the DEM. The DEM application used in this paper is presented, stressing the description of the calculation cycle. Seven examples of numerical analyses of gravity masonry dams are presented. Three of them consider the discontinuous nature of the dam body, in order to study the loss of cohesion scenario, the crack propagation scenario and the seismic performance of a masonry dam. The remainder four examples are aimed at stress analysis, global stability, hydromechanical analysis and the permanent sliding resulting from a seismic event.
Year: 2014
Number Pages:
11p.
Author(s): Bretas, E. M.; Lemos, J. V.; Lourenço, P.
Editor: Universidade do Minho
Keywords: Elementos discretos; Modelação numérica; Barragens de alvenaria
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Representation of rock discontinuities in safety analysis of large dams
The application of discontinuum idealizations to the analysis of dam foundations is addressed.The options for the representation of the rock mass discontinuities are discussed, from the perspective of assessingfailure modes involving the rock mass. An example of concrete gravity dam analysis is presented, consideringvarious patterns of rock mass jointing. Issues involved in modeling rock bridges in non-persistent joint setsare examined. The study of arch dam foundations with discrete element block models is discussed, reviewingmethods and choices available for building efficient models. Several practical cases exemplify the informationthese analyses provide about the structural and rock mass behavior.
Year: 2014
Number Pages:
29-38pp.
Author(s): Lemos, J. V.
Editor: Taylor & Francis
Keywords: Jointed rock; Safety analysis; Numerical modelling; Concrete dams
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Um modelo discreto de partículas 3D para o estudo da fratura em rocha: calibração dos parâmetros micromecânicos
Os modelos detalhados de partículas, MP, ao terem em consideração a estrutura granular da rocha incluem de forma explícita a aleatoriedade do material e introduzem um tamanho limite à localização do dano. Neste trabalho é apresentado um modelo de partículas rígidas esféricas que tem sido desenvolvido tendo em vista o estudo da fratura em betão e em rocha. A interação entre partículas é definida com base na estrutura de Voronois dos centros de gravidade das partículas esféricas. Adota-se um modelo de contacto múltiplo, no qual a área da superfície de contacto é dada pela área da faceta comum dos Voronois associados a cada partícula. Vários estudos paramétricos são apresentados de modo a demonstrar a influência dos parâmetros micromecânicos, elásticos e resistentes, na resposta macroscópica dos sistemas de partículas.
Year: 2014
Number Pages:
14pp.
Author(s): Azevedo, N.
Keywords: Rocha; Fractura; Modelos de partículas
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Global methodology for evaluation of the stress field in a rock mass from in situ tests. Application to the Salamonde II powerhouse cavern.
This paper presents the results of in situ stress measurements and the application of a global interpretation model for evaluation of the most likely in situ stress field in the rock mass of the underground powerhouse cavern of the Salamonde II re-powering scheme, located in a mountainous zone of the North of Portugal. The objective of the study was to obtain the stress field prior to the powerhouse cavern excavation, for design purposes. Overcoring tests were performed in boreholes, before construction started. During early construction stages, when direct access to the vicinity of the cavern was created, flat jack tests were performed. For estimating the most likely state of stress in the rock mass, a global inverse analysis was carried out, which combined the overcoring and the flat jack tests results, using an appropriate methodology and a three dimensional numerical model. In order to assess the influence of time dependent effects on the in situstresses, a viscoelastic gravitational analysis was also performed using the same numerical model. The resultsobtained are compared and discussed.
Year: 2013
Number Pages:
6p..
Author(s): Espada, M.; Lamas, L.; Leitão, N. S.; Figueiredo, B.
: Rock Mechanics for Resources, Energy and Environment
Editor: CRC Press
Info
Modelo tridimensional para análise global dos ensaios de medição de tensões in situ no maciço rochoso da caverna da central de Salamonde II
Neste trabalho apresenta-se um modelo interpretativo tridimensional, que permite estimar o estado de tensão mais provável num maciço rochoso, integrando os resultados provenientes de ensaios de medição do estado de tensão in situ. Apresenta-se o caso de estudo da caverna da central subterrânea do reforço de potência do empreendimento hidroelétrico de Salamonde, localizado no rio Cávado, em Portugal. Neste caso de estudo, foiefetuada uma análise global integrando os resultados de dois tipos de ensaios, realizados em diferentes locais do maciço rochoso: i) ensaios de sobrecarotagem (STT), executados em furos de sondagens, antes de se iniciarem as obras do reforço de potência e; ii) ensaios de reposição de tensões com macacos planos (SFJ), realizados já em fase de execução da obra. Foi utilizado um modelo numérico tridimensional e uma metodologia apropriada, incluindo a geometria das escavações na altura da execução dos ensaios e a topografia do terreno, de forma a permitir uma estimativa do estado de tensão mais provável na zona da caverna da central.
Year: 2013
Number Pages:
17p.
Author(s): Espada, M.; Lamas, L.; Leitão, N. S.
Editor: Sociedad Española de Métodos Numéricos en Ingeniería (SEMNI)
Keywords: Maciço rochoso; Ensaios de medição de tensões in situ; Estado de tensão in situ; Modelo numérico tridimensional
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Dam foundation failure analysis. Discontinuum models and rock mass parameters
Identification of potential failure mechanisms defined by the rock mass discontinuities or the concrete-rockinterface plays an important role in the safety assessment of concrete dam foundations. The paper presentsinstances of application of discrete elements deformable block models for analysis of these failure scenarios,representing the rock mass foundation and the concrete dam. The rock mass characterization needs and themethodologies for obtaining the input parameters for these models are discussed.
Year: 2012
Number Pages:
12p.
Author(s): Lemos, J. V.; Muralha, J.; Lamas, L.
Editor: Instituto Brasileiro do Concreto - IBRACON
Keywords: Safety analysis; Rock mass parameters; Discontinuum models; Dam foundations
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Determinação da deformabilidade de maciços rochosos por meio de ensaios de almofadas planas de grande área
Os ensaios de macacos planos de grande área são utilizados para medir a deformabilidade de maciços rochosos e fornecem dados importantes para o projeto de grandes obras. Este ensaio consiste na abertura de um rasgo no maciço rochoso no qual é inserido um macaco plano de grande área. O macaco aplica pressão às paredes do rasgo através de óleo bombeado para o seu interior e são medidos os deslocamentos no maciço. A maior dificuldade na interpretação do ensaio reside no efeito provocado pela abertura de uma fenda de tração durante a aplicação de pressão pelo macaco plano. Para melhorar a compreensão sobre os efeitos da fenda de tração e assim melhorar a interpretação dos resultados do ensaio, desenvolveu-se um modelo numérico tridimensional do ensaio. O modelo permite estabelecer relações entre a tensão in situ perpendicular aos rasgos, a resistência à tração do maciço, as pressões aplicadas e a profundidade da fenda.
Year: 2012
Number Pages:
12.
Author(s): Figueiredo, B.; Lamas, L.; Muralha, J.
Keywords: Modelo numérico; Estado de tensão in situ; Fenda de tracção; Ensaios de almofadas planas de grande área; Deformabilidade
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Effect of topophaphy on the distribution of in situ stresses due to gravity and tectonic loadings at Paradela site (Portugal)
A methodology is proposed for dealing with the unbalanced stresses that arise from numerical models due to topography effects when horizontal stresses are applied at the vertical boundaries. The proposed methodology is used for understanding the role of topography on the distribution of in situ stresses due to both gravity and tectonic loadings. In particular, the influence of Poisson
Year: 2012
Number Pages:
14.
Author(s): Figueiredo, B.; Lamas, L.; Muralha, J.
Keywords: Boundary conditions; Numerical model; Tectonic and gravitational stresses; Topography
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Books
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Computational modeling of masonry structures using the discrete element method
Masonry is a combination of units such as stones, bricks or blocks usually laid in a cementitious or limemortar. It is probably the oldest material used in construction and has proven to be both simple to buildand durable. Over the years, existing masonry constructions have inevitably suffered damage with time.Earthquakes, soil settlements, material degradation and lack of maintenance are the main reasons forthat. Careful and periodic assessment of such structures is necessary in order to evaluate their structuralcapacity and safety levels. However, performing the structural analysis of masonry construction is notan easy task. A review is presented of the main models based on the discrete element method and the available related numerical techniques that have been proposed for the analysis of masonry. The essential assumptions adopted by these models and numerical implementation issues are discussed. Differences between available models are illustrated by applications to various masonry problems including static and dynamic analysis of masonry arch bridges, walls, vaults, domes and ancient colonnades.This book is composed of 17 chapters authored/co-authored by 25 outstanding researchers from 11countries (Canada, France, Greece, Hungary, Iran,Italy, Mexico, Norway, Portugal, UK, USA), whichwere reviewed by 60 referees.
Year: 2016
Number Pages:
505p.
Author(s): Sarhosis, V.; Bagi, K.; Lemos, J. V.; Milani, G.
Editor: IGI Global
Keywords: Elementos discretos; Modelação numérica; Alvenaria
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Contribuição de Manuel Rocha para a mecânica das rochas e as fundações de barragens
N/A
Year: 2013
Number Pages:
296pp.
Author(s): Lemos, J. V.; Lamas, L.
Editor: LNEC
Keywords: Investigação científica e técnica; Barragem de betão; Fundação rochosa; Fundação de barragem; Mecânica das rochas; Pt
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Capítulo de Livro
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Chapter 5 Discrete Element Modeling
This chapter consists of two parts. First a general overview is given: the exact definition of the Discrete Element Method is provided, and the main types of existing models are introduced; then the theoretical fundaments of the most important approaches available today for masonry analysis are given. The second part of the chapter focuses on 3DEC, the most widespread commercial DEM code for masonry analysis. This second part begins with a theoretical overview. Application issues for masonry structures are then considered (block material behaviour, contact representation, structural elements like cables or bars etc.). Among the practical examples arches, barrel vaults, walls, coloumns and complete structures (like houses) are presented, including the issues of quasi-static versus dynamic analysis and of block fracture as well. The readers can find helpful advice on how to simulate their own problems most effectively.
Year: 2023
Author(s): Lemos, J. V.; Bagi, K.
: Discrete Computational Mechanics of Masonry Structures
Editor: Springer
Keywords: Masonry models
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Discrete Element Modelling of Masonry Arch Bridges, Arches and Vaults
N/A
Year: 2022
Author(s): Lemos, J. V.; Gobbin, F.; Forgacs, T.; Sarhosis, V.
: From Corbel Arches to Double Curvature Vaults.
Editor: Springer
Keywords: numerical modelling; masonry
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DEM modelling of the non-linear static and dynamic response of masonry structures
Discrete element models have become a major tool for masonry analysis, allowing a suitable representation of its discontinuous nature and marked nonlinear behaviour. The chapter reviews the fundamental assumptions of the main DEM formulations available. It focuses more specifically on the widely used UDEC and 3DEC codes, explaining their relation with the other approaches, and the most relevant issues arising in their application to masonry. Applications to the main types of structures are reviewed, considering both static and dynamic analyses. Recent research providing comparisons of the numerical models with experimental and field data is particularly covered. The discussion of the different examples is aimed at clarifying the key capabilities of DEM and demonstrating the most effective ways of using it in a variety of masonry analysis situations.
Year: 2019
Number Pages:
469-501pp.
Author(s): Sarhosis, V.; Lemos, J. V.; Bagi, K.
: Numerical Modeling of Masonry and Historical Structures - From Theory to Application
Editor: Elsevier
Keywords: DEM; Masonry structures
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Seismic and Structural Health Monitoring of Dams in Portugal
This chapter is focused on the Portuguese experience on the developmentand exploration of systems for continuously monitoring dam vibrations, usingaccelerometers. The pioneer system for seismic and structural health monitoring(SSHM) installed in Cabril dam (the highest Portuguese arch dam: 132 m high) isdescribed in detail. The design of this system was the result of a long-term LNECresearch program, still ongoing. These monitoring systems should include softwaredeveloped to automatically perform the analysis of collected data, including theautomatic comparison with numerical results from 3DFE models. In view of thegood results obtained with the system in operation in Cabril dam since 2008, similarsystems have been installed in other large dams in Portugal, particularly in recentlybuilt dams. Finally, Baixo Sabor dam is presented as an example of a new Portuguesedam with a complete SSHM system, in operation since 2015. Themain experimentalresults obtained for both dams are shown, namely the evolution of natural frequenciesover time, mode shapes and the measured seismic response to earthquake events.
Year: 2019
Number Pages:
87-113pp..
Author(s): Oliveira, S.; Alegre, A.
: Seismic Structural Health Monitoring - From Theory to Successful Applications
Editor: Springer
Keywords: Modal identification · Concrete dams · Ambient and seismic vibrations
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Tese de Doutoramento
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Análise experimental de cenários de rotura em fundações de barragens de betão
Para verificação do cumprimento das exigências de segurança das barragens,tanto relativamente à funcionalidade (cenários correntes), como em relação àsegurança ao colapso (cenários de rotura), é essencial utilizar modelos de simulação oude interpretação (no caso de obras existentes) do seu comportamento. Estes modelossão idealizações (simplificações) da realidade, tanto no que diz respeito às acções(modelos das acções), como no que respeita à componente estrutural (modelos estruturais).A solução destes modelos, através de adequados métodos de análise, quantificaparâmetros da resposta das estruturas que permitem avaliar a sua segurança, utilizandocritérios de segurança previamente definidos.A validação destes modelos pode ser feita, no caso de cenários correntes,através da sua comparação com os resultados da observação do comportamento debarragens. No caso de cenários de rotura, não existe muita experiência de comparaçãodestes resultados com situações reais: é pequeno o número de acidentes ocorrido e,mesmo nestes, o volume de informação é reduzido. Desta forma, o recurso a métodosexperimentais, para o estudo de cenários de rotura, tem uma importância acrescida.Assim o principal objectivo deste trabalho é contribuir para melhorar a capacidade deavaliação da segurança de barragens de betão envolvendo cenários de rotura pela fundação.Neste trabalho desenvolveram-se dois ensaios experimentais em modelosfísicos: um primeiro envolvendo uma barragem abóbada, para o estudo de cenários derotura da fundação para acções estáticas; e um segundo de uma barragem gravidadeensaiado em mesa sísmica, com vista a estudar a rotura pela fundação para acçõesdinâmicas.A previsão e interpretação dos ensaios foram efectuadas com modelosmatemáticos adequados, que permitiram a sua validação e posterior utilização no estudode outros cenários.
Year: 2009
Author(s): Gomes, J. P.
Keywords: Método dos elementos discretos; Método dos elementos finitos; Modelos numéricos; Mesa sísmica; Análise dimensional; Modelos físicos; Análise até à rotura; Controlo da segurança de barragens; Barragens de betão
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Relatório Científico
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DEMRock6m
Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto DEMRock6m do P2I/LNEC 2013-2020. Os resultados da atividade desenvolvida são analisados e avaliados em face dos objetivos inicialmente previstos.
Year: 2024
Author(s): Muralha, J.; Lemos, J. V.; Lamas, L.
Keywords: Estruturas de alvenaria; Barragens de betão; DEMRock6m; Mecânica das rochas; Modelos de elementos discretos; Modelos numéricos
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MEBAD
Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto MEBAD do P2I/LNEC 2013-2020, no período 2016-2023. Os resultados da atividade são analisados e avaliados, em face dos objetivos previstos.
Year: 2023
Author(s): Lemos, J. V.; Batista, A. L.; Gomes, J. P.
Keywords: Estruturas de alvenaria; Barragens de betão; MEBAD; Mecânica das rochas; Modelos de elementos discretos; Modelos numéricos
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RockGeoStat
Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto RockGeoStat do P2I/LNEC 2013-2020. Os resultados da atividade desenvolvida são analisados e avaliados em face dos objetivos inicialmente previstos.
Year: 2023
Author(s): Lamas, L.; Muralha, J.; Pereira, R.
Keywords: Modelação numérica; Heterogeneidade; Mecânica das rochas; RockGeoStat
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Development of DamDamage3D1.0 - A MATLAB program for non-linear analysis of arch dams using a damage model
The main goal of this report is to present DamDamage3D1.0, a 3D finite element-based program for non-linear static analysis of arch dams, developed using MATLAB. The non-linear simulations are performed using a damage law and an iterative numerical method based on the stress-transfer technique, considering the redistribution of unbalanced forces in each iteration due to material damage. The concrete
Year: 2019
Author(s): Alegre, A.; Oliveira, S.
Keywords: Non-linear behaviour; Cabril dam; Compression damage; Tension damage; DamDamage3D1.0; Damage model; Concrete strength decrease scenario; Concrete arch dams; MATLAB 3DFEM program
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Development of DamDamage3D1.0. A MATLAB program for non-linear analysis of arch dams using a damage model
The main goal of this report is to present DamDamage3D1.0, a 3D finite element-based program for non-linear static analysis of arch dams, developed using MATLAB. The non-linear simulations are performed using a damage law and an iterative numerical method based on the stress-transfer technique, considering the redistribution of unbalanced forces in each iteration due to material damage. The concrete
Year: 2019
Author(s): Alegre, A.; Oliveira, S.
Editor: LNEC
Keywords: DamDamage3D1.0 / MATLAB 3DFEM program / Concrete arch dams / Cabril dam / Non-linear behaviour / Concrete strength decrease scenario / Damage model / Tension damage / Compression damage
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Development of GDams2D 1.0 - A MATLAB code for structural analysis of gravity dams using Lagrangian finite elements with 9 nodes
In this work we present the version 1.0 of the GDams2D 1.0 program developed for 2D analysis of gravity dams using the finite element method. This initial version of the program is prepared to analyze the structural behavior of gravity dams for static loads, considering linear-elastic behavior, and using Lagrange finite elements of 4 sides, with 9 nodal points. The GDams2D 1.0 program, developed in MATLAB, includes a module for automatic generation of meshes with a great level of refinement (generated from coarse meshes of quadrilaterals, with 4 nodal points at the vertices) and is designed for easy adaptation to non-linear analyzes, using stress-transfer modules such as those recently developed for the DamSlide3D and DamDamage3D programs. After a brief reference to the fundamentals of solid mechanics and to the simplified hypotheses of plane elasticity, the Fundamentals of the Finite Element Method (FEM) are presented, referring in particular the formulation of the four-node, linear and isoparametric, finite element (FE4nos), with two translation d.o.f per node, and the quadrangular FEs of 9 nodes (FE9nos) used in GDams2D 1.0. Based on some examples of application to simple 2D structures whose response is knownanalytically, the advantages of FEs are emphasized in relation to FE4nos and the verification and operability of GDams2D 1.0 is made using various discretizations. Finally, the case of a gravity dam (25 m high) is presented. The dam
Year: 2019
Author(s): Rodrigues, M.; Oliveira, S.
Keywords: Solid mechanics; p-refinement and h-refinement; Gravity dams; 2D Lagrangian finite elements; FEM convergence; Linear-elastic behavior
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Structural analysis of gravity dams considering non-linear behavior in the dam-foundation interface - Development of a 3DFE code using MATLAB: DamSlide3D
The main objective of this work is the development and presentation of a three-dimensional finite element program, DamSlide3D, to study the behavior of gravity dams for scenarios of sliding through the dam-foundation interface. The DamSlide3D, developed using MATLAB, includes cube-type finite elements with 20 nodal points ("serendipity") and finite interface elements with 16 nodal points (joint elements). Initially, we present the fundamental equations of Solid Mechanics, referring to the main simplified hypotheses considered in the computationally implemented formulation, which is presented mathematically as a problem of boundary values using a displacement formulation. For the structure body and for the foundation, the hypothesis of isotropic materials with linear elastic behavior is assumed and for the interfaces the hypothesis of non-linear behavior is considered using the Mohr- Coulomb criterion. The DamSlide3D input data is provided in an excel file and includes structure geometry data, material properties, support conditions and load parameters. As output, the program graphically displays the stress field (principal stresses) and the displacement field (deformed structure). The program was verified throughout three numerical tests with known theoretical solutions. In these tests a simple structure was used, composed by a column discretized in 3DFE. At the contact surface between the column and the base (horizontal surface) it was considered an interface discretized using joint finite elements. A plane surface that crosses the column with a given slope is also considered, discretized using the same type of joint finite elements. In the first test, the field of elastic stresses at the base, due to self-weight (SW) and hydrostatic pressure (HP), was compared with the theoretical results. In the second test the nonlinear column response was studied for different values of thefriction angle at the inclined interface (in this test the structure is only submitted to SW). In the third test, for the main SW + HP loads, the stability of the column is studied for a variation of the friction angle, and for a variation of the water level. In these three numerical tests the results were always consistent with the theoretical solutions. Finally, as an example of application, a gravity dam structural behavior was analyzed considering the non-linear behavior in the dam-foundation interface. The dam was subjected to self-weight and hydrostatic pressure. A parametric study was developed in order to study the dam stability for differentvalues of water level and friction angle.
Year: 2019
Author(s): Rodrigues, M.; Oliveira, S.
Keywords: Dam-foundation interface friction angle; Gravity dam; Mohr-Coulomb failure criterion; Stress-transfer; Interface non-linear behavior; Joint finite elements; 3D solid finite elements
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CoMatFail
Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto CoMatFail até ao final de 2017. É feita a apreciação da atividade desenvolvida, nomeadamente quanto ao grau de cumprimento do plano de trabalhos, bem como dos objetivos específicos e dos indicadores de desempenho propostos na ficha de projeto. São ainda referidas as aplicações dos resultados da investigação em trabalhos contratados ao LNEC e as candidaturas a financiamento externo desenvolvidas no âmbito do projeto. Inclui-se em anexo a ficha do projeto atualizada, que contempla a revisão do plano de trabalhos.
Year: 2018
Author(s): Dias, I. M.; Lemos, J. V.; Mata, J.
Keywords: Análise até à rotura; Controlo de segurança; CoMatFail; Barragens de betão; Modelação numérica; Fratura material
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DEMRock6m
Neste relatório apresenta-se de forma sucinta a descrição da atividade de investigação realizada no âmbito do projeto DEMRock6m no período 2016-2017. Os resultados da atividade são analisados e avaliados em face dos objetivos inicialmente previstos, sendo proposta uma revisão do plano de atividades para os próximos três anos.
Year: 2018
Author(s): Muralha, J.; Lemos, J. V.; Espada, M.; Lamas, L.
Keywords: Estruturas de alvenaria; Barragens de betão; DEMRock6m; Mecânica das rochas; Modelos de elementos discretos; Modelos numéricos
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RockGeoStat
Neste relatório apresenta-se, de forma sucinta, a descrição da atividade de investigação realizada no âmbito do projeto RockGeoStat no período 2016-2017. Os resultados da atividade são analisados e avaliados em face dos objetivos inicialmente previstos, sendo proposto um prolongamento do projeto até ao final de 2018.
Year: 2018
Author(s): Lamas, L.; Muralha, J.; Espada, M.
Keywords: Modelação numérica; Heterogeneidade; Mecânica das rochas; RockGeoStat
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Identification of transversely isotropic parameters in overcored rock specimens - A back analysis approach
This document presents a back analysis procedure for identification of the elastic parameters of transversely isotropic rock cores, containing an overcoring triaxial strain probe, from the strains measured during a biaxial test. A three-dimensional finite element model was developed to simulate the biaxial test on the overcored rock specimen and to compute the strains at the location of the strain gauges. Different optimisation algorithms were tested and the most suitable one was selected. The back analysis procedure was tested for identification of the five elastic parameters and the two orientation angles that characterise a transversely isotropic rock core. In spite that, with the developed methodology, convergence was reached and all those parameters could be identified, sensitivity analyses demonstrated that the results obtained were not stable and therefore they were not reliable. By introducing constrains based on common practice and previous experience, a stable and robust methodology was achieved: the three elastic parameters, E1, E2 and ?2, are reliably identified using the value of G2 calculated with Saint-Venants expression and a fixed value of ?1, while the orientation parameters are obtained from observation of overcored rock. Analysis of the results shows that application of this methodology represents an enormous step forward when compared with the traditional use of isotropy. Besides, the methodology is general and can also be used with other types of overcoring equipment. The five elastic parameters and the two orientation angles obtained can then be used, together with the overcoring strains, to compute the complete in situ state of stress.
Year: 2018
Author(s): Espada, M.; Lamas, L.
Keywords: Transversely isotropic rock; Numerical method; Rock test; Optimisation; Triaxial strain probe; In situ stress; Overcoring; Biaxial test
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Stability analysis of excavation slopes of Baihetan arch dam foundation - Reliability analysis by application of the response surface method
This document presents the work developed by the PhD student Margarida Espada in the scope of the course unit Risk Analysis in Geotechnical Works of the Doctoral Program in Civil Engineering of the Faculty of Engineering of the University of Porto (FEUP). This work presents a reliability analysis, using the response surface method (RSM), for the case study of the left bank excavation slopes of the Baihetan arch dam foundation, which is one of the case studies of Margarida Espada's PhD thesis. The aim was to approximate an implicit limit state function by computing safety factors, using a discrete element model of the Baihetan left bank developed in 3DEC software, where the shear strength parameters of two important rock discontinuities were considered as random variables. The probability of failure was then obtained through an iterative process, using approximation methods. This work presents the 3DEC model developed to analyse the stability conditions in the Baihetan left bank and the results of the reliability analysis.
Year: 2018
Author(s): Espada, M.
Keywords: Dam foundation; Baihetan dam; Discrete element method; Reliability; Slopes stability
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Contribuição para o problema da existência e suavidade da solução da equação de Navier- Stokes
O problema da solução das equações de Navier Stokes é abordado neste trabalhopropondo-se uma técnica de representação das incógnitas deslocamentos e pressõesvariáveis no espaço e no tempo em série de Delta de Dirac e suas derivadas no tempocujos coeficientes se determinam com base na solução de sistemas de equaçõesdiferenciais definidos no espaço (problema com três variáveis espaciais independentesque pode ser estudado pelo método de Monge).
Year: 2011
Number Pages:
12pp.
Author(s): Câmara, R.
Editor: LNEC
Keywords: Equação de navier-stokes
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Elastodinâmica
Neste relatório apresentam-se as equações básicas da elastodinâmica linear, as soluçõesfundamentais e o teorema da representação no domínio de tempo e de frequência.Para movimentos finitos de casca formula-se o teorema dos trabalhos virtuais e a suaimplementação pelo método dos elementos finitos.
Year: 2007
Number Pages:
54pp.
Author(s): Câmara, R.
Editor: LNEC
Keywords: Método dos elementos finitos; Elastodinâmica
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Modelação sísmica de barragens abóboda
Neste relatório apresentam-se os principais aspectos da modelação sísmica de barragensabóbada. Assim propõe-se: modelos numéricos de geração de sismos por uma falha; aforma como o sismo actua na barragem; modelos para estudar a influência da albufeirana vibração do conjunto; métodos para solução das equações do movimento; e novasformulações de elementos finitos para o problema estrutural.
Year: 2005
Number Pages:
72pp.
Author(s): Câmara, R.
Editor: LNEC
Keywords: Método dos elementos finitos; Simulação numérica; Comportamento sísmico de estruturas; Comportamento de barragens; Barragem abóboda
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An experimental and numerical study for analysis of the hydromechanical behavior of the Alto Lindoso high pressure circuit
In pressure tunnels and shafts, in addition to the mechanical effect that excavation has on the rock mass and the disturbance that it introduces in the water flow, also the contained water can interact from the mechanical and hydraulic points of view with the rock mass. Seepage in fractured rock masses is dominated by the flow that takes place through the joints, and this is highly d(;pendent on their properties, namely aperture and roughness. Joint aperture, in tum, i::; very sensitive to stress changes. Special attention must therefore be paid to the joints in hydromechanical analyses. In this report are presented some studies that were carried out for the hydromechanical characterization of joints of the Alto Lindoso rock mass and numerical simulations of the hydromechanical behaviour of two selected sections of the high pressure circuit.
Year: 1994
Author(s): Lamas, L.
Keywords: Simulação numérica; Barragem de Alto Lindoso; Percolação no solo; Maciço rochoso; Comportamento hidromecânico; Interacção solo-água-estrutura; Circuito hidráulico
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