Artigos de Revista
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Modal tracking under large environmental influence
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The installation of vibration-based structural health-monitoring systems relying in the study of natural frequencies to assess the condition of civil engineering structures is becoming more and more common. The extraction of these monitoring features can be achieved through automated operational modal analysis, combining output-only identification methods with cluster analyses, and comparing the identified modal properties with references, in a process known as modal tracking. However, changing environmental and operational conditions affect the dynamic behaviour of structures, disturbing the process of modal tracking, which may lead to the loss of important information and to misidentifications. In this context, this paperproposes a new methodology for modal tracking within the scope of automated operational modal analysis, especially prepared for scenarios with strong external influence on modal properties. A concrete arch dam with large variations of some natural frequencies is used as case study, and the proposed methodology is compared to a standard procedure using a quite unique monitoring data set continuously collected for 3 years.
Ano: 2021
Autor(es): Pereira, S.; Magalhães, F.; Gomes, J. P.; Cunha, A.
Revista: Journal of Civil Structural Health Monitoring
Editor: Springer
Keywords: Dam monitoring; Modal tracking; Operational and environmental effects; Operational modal analysis; Vibration-based monitoring
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Modelos descontínuos na análise tridimensional do comportamento hidromecânico de fundações de barragens de betão
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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 as vantagens do modelo proposto no estudo do comportamento hidromecânico de fundações de barragens.
Ano: 2021
Número Páginas:
5-32.
Autor(es): Azevedo, N.; Braga Farinha, M. L.; Sá, M.; Rocha de Almeida, J.
Revista: Geotecnia
Editor: Sociedade Portuguesa de Geotecnia
Volume:
151.
Keywords: modelação numérica tridimensional; comportamento hidromecânico; fundações de barragens de betão
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Numerical procedures for the analysis of collapse mechanisms of masonry structures using discrete element modelling
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Earthquake damage in historic masonry buildings is generally caused by the collapse of individual portions thatbecome detached form the structure and fail by overturning. These mechanisms are mainly governed by thediscrete nature and geometry of the block units. Analyses based on explicit micro-modelling in which each blockis considered separately are therefore of increasing importance. This paper offers a robust tool for the seismicassessment of masonry structures under either, quasi-static or dynamic loading. Algorithms for performing dynamicpulses and pushover analyses through the Discrete Element Method are developed and described, takinginto account the actual discrete nature and geometry of masonry. A numerical procedure is proposed thatautomatically detects the collapse mode and follows the evolution of the analysis until collapse. The implementedmethod is able to give a reliable estimate of the expected failure mechanism, providing the seismicacceleration required to trigger the motion and the ultimate displacement beyond which the collapse occurs.Finally, the implemented algorithms are applied to two case studies and the results are compared with thetraditional analysis based on rigid-block kinematics to outline the features and potentialities of the proposedapproach.
Ano: 2021
Autor(es): Gobbin, F.; De Felice, G.; Lemos, J. V.
Revista: Engineering Structures
Editor: Elsevier
Volume:
246.
Keywords: Estruturas de alvenaria
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Seismic Vulnerability Assessment of a Stone Arch Using Discrete Elements
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Conservation of the European-built heritage is nowadays closely related to interventions in masonry construction. Since a significant part of these structures are located in earthquake prone zones, designing protective measures that ensure their preservation requires the assessment of the associated seismic vulnerability and the understanding of their degradation mechanisms. However, due to the presence of discontinuities between its constituent elements, the numerical simulation of the non-linear response of masonry structures subjected to strong earthquakes is a cumbersome task, especially when performed using the traditional finite element method. As an alternative, the discrete element method is particularly suitable for the numerical analysis of such structures under large, damaging loads. By allowing discrete displacements/rotations of individual bodies, and by automatically recognising new contacts between bodies, while eliminating obsolete ones, this numerical approach can simulate the complete detachment of discrete bodies initially in contact.The present paper illustrates the use of the discrete element method to assess the seismic vulnerability of stone arches. A probabilistic approach allows to consider the variability of theseismic action and the uncertainties in the definition of the material properties. First, an unreinforced masonry arch is considered. Based on non-linear multi-directional incremental dynamic analyses, five damage states are proposed and the respective fragility curves are elaborated. Toimprove the arch
Ano: 2021
Autor(es): Cismasiu, C.; Silva, P.; Cismasiu, I.; Lemos, J. V.
Revista: International Journal of Architectural Heritage
Editor: Taylor & Francis
Keywords: Estruturas de alvenaria
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Seismic vulnerability assessment of masonry arch bridges
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A seismic assessment study of two historical masonry arch bridges, with different geometries and spans, ispresented. The seismicity of the two locations was analyzed in order to define the seismic action to be applied.Artificial ground motion records were generated accordingly, and real ground motions were also used. The twonumerical models were created with a 3D discrete element code. The accuracy of the deformability of the blockmodels was verified by comparison with a finite element model. In situ measurements of the natural frequencieswere available for one of the bridges, providing further means for model calibration. Time domain dynamicanalyses were performed with each set of ground motions, allowing an evaluation of damage and failure modesunder seismic action. The shorter span bridge was found to withstand the regulatory records with minimumdamage. In contrast, the longer span bridge displayed a significant vulnerability to earthquake action. The studyshows that rigid block models have the ability to represent effectively the dynamic elastic response of the bridgesand can be calibrated by ambient vibration measurements. Furthermore, the discrete element models provide apowerful tool to investigate the nonlinear dynamic response and failure of these structures, which has to be basedon a comprehensive set of dynamic records.
Ano: 2021
Autor(es): Saygili, O.; Lemos, J. V.
Revista: Structures
Editor: Elsevier
Volume:
33.
Keywords: Estruturas de alvenaria
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Sliding stability analyses of a rock slope using deterministic, semiprobabilistic and probabilistic methods
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Stability analyses of geotechnical structures in rock are traditionally performed using deterministic methods. In Europe, Eurocode7, introduced in the beginning of the 21st century, adopts limit state design and semi-probabilistic methods, using partial factors for the design of geotechnical structures. Meanwhile, reliability-based design, using probabilistic methods, is becoming more common in practical cases. The paper considers an intentionally simple case study?the analysis of a slope in a rock mass with one discontinuity, considered in a discrete way, forming a rock block to be stabilised by anchors?to compare the results obtained with the different methods. The objective is to calculate the force applied by the anchors so that the ultimate limit states of sliding of the rock block is verified. Deterministic-based design optimization considering both the traditional global safety factor approach and the partial factor approach following the Eurocode 7 are first applied. A reliability-based design optimization procedure?which takes geometrical and mechanical properties of the discontinuities as random variables?is then used, and the results are compared to the former ones. A discussion is presented concerning the consistency of the obtained results.
Ano: 2021
Autor(es): Pereira, R.; Lamas, L.; Muralha, J.
Revista: IOP Conf. Series: Earth and Environmental Science
Editor: IOP Publishing
Volume:
833.
Keywords: Ground reinforcement; Reliability-based design; Eurocode 7; Geotechnical design; Rock engineering
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Vibration-based damage detection of a concrete arch dam
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Civil engineering structures are generally supposed to have long operation life spans during which they aresubmitted to many factors, both environmentally and human-induced, that degrade their condition and performance,gradually leading to the occurrence of damages and malfunctions. Therefore, systems capable ofmonitoring and assessing structural performance automatically are highly desirable.In this context, this paper describes the vibration-based structural health monitoring of Baixo Sabor arch dam,in Portugal, detailing results from the several processing stages needed to achieve the ability to detect damage.Automated operational modal analysis is applied to the data obtained during the first three years of monitoring,after which environmental and operational conditions affecting modal properties are studied and their effectsminimised through the combined application of weighted regression models and principal components analysis.Finally, damages are simulated in a numerical model of the dam, and the results are used to test the ability ofdamage detection tools to find these anomalies.The present paper uses a quite unique set of experimental data to test for the first time the ability of avibration-based SHM system to identify realistic damages in an arch dam.
Ano: 2021
Autor(es): Pereira, S.; Magalhães, F.; Gomes, J. P.; Cunha, A.; Lemos, J. V.
Revista: Engineering Structures
Editor: Elsevier
Volume:
235.
Keywords: Damage detection; Data normalisation; Operational and environmental effects; Continuous dynamic monitoring; Concrete arch dam
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A Discrete Element Model for Masonry Vaults Strengthened with Externally Bonded Reinforcement
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The paper investigates the effectiveness of two-dimensional Discrete Element Method as a tool forstructural analysis of arches provided with buttresses and backfill and strengthened with externallybonded reinforcement. Masonry vault and buttresses are modelled as an assembly of 2Drigid blocks interacting through non-linear contact joints, the backfill is discretized into deformableelastic-plastic triangular elements, while the reinforcement is modelled by means of trusselements bonded to the substrate through non-linear springs. A parametric analysis on theinfluence of material parameters and the effect of the discretization of the backfill is carriedout, and the outcome of different reinforcement systems, consisting of Steel Reinforced Groutapplied either at the intrados or at the extrados, are analysed. The comparison with experimentalfull-scale tests proved the ability of the numerical approach to capture hinges position, loadbearing capability, as well as the increase in deflection and load capacity provided by thereinforcement.
Ano: 2020
Autor(es): Gobbin, F.; De Felice, G.; Lemos, J. V.
Revista: International Journal of Architectural Heritage
Editor: Taylor & Francis
Keywords: Discrete Element Method; masonry; numerical modelling; Steel Reinforced Grout
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À priori uplift pressure model for concrete dam foundations based on piezometric monitoring data
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The uplift pressures change the stress state of the rock mass foundation in a coupled hydromechanical process and may compromise the dam stability. Consequently, dam safety regulations specify the maximum values of the hydraulic conductivity and uplift pressures that can usually only be fulfilled after the execution of seepage and uplift control measures. The design of waterproofing and drainage systems is still based on an equivalent continuum approach, even though rock mass foundations are discontinuous media. The analysis of the piezometric monitoring data of several Portuguese large concrete dam foundations reveals that uplift pressures are site-specific and may even vary considerably across a given site, which can be critical for the safety assessment. From the data gathered in several dams, a probabilistic model that can be seen as an a priori prediction model for uplift pressures is proposed. Considering the difficulty in classifying the geologic foundation conditions beneath each piezometer in existing dams, it is assumed that the data come from a mixture of two beta distributions, representing foundations with regular and unfavorable geologic conditions. This model is a significant improvement over available approaches and will be instrumental for the assessment of existing dams and the design of new dams.
Ano: 2020
Autor(es): Pereira, R.; Batista, A. L.; Neves, L.; Casaca, J. M.
Revista: Structure and Infrastructure Engineering - Maintenance, Management, Life-Cycle Design and Performance
Editor: Taylor & Francis
Volume:
17.
Keywords: Uplift pressures; Uncertainty modelling; Reliability analysis; Probabilistic model; Piezometric data; Monitoring; Concrete dams; Beta distribution
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Characterization of the dynamic behavior of a concrete arch dam by means of forced vibration tests and numerical models
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The characterization of the dynamic behavior of an arch dam, and its evolutionthroughout the structure's lifetime, provides important data for the safetycontrol process. Forced vibration tests remain a reliable technique for this purpose.The Baixo Sabor dam is a 123 m high arch dam recently built in Portugal.Forced vibration tests were performed before and after the reservoir filling.Two techniques for forced vibration test are compared, discrete frequencyscanning, the standard methodology, and continuous frequency scanning (sinesweep), a new proposed methodology, which allowed faster results withoutloss of precision. For the interpretation of test results two numerical models ofthe dam-reservoir-foundation system were built, and calibrated with the experimentaldata. A good match of numerical and experimental results wasobtained for the six lowest frequencies and corresponding mode shapes.
Ano: 2020
Autor(es): Gomes, J. P.; Lemos, J. V.
Revista: Earthquake Engineering & Structural Dynamics
Editor: wiley
Volume:
2020, 49.
DOI:
10.1002/eqe.3259
Keywords: numerical models; force vibration test; dynamic behavior; dam-water interaction; concrete arch dam
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Comunicações
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Influence of the intake tower dynamic behaviour on modal identification of Cabril dam
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This paper presents a study, which describes the influence of the dynamic behaviour of the intake tower on the experimental results obtained from operational modal analysis of Cabril dam. A 3D finite element model, for the intake tower of Cabril dam, was developed in order to study the dynamic behaviour of this neighbour structure of the dam. The main dynamic parameters computed and evaluated experimentally for this structure are summarized and discussed, to understand how they can interfere in the modal identification of Cabril dam.
Ano: 2009
Número Páginas:
89-94pp.
Autor(es): Mendes, P.; Oliveira, S.
Keywords: Dinâmica de estruturas; Barragens
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Joint Statistics
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The paper aims at presenting some achievements of joint statistics. The different statistical distributions used for the description of the main parameters of the joint sets (attitude, intensity, area, and aperture) are introduced. For the attitude, a comparison of the existing distribution functions is made. For the intensity, the formulas for its determination are given, the applicable statistical models are presented, and the Poisson model for the occurrence of the discontinuities in rocks is discussed in depth. The statistical models for the distribution of the volume of the blocks of a rock mass are introduced. For the area, again, the formulas for its determination are given, and the applicable statistical models presented. Finally, the distribution function for the aperture is referred to, as well as a note on the roughness and waviness.
Ano: 2009
Número Páginas:
20 p..
Autor(es): Grossmann, N.
Editor: Finish Tunnelling Association (FTA) & The Finish National Group of ISRM
Keywords: Estatísticas de diaclases; Compartimentação; Mecânica das rochas
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Modelação numérica para interpretação dos ensaios de determinação do estado de tensão no maciço rochoso da nova central da Bemposta
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A libertação do estado de tensão inicial nos maciços rochosos é a principal acção a considerar em escavações subterrâneas. Como o estado de tensão é muito influenciado pela topografia e por condições geológicas particulares de cada local, a sua determinação a partir de ensaios de campo necessita de uma abordagem particular que, tendo em conta a natureza pontual dos ensaios e a sua variabilidade, permita estimar o estado de tensão global no maciço. Apresentam-se os ensaios realizados para o projecto de uma central subterrânea, com destaque para a modelação numérica que permitiu integrar os resultados dos ensaios e determinar o estado de tensão global mais provável. Os modelos usados permitiram considerar no estado de tensão inicial o efeito erosivo do rio ao escavar o vale e da abertura das galerias onde os ensaios foram executados.
Ano: 2009
Número Páginas:
19p.
Autor(es): Muralha, J.; Figueiredo, B.; Lamas, L.
Keywords: Modelos 2d e 3d; Obras subterrâneas; Estado de tensão; Maciço rochoso
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Site characterization and rock testing for the evaluation of design parameters
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This paper deals with issues related to the evaluation of design parameters from some types of in situ and laboratory tests performed, during the geotechnical investigations, to characterize the most relevant geotechnical properties of the rock mass and also the actions. Some considerations regarding safety evaluation and limit state design are presented. Several types of Rock Mechanics tests are introduced in some detail, and a few application examples covering different Rock Engineering projects are presented to show how test results can be analysed to determine their values to be used in the design. The following examples are shown: triaxial tests to determine the strength of the intact rock, a joint network study for a dam foundation, laboratory shear tests to assess the shear strength of rock joints, flat jack and overcoring tests to estimate the in situ state of stress for an underground cavern, and borehole dilatometer and large flat jack tests to evaluate the deformability of a concrete dam foundation.
Ano: 2009
Número Páginas:
73-86pp.
Autor(es): Muralha, J.; Lamas, L.; Grossmann, N.
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State of stress assessment for the Picote II underground powerhouse design
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The paper presents a description of the Picote II site, the objectives of the study that was carried out to assess the in situ state of stress in the rock mass, details of the testing programme and the methodology used for its interpretation. An overcoring testing programme was performed at the design stage, and a specific methodology was developed for the global interpretation of the test results, making use of a numerical model and considering the effect of the existing canyon on the stress field. This enabled to make recommendations regarding the initial stress field to consider in the design of the powerhouse cavern.Owing to the scarce information obtained at the design stage and to the high values of the calculated horizontal stresses, it was decided to perform additional stress measurement tests, using small flat jacks, once construction started and excavation of the adits reached the proximity of the underground powerhouse. Numerical simulations were also done for its interpretation and they confirmed the stress levels obtained at the design stage. The monitoring scheme implemented in the powerhouse cavern includes instrumentation to measure stress changes, which will occur during the excavation. Finally, the significance of the state of stress assessment to the powerhouse design and to the interpretation of monitoring data collected during construction is discussed.
Ano: 2009
Número Páginas:
6p.
Autor(es): Muralha, J.; Lamas, L.; Esteves, C.
Keywords: Monitoring; Flat jack tests; Overcoring tests; Underground cavern; In situ stresses
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Análise tridimensional de uma abóbada de alvenaria
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O Aqueduto das Águas Livres, localizado em Lisboa, hoje desactivado, entrou em funcionamento em 1748. Construído em alvenaria de pedra e tendo uma extensão de 14 km desde a nascente principal, é ainda constituído por diversos aquedutos subsidiários e de distribuição,com um total de 58 km de extensão.Num dos muitos canais subterrâneos existentes está localizada uma abóbada que permite a intersecção de dois alinhamento de túneis. Esta abóbada encontra-se sobre uma importante artéria da cidade de Lisboa com um trânsito automóvel bastante intenso.O estado de conservação da abóbada tem suscitado interrogações quanto à sua capacidade resistente, verificando-se recentemente o desprendimento de um bloco de alvenaria e o deslizamento parcial de outros, o que motivou uma medida de segurança imediata que passou pelo total escoramento da estrutura.Procedeu-se a análise estrutural da abóbada de alvenaria através do 3DEC. Esta aplicação baseia-se no Método dos Elementos Discretos (MED) e tem vindo a ser utilizada, com crescente interesse, no estudo das estruturas de alvenaria.O presente artigo aborda alguns aspectos relacionados com o MED, descreve os procedimentos adoptados para execução do modelo e apresenta resultados quanto a capacidade resistente. A parte final é dedicada avaliação dos resultados e apresentação de soluções para a sua reabilitação e reforço.
Ano: 2008
Número Páginas:
15.
Autor(es): Bretas, E. M.; Gomes, J. P.; Lemos, J. V.
Keywords: Elementos discretos; Abóbada; Alvenaria
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Análise do comportamento dinâmico da barragem do cabril com base num modelo de elementos discretos considerando a influência das juntas de contracção
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Neste trabalho apresenta-se um modelo tridimensional de elementos discretos paraanálise do comportamento dinâmico da barragem do Cabril tendo em conta o efeito das juntas decontracção. Os resultados são comparados com os de um modelo de elementos finitostridimensionais na hipótese de continuidade. O estudo da barragem é efectuado para diferentescotas de água na albufeira, simulando-se o efeito das pressões hidrodinâmicas com base nahipótese de massas de água associadas, proposta por Westergaard. A influência do nível da águana resposta dinâmica do conjunto é estudada com base na análise das variações das frequênciaspróprias comparando-se resultados numéricos e experimentais.
Ano: 2007
Número Páginas:
16p.
Autor(es): Lemos, J. V.; Oliveira, S.; Mendes, P.; Dias, I. M.; Câmara, R.
Editor: APMTAC/FEUP
Keywords: Juntas de Contracção; Barragens Abóbada; Frequências Próprias; Comportamento Dinâmico; Modelos Numéricos
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Análise sísmica da barragem da Chicamba (Moçambique)
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Apresentam-se os resultados do estudo, em modelo numérico, do comportamento sísmico da barragem da Chicamba, em Moçambique. Foram realizados cálculos em regime elástico e cálculos não lineares tendo em consideração o comportamento das juntas verticais de contracção das abóbadas. Os resultados da análise permitiram avaliar as condições de segurança da obra para acções sísmicas.
Ano: 2006
Número Páginas:
14p.
Autor(es): Lemos, J. V.; Batista, A. L.; Dias, I. M.; Câmara, R.
Editor: APEE
Keywords: Análise não linear; Modelação numérica; Acções sísmicas; Barragens de betão
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Livros
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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.
Ano: 2016
Número Páginas:
505p.
Autor(es): 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
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Ano: 2013
Número Páginas:
296pp.
Autor(es): 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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Capítulos de Livros
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Chapter 5 Discrete Element Modeling
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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.
Ano: 2023
Autor(es): Lemos, J. V.; Bagi, K.
Revista: 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
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Ano: 2022
Autor(es): Lemos, J. V.; Gobbin, F.; Forgacs, T.; Sarhosis, V.
Revista: 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
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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.
Ano: 2019
Número Páginas:
469-501pp.
Autor(es): Sarhosis, V.; Lemos, J. V.; Bagi, K.
Revista: 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
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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.
Ano: 2019
Número Páginas:
87-113pp..
Autor(es): Oliveira, S.; Alegre, A.
Revista: Seismic Structural Health Monitoring - From Theory to Successful Applications
Editor: Springer
Keywords: Modal identification · Concrete dams · Ambient and seismic vibrations
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Teses de Doutoramento
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Análise experimental de cenários de rotura em fundações de barragens de betão
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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.
Ano: 2009
Autor(es): 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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Relatórios
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Barragem do Cabril - Sistema para monitorização de vibrações em contínuo medição e análise automática da resposta dinâmica sob excitação ambiente/operacional e sob ações sísmicas
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Neste trabalho apresenta-se o sistema para monitorização em contínuo do comportamento dinâmico da barragem do Cabril que foi instalado em 2008, pelo LNEC e pela EDP, referindo alguns dos principais resultados que têm sido obtidos a partir da análise dos dados recolhidos, quer sob excitação ambiente/operacional, quer sob ações sísmicas. Salienta-se a importância do desenvolvimento do software para tratamento, análise e gestão automática dos dados e apresentam-se os programas que têm vindo a ser desenvolvidos no LNEC, em MATLAB, para apoio a este tipo de sistemas, nomeadamente programas de identificação modal (Modal_ID2.0 e Modal_ID_Auto2.0) e programas de elementos finitos tridimensionais para análise do comportamento dinâmico de sistemas barragem-fundação-albufeira (DamDySSA2.0).
Ano: 2017
Autor(es): Oliveira, S.; Silvestre, A.
Keywords: Densidade espetral de potência; Amortecimentos modais; Comportamento dinâmico de barragens; Modos de vibração; Frequências naturais; Interação dinâmica barragem-albufeira; Análise espetral; Monitorização de vibrações em contínuo
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Discrete element modelling of rock engineering structures for seismic safety analyses - PhD thesis research plan of Margarida Espada
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This document presents the research plan for the doctoral thesis of LNEC's Junior Research Fellow Margarida Espada. This work, to be submitted to the Faculty of Engineering of the University of Porto (FEUP), will be developed in the Modelling and Rock Mechanics Unit of the Concrete Dams Department, and it is part of the on-going P2I research project DEMRock6m. This work aims at developing more efficient methodologies to perform safety studies and seismic analysis of rock engineering structures, based on discrete element models and in the integrated use of probabilistic models for the geometric and shear strength parameters and for the water pressures in rock discontinuities. This will allow a more realistic definition of the rock mass in discrete element models and an adequate identification of the potential failure mechanisms.
Ano: 2016
Autor(es): Espada, M.; Muralha, J.; Lemos, J. V.; Couto Marques, J.
Keywords: Dam foundations; Rock discontinuities; Seismic analysis; Probabilistic analysis; Safety analysis; Discontinuities generation tool; Discrete element models
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Método de Euler não linear aplicado a órbitas do sistema n-CORPOS
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Neste relatório é apresentado o método de Euler para calcular as órbitas do sistema n-corpos,por exemplo, o dos planetas do sistema Solar, tendo em conta a propagação das forçasgravíticas entre o Sol e os planetas e entre os planetas entre si. Apenas requer como dadosiniciais uma observação anterior das órbitas em termos de posição e velocidade. A correcçãoda interacção entre planetas não é suavizada, o que se justifica pelos seus valores. A correcçãorelativista é importante.
Ano: 2013
Número Páginas:
11pp.
Autor(es): Câmara, R.
Editor: LNEC
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Soluções distribucionais das equações de Navier-Stokes
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As equações de Navier-Stokes são equações de derivadas parciais. As incógnitas nocaso de incompressibilidade consistem no campo de velocidades. As pressões numa 1ªaproximação resultam de um equilíbrio estático.A principal causa de problemas relacionados com a solução destas equações é devida àparcela das acelerações convectivas que está na origem da turbulência.Pesando estas equações e integrando duas vezes por partes obtém-se uma forma fracadestas equações.Em problemas 3D as variáveis independentes são 3 espaciais e 1 temporal. Admite-seque o campo de velocidades pode ser desenvolvido em série de distribuições de Delta deDirac espaciais e suas derivadas com coeficientes funções do tempo. Com funções deteste polinomiais obtém-se a formulação distribucional proposta das equações deNavier-Stokes.
Ano: 2013
Número Páginas:
15pp.
Autor(es): Câmara, R.; Azevedo, N.
Editor: LNEC
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Análise térmica de barragens de betão - Ações térmicas ambientais
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N/A
Ano: 2012
Número Páginas:
114pp.
Autor(es): Leitão, N. S.
Editor: LNEC
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Ondas esféricas quânticas
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O objectivo deste relatório é o estudo da matemática aplicada à solução de problemasfísicos de propagação de ondas esféricas com operador espacial biharmónico,consideradas quânticas.As técnicas matemáticas usadas incluem a transformada de Laplace da função de ondaf e o cálculo de sua inversa tal como sugerida por Pipes e Harvill.O método matemático usado para descrever as ondas esféricas quânticas é compequenas adaptações o método causal não-linear descrito por Croca.
Ano: 2011
Número Páginas:
12pp.
Autor(es): Câmara, R.
Editor: LNEC
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Tópicos sobre equações de derivadas parciais
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N/A
Ano: 2011
Número Páginas:
15pp.
Autor(es): Câmara, R.
Editor: LNEC
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Ensaios de juntas de argamassa para um modelo físico de uma barragem abóbada a ensaiar na mesa sísmica
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N/A
Ano: 2009
Número Páginas:
64pp.
Autor(es): Muralha, J.
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RADIAÇÃO SÍSMICA DUMA FALHA PARA UMA BARRAGEM ABÓBADA
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N/A
Ano: 2007
Número Páginas:
50pp.
Autor(es): CÂMARA, R.
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Geração de malhas de elementos finitos tridimensionais. Desenvolvimento e apresentação do módulo computacional GeTMEF1.0
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A análise do comportamento de barragens de betão com base em modelos de elementos finitos tridimensionais exige a definição da discretização a adoptar para o conjunto barragem-fundação, ou barragem-fundação-albufeira. A realização desta tarefa sem o recurso a programas de geração automática é muito dispendiosa pelo que tem vindo a ser desenvolvido no NMMF um módulo computacional para geração automática de malhas de elementos finitos tridimensionais especialmente adaptado para a geração de malhas tridimensionais de barragens abóbada. Inicialmente desenvolvido em FORTRAN, o referido módulo computacional para geração de malhas de elementos finitos tridimensionais tem vindo a ser objecto de diversos melhoramentos, os mais recentes centrados ao nível da interface com o utilizador. Assim, apresenta-se neste relatório o módulo computacional
Ano: 2006
Autor(es): Dias, I. M.; Oliveira, S.
Keywords: Barragens; Hexaedros; Geração de malhas de elementos finitos
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Informações Científicas e Técnicas
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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.
Ano: 2018
Autor(es): 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.
Ano: 2018
Autor(es): 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
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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).
Ano: 2011
Número Páginas:
12pp.
Autor(es): Câmara, R.
Editor: LNEC
Keywords: Equação de navier-stokes
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Elastodinâmica
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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.
Ano: 2007
Número Páginas:
54pp.
Autor(es): Câmara, R.
Editor: LNEC
Keywords: Método dos elementos finitos; Elastodinâmica
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Modelação sísmica de barragens abóboda
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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.
Ano: 2005
Número Páginas:
72pp.
Autor(es): 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.
Ano: 1994
Autor(es): 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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