Artigos de Revista
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Analysis and prediction of masonry wallette strength under combined compression-bending via stochastic computational modeling
The out-of-plane flexural bending capacity of masonry is a fundamental property for understanding the behavior of masonry structures. This study investigates the behavior of unreinforced masonry wallettes subjected to combined compression-flexural loading using the discrete element method (DEM), and provides a novel framework to estimate the masonry strength. A simplified micro-modeling strategy is utilized to analyze a masonry wallette, including the variation of the mechanical properties in masonry units and joints. Stochastic DEM analyses are performed to simulate brickwork assemblages, assuming a strong unit-weak joint material model typical of most masonry buildings, including historical ones. Once the proposed computational approach is validated against the experimental findings, the effect of spatial and non-spatial variation of mechanical properties is explored. Two failure types are identified: joint failure and brick failure. For each failure mechanism, the variability of the response and the effects of the modeling parameters on the load-carrying capacity is quantified. Afterward, Lasso regression is employed to determine predictive equations in terms of the material properties and vertical pressure on the wallette. The results show that the most important parameters changing the response are the joint tensile strength and the amount of vertical stress for joint failure, whereas the unit tensile strength dominates the response for brick failure. Overall, this research proposes a novel framework adopting validated advanced computational models that feed on simple test results to generate data that is further utilized for training response prediction models for complex structures.
Ano: 2023
Autor(es): Erduran, E.; Tuncay, K.; Lemos, J. V.; Lourenço, P.; Pulatsu, B.; Gonen, S.
Editor: Elsevier
Keywords: Masonry
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Application of Bonded-Block Models to Rock Failure Analysis
Discrete element models are being increasingly applied to model rock failure processes.Bonded-particle models, based on circular or spherical particle systems, have been successfully usedfor two decades. More recently, bonded-block models, using polygonal or polyhedral elements, have proven to be a powerful alternative. This paper describes the basis of the application of these models in the numerical simulation of failure in rock materials. The critical governing parameters are identified, and their influence is discussed. The model calibration procedure based on the analysis of laboratory tests is discussed. An application example of an underground excavation problem is presented using a simple bonded-block model employing rigid blocks and a bilinear softening contact model. The results show the capability of this approach to reproduce observed failure modes involving block fractures.
Ano: 2023
Autor(es): Lemos, J. V.
Editor: MDPI
Keywords: rock mechanics
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Dynamic analysis of masonry arches using Maxwell damping
Masonry arches are a fundamental component of historical structures. The assessment of the vulnerability ofthese heritage constructions to seismic loading requires reliable and efficient numerical models. Discrete element models are an alternative to finite element models, being particularly effective in modelling collapse mechanisms created by shearing and separation of the units along the joints. Discrete element codes typically rely on explicit methods of integration of the equations of motion for dynamic analysis, which may require large run times when the recommended stiffness-proportional component of Rayleigh damping is applied. A novel approach is proposed using an alternative damping model, Maxwell damping, which involves placing multiple spring-dashpot elements in the joints, in parallel with the standard stiffness springs. This damping model is tested in the dynamic analysis of masonry arches, under pulse and earthquake loading. The results obtained in this early investigation show a good performance in the simulation of collapse under dynamic loads, in general agreement with the analyses conducted with classical stiffness-proportional damping, but reducing significantly the computational effort.
Ano: 2023
Autor(es): Sarhosis, V.; Lemos, J. V.
Revista: Structures
Editor: Elsevier
Keywords: Masonry arches
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Impact of Rejuvenator-Modified Mastic on Asphalt Mixture Stiffness: Meso-Scale Discrete Element Method Approach
Encapsulated rejuvenators embedded in asphalt mixtures are a promising technology toextend the service life of asphalt pavements. However, their effects on the asphalt mixture
Ano: 2023
Número Páginas:
22p..
Autor(es): Micaelo, R.; Azevedo, N.; Câmara, G.
Revista: Buildings
Editor: MDPI
Volume:
13.
Keywords: capsules; encapsulated rejuvenator; rejuvenator-modified mastic; asphalt mixture; self-healing; discrete element modeling
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Numerical evaluation of transverse steel connector strengthening effect on the behavior of rubble stone masonry walls under compression using a particle model
The structural rehabilitation of historic/traditional rubble masonry wall constructionsrequires consolidation and retrofitting solutions to be employed in order to withstand dynamic loads,high vertical loads, and differential settlements. One of these strengthening techniques is basedon the use of steel bar connectors perpendicular to the wall, considered individually or integratedinto more complex strengthening techniques. The aim of this study is to evaluate numerically thestrengthening effect of transverse steel connectors on rubble masonry walls. With this purpose, a 2Dparticle-reinforced model (2D-PMR) was devised and applied to model uniaxial compression tests.The results presented show that predictions calculated using the proposed 2D-PMR model are veryclose to known experimental results, particularly in the corresponding failure modes, the increase ofthe maximum uniaxial compression value, and ductility. Parametric studies are also conducted byvarying the diameter of the steel bars and the level of strengthening to assess the influence of thebar-bond effect and lateral plates. The presented parametric numerical studies show that (i) a two-level strengthening solution guarantees a similar response to the three-level strengthening solutionadopted in the experiments; (ii) it is not relevant to apply a grout injection during the applicationprocess of the steel connectors if lateral plates are adopted; and (iii) the 2D-PMR model can be usedin the definition of the steel bar diameter and properties; as shown, a smaller (8 mm) bar diameterpredicts a similar strengthening effect to the (12 mm) bar size adopted in the experiments. Given theperformance of the proposed 2D-PMR model, further work is underway that will allow the 2D-PMRmodel to numerically assess other reinforcement techniques, namely, reinforced micro-concrete layersand textile reinforced mortar.
Ano: 2023
Número Páginas:
27p.
Autor(es): Pinho, F.; Azevedo, N.; Cismasiu, I.
Editor: MDPI
Keywords: uniaxial compression; transverse steel connectors; strengthening; rubble-stone masonry; particle model
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Site Specific Hazard Assessment and Multi-Level Seismic Performance Evaluation of Historical Mosque
This study highlights the continued need for numerical simulation methods to predict the earthquakeresponse and damage of masonry mosques, despite recent advances in research. TheKamanl
Ano: 2023
Autor(es): Moghimi, S.; Lemos, J. V.; Saygili, O.
Editor: Taylor & Francis
Keywords: seismic vulnerability
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A flexible particle model for rock fracture: Validation and assessment of the Influence of deformability on the macroscopic response
Circular/spherical rigid particle models that were initially applied to rock fracture studies were not able to match the ratio of the compressive strength to tensile strength that occurs in rock. In addition, the predicted macroscopic friction angle was much lower than the known hard rock experimental values. Several enhancements have been proposed to address these issues, namely the use of a clumped particle logic or the adoption of polygonal/polyhedral grain structures, either rigid or flexible. In this work, a flexible 2D DEM based particle model (PM) that allows deformable particles to interact in a simplified way is presented. The proposed flexible PM model keeps the contact interaction simplicity and the reduced computational costs characteristic of circular rigid particle models. The PM model is tested using biaxial tests and Brazilian tests. A discussion re- garding the influence of the grain deformability on the macroscopic elastic and strength response is presented. It is shown that, when compared with a rigid model, the proposed flexible PM model predicts more reasonable indirect tensile strength to direct tensile strength ratio and requires a smaller value of contact fracture energy to give a good agreement with known experimental data. It is also shown that the proposed flexible PM model can predict a behaviour similar to that ob- tained using a flexible PM model through inner particle discretization that is more computationally demanding.
Ano: 2022
Número Páginas:
27p.
Autor(es): Azevedo, N.; Braga Farinha, M. L.; Oliveira, S.
Revista: Geotechnics
Editor: MDPI
Volume:
2.
Keywords: grain deformability; discrete element; particle model; fracture; rock
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Application of Maxwell damping in the dynamic analysis of masonry structures with discrete elements
Discrete element models are widely used in the analysis of masonrystructures, as they provide an effective approximation of the observedbehaviour, namely for modelling collapse modes governed by thediscontinuities. Assessment of the response under earthquakes is an importantapplication of these models, which perform time domain dynamic analysisusing explicit algorithms. Rayleigh damping is generally used, but itsmass-proportional component has potential adverse effects, and the small stepsrequired by explicit solutions lead to large computational costs. An alternativedamping formulation employing Maxwell elements in parallel with the jointstiffness is proposed and tested. Problems involving linear elastic analysis ofcolumn bending, rocking of rigid blocks, and out-of-plane failure of masonrywalls under seismic loading are examined. The proposed damping approachdisplayed a sound mechanical performance and is computationally efficient.These early results justify further investigation of the technique for a broaderapplication in masonry structural dynamics.
Ano: 2022
Autor(es): Cheng, Z.; Dawson, E.; Lemos, J. V.
Revista: Int. J. Masonry Research and Innovation
Editor: Inderscience
Volume:
Vol. 7, No. 6.
Keywords: numerical modelling; structural dynamics; masonry
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Computational investigations on the combined shear
This research explores the mechanical behavior of dry-joint masonry subjected to combined shear
Ano: 2022
Autor(es): Hazzard, J.; Lemos, J. V.; Loureno, P.; Gonen, S.; Pulatsu, B.
Revista: Computational Particle Mechanics
Editor: Springer
Keywords: discrete elements; numerical modelling; masonry
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Deduction of ultimate equilibrium limit states for concrete gravity dams keyed into rock mass foundations based on large displacement analysis
Concrete gravity dams are mass concrete structures, often built on rock mass foundations, conceived to rely upon their weight for stability. To prevent sliding, these structures are usually keyed/embedded into the foundation, a good construction practice particularly relevant in medium to high intensity seismic zones. In stability analysis, the extra strength obtained by keying the dam into the foundation is usually either neglected or taken as a passive resistance, which, such as explored in this paper, do not reflect the real structural response in pre-collapse situations. Limit state philosophy requires the ultimate equilibrium conditions to be expressed as accurately as possible. In this paper, the rigid-body equilibrium of a wedgy model representing the dam and a downstream rock wedge is analyzed according to the large displacement regime. Failure mechanisms were identified, analytically described and numerically validated. Application to two Portuguese large concrete gravity dams led to safety factors considerably larger than those computed assuming the usual practice. The proposed approach is intended to support probabilistic and/or semi-probabilistic methodologies for safety assessment of concrete gravity dams, in the design and feasibility phases, in which the limit state approach is inherently followed.
Ano: 2022
Número Páginas:
1180-1190.
Autor(es): Pereira, R.; Batista, A. L.; Neves, L.; Lemos, J. V.
Revista: Structures
Editor: Elsevier
Volume:
38.
Keywords: Large displacement analysis; Ultimate equilibrium; Limit state approach; Analytical modeling; Stability analysis; Keyed profiles; Concrete gravity dams
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Comunicações
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Tracking the modal parameters of baixo sabor concrete arch dam with uncertainty quantification
During the last decade, many vibration-based structural health monitoring systems have been successfully implemented in different structures such as bridges, towers, stadia roofs and wind turbines, with the aim of studying the structures dynamics and its evolution over time and even-tually detect the occurrence of novel structural behaviour that may indicate the presence of damage. Such vibration-based monitoring systems generally rely on the identification of modal proper-ties, which are then used as monitoring features. Therefore, from operational modal analysis to the tracking of the said features, many processing steps occur that depend on the accuracy of the identified modal properties in order to produce good results. Thus, the calculation of the uncertainties associated with the identified modal properties may act as an important tool in this process. In this context, data obtained from the continuous dynamic monitoring of a concrete arch dam has been used to test the effect of taking the uncertainties of identified modal properties into consideration when performing operational modal analysis and modal tracking.
Ano: 2019
Autor(es): Pereira, S.; Reynders, E.; Magalhães, F.; Cunha, A.; Gomes, J. P.
Editor: UNCECOMP 2019 - 3rd International Conference on Uncertainty Quantification
Keywords: Concrete arch dam; Continuous dynamic monitorin; Operational modal analysis; Uncertainties in modal properties
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Análise e interpretação do comportamento observado da barragem de Pretarouca durante o primeiro enchimento da albufeira e o primeiro período de exploração
A barragem de Pretarouca, no rio Balsemão (serra de Montemuro, concelho de Lamego), tem 29,70 m de altura e 305 m de desenvolvimento. A albufeira tem 3,2 hm3, destinando-se a água a abastecimento público. A obra, construída entre 2007 e 2009, é explorada pela empresa Águas do Norte, do grupo Águas de Portugal, com o apoio do LNEC nos aspetos relacionados com a segurança estrutural. Na comunicação apresentam-se os aspetos relevantes da análise e interpretação do comportamento observado da barragem durante o primeiro enchimento da albufeira, ocorrido em 2009, e o período de exploração subsequente. Na análise estrutural considerou-se um modelo plano do conjunto barragem-fundação, o comportamento viscoelástico dos materiais, a variação das ações da água e as variações térmicas que ocorreram no betão da obra. Os resultados numéricos são comparados com os resultados da observação contínua da obra, apresentando uma boa concordância.
Ano: 2018
Número Páginas:
954-963pp.
Autor(es): Dias, I. M.; Batista, A. L.; Paixão, J. B.
Editor: GPBE
Keywords: Método dos elementos finitos; Barragem de Pretarouca; Observação; Primeiro período de exploração; Primeiro enchimento da albufeira
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Analysis and interpretation of the structural behaviour of Bouçoais-Sonim dam during the first filling of the reservoir and the following 10 years of operation
This paper presents the relevant monitoring data and the main results of the analysis and interpretation of the structural behaviour of Bouçoais-Sonim dam, a medium-size gravity concrete dam of 42.5 m high, during the first filling of the reservoir, in March 2005, and the subsequent 10 years of operation. As usual, the dam safety control is performed by considering the data provided by the monitoring system, which is analysed and interpreted with the support of numerical models. These activities are particularly relevant during the first filling of the reservoir, which is a real load testing, and during the first years of operation, when the dams body and its foundation adapt to the local serviceability conditions. A three-dimensional finite element model of the dam and of the rock mass foundation, considering the concrete viscoelastic behaviour and the variation of the reservoir water level and temperatures, allows simulating numerically the thermal and structural dam behaviour. The dams concrete delayed behaviour was represented by the Baant and Panulas basic creep function, evaluated from ordinary concrete laboratory tests. The monitoring results, namely the displacements measured through plumb-lines, exhibit a good agreement with those obtained by the structural analysis, showing that the observed response is coherent with the evolution of the main actions.
Ano: 2018
Número Páginas:
14p.
Autor(es): Dias, I. M.; Batista, A. L.; Pereira, R.
Editor: LNEC \ IBRACON
Keywords: Finite element method; Monitoring; First period of operation; Bouçoais-Sonim dam; Thermal and structural modelling; First filling of the reservoir
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Apoio do LNEC no projeto, construção e exploração de barragens de betão
O Laboratório Nacional de Engenharia Civil (LNEC), desde a sua criação, em 1946, tem dado um apoio significativo ao projeto, à construção e à exploração de barragens de betão e obras subterrâneas associadas, tanto em Portugal como no estrangeiro. Esta atividade tem sido muito diversificada e abrange todas as fases de vida das obras, podendo salientar-se os estudos e atividades relacionados com a caracterização dos maciços rochosos, a definição de formas estruturais e hidráulicas, utilizando modelação física e matemática, a análise estrutural por métodos experimentais e numéricos, a observação do comportamento e o controlo da segurança. No sentido de reduzir a dependência energética de Portugal, nos últimos anos tem vindo a ser aumentada a capacidade de produção hidroelétrica, com o reforço de potência de aproveitamentos existentes e com a construção de novos aproveitamentos. O presente trabalho apresenta os aspetos principais de algumas obras em que o LNEC tem estado envolvido, colaborando com a autoridade nacional, os donos de obra, os projetistas e os construtores. As atividades descritas têm vindo a ser desenvolvidas por uma vasta equipa de especialistas do LNEC, entre os quais se incluem os autores do presente trabalho.
Ano: 2018
Autor(es): Gomes, J. P.; Batista, A. L.; Lemos, J. V.; Lamas, L.; Tavares de Castro, A.
Editor: Associação Portuguesa de Análise Experimental de Tensões
Keywords: Observação; Exploração; Cosntrução; Projeto; Obras Subterrâneas; Fundações; Barragens
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Installation and results from the first 18 months of operation of the dynamic monitoring system of Baixo Sabor arch dam
The Baixo Sabor hydroelectric power plant, located in the northeast of Portugal, includes a reservoir with a storage capacity of 630 million m3 of water created by a concrete double-curvature arch dam, 100 m high, which was equipped with a vibration based structural health monitoring system. This system involves 20 uni-axial accelerometers, 12 of them radially disposed in a gallery close to the dam crest, and the other 8 radially placed along two other galleries. The accelerometers are connected to a set of digitizers distributed in the three instrumented galleries and synchronized by GPS. This paper presents the main characteristics of the monitoring system and the results obtained during the first 18 months of operation, which include the first filling of the reservoir. These results include in particular the characterization of the accelerations amplitude and the evolution of the dam modal parameters (natural frequencies, modal damping ratios and mode shapes), as well as of the influence of the water level and tem-perature on the modal parameters. Suitable statistical models are applied to mitigate those effects in order to obtain time series of natural frequencies suitable for detection of structural changes.
Ano: 2018
Autor(es): Pereira, S.; Gomes, J. P.; Magalhães, F.; Lemos, J. V.; Cunha, A.
Editor: The Sixth International Symposium on Life-Cycle Civil Engineering
Keywords: Dynamic monitoring; Operation Modal Analysis; Concrete arch dams
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Modelação da fendilhação por origem térmica de uma barragem de betão em arco
No 14º encontro internacional de modelação numérica em barragens, organizado pela ICOLD, foi proposta a análise numérica de uma barragem de betão em arco localizada na Suécia sujeita a gradientes térmicos significativos ao longo do ano. Nesta comunicação apresentam-se os resultados numéricos obtidos com base numa discretização mais refinada do corpo da barragem, quando comparada com o modelo adotado no encontro internacional. A análise térmica transiente é realizada com um modelo de elementos finitos com condições de fronteira de Dirichlet (betão/água e fundação/água) e condições de fronteira de Robin (betão/ar e fundação/ar). A análise mecânica não linear é realizada numa primeira fase com elementos finitos do tipo cubo de 8 nós tendo por base os gradientes de temperatura obtidos na análise térmica. A armadura existente no paramento de montante e no paramento de jusante é modelada com elementos planos quadrangulares cujos pontos nodais se encontram rigidamente ligados aos elementos de volume tipo cubo. De modo a simular adequadamente o comportamento da ligação da barragem à fundação considerou-se de forma explícita a interface barragem/fundação mediante elementos de junta. Os resultados da análise mecânica realizada com um modelo de fenda discreta, em que se admite que cada elemento finito do tipo cubo adotado na discretização da barragem interage com os elementos vizinhos através de elementos de junta com comportamento não linear em tração e corte, são comparados com as observações in situ. Verifica-se que o modelo estrutural mais refinado permite obter resultados mais próximos dos observados, nomeadamente a distribuição de fendilhação no paramento de jusante e o campo de deslocamentos. Analisa-se ainda o efeito das armaduras distribuídas colocadas junto ao paramento de montante e ao paramento de jusante no controlo de deformação e fendilhação.
Ano: 2018
Autor(es): Azevedo, N.; Santos, E.; Leitão, N. S.; Braga Farinha, M. L.; Câmara, R.
Editor: GPBE - Grupo Português de Betão Estrutural
Keywords: Modelo de fenda discreta; Barragens de betão; Análise térmica
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Modelação do maciço rochoso para avaliação do comportamento de barragens de betão sujeitas a vibrações explosivas
Pretende-se com este trabalho estudar o efeito das vibrações provocadas pelas explosões devidas a desmontes no comportamento da barragem de betão e respetiva fundação, avaliando a sua seguran-ça estrutural através de um modelo numérico híbrido descontínuo de elementos discretos e elemen-tos finitos recorrendo ao 3DEC. Apresentam-se os resultados do modelo numérico comparando-o com as medições de velocidades efetuadas no decorrer das obras envolvendo desmontes a fogo, sendo posteriormente analisado os efeitos na barragem. O presente trabalho deu origem ao desenvolvimento de um modelo numérico capaz de representar a resposta da estrutura às vibrações, minimizando a subjetividade da classifica-ção do seu grau de resistência.
Ano: 2018
Autor(es): Fonseca, R.; Gomes, J. P.; Lemos, J. V.; Resende, R.
Editor: Associação Brasileira de Mecânica dos Solos
Keywords: Método elementos discretos; Modelação numérica; Análise dinâmica; Explosivos; Vibrações; Barragens
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Modelação numérica e experimental da rotura pela fundação de barragens de betão para ações estáticas e dinâmicas
O dimensionamento de barragens, de acordo com a regulamentação portuguesa, engloba a verifica-ção da segurança da obra para diversos cenários de rotura. Nesta comunicação, apresenta-se um exemplo de aplicação conjunta de métodos experimentais e numéricos para: i) determinação do coe-ficiente de segurança de uma barragem abóbada num cenário de rotura por deslizamento de parte do maciço de fundação para ações estáticas, ii) o estudo do comportamento dinâmico até à rotura uma barragem de gravidade por deslizamento ao longo da fundação. Os resultados experimentais foram comparados com os obtidos a partir de modelações matemáticas devidamente calibradas.
Ano: 2018
Autor(es): Gomes, J. P.; Lemos, J. V.
Editor: Associação Brasileira de Mecânica dos Solos
Keywords: Modelos numéricos; Modelos físicos; Rotura pela fundação; Barragens de betão
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Seismic monitoring system of Baixo Sabor scheme for structural dynamic behaviour monitoring and risk management
This paper presents the Hydropower Scheme of Baixo Sabor, a brief description of the tectonic framework scheme area, the studies to predict the seismic actions envisaging the dams design and the dynamic monitoring systems that have been installed in the dams and in the reservoir surrounding. The dynamic monitoring includes a seismic monitoring system that enables to record the behavior of the dams during seismic events and also to characterize the action applied to the structures, and a continuous dynamic monitoring system for evaluation of the dynamic parameters of the dam along the time and detection of variations that might be associated with the appearance of damages. The main technical characteristics, the constraints associated to the equipment selection and the systems features are described in detail. Both systems are operational and fully automatic, providing an additional and useful tool in the safety control of these important structures. The features implemented in both systems revealed excellent efficiency and demonstrated a perfect suitability. The results showed a direct relation with the variation of actions. These systems proved already to be extremely useful to evaluate the behavior of these structures during seismic events and to provide relevant information for the development of numerical models including new behavior models. So, they demonstrate to be a very important tool concerning dam safety control and seismic risk management.
Ano: 2018
Autor(es): Gomes, J. P.; Magalhães, F.; Monteiro, G.; Palma, J.; Pereira, S.; Matos , D.
Editor: ICOLD 2018
Keywords: Concrete dam; Seismicity; Seismic hazard; Safety of dams; Induced seismicity; Feiticeiro dam; Dynamic monitoring; Baixo Sabor dam; Automated monitoring
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Non-linear earthquake response of three minarets in Istanbul
Minarets are important elements of mosques. These slender structures have suffered notable damage as a result of past earthquakes. In this paper three historical masonry minarets located in Istanbul, Turkey are studied in the inelastic range using the Discrete Element Method. They are the minarets of the Hagia Sophia Museum, Süleymaniye Mosque and Mihrimah Sultan Mosque. The selected minarets are 16th century structures having different heights and body diameters. Dynamic behavior is simulated by means of ten different loading configurations as real and simulated earthquake time histories. Nonlinear dynamic response is characterized by the relative horizontal and normal dislocations of adjacent drums along the minaret body, as well as by its top displacement, all normalized by the body diameter. Damage patterns and collapse mechanisms are studied.
Ano: 2017
Número Páginas:
Paper N° 2903.
Autor(es): Cakti, E.; Saygili, O.; Oliveira, C.S.; Lemos, J. V.
Editor: 16 WCEE
Keywords: Masonry; Slender structures
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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 lime mortar. It is probably the oldest material used in construction and has proven to be both simple to build and 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 for that. Careful and periodic assessment of such structures is necessary in order to evaluate their structural capacity and safety levels. However, performing the structural analysis of masonry construction is not an 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 11 countries (Canada, France, Greece, Hungary, Iran,Italy, Mexico, Norway, Portugal, UK, USA), which were 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
N/A
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
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): Bagi, K.; Lemos, J. V.
Revista: Discrete Computational Mechanics of Masonry Structures
Editor: Springer
Keywords: Masonry models
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Seismic and Structural Health Monitoring of Dams in Portugal
This chapter is focused on the Portuguese experience on the development and exploration of systems for continuously monitoring dam vibrations, using accelerometers. The pioneer system for seismic and structural health monitoring (SSHM) installed in Cabril dam (the highest Portuguese arch dam: 132 m high) is described in detail. The design of this system was the result of a long-term LNEC research program, still ongoing. These monitoring systems should include software developed to automatically perform the analysis of collected data, including the automatic comparison with numerical results from 3DFE models. In view of the good results obtained with the system in operation in Cabril dam since 2008, similar systems have been installed in other large dams in Portugal, particularly in recently built dams. Finally, Baixo Sabor dam is presented as an example of a new Portuguese dam with a complete SSHM system, in operation since 2015. Themain experimental results obtained for both dams are shown, namely the evolution of natural frequencies over 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
Para verificação do cumprimento das exigências de segurança das barragens, tanto relativamente à funcionalidade (cenários correntes), como em relação à segurança ao colapso (cenários de rotura), é essencial utilizar modelos de simulação ou de interpretação (no caso de obras existentes) do seu comportamento. Estes modelos são 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, quantifica parâmetros da resposta das estruturas que permitem avaliar a sua segurança, utilizando critérios 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 de barragens. No caso de cenários de rotura, não existe muita experiência de comparação destes 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 métodos experimentais, para o estudo de cenários de rotura, tem uma importância acrescida. Assim o principal objectivo deste trabalho é contribuir para melhorar a capacidade de avaliação da segurança de barragens de betão envolvendo cenários de rotura pela fundação. Neste trabalho desenvolveram-se dois ensaios experimentais em modelos físicos: um primeiro envolvendo uma barragem abóbada, para o estudo de cenários de rotura da fundação para acções estáticas; e um segundo de uma barragem gravidade ensaiado em mesa sísmica, com vista a estudar a rotura pela fundação para acções dinâmicas. A previsão e interpretação dos ensaios foram efectuadas com modelos matemáticos adequados, que permitiram a sua validação e posterior utilização no estudo de 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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Dissertações de Mestrado
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Análise de estruturas de membrana com comportamento ortotrópico utilizando o método de Galerkin livre de elementos
As estruturas de membrana são caracterizadas por terem secções transversais muito pequenas (espessura no caso da membranas). Desta forma verifica-se que este tipo de estruturas não tem capacidade para desenvolver esforços de flexão e portanto, a única maneira de equilibrar as acções transversais é adaptando a sua forma ao carregamento. Contrariamente ao tradicional método dos elementos finitos (FEM), o método de Galerkin livre de elementos desenvolvido por Belytschko [1] não necessita de elementos na aproximação do campo de variáveis. No EFGM, os elementos são substituídos por um conjunto de nós em que cada um possui um determinado domínio de influência. Assim, a função de aproximação é construída em cada ponto com base nos nós incluídos no seu domínio de influência. As funções de aproximação são obtidas utilizando o método dos mínimos quadrados móveis (MLS) que não é mais do que um método de mínimos quadrados que se move consoante o domínio de influência do nó em questão. Neste trabalho é apresentado a implementação de um método sem malha, o método livre de elementos de Galerkin para a análise de estruturas de membrana com comportamento ortotrópico. Para a utilização deste método na análise de estruturas de membrana utilizou-se uma técnica de mapeamento da geometria tridimensional para um espaço bidimensional, sendo que as bases deste sistema são utilizadas na expressão das componentes de deformação e tensão na equação do princípio dos trabalhos virtuais. Com base nesta técnica, os nós da malha são gerados no espaço bidimensional e as suas coordenadas são utilizadas no método dos mínimos quadrados móveis para a aproximação do campo de deslocamentos. Para uma estrutura de membrana, a rigidez geométrica da estrutura de suporte não pode ser desprezada sendo que a análise geometricamente não linear é essencial na formulação do problema. Para tal, com base numa formulação Lagrangeana total desenvolveu-se uma formulação de análise geometricamente não linear considerando o método livre de elementos de Galerkin. Neste trabalho foram analisados alguns exemplos de estruturas de membrana com comportamento isotrópico e ortotrópico para validar o método proposto sendo que os respectivos resultados foram comparados directamente com os resultados obtidos com o programa generalista de elementos finitos ADINA .
Ano: 2007
Autor(es): Figueiredo, B.
Keywords: Matlab; Adina; Ortotropia; Isotropia; Formulação lagrangeana total; Análise geometricamente não linear; Método de galerkin livre de elementos; Estruturas de membrana
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Relatórios
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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.
Ano: 2024
Autor(es): Lamas, L.; Lemos, J. V.; Muralha, J.
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.
Ano: 2023
Autor(es): Gomes, J. P.; Batista, A. L.; Lemos, J. V.
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.
Ano: 2023
Autor(es): Pereira, R.; Muralha, J.; Lamas, L.
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 concretes non-linear behaviour up to failure is simulated using an isotropic damage model with softening, considering two independent scalar damage variables: d+ for tension damage and d- for compression damage. The implemented code was verified and optimized for a simple test structure, more specifically a concrete frame structure with three columns. According to the defined material properties for the structural elements, the concrete failure is expected to occur only at the central column without causing the collapse of the structure, which remains in equilibrium. DamDamage3D1.0 is used to evaluate the structural safety of Cabril arch dam (132 m high) for the concrete strength decrease scenario, considering the material deterioration under tension and compression. This failure scenario is usually considered in the scope of the safety control of dams, and the main goal is to obtain a global safety factor ?s that indicates how many times the materials resistance can be reduced without causing the dams structural collapse. This way ?s is the maximum admissible multiplying factor of the applied loads. The non-linear behaviour of the dam is analysed for the load combination with the self-weight (SW) and the hydrostatic pressure (HP) at the upstream face (full reservoir), using a 3D finite element mesh with three elements in thickness. The numerical simulations are performed using two different constitutive damage laws to evaluate the influence of the compression softening phenomenon in the global resistant capacity of the dam. The main results include displacements and stress fields and the distributions of tension and compression damage in the dam body.
Ano: 2019
Autor(es): 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 concretes non-linear behaviour up to failure is simulated using an isotropic damage model with softening, considering two independent scalar damage variables: d+ for tension damage and d- for compression damage. The implemented code was verified and optimized for a simple test structure, more specifically a concrete frame structure with three columns. According to the defined material properties for the structural elements, the concrete failure is expected to occur only at the central column without causing the collapse of the structure, which remains in equilibrium. DamDamage3D1.0 is used to evaluate the structural safety of Cabril arch dam (132 m high) for the concrete strength decrease scenario, considering the material deterioration under tension and compression. This failure scenario is usually considered in the scope of the safety control of dams, and the main goal is to obtain a global safety factor ?s that indicates how many times the materials resistance can be reduced without causing the dams structural collapse. This way ?s is the maximum admissible multiplying factor of the applied loads. The non-linear behaviour of the dam is analysed for the load combination with the self-weight (SW) and the hydrostatic pressure (HP) at the upstream face (full reservoir), using a 3D finite element mesh with three elements in thickness. The numerical simulations are performed using two different constitutive damage laws to evaluate the influence of the compression softening phenomenon in the global resistant capacity of the dam. The main results include displacements and stress fields and the distributions of tension and compression damage in the dam body.
Ano: 2019
Autor(es): 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 known analytically, 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 dams structural behavior for the main loads, self-weight and hydrostatic pressure, is simulated with GDams2D 1.0. The results obtained are analyzed based on the post-processing module of GDams2D 1.0, also developed in MATLAB in the scope of the present work. This module allows several types of representation of the displacement field and stress field.
Ano: 2019
Autor(es): 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 the friction 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 different values of water level and friction angle.
Ano: 2019
Autor(es): 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 Técnicas avançadas para modelação numérica de processos de fratura material. Aplicações práticas e desenvolvimento de um programa de elementos finitos - Relatório de progresso do projeto d
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.
Ano: 2018
Autor(es): 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 Discrete element modelling of rock engineering structures for seismic safety analyses - Relatório de progresso 2016-2017 do projeto do P2I/LNEC
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.
Ano: 2018
Autor(es): 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 Modelação de maciços rochosos marcadamente heterogéneos - Relatório de progresso 2016-2017 do projeto do P2I/LNEC
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.
Ano: 2018
Autor(es): Lamas, L.; Muralha, J.; Espada, M.
Keywords: Modelação numérica; Heterogeneidade; Mecânica das rochas; RockGeoStat
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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
O problema da solução das equações de Navier Stokes é abordado neste trabalho propondo-se uma técnica de representação das incógnitas deslocamentos e pressões variáveis no espaço e no tempo em série de Delta de Dirac e suas derivadas no tempo cujos coeficientes se determinam com base na solução de sistemas de equações diferenciais definidos no espaço (problema com três variáveis espaciais independentes que 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
Neste relatório apresentam-se as equações básicas da elastodinâmica linear, as soluções fundamentais 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 sua implementação 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
Neste relatório apresentam-se os principais aspectos da modelação sísmica de barragens abóbada. Assim propõe-se: modelos numéricos de geração de sismos por uma falha; a forma como o sismo actua na barragem; modelos para estudar a influência da albufeira na vibração do conjunto; métodos para solução das equações do movimento; e novas formulações 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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