Artigos de Revista
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A Hybrid Particle/Finite Element Model with Surface Roughness for Stone Masonry Analysis
Circular and spherical particle models are a class of discrete elements (DEM) that have been in-creasingly applied to fracture studies of quasi-brittle materials, such as rock and concrete, due to their proven ability to simulate fracture processes through random particle assemblies repre-senting quasi-brittle materials at the grain scale. More recently, DEM models have been applied to old stone masonry fracture studies. In order to extend its applicability to structures of larger di-mensions, an enhanced hybrid particle model is here proposed that allows finite elements with a given surface roughness, provided by the discretization of the element boundary with particles, to interact with the particulate media in which they are embedded. The performance of the hybrid model is compared with that of a traditional all-particle model under uniaxial testing. It is shown that similar results are obtained, namely in the elastic phase, figures of rupture, pre-peak and post-peak behaviour, while the hybrid model allows a significant computational run time re-duction of 20% to 25% in the coarse particle assemblies. Finally, the proposed hybrid model is applied in the simulation of shear tests of stone masonry walls, dry and mortared joints, providing a reasonably good agreement with both experimental results and predictions. For the rubble masonry tests, the hybrid model allows a computation run time reduction of around 40%, when compared with an all-particle model.
Ano: 2022
Número Páginas:
20p.
Autor(es): Azevedo, N.; Lemos, J. V.
Revista: Applied mechanics
Editor: mdpi
Volume:
3.
Keywords: fracture; hybrid model; finite element; discrete element; stone masonry
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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): Lemos, J. V.; Dawson, E.; Cheng, Z.
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): Pulatsu, B.; Gonen, S.; Lourenço, P.; Lemos, J. V.; Hazzard, J.
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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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
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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Discrete element bonded-block models for detailed analysis of masonry
A detailed modelling approach to represent masonry at the meso-scale is proposed, basedon the discrete element method, considering the nonlinear behavior of the joints and the units. Thefracture of units is represented by the bonded-block concept, in which a random network of potentialcracks is created, allowing the progressive development of failure mechanisms. For simplicity, onlythe 2D case is presented, but the extension to 3D is straightforward. A key component of the proposedmodel is a framework for a joint or interface constitutive model, including the post-peak softeningrange, taking into account the experimental fracture energies. In this model, the softening curves intension or shear are defined by piecewise linear segments, calibrated to reproduce the most commonmasonry constitutive models. The essential issues involved in the application of bonded-blockmodels to masonry are examined, namely the block shape, either Voronoi polygons or triangles; size;deformability; and the influence of the main constitutive parameters. Uniaxial compression tests areanalyzed in detail. The simulation of a well-known experiment of a brick panel under shear showsthe good performance of the proposed approach. The investigation results demonstrate the model
Ano: 2022
Número Páginas:
25p.
Autor(es): Lemos, J. V.; Sarhosis, V.
Revista: Infrastructures
Editor: MDPI
Volume:
vol 7, artigo no. 31.
Keywords: fracture; numerical modelling; masonry
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Prediction of rubble-stone masonry walls response under axial compression using 2D particle modelling
To predict the structural behaviour of ancient stone masonry walls is still a challenging taskdue to their strong heterogeneity. A rubble-stone masonry modeling methodology using a 2D particlemodel (2D-PM), based on the discrete element method is proposed given its ability to predict crackpropagation by taking directly into account the material structure at the grain scale. Rubble-stone(ancient) masonry walls tested experimentally under uniaxial compression loading conditions arenumerically evaluated. The stone masonry numerical models are generated from a close mappingprocess of the stone units and of the mortar surfaces. A calibration procedure for the stone-stoneand mortar-mortar contacts based on experimental data is presented. The numerical studies showthat the 2D-PM wall models can predict the formation and propagation of cracks, the initial stiffnessand the maximum load obtained experimentally in traditional stone masonry walls. To reducethe simulation times, it is shown that the wall lateral numerical model adopting a coarser mortardiscretization is a viable option for these walls. The mortar behaviour under compression with lateralconfinement is identified as an important micro-parameter, that influences the peak strength and theductility of rubble-masonry walls under uniaxial loading.
Ano: 2022
Número Páginas:
20p.
Autor(es): Azevedo, N.; Pinho, F.; Cismasiu, I.; Souza, M.
Revista: Buildings
Editor: MDPI
Keywords: Micro-parameters identification; Uniaxial compression; Prediction; Validation; Particle model; Rubble-stone masonry
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Seismic and Structural health monitoring systems for large dams: theoretical, computational and practical innovations
This paper is focused on the study of the dynamic behaviour of two large arch dams, and it presents some innovations for the improvement of Seismic and Structural Health Monitoring (SSHM) systems for dams. The work describes a methodology based on the integrated use of software for automatic monitoring data analysis and of computational 3D finite element (3DFE) models for dam dynamic behaviour simulation. The monitoring data analysis software was developed for automatic modal identification, in order to obtain natural frequencies and mode shapes, for automatic detection of vibrations induced by seismic events, to be distinguished from those caused by other operational sources, and for comparison between results retrieved from measured vibrations and numerical results from 3DFE modelling. The numerical simulations are carried out using a 3DFE program developed for dynamic analysis of dam-reservoir-foundation systems, based on a solidfluid coupled formulation and considering the dam-water dynamic interaction, including calculation modules for complex modal analysis and for linear and non-linear seismic analysis. The case studies are two large arch dams that have been under continuous dynamic monitoring over the last ten years: Cabril dam (132 m high), the highest dam in Portugal, and Cahora Bassa dam (170 m high), in Mozambique, one of the highest dams in Africa. The SSHM systems installed in both dams have similar schemes and were designed to continuously record accelerations in several locations at the upper part of the dam body and near the dam-foundation interface, using uniaxial and triaxial accelerometers. The most significant experimental results from continuous dynamic monitoring are presented and compared with numerical results for both dams, with emphasis on the evolution of natural frequencies over time, including the vibration mode shapes for various water levels, and on the measured accelerations during low-intensity seismic events. Furthermore, the main results of non-linear seismic response simulations are provided, considering the effects due to joint movements and tensile and compressive concrete damage, aiming to assess the seismic performance of both dams based on the Endurance Time Analysis method.
Ano: 2022
Autor(es): Oliveira, S.; Alegre, A.; Carvalho, E.; Mendes, P.; Proença, J.
Revista: Bulletin of Earthquake Engineering
Editor: Springer
Keywords: Dynamic behaviour of large concrete dams · Finite element numerical modelling · Seismic and structural health monitoring · Safety control · Dam-reservoirfoundation systems · Evolution of natural frequencies · Vibration modes · Seismic response
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Back-analysis of the Collapse of a Tetrastyle Canopy during the April 25, 2015 Nepal Earthquake
A monumental tetrastyle canopy (four columns topped by a hollow cap overlaying a statue), built in1948 at the centre of Kathmandu, Nepal, has suffered full collapse during the April 25, 2015 Mw7.8earthquake. Two video camera recordings let us recover the most important movements of thestructure. At a distance of 2.9 km from the monument, an accelerometric station (KATNP) recordedthe motion which we used as input of a model structure made with DEM. Geometry and dimensionsof main elements were mostly obtained from satellite images. Concrete and steel in columns wereconsidered as the common practice at that time. We performed some sensitivity analyses varyingthe mechanical properties due to the possibility of aging alterations in concrete and steel and toincorporate uncertainties on the geometric characteristics. Albeit the response has a significantvariability, results show that it is possible to reproduce well the video images, attesting theimportance of video cameras to capture the dynamic performance of structures, providing insightinto their behaviour and data to support numerical investigations.
Ano: 2021
Autor(es): Oliveira, C.S.; Lemos, J. V.
Revista: International Journal of Architectural Heritage
Editor: Tayloer & Francis
Keywords: Estruturas de alvenaria
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In-plane structural performance of dry-joint stone masonry Walls: A spatial and non-spatial stochastic discontinuum analysis
In this study, the in-plane structural behavior, capacity, and performance of dry-joint stone masonry walls (DJSMWs)and the effects of the vertical stress level on these factors are investigated via a stochastic discontinuumanalysis that considers the material uncertainty. A discontinuum type of analysis is performed based on thediscrete element method (DEM), where each stone masonry unit is explicitly represented in the computationalmodel. To better simulate the cracking and shear failure modes within the stone units, a coupled fracture energybasedcontact constitutive model is implemented into a commercial discrete element code, 3DEC. First, theproposed modeling approach is validated by comparing to experimental findings in literature. Then, theapproach is used to explore the failure mechanism and the force
Ano: 2021
Autor(es): Pulatsu, B.; Erdogmus, E.; Lourenço, P.; Lemos, J. V.
Revista: Engineering Structures
Editor: Elsevier
Volume:
242.
Keywords: Estruturas de alvenaria
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Comunicações
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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 dam
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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Installation and results from the first 6 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 20-channel vibration based structural health monitoring system.This paper, apart from describing the dam, presents the main characteristics of the monitoring system and the results obtained during the first 6 months of operation and 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). It is particular interesting to observe the influence of the water level on the modal parameters and the development of statistical models to mitigate this effect.
Ano: 2017
Autor(es): Pereira, S.; Magalhães, F.; Gomes, J. P.; Cunha, A.; Lemos, J. V.
Editor: Sapienza University of Rome
Keywords: Operational modal analysis; Dynamic monitoring; Arch dam
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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
Autor(es): Cakti, E.; Saygili, O.; Oliveira, C.S.; Lemos, J. V.
Editor: 16WCEE
Keywords: Nonlinear dynamic modelling; Masonry; Slender structures
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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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Stress measurements for underground powerhouses
Release of the in situ state of stress is often the most relevant action during the excavation of underground structures in rock masses, such as powerhouse caverns for hydroelectric schemes, which are often excavated at great depth and have large dimensions. Design of the supports, namely using numerical models, requires an estimate of the magnitude and direction of the principal stresses. However, a large number of factors influence the in situ stress field and its characterisation is a difficult task. Besides, the number of tests carried out for determination of the in situ stresses in rock masses is usually small, due to cost and time constraints, and all the testing methods have limitations inherent to their nature.The paper presents methodologies for analysis of the stress field obtained from the results of in situ stress measurements using three methods: overcoring, hydraulic fracturing and flat jacks. These methodologies integrate all stress measurements and use numerical models of the rock mass that represent the ground topography, the lithology and the underground openings geometry, so that the most likely stress field in the zone of interest for the design of the underground openings is obtained. Instances of application to three underground powerhouses are presented.
Ano: 2017
Número Páginas:
24p.
Autor(es): Lamas, L.; Espada, M.; Figueiredo, B.; Muralha, J.
Editor: The Southern African Institute of Mining and Metallurgy
Keywords: Underground powerhouse; Stress measurements; Rock mechanics
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VGCM3D - A 3D rigid particle model for rock fracture following the Voronoi tessellation of the grain structure: Formulation and validation
Detailed particle models by taking into account the material grain structureexplicitly consider the material randomness, including a size limiter for damage localization.A VGMC3D contact model is presented that considers the polyhedral particle shape in anapproximate way. The VGCM3D flexible contact model is validated against knownexperimental data on a granite rock, namely triaxial tests and Brazilian tests.
Ano: 2017
Número Páginas:
99-110pp.
Autor(es): Candeias, M.; Azevedo, N.; Braga Farinha, M. L.
Editor: International Center for Numerical Methods in Engineering (CIMNE)
Keywords: Calibration; Particle shape; Particle models; Fracture
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Análise Sísmica da Igreja de Kuño Tambo
Esta comunicação apresenta um estudo sobre a vulnerabilidade sísmica da igreja deKuño Tambo (Peru) com recurso ao Método dos Elementos Discretos. A avaliação docomportamento sísmico da igreja foi efetuada através de dois modelos numéricos,nomeadamente: (a) Modelo da secção transversal da parede da nave considerando amorfologia do aparelho da alvenaria, tendo por objetivo avaliar o seu comportamentopara fora do plano; (b) Modelo 3D da fachada com parte das paredes ortogonais danave, tendo por objetivo avaliar a sua resposta para fora do plano. Os resultados daanálise permitiram concluir que a ligação entre paredes ortogonais têm influênciasignificativa no comportamento da fachada.
Ano: 2016
Autor(es): Mendes, N.; Zanotti, S.; Lourenço, P.; Lemos, J. V.
Editor: SPES
Keywords: Análise sísmica; Adobe; MED
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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
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): 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
N/A
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
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
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
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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Applications of computational mechanics to underground structures ln hydraulic projects
A brief description of the phenomena and problems associated with underground structures in hydraulic projects is presented, namely in what concerns the powerhouses, surge chambers and pressure tunnels and shafts. An analysis of the calculation methodologies followed in the structural design of this works is presented, as well as of the numerical models usually adopted, namely finite and boundary element models. Finally, some applications of computational mechanics are presented. First, a parameter study for underground powerhouses, with special emphasis in the definition of shapes, existence of several caverns,and in the tridimensional equilibria is described. Afterwards, examples of application to some hydraulic projects are illustrated: a large underground powerhouse in Mozambique, the Alto Lindoso hydroelectric power scheme in construction in the north of Portugal, and the Castelo do Bode tunnel, in operation, integrated in the water supply system to Lisbon.
Ano: 1992
Autor(es): Sousa, L.; Lamas, L.; Martins, C. S.
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Estado de tensão dos maciços rochosos
O presente trabalho aborda a origem do estado de tensão interna dos maciços rochosos e apresenta os factores que o influenciam. Apresentam-se as técnicas e a aparelhagem correntemente utiiizada na determinação do estado de tensão, bem como a interpretação dos ensaios mais comuns, dando-se maior relevo aos ensaios com macacos planos pequenos (S F J) e com o extensómetro tridimensional (S T T),efectuados correntemente pelo LNEC.
Ano: 1989
Autor(es): Loureiro Pinto, J.
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Estudo da compartimentação de maciços rochosos por uma técnica de amostragem linear e dos blocos formados pelas descontinuidades - Aplicação a uma galeria do Alto Lindoso
Descreve-se sucintamente uma técnica para amostragem linear de descontinuidades em faces expostas de maciços rochosos e referem-se métodos para tratamento dos dados de campo com vista à definição defamílias de descontinuidades e caracterização de uma forma estatística da sua orientação, espaçamento e extensão. Apresentam-se os resultados obtidos para o caso de uma galeria subterrânea no aproveitamentohidroeléctrico do Alto Lindoso. Para as famílias de descontinuidade identificadas apresenta-se um estudo dos blocos tetraédricos que se poderão formar nas diferentes faces de rocha e analisam-se as suas condições de estabilidade.
Ano: 1989
Autor(es): Lamas, L.
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Relatório de actividades do estagiário de investigação António Lopes Baptista
N/A
Ano: 1988
Autor(es): Batista, A. L.
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Aplicação do método dos elementos de fronteira na análise de estruturas subterrâneas
Apresentam-se, neste relatório, modelos numéricos baseados no método dos elementos da fronteira, desenvolvidos no LNEC para análise de estruturas subterrâneas. Tecem-se algumas considerações sobre o método dos elementos de fronteira, descrevem-se os modelos desenvolvidos para equilíbrios planos e tridimensionais e apresentam-se alguns exemplos de aplicação.
Ano: 1985
Autor(es): Lamas, L.; Frazíllio, E. M.; Sousa, L.; Martins, C. S.
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Modelo tridimensional de elementos de fronteira para análise de estruturas subterrâneas
N/A
Ano: 1984
Autor(es): Lamas, L.
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Estudo das fundações da barragem de Cabora-Bassa - lº. Relatório (Deformabilidade e fluência do maciço rochoso e das rochas constituintes da fundação da barragem)
N/A
Ano: 1969
Autor(es): Peres Rodrigues, F.; Loureiro Pinto, J.; Almeida, A. C.
Keywords: Maciço rochoso; Fundação de barragem; Barragem de Cabora-Bassa
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Estudo das condições de fundação dos contrafortes da barragem do Caia
N/A
Ano: 1966
Autor(es): Silveira, A. F.; Peres Rodrigues, F.; Barroso, M.
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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 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
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
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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