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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Non-linear seismic analysis of arch dams considering joint movements and a concrete damage model
This paper presents a study on the non-linear seismic response of Cabril arch dam (Portugal), for a load combination including the dams self-weight, the hydrostatic pressure (full reservoir) and the seismic loading (10 s generated accelerograms) applied at the dam base. The main results are presented considering two accelerograms, with peak ground accelerations of 0.2g and 0.6g. The investigation is focused on the effects of the non-linear behaviour of joints on the structural response of an arch dam under stronger earthquakes and on the resulting concrete damage distributions. The numerical simulations are performed using DamDySSA4.0, a 3D finite element program developed in LNEC for dynamic analysis of concrete dams, including a recently developed module for non-linear seismic analysis. The dynamic behaviour of the dam-reservoir-foundation system is simulated using a coupled model in displacements and pressures, considering the dam-water interaction and non-proportional damping, and using a sub-structuring technique to simulate the foundation. The non-linear seismic response is computed using a time-stepping algorithm, based on the Newmark method, and the stress-transfer method. The non-linear behaviour of concrete is considered using an isotropic damage model with softening and two independent damage variables (d+ for tension and d- for compression), and the opening/closing/sliding movements of joints are simulated using joint finite elements and the classic Mohr-Coulomb law, for vertical contraction joints, dam-foundation interface and existing cracks. The aim is to summarise the implemented formulations and show the potential of DamDySSA4.0 for predicting the non-linear seismic behaviour of concrete dams and to support seismic safety verifications.
Ano: 2020
Número Páginas:
605-618.
Autor(es): Alegre, A.; Oliveira, S.
Revista: Proc. 4th Dam World Conference
Editor: DW2020
Volume:
Vol.1.
Keywords: Non-linear seismic analysis, Arch dam, Concrete damage model, Non-linear joints, Dam-reservoir-foundation dynamic interaction
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Preliminary identification of the structural effects of concrete swelling in Chicamba dam (Mozambique)
This paper presents the relevant results of the monitoring data analysis of the Chicamba dam (Mozambique), which confirmed the existence of an ongoing concrete swelling process in the dams body. The performed analysis was based in the qualitative evaluation of the monitoring results complemented with the quantitative interpretation of some physical quantities. The Chicamba dam is a concrete dam, 75 m high, composed by two independent arch structures linked by an artificial abutment, built in two stages in the decades of 50 and 60 of the last century. The monitoring system had the last large rehabilitation and strengthening in 2010 and 2011. The safety control of the dam is based on the data provided by the monitoring system and on regular inspections. About ten years ago, the first signs of alkali aggregate reactions were identified by tests performed in concrete samples extracted from the dams body for the installation of rod extensometers in the foundation. The available monitoring results, namely the displacements measured through plumb lines and by geodetic methods, were properly treated to estimate the swelling structural effects in the last 10 years. These effects are moderate and the apparent cracking is limited to specific areas of the structure, but the accumulated swelling effects over time are not known. To evaluate the development of this pathology, an experimental study using cores to be extracted from the dams body is planned to be carried out.
Ano: 2020
Número Páginas:
833-853.
Autor(es): Dias, I. M.; Batista, A. L.; Campira, J.
Revista: Proceedings of the Fourth International Dam World Conference
Editor: LNEC
Volume:
Volume 1.
Keywords: Swelling effects; Structural behaviour; Monitoring; Chicamba dam
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Seismic analysis of Cabril dam. Measured response and comparison with numerical results from Code_Aster and DamDySSA
This paper presents a study on the seismic response of the 132 m high Cabril arch dam, for an earthquake measured in-situ with the installed Seismic and Structural Health Monitoring system (in operation since 2008). The measured acceleration time histories are compared with results from finite element analysis in various positions in the dam body, using the seismic accelerations recorded at the dam-rock interface as inputs. The numerical simulations are conducted using two programs: i) DamDySSA4.0, a 3D finite element program develop in LNEC for dynamic analysis of arch dams the dam-reservoir-foundation system is simulated based on a coupled model, using a formulation in displacements and pressures, considering the substructure method to simulate the foundation; and ii) Code_Aster, a finite element program developed in EDF dam-water interaction is considered based on the potential fluid approach and the mass of the foundation is taken into account with absorption of the waves radiating from the dam by viscous-spring boundaries around the foundation. The investigation is focused on the required damping ratios, in the dam and foundation, to fit the computed results to the measured response, which is a key aspect to consider in arch dam seismic analysis.
Ano: 2020
Autor(es): Alegre, A.; Robbe, E.; Oliveira, S.
Editor: LNEC
Keywords: Cabril arch dam, Seismic monitoring, FE seismic analysis, Damping, Substructure foundation method, Energy dissipating foundation.
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SEISMIC MONITORING SYSTEMS IMPLEMENTED ON RECENT PROJECTS
In the last decade Portugal made a significant set of investments in new hydroelectric projects under the National Dams Program with High Hydroelectric Potential. EDP Produção SA, a company of EDP - Energias de Portugal Group, played a fundamental role in the construction of these projects, in which new dams and reservoirs of significant dimensions are integrated. According to Portuguese legislation, with relevance to the RSB-Dam Safety Regulation (Decree-Law no. 21/2018 of 28 March), the DTA-Technical Documents to Support the RSB and taking into account the seismic risk associated with the region where the dams were built, it was recommending the implementation of a set of Seismic Monitoring Systems (SMS) to characterize the seismic actions and the respective structural response, as well as the assessment of the reservoirs induced seismicity. For that, it was necessary, in the design phases, to carry out several studies to define the type of dynamic monitoring systems, especially those related to the seismic monitoring systems (SMS). In their most extensive configuration, these systems, based on triaxial accelerometers sensors, may incorporate remote stations installed along the reservoirs for studying the propagation of seismic actions. For the higher dams, and to ensure a good characterization of the dynamic behaviour, continuous dynamic monitoring system (CDMS) was also installed. This paper presents the main aspects of the legislation, refers the main studies and methodologies that were used, and the general aspects of the regional geological and tectonic framework. Also, is presented several seismic monitoring systems that were implemented by EDP, namely those related to the hydroelectric projects of Baixo Sabor, Foz Tua, Ribeiradio and Alto Ceira II dams.
Ano: 2020
Número Páginas:
Fourth International Dam World Conference.
Autor(es): Monteiro, G.; Pinho, P.; Gomes, J. P.
Editor: LNEC
Keywords: Seismic Studies; Seismic Monitoring Systems; Portuguese Legislation; Safety; Dams
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Vibration monitoring of Cahora Bassa dam
This paper focuses on the experience gathered from the continuous dynamic monitoring of Cahora Bassa dam, a 170 m high arch dam in Mozambique, over the past decade. The installed Seismic and Structural Health Monitoring system was designed to continuously record acceleration time series in several locations in the dam body (crest gallery) and near the dam-rock interface, under ambient/operational vibrations and during seismic events, using uniaxial and triaxial accelerometers. The system was complemented with the development of software for automatic modal identification and automatic detection of seismic vibrations. The numerical simulations are carried out using a 3D finite element program, based on a solid-fluid coupled formulation to simulate the dam-reservoir-foundation system, considering dam-water dynamic interaction and propagation of pressure waves throughout the reservoir. The main experimental outputs are presented and compared with results from 3D finite element analysis, including the evolution of identified natural frequencies over time, vibration mode shapes for specific water levels, and the dynamic response in accelerations under seismic ground motion.
Ano: 2020
Autor(es): Oliveira, S.; Carvalho, E.; Matsinhe, B.; Mendes, P.; Alegre, A.; Proença, J.
Editor: LNEC
Keywords: Cahora-Bassa dam, Seismic and Structural Health Monitoring, Modal identification, Natural Frequencies, Seismic response, Finite element analysis.
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Análise sísmica de grandes barragens abóbada com base em modelos de EF3D. Aplicação ao caso de uma barragem com 290 metros de altura
Neste trabalho efetuam-se estudos de simulação numérica da resposta sísmica de uma grande barragem abóbada, considerando uma dada lei de amortecimento de Rayleigh com vista a analisar a influência da cota da albufeira. A modelação do sistema barragem-fundação-albufeira é efetuada com um modelo coupled, baseado numa formulação em deslocamentos e pressões, que permite simular a interação dinâmica barragem-albufeira considerando a propagação de ondas de pressão na albufeira. A discretização do sistema coupled é efetuada utilizando elementos finitos 3D com 20 nós. A resposta sísmica é calculada por meio de integração direta no domínio do tempo com base no método de Newmark. São apresentados os resultados da análise sísmica de uma barragem com 290 m de altura, utilizando acelerogramas sísmicos em três direções, com aceleração de pico máxima de 0.3g na direção montante-jusante. Nomeadamente, analisam-se os campos de deslocamentos e de tensões no corpo da obra para diferentes cotas de água na albufeira.
Ano: 2019
Autor(es): Alegre, A.; Oliveira, S.
Editor: IST
Keywords: Análise sísmica de barragens abóbada; Sistema Barragem-Fundação-Albufeira; Formulação coupled em pressões e deslocamentos.
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Avaliação do comportamento dinâmico da barragem do Baixo Sabor com base em métodos experimentais e numéricos
A determinação da resposta dinâmica das obras e o acompanhamento da evolução do seu comportamento durante as várias fases da vida é muito importante, estando inserido nas atividades do controle de segurança estrutural. A realização de ensaios de vibração forçada em barragens de betão para a determinação do comportamento dinâmico continua a ser uma das técnicas mais fiáveis nesta área. Nesta comunicação descreve-se a metodologia de ensaio, e apresentam-se os resultados relativos a um caso de estudo, referente à caraterização do comportamento dinâmico da barragem do Baixo Sabor. Foi desenvolvido um modelo numérico, com representação do sistema barragem-albufeira-fundação, para apoio na preparação do ensaio e interpretação dos resultados experimentais.
Ano: 2019
Autor(es): Gomes, J. P.; Lemos, J. V.
Editor: Comité Brasileiro de Barragens
Keywords: Modelo numérico Barragens de betão; Ensaios de vibração forçada; Comportamento dinâmico; Barragens de betão
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Avaliação do efeito das explosões de desmonte de rocha em barragens de betão com base num modelo numérico do maciço e barragem e comparação com resultados observados
Os trabalhos de escavação para a implantação de grandes obras, (barragens, centrais subterrâneas, tuneis, etc.) utilizam frequentemente metodologias de desmonte da rocha com recurso a explosivos. Esta técnica sendo rápida e eficientemente produtiva, obriga ao controle da propagação de vibrações no meio circundante com ênfase ao parque edificado e respetivas infraestruturas. Recentemente foram efetuadas obras de aumento da capacidade de descarga de uma barragem de betão, nas quais, foi necessário efetuar desmonte de rocha com o recurso a explosivos nas imediações da barragem existente. Estes pressupostos impulsionaram ao desenvolvido de um modelo numérico híbrido descontínuo de elementos discretos e elementos finitos recorrendo ao 3DEC, representando os blocos da abóbada, as juntas de contração e o maciço de fundação. O objetivo deste modelo é estudar o efeito das vibrações provocadas pelas explosões no comportamento da barragem de betão e respetiva fundação, avaliando a sua segurança estrutural. A correta modelação do comportamento da fundação é fundamental para uma avaliação estrutural adequada. No presente trabalho apresentam-se os resultados do modelo numérico comparando com as medições de velocidades efetuadas em vários pontos da fundação e da estrutura no decorrer das obras, sendo posteriormente analisado os efeitos na barragem. O presente trabalho, deu início ao desenvolvimento de um modelo numérico capaz de representar a resposta da estrutura às vibrações, minimizando a subjetividade da classificação do seu grau de resistência. A elaboração deste modelo numérico permitiu desenvolver novas abordagens para a simulação das explosões, da propagação ao longo do maciço e respetivos efeitos na estrutura. Estas abordagens, devidamente adaptadas, são passiveis de serem implementadas em estudos futuros.
Ano: 2019
Autor(es): Fonseca, R.; Gomes, J. P.; Lemos, J. V.; Resende, R.
Editor: CMN 2019 - Congress on Numerical Methods in Engineering,
Keywords: Método elementos discretos; Modelação numérica; Análise dinâmica; Explosivos; Vibrações; Barragens
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Baixo Sabor concrete arch dam: dynamic monitoring and numerical damage simulation
. The nowadays-available dynamic monitoring equipment integrating very sensitive low noise sensors creates an opportunity to implement continuously operating dynamic monitoring systems in dams and validate the suitability of these systems to monitor such massive structures with the goal of detecting damage. The detection of abnormal structural behaviour, that may indicate the occurrence of damage, can be based on control charts and is associated with shifts in the modal parameters values that are not explained by other physical phenomena but a change in the structures stiffness. To test these statistical tools, modal parameters obtained from real field measured time series may be contaminated with simulated damages. In this context, this paper describes the continuous dynamic monitoring of Baixo Sabor arch dam, which has been carried out by both ViBest/FEUP (Laboratory of Vibrations and Structural Monitoring) and LNEC (National Laboratory for Civil Engineering). Moreover, it is presented the simulation of a set of plausible damage scenarios and their influence in the dam dynamic properties, namely the natural frequencies, with the aim of testing the ability of the said control charts to identify the emergence of abnormal structural behaviour. For this, a numerical model of the dam developed at LNECs Concrete Dams Department has been used.
Ano: 2019
Autor(es): Pereira, S.; Gomes, J. P.; Lemos, J. V.; Magalhães, F.; Cunha, A.
Editor: 3rd Meeting of EWG Dams and Earthquakes
Keywords: simulation of damage; numerical modelling; Continuous dynamic monitoring; Concrete archa dams
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Dynamic behavior of high arch dams under recorded seismic accelerograms. Study on the influence of reservoir water level
In this paper the seismic response of a large arch dam (290 m high), located in a high seismicity region, is analysed. The goal is to study the influence of the reservoir water level in the dams dynamic response under recorded seismic accelerograms. The numerical calculations are carried out using a 3D finite element program (DamDySSA3.0), developed in MATLAB, for linear dynamic analysis of arch dams. The 3DFEM model is based on a formulation in pressures and displacements, considering a state space approach to solve the coupled eigenproblem with damping, while the seismic response is computed by means of direct integration in time domain using the Newmark method. The dam-reservoir-foundation system is discretized using cubic 3D finite elements with 20 nodal points. The seismic analysis of the dam is performed for the Jiashi earthquake (April5, 1997), using the recorded seismic accelerogram as input, and considering two different reservoir water levels, a massless foundation and a global damping of about 5%. The main numerical results are presented, including displacement and acceleration time histories, as well as the hoop and cantilever stresses envelopes.
Ano: 2019
Autor(es): Alegre, A.; Oliveira, S.; Espada, M.; Câmara, R.
Editor: LNEC
Keywords: Seismic response of high arch dams, Recorded accelerograms, Reservoir water level.
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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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