Publicações

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.

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.

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.

Rigid particle models based on the discrete element method (DEM) have been adopted to model creep, fracture, and the viscoelastic behaviour of asphalt mixtures considering an irregular micro-structure and particle contacts. Within a DEM framework, the Burgers contact model, which is known to have a narrow frequency and temperature range, is usually adopted to model viscoelastic properties. In this study, a new explicit three-dimensional generalised Kelvin (GK) contact model formulation for the DEM model is proposed for asphalt materials. The model is implemented following two different methodologies (GK and GK). The models are validated in uniaxial tension-compression sinusoidal tests for predicting the dynamic modulus () and phase angle (

Encapsulated rejuvenators embedded in asphalt mixtures are a promising technology toextend the service life of asphalt pavements. However, their effects on the asphalt mixture

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This paper describes the study of the metrological quality of the excitation force inthe context of force vibration test of concrete dams. For this purpose, a measurementuncertainty evaluation was performed, based on available probabilistic information about theinput quantities

A conjugação entre os modelos numéricos e os resultados observadosdo comportamento das obras é uma ferramenta fundamentalno apoio ao controle de segurança de grandes obras. A barragemdo Baixo Sabor possui um sistema de monitorização dinâmicaem continuo, e foram realizados dois ensaios de vibração forçadapara duas cotas de albufeira. Neste contexto foram desenvolvidosmodelos numéricos da barragem do Baixo Sabor incorporando oconjunto barragem-fundação-albufeira. Neste artigo, apresentamseos resultados dos modelos numéricos desenvolvidos para váriosníveis da albufeira comparando com os resultados experimentais.

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.

he current first generation of Eurocodes is a suite of ten Euro-pean standards for the design of buildings and civil engineeringworks, whose implementation started in 2010. EN 1990 sets thebasis of structural design, with the other Eurocodes dealingwith different materials and specific aspects of design. Geo-technical aspects of design are covered by EN 1997

Os modelos detalhados de partículas, MP, ao terem em consideração a estrutura granular da rocha incluem de forma explícita a aleatoriedade do material e introduzem um tamanho limite à localização do dano. Neste trabalho é apresentado um modelo de partículas rígidas esféricas que tem sido desenvolvido tendo em vista o estudo da fratura em betão e em rocha. A interação entre partículas é definida com base na estrutura de Voronois dos centros de gravidade das partículas esféricas. Adota-se um modelo de contacto múltiplo, no qual a área da superfície de contacto é dada pela área da faceta comum dos Voronois associados a cada partícula. Vários estudos paramétricos são apresentados de modo a demonstrar a influência dos parâmetros micromecânicos, elásticos e resistentes, na resposta macroscópica dos sistemas de partículas.

This paper presents the results of in situ stress measurements and the application of a global interpretation model for evaluation of the most likely in situ stress field in the rock mass of the underground powerhouse cavern of the Salamonde II re-powering scheme, located in a mountainous zone of the North of Portugal. The objective of the study was to obtain the stress field prior to the powerhouse cavern excavation, for design purposes. Overcoring tests were performed in boreholes, before construction started. During early construction stages, when direct access to the vicinity of the cavern was created, flat jack tests were performed. For estimating the most likely state of stress in the rock mass, a global inverse analysis was carried out, which combined the overcoring and the flat jack tests results, using an appropriate methodology and a three dimensional numerical model. In order to assess the influence of time dependent effects on the in situstresses, a viscoelastic gravitational analysis was also performed using the same numerical model. The resultsobtained are compared and discussed.

Neste trabalho apresenta-se um modelo interpretativo tridimensional, que permite estimar o estado de tensão mais provável num maciço rochoso, integrando os resultados provenientes de ensaios de medição do estado de tensão in situ. Apresenta-se o caso de estudo da caverna da central subterrânea do reforço de potência do empreendimento hidroelétrico de Salamonde, localizado no rio Cávado, em Portugal. Neste caso de estudo, foiefetuada uma análise global integrando os resultados de dois tipos de ensaios, realizados em diferentes locais do maciço rochoso: i) ensaios de sobrecarotagem (STT), executados em furos de sondagens, antes de se iniciarem as obras do reforço de potência e; ii) ensaios de reposição de tensões com macacos planos (SFJ), realizados já em fase de execução da obra. Foi utilizado um modelo numérico tridimensional e uma metodologia apropriada, incluindo a geometria das escavações na altura da execução dos ensaios e a topografia do terreno, de forma a permitir uma estimativa do estado de tensão mais provável na zona da caverna da central.

Identification of potential failure mechanisms defined by the rock mass discontinuities or the concrete-rockinterface plays an important role in the safety assessment of concrete dam foundations. The paper presentsinstances of application of discrete elements deformable block models for analysis of these failure scenarios,representing the rock mass foundation and the concrete dam. The rock mass characterization needs and themethodologies for obtaining the input parameters for these models are discussed.

Os ensaios de macacos planos de grande área são utilizados para medir a deformabilidade de maciços rochosos e fornecem dados importantes para o projeto de grandes obras. Este ensaio consiste na abertura de um rasgo no maciço rochoso no qual é inserido um macaco plano de grande área. O macaco aplica pressão às paredes do rasgo através de óleo bombeado para o seu interior e são medidos os deslocamentos no maciço. A maior dificuldade na interpretação do ensaio reside no efeito provocado pela abertura de uma fenda de tração durante a aplicação de pressão pelo macaco plano. Para melhorar a compreensão sobre os efeitos da fenda de tração e assim melhorar a interpretação dos resultados do ensaio, desenvolveu-se um modelo numérico tridimensional do ensaio. O modelo permite estabelecer relações entre a tensão in situ perpendicular aos rasgos, a resistência à tração do maciço, as pressões aplicadas e a profundidade da fenda.

A methodology is proposed for dealing with the unbalanced stresses that arise from numerical models due to topography effects when horizontal stresses are applied at the vertical boundaries. The proposed methodology is used for understanding the role of topography on the distribution of in situ stresses due to both gravity and tectonic loadings. In particular, the influence of Poisson

Recent regulations introduced a limit state approach to geotechnical design by using representative values of the actions and of the strength parameters, partial safety factors that affect them, and by including safety margins in the calculation models. Moreover, Eurocode 7 stresses the importance of making use of test results for establishing ground parameters, and so rock joint shear tests are set to play a relevant role in the assessment of the shear strength required in the design of important projects, such as concrete dams, large bridge foundations, slopes, or underground excavations. In this keynote, joint shear tests are described, along with a presentation of their equipments and different procedures. Test results and calculations for the assessment of relevant shear strength parameters are illustrated, and several topics regarding sampling and variability are discussed. Opportunity is taken to present a practical apparatus allowing to perform simple shear tests (push tests) under very low normal stresses with advantages over tilt or pull tests.

The New Alto Ceira Dam is a 41 m high and 133 m long at the crest concrete arch dam, located in the middle zone of Portugal. The objective of the dam

Este documento descreve a rotura ocorrida na barragem indiana de Bhandardara,constituída por alvenaria, cujas causas estão relacionadas com problemas defissuração e acção da pressão da água no seu interior. O documento apresentatambém uma avaliação da segurança estrutural, com base em modelos numéricoselaborados através do Método dos Elementos Discretos, das obras de reabilitaçãopreconizadas que incluíram a utilização de ancoragens e pregagens.

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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.

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This chapter consists of two parts. First a general overview is given: the exact definition of the Discrete Element Method is provided, and the main types of existing models are introduced; then the theoretical fundaments of the most important approaches available today for masonry analysis are given. The second part of the chapter focuses on 3DEC, the most widespread commercial DEM code for masonry analysis. This second part begins with a theoretical overview. Application issues for masonry structures are then considered (block material behaviour, contact representation, structural elements like cables or bars etc.). Among the practical examples arches, barrel vaults, walls, coloumns and complete structures (like houses) are presented, including the issues of quasi-static versus dynamic analysis and of block fracture as well. The readers can find helpful advice on how to simulate their own problems most effectively.

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Discrete element models have become a major tool for masonry analysis, allowing a suitable representation of its discontinuous nature and marked nonlinear behaviour. The chapter reviews the fundamental assumptions of the main DEM formulations available. It focuses more specifically on the widely used UDEC and 3DEC codes, explaining their relation with the other approaches, and the most relevant issues arising in their application to masonry. Applications to the main types of structures are reviewed, considering both static and dynamic analyses. Recent research providing comparisons of the numerical models with experimental and field data is particularly covered. The discussion of the different examples is aimed at clarifying the key capabilities of DEM and demonstrating the most effective ways of using it in a variety of masonry analysis situations.

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.

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.

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.

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.

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.

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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.

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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-Venant’s 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.

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.

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).

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.

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.

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.