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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

Micromechanical modelling based on the Discrete Element Method (DEM) has been widely used to investigate asphalt behaviour due to its ability to represent an irregular microstructure with variable-sized aggregates, bitumen and voids. The 3D rigid particle models with randomly distributed spherical particles and adopting elastic and/or simple viscoelastic models at the contacts are the standard approach, however, in recent years, a significant research effort is noted to incorporate real particle morphologies in the numerical models.In this study, a previously developed 3D DEM model of asphalt employing a generalised Kelvin contact model formulation for the viscoelastic contacts is further improved with realistic particle shapes representing the coarse aggregates. A digital library of aggregate shapes was created from the X-ray computed tomography (CT) scan of an asphalt specimen, using an adaptive image-processing method to separate the aggregates in the CT images and the Delaunay triangulation method to define the aggregate 3D surface model. Several virtual aggregates with different sizes were selected from the library to represent the coarse aggregate gradation of the modelled 3D DEM asphalt specimen. Each virtual aggregate is discretized with smaller spherical particles and its deformability is taken into account through the inner particle contacts. The numerical asphalt specimens with realistic particle shapes were submitted to uniaxial tension-compression cyclic tests to determine the stiffness properties, and the results were compared with those of the numerical specimens with all constituents represented by single spherical rigid particles. As shown, the proposed methodology greatly enhances the 3D DEM model's ability to simulate the asphalt behaviour.

A avaliação da resposta dinâmica das obras e o acompanhamento da evolução do seu comportamento durante as várias fases da vida é muito importante, estando inserida nas atividades do controle de segurança estrutural. A barragem do Baixo Sabor possui sistemas de monitorização dinâmica em continuo e sísmica, tendo sido realizados dois ensaios de vibração forçada para duas cotas de albufeira. Foram desenvolvidos modelos numéricos incorporando o conjunto barragem-fundação-albufeira, calibrados com os resultados experimentais. Apresentam-se os resultados dos modelos numéricos desenvolvidos para vários níveis da albufeira comparando com a monitorização, durante a operação normal e a ocorrência de eventos sísmicos, verificando-se uma boa concordância.

The Baixo Sabor dam is a 123 meters high concrete arch dam located in the north of Portu-gal. After the performance of a forced vibration test, a quite unique experimental programme was initiated in the dam during the first filling of the reservoir, with the installation of a con-tinuous dynamic monitoring system in December 2015. The implementation of such a system aimed to study the evolution of the dam

Stability analysis of rock slopes is an exercise that poses a variety of challenges to arock engineer. Field information is often lacking and subjective modelling of the rock mass isrequired. Expert judgment also influences the quantification of the targeted safety level, reflectingthe confidence of the designer in his own assumptions and hypothesis. With the introduction of theEN1997 in Europe, structural reliability concepts were brought to the design of geotechnicalstructures, now also including rock masses after its current revision. Yet, fully-probabilistic methodsare still considered valid alternatives to the partial safety method recommended there. Understandinghow to address rock engineering problems from a probabilistic perspective becomes essential tomove beyond the traditional practice. In this study, a simple problem relating to the stability of a rockslope is explored. Limit states for foreseeable failure mechanisms are defined and the systemreliability problem is formulated and solved.

O artigo considera um caso de estudo intencionalmente simples

The Castelo do Bode hydraulic tunnel is part of the Lisbon water supply system. During its con-struction a monitoring system was implemented, aiming at monitoring the behaviour of the con-crete tunnel lining and of the surrounding rock mass, and including visual inspections.This work presents the monitoring system and introduces the relevant aspects of the analysis of the tunnel lining behaviour, based on the observed structural response to the imposed actions, namely the hydrostatic internal and external pressures, thermal variations, contact pressures and time effects. Two types of models are used: i) a structural model, based on axisymmetric analyt-ical solutions of concentric permeable rings allows setting a reference situation from which it is possible, by comparison, to assess the tunnel

This paper presents the analysis, interpretation and prediction of the structural behavior of CahoraBassa dam, which concrete is affected by a moderate ongoing swelling process, of the alkali-silica (ASR)type. To estimate the evolution of the dam

Uma das técnicas de reforço usadas na reabilitação e reforço estrutural de paredes deedifícios antigos em alvenaria de pedra é o confinamento transversal simples através deelementos de aço fixados perpendicularmente à parede. Neste estudo apresenta-se osresultados numéricos da simulação de ensaios de compressão simples de paredes reforçadoscom esta técnica, utilizando um modelo de partículas 2D (MP-2D). Os estudos numéricosapresentados demonstram que os modelos do tipo MP-2D apresentam uma boa concordânciacom ensaios experimentais, nomeadamente no acréscimo do valor máximo em compressãosimples. Demonstra-se assim, que os modelos MP-2D podem ser adotados nodesenvolvimento de soluções de reforço deste tipo, nomeadamente na definição dascaracterísticas das barras, posicionamento e quantificação.

This paper presents the study of the influence of temperature and stress field seasonal variations in thedevelopment of concrete swelling in dams, considering the case study of Covão do Meio arch dam, inPortugal, which concrete is affected by a moderate ongoing swelling process, of the alkali-silica (ASR)type, and which reservoir empties every year in the dry season.In a first step, a three-dimensional model of the dam and of the rock mass foundation, solved by thefinite element method, was used for the interpretation of the dam

A barragem do Covão do Meio, localizada na vertente sul da serra da Estrela a uma altitudede 1650 m, é uma estrutura em abóbada com 28 m de altura máxima cujo betão está afetadopor reações expansivas de moderada magnitude, do tipo álcalis-sílica.Para interpretar o comportamento observado da barragem e os efeitos estruturais dasexpansões, desenvolveram-se modelos de elementos finitos da obra, nas vertentes estruturale térmica, tendo os resultados da modelação apresentado uma boa concordância comresultados da observação contínua. Numa segunda fase foi feita a previsão docomportamento da obra para um horizonte temporal de 20 anos, tendo em conta dois cenários,um otimista, em que as expansões estabilizam a médio prazo com valores finais moderados,e um pessimista, em que o potencial remanescente de expansão é mais significativo.

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.