Artigos de Revista

A numerical model for the hydromechanicalanalysis of masonry dams based on the discrete elementmethod is presented. The dam and the rock foundation arerepresented as block assemblies, and a coupled flow-stressanalysis is performed in an integrated manner for the entiresystem. Complex block shapes may be obtained byassembling elementary blocks into macroblocks, allowingthe application of the model to situations ranging fromequivalent continuum to fully discontinuum analysis.A contact formulation was developed based on an accurateedge

An image analysis technique is used to estimate the two-dimensional instantaneous densityfield of unsteady gravity currents produced by full-depth lock-release of saline water. Anexperiment reproducing a gravity current was performed in a 3.0 m long, 0.20 m wide and0.30 m deep Perspex flume with horizontal smooth bed and recorded with a 25 Hz CCD videocamera under controlled light conditions. Using dye concentration as a tracer, a calibrationprocedure was established for each pixel in the image relating the amount of dye uniformlydistributed in the tank and the greyscale values in the corresponding images. The results areevaluated and corrected by applying the mass conservation principle within the experimentaltank. The procedure is a simple way to assess the time-varying density distribution within thegravity current, allowing the investigation of gravity current dynamics and mixing processes.

Neste artigo apresentam-se as linhas gerais da Estratégia de Investigação e Inovação (I&I) do Laboratório Nacional de Engenharia Civil para o período 2013-2020 e refere-se a contribuição do LNEC, enquanto instituição de I&I parceira das universidades portuguesas, para o ensino superior em engenharia civil.

Pluvial or surface flooding can cause significant damage and disruption as it often affects highlyurbanised areas. Therefore it is essential to accurately identify consequences and assess the risksassociated with such phenomena. The aim of this study is to present the results and investigate theapplicability of a qualitative flood risk assessment methodology in urban areas. This methodologybenefits from recent developments in urban flood modelling, such as the dual-drainage modellingconcept, namely one-dimensional automatic overland flow network delineation tools (e.g. AOFD) and1D/1D models incorporating both surface and sewer drainage systems. To assess flood risk, theconsequences can be estimated using hydraulic model results, such as water velocities and waterdepth results; the likelihood was estimated based on the return period of historical rainfall events. Totest the methodology two rainfall events with return periods of 350 and 2 years observed inAlcântara (Lisbon, Portugal) were used and three consequence dimensions were considered:affected public transportation services, affected properties and pedestrian safety. The most affectedareas in terms of flooding were easily identified; the presented methodology was shown to be easyto implement and effective to assess flooding risk in urban areas, despite the common difficulties inobtaining data.

The occurrence of discoloured water at the tap is one of the most frequent reasons for customers tocomplain. Water discolouration arises from the re-suspension of loose deposits (LD) that accumulatein drinking water pipes, due to velocity increase. Because of its typical brownish/reddish colour,discoloured water is traditionally perceived as a consequence of cast-iron pipe corrosion, even innetworks devoid of cast-iron pipes. Current approaches for LD sampling imply the use of high flowvelocities within the range of those used for pipe self-cleaning (0.40 m/s) and/or pipe cleaning(1.50 m/s). Although useful for quantitative identification of critical zones and diagnosis of LDaccumulation, the application of such high-velocities as routine methodologies for LD sampling maybe difficult to perform on the field and provide samples with materials other than discolourationcausing LD. In this study, sampling velocities from 0.02 to 0.52 m/s yielded relatively large samples(up to 2 g dry weight), thus allowing for extensive qualitative LD analysis and testing. Samplerepresentativeness was analysed through the characterisation of LD key-constituents total iron (Fet)and volatile solids (VS). Turbidity decay trends showed the flocculent behaviour of discolourationcausing LD.

A presente comunicação descreve as temáticas desenvolvidas no âmbito da conceção e desenvolvimento de um sistema óptico de visão computacional visando a medição do deslocamento tridimensional a V2 vão da viga de rigidez de pontes suspensas. É apresentado o estado da arte no que respeita a sistemas de medição dimensional a longa distância e é mencionada a motivação para o recurso aos sistemas ópticos de visão computacional. Descrevem-se os principais aspetos do método de medição proposto, em particular, os sistemas de compensação da refração atmosférica e do comportamento dinâmico relativo a câmaras e turbulência atmosférica. É, ainda, descrito o processo de simulação numérica visando a validação dos algoritmos de suporte computacional desenvolvidos neste contexto, nomeadamente, no que respeita aos algoritmos de reconhecimento de alvo, parametrização, triangulação e redundância. Finalmente, é exposto o conjunto de atividades experimentais planeadas para a caracterização do sistema óptico de medição proposto mediante ensaio metrológico e calibração com recurso a protótipo de padrão de referência, assegurando-se a rastreabilidade do sistema de medição ao SI de Unidades e o conhecimento do seu nível de exatidão suportado na respetiva avaliação de incertezas de medição.

The microstructural development of lime putty is widely recognized and commonly associated with an increase in quality. Many heritage institutions encourage the systematic application of lime putties in conservation; however, all the issues associated with age are not fully understood. Changes occur during storage underwater, which traditionally took place in pits to prevent carbonation. The properties of mortars, plasters, and decorative finishes formed from lime putties are intimately linked to manufacturing parameters such as storage time. The hydration of calcium oxide was investigated using an environmental scanning electron microscope with particular attention to the nucleation of calcium hydroxide crystals on the surface of calcium oxide. Crystal modifications were monitored. The results obtained confirm and quantify the influence of slaking time in the microstructure of lime putties that is also reflected in the current referred special characteristics of the mortars produced with them, such as greater plasticity, water retention, and reactivity of mortars. The results also emphasize that the most significant microstructural changes of the lime putties start to consolidate after 8 months of slaking and appear to continue to develop, even though at a slower rate, until at least 5 years.

The concrete degradation caused by internal expansive reaction (IER) is a problem that affects many structures in the world. These reactions, which include the alkali-silica reaction (ASR)and the internal sulphate reaction (ISR) related with delayed ettringite formation, are very dangerous, due the expansive behavior of products formed, that cause the cracking of concrete. So it is urgent to find preventive methods to avoid or mitigate the onset of these reactions in new structures. This work aims to show the applicability of sludge from a tungsten mine in the mitigation of the IER. To evaluate the effect of sludge in the mitigation of ASR and ISR, mortar and concrete mixes were produced with 30% (%in mass) of cement replacement. The results obtained so far allow stating that tungsten mine sludge as Portland cement replacement could be effective in the ASR and ISR mitigation.

A predictive model integrating adsorption kinetics and competitive isotherm models (Homogeneous Surface Diffusion Model, Freundlich-type and Fritz& Schlunder isotherms) was developed to describe and understand the competing mechanism(s) and the ionic strength (IS) role on microcystins (MC) and tannic acid (TA) competitive adsorption. The developed model showed good agreement with the experimental data obtained from batch adsorption tests and isotherms conducted with MC extracts and TA model solutions (single-solute and multicomponent, IS presence and absence) using a mesoporous powdered activated carbon (PAC). Results con

A predictive model integrating adsorption kinetics and competitive isotherm models (Homogeneous Surface Diffusion Model, Freundlich-type and Fritz & Schlünder isotherms) was developed to describe and understand the competing mechanism(s) and the ionic strength (IS) role on microcystins (MC) and tannic acid (TA) competitive adsorption. The developed model showed good agreement with the experimental data obtained from batch adsorption tests and isotherms conducted with MC extracts and TA model solutions (single-solute and multicomponent, IS presence and absence) using a mesoporous powdered activated carbon (PAC). Results confirm that similar size molecules such as MC and TA are strong competitors and tannin-rich waters may severely affect MC residuals in the treated water. Unlike usually considered, both direct site and pore blockage mechanisms seem relevant. Competition effects appear to be more dependent on the competitor/contaminant molar ratio than on the initial concentrations. The IS affects the extent and the mechanisms of MC-TA competitive adsorption, reducing PAC dose for safe control of MC residuals. The developed model, including a Ds analysis, is an important tool to understand the competitive adsorption of similar size adsorbates.