5678 research outputs found
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Ensaios de resistência ao fogo de ligações viga-pilar em madeira
No full textNesta comunicação são apresentados os resultados de uma extensa campanha
experimental relativa à resistência ao fogo de ligações estruturais viga-pilar, em madeira, sujeitas a esforço transverso. Nesta campanha, o comportamento ao fogo destas ligações foi abordado de forma sistemática, tendo sido ensaiadas várias tipologias vulgarmente utilizadas, contribuindo-se de forma significativa para o estudo do seu desempenho em situação de incêndio e para o desenvolvimento de métodos de dimensionamento.Os autores agradecem à Fundação para a Ciência e a Tecnologia (Bolsa de Doutoramento
SFRH-BD-70459-2010).12415ppDE/NEM201426 a 28 de novembr
Internal Expansive Reactions in Concrete Structures – Deterioration of the mechanical properties
No full textA significant number of problems related to concrete deterioration have been detected in Portugal and worldwide as a result of the deleterious development of internal expansive reactions (IER). Their negative effect has important economic implications because they are the main cause of degradation of large concrete structures (e.g. dams and bridges). In addition, the work necessary to remediate the problem involves large areas of reconstruction and complex and expensive rehabilitation techniques and materials. Moreover, IER diminishes the affected structure service life, may involve the interruption of its function and, ultimately, can lead to its decommissioning and demolishing. The importance of these structures, the number of structures in which IER was already identified or is very likely to be diagnosed in a near future, the large number of structures that are under or planned for construction, which may also come to develop IER is why, today, they are still a major concern. Therefore, a study is being conducted at LNEC to diminish the negative impact of IER by increasing knowledge on how to reliably assess their extent and potential for future development in existing structures, so that the risks to structural integrity and need for mitigation/remediation actions can be properly assessed. To study the effect that internal expansion has in the deterioration of the concrete mechanical properties, the common practice is to perform tests on specimens exposed to an artificial environment that promotes IER. However, these tests take several months or even years to produce results. Thus, this communication presents the preliminary work carried out to devise a method capable of producing internal damage to concrete in a short period and in a way that the produced deterioration affects the concrete mechanical properties similarly to IER. From the several methods studied, one appears promising and it is detailed in the main body of the paper.DM/NBPC20141 a 4 de Setembr
Linking water consumption smart metering with census data to improve demand management
No full text17papresentação oralDHA/NES201421 a 26 de setembr
Viver ao nível térreo - I. Habitações térreas e opções domésticas e urbanas
No full textUma das grandes opções de viver o habitar – habitação e vizinhança e vice-versa – joga-se, sempre que tal é possível (e assim foi, frequentemente, ao longo de milénios), na escolha de habitações que tenham relação direta com o espaço público ou de uso público, ou indireta através de espaços exteriores de uso privado (quintais e pátios privativos); uma opção que se sintetiza com a ideia de poder “viver ao nível térreo”, ou bem perto dele e um viver ao nível térreo que é, também, viver mais intensamente a natureza e o exterior de vizinhança.3 fig5 pInfohabitar, Ano X, n.º 475DED/NUTRevista Infohabita
Durabilidade das estruturas de betão nas EN 206 e EN 1992-1-1. Uma perspetiva para 2020
No full textAs prescrições clássicas relativas à durabilidade das estruturas de betão encontram-se atualmente distribuídas pelas normas europeias EN 206 e EN 1992-1-1. Vem-se assistindo a uma pressão crescente para substituir estas prescrições baseadas na composição do betão por outras centradas no seu desempenho. Por outro lado, a durabilidade é sem dúvida uma parte do projeto de estruturas, sendo previsível que as correspondentes disposições venham a ser centradas no eurocódigo relevante, assumindo a EN 206 o estatuto principal de norma de produto. Neste artigo faz-se uma análise da situação atual e apresenta-se uma perspetiva da evolução da normalização no domínio da durabilidade das estruturas de betão, tendo como referência o documento elaborado por um grupo de trabalho conjunto dos dois comités do CEN que tratam do betão e dos eurocódigos estruturais.1-16ppDM/CHEFI
Optical measurement of the alteration kinetics of porous building materials during salt crystallization
No full textIn salt crystallization tests, porous building materials are typically subjected to extreme conditions, such as high temperatures or successive wet/dry cycles, in order to obtain measurable changes within a reasonable period of time. However, the unrealistic testing conditions may distort the results. This can be particularly significant for salts such as sodium sulfate, which can give rise to massive contact- or temperature-induced crystallization processes that hardly occur in the architectural heritage.
Here, we propose a new method where the small changes undergone by the porous material are measured by a non-contact optical technique at the micrometer scale. This allows using test conditions more representative of those that generally occur on site. Topographic profiles are obtained during the process, from which an alteration kinetics curve is afterwards calculated [1]. The alteration curve can be combined and compared to the drying kinetics curve since the system, due to a recent update, permits simultaneous gravimetric measurements [2]. It also allows carrying out time-lapse photography, which may provide animations of the macroscopic alteration process.
We report, as an example, sodium sulfate crystallization tests consisting of a single isothermal drying event at 20ºC and 50% RH. The tests were performed on natural stones, relevant for the architectural heritage, which developed either delamination or simply efflorescence. Both types of alteration were successfully characterized by the above described method. The results show that, under the chosen conditions, sodium sulfate can develop decay patterns similar to those frequently observed on site.
The proposed method opens new perspectives for the development of salt crystallization tests that are more appropriate than those currently available to study decay processes and to evaluate materials and treatments for the architectural heritageThis work was performed under the research project DRYMASS (ref. PTDC/ECM/100553/2008) which is supported by national funds through the Fundação para a Ciência e a Tecnologia (FCT) and LNEC.55155DM/NBPC201411-13 Jun
A comparison of wave characteristics at Caparica beach, Portugal, using in-situ and transferred wave data
No full textThe HIDRALERTA system is current1y being implemented as a novel ear1y warning system to assess the risk of flooding in coastal and port region areas. With forecasted sea wave conditions at coastal and port areas, the system is able to determine the effects of waves in terms of wave overtopping and flooding, to compare those results with pre-specified thresholds, to build alert maps, and, if necessary, to issue alert messages. The system will be applied to two case studies: Praia da Vitória harbor, in Terceira Island, Azores, and Caparica beach, near Lisbon. One of the major inputs of this integrated system is the characterization of sea wave conditions at the site of interest, so that both measured wave data and selected numerical models are used. Numerical models, however, should be calibrated for each area of application. This paper is a contribution to get a better insight of the wave characteristics at one of those case studies, the Caparica beach, to provide adequate calibration of the mentioned numerical models. Therefore, two measurement campaigns were organized at that location, using several instruments. Data was collected and analyzed, then compared with those transferred from the Port of Lisbon wave buoy, by using numerical wave propagation models, which then enabled one to evaluate SWAN's performance and to calibrate some of its parameters. Thus, the paper describes the sea wave characterization using both in-situ data and transferred data from the Port of Lisbon wave buoy, and discusses the SWAN' s strengths and weaknesses to simulate the
wave conditions measured at the two above mentioned campaigns.161-170ppCoastlab 2014 - 5th International Conference on The Application of Physical Modelling to Port and Coastal ProtectionDHA/NP
Discolouration loose deposits: balancing views and practices
No full textTap water discolouration incidents may occur due to resuspension of loose deposits (LD) that accumulate in drinking water distribution systems (DWDS), due to velocity increases or rapid changes. While lowering the consumers’ confidence in tap water’s safety, they are often a cause of customer complaints, especially when recurrent. Owing to the lack of knowledge on LD dynamics and build-up processes in DWDS, however, LD control and prevention strategies are still ineffective to counteract LD accumulation and prevent tap water discolouration incidents. In this paper, supported by relevant literature and results from a four year study on LD sampling and characterisation, a conceptual model for LD dynamics and build-up processes in DWDS is proposed. The model description together with the expected LD build-up rates were used to interpret discolouration phenomena. The model’s practical implications and recommendations were also discussed, including the potential strategies for LD control and prevention in DWDS. Overall, it was concluded that LD accumulation is most critical at mid-range velocities and that, under this range, it may occur exponentially in DWDS. The possible changes in the relative composition of LDs occurring over accumulation were studied and related with LD resuspension potentials, along with LD ageing and residence times.8 pComunicação apresentada no Congresso Mundial da Água, 2014DHA/NE
Avaliação da probabilidade de ocorrência de galgamentos não admissíveis no posto 2 do Terminal de granéis líquidos do porto de Sines
No full textDescrevem-se os procedimentos para avaliar o caudal médio galgado sobre um trecho de um quebra-mar de taludes
a partir das caraterísticas da agitação marítima incidente no mesmo trecho. Apresenta-se uma metodologia para
estimação de valores extremos daquele caudal, partindo das séries temporais da mesma variável, e ilustram-se esses
procedimentos num trecho do molhe oeste do porto de Sines que protege o posto 2 do terminal de granéis líquidos da
ação da agitação marítima. Este regime de extremos do caudal médio galgado é fundamental para a avaliação do risco
de ocorrência de galgamentos não admissíveis no posto 2.131395-113pp21DHA/NPETerritoriu
Alteration kinetics of natural stones due to sodium sulfate crystallization: can reality match experimental simulations?
No full textSalt decay is a very destructive mechanism that frequently affects the porous building materials of our architectural heritage. Sodium sulfate is one of the salts found in this context. It usually demonstrates high destructive power in salt crystallization tests because it can crystallize not only during evaporative processes but also when the temperature drops or when the salt solution comes into contact with pre-existing crystals. However, the use of extreme temperatures or successive wet/dry cycles also makes these tests unrepresentative of reality.
To verify whether sodium sulfate can also be so destructive in field conditions, we have performed crystallization tests consisting of a single isothermal drying event. Three natural stones, relevant for the architectural heritage, were used for the purpose: Bentheimer sandstone, Ançã limestone, and a current Portuguese limestone of low porosity. The stones gave rise to distinct salt decay patterns: efflorescence, multilayer delamination and unilayer delamination, respectively. These morphological alterations were characterized at the micrometre scale by a new method based on what we have called the alteration kinetics curve. Such curve is calculated from topographic profiles obtained by a non-contact optical technique. The multilayer and unilayer delamination decay were also monitored by time-lapse photography.
The work led us to conclude that sodium sulfate can indeed be also very destructive in field-representative conditions. Moreover, it showed that the optical method can be a valuable aid in the development of more realistic salt crystallization tests.This work was performed under the research project DRYMASS
(ref. PTDC/ECM/100553/2008) which is supported by national funds through the Fundação para a Ciência e a Tecnologia (FCT) and the Laboratório Nacional de Engenharia Civil (LNEC).102NAWe are grateful to Tiago Enes Dias for carrying out the time-lapse photography. We would like to acknowledge also the contributions, in different aspects of the work, of Silvia Pereira, José Delgado Rodrigues, Veerle Cnudde, Timo G. Nijland, Manuel Francisco Pereira, Leo Pel, João Palma, Luís Nunes, José Costa and Graça Tomé.NADM/NPCEnvironmental Earth Science