5678 research outputs found
Sort by
Seismic analysis of gravity dams: a comparative study using a progressive methodology
No full textIn structural analysis, it is widely accepted that simplified methods, that require fewer resources, should produce more conservative results, while more sophisticated methods, which require greater resources, allow the calculation of more realistic results. For gravity dams, (i) pseudo-static methods, (ii) pseudo-dynamic methods, (iii) linear time history analysis, and (iv) non-linear time history analysis are common techniques. The aim of this paper is to investigate the effectiveness of a progressive analysis methodology, using the four mentioned methods (i -iv) for seismic analysis, and define the scope of its applicability. The study of 52 gravity dam models, representing dams with different heights and properties, was performed by this progressive methodology, regarding the stress distribution along the base of the dam, the sliding safety factor (SSF) and the permanent sliding of the dam. The results show that the pseudo-static method gives a good approximation of the SSF, but the stresses are generally lower, when compared with the values obtained by more sophisticated method s. The pseudo-dynamic method gives a good approximation of the SSF and the stresses on the base of the dam, while the linear time history analysis did not give additional information for the dams analysed with SSF > 1when compared with the pseudo-dynamic method. The nonlinear time history analysis confirms the dam behavior against a sliding failure scenario, even after the stress redistribution, giving an actual time-history of the SSF and stress during an earthquake. The results show that the proposed progressive methodology, is a beneficial procedure to conduct gravity dam safety assessment.8pCD/C
Modelling water and n in Lisbon Urban Farms
No full textPresentation at the COST Action TU1201, Allotment Gardens in European Cities, 3rd Plenary Session, March 19 – 22, 2014DHA/NR
Monopolos auto-suportados para telecomunicações. A influência dos equipamentos na definição da ação do vento
No full textNeste trabalho são apresentados e discutidos os resultados obtidos num estudo paramétrico realizado com o intuito de quantificar a influência relativa dos equipamentos utilizados em monopolos auto-suportados para telecomunicações, aquando da definição da ação do vento sobre estas estruturas. Pretende-se dar a conhecer a importância global do conjunto dos equipamentos utilizados neste tipo de estruturas, abordando-se ainda algumas matérias particulares como, por exemplo, o efeito de interferência entre antenas e interfaces, o efeito de escudo entre escadas e fuste, e o efeito de bloco dos caminhos de cabos.16pDE/NC
Modeling the beginning of expansion acceleration due to alkali silica reaction in concrete. Part 1- model rationale, structure and parameter evaluation by data fitting
No full textService life, in alkali-silica reaction (ASR) affected concretes, is reached when expansions no longer allow normal use of a structure. ASR expansions are detected only after a long period, accelerating after that, similarly to reactions having an induction period in Chemical Kinetics
This study deals with service life as a conventional induction time, and uses kinetic methods in its estimate. The classical Unreacted Shrinking Core (USC) model with diffusion control and induction time was selected among other models. Both plane and spherical interfaces were considered adapting their models to expansion data. ASTM C 1260 setup and test conditions were selected, its near constant alkalinity being closer to initial conditions in concrete.
Mortar bars prepared with a reactive Tagus river aggregate were tested at temperatures of 80, 70, 60, 50 and 37ºC. Plane and spherical expansion models were fitted to the isothermal curves obtained; depicting their kinetic parameters in Arrhenius plots suggests the spherical model as better. The main interest of this study is to, in what concerns the potential for alkali-silica Reaction (ASR), discuss and foresee possible problems allowing to schedule monitoring and/or the needs of adequate interventions at a stage as early as possible.
The extension of service life allows savings in raw materials and energy, improvement of the investment economics and, on a long term basis, lower investment requirements, contributing to an improvement of the sustainability of all related sectors.10pThe authors thank the financial support provided by Fundação para a Ciência e Tecnologia (FCT), through the project EXREACT (PTDC/CTM/65243/2006).DM/NM
Aniceto Rapozo’s cabinet at the Lisbon Academy of Sciences
No full textFrom the end of the eighteenth until the beginning of the nineteenth century, wood samples were regularly sent to the Royal Army Arsenal in Lisbon for testing. The large number and variety of samples, as well
as increasing interest on Brazil, explain why, in 1805, the Prince Regent of Portugal commissioned the preparation of four collections containing 1,213 timber specimens from Brazil and twelve from other
origins. One of these collections, housed in a cabinet at the Lisbon Academy of Sciences, is now being studied in order to reveal its origins and to identify the wood samples. Botanical identifications will provide
valuable information about the wood resources and the species used by furniture-makers in the late eighteenth and early nineteenth centuries.The authors acknowledge the support of the Fundação para a Ciência e Tecnologia through the Research Project HC/0074/2009, Percurso científico do Património do Museu da Academia das Ciências de Lisboa. They also acknowledge the Fundação Biblioteca
Nacional, Rio de Janeiro; the Natural History Museum, London; the Biblioteca Nacional and the Arquivo Histórico Ultramarino, Lisbon, for access to manuscripts and further documentation.513DE/NCEJournal of the History of Collection
Energy auditing as a tool for improving service efficiency of water supply systems
No full textThe current paper aims at presenting a standardized auditing scheme for assessing energy efficiency in water supply systems. The proposed scheme has been developed based on the existing methodologies and International Water Association (IWA) water
balance principles. The main innovation is the direct link to the water auditing in order to encourage water utilities to carry out the joint management of water losses and related energy efficiency. Key energy efficiency performance indices are calculated
based on the energy auditing without the need of using hydraulic modelling. Two case-studies are explored and discussed. This
paper shows that specific energy consumption and pump efficiency are not sufficient to evaluate the energy efficiency of a given
system. The energy balance proposed herein allows the development of a preliminary diagnosis and the identification of the
critical areas in terms of energy efficiency, and thereby, supports the tactical and operational management of water supply systems.568DHA/NES201414 a 17 de julh
Madeira: um mundo de possiblilidades
No full textQuando, no início de 2007, aceitei o desafio da Construção Magazine para uma colaboração regular na coluna “Estruturas de Madeira”, fi-lo com a esperança de contribuir, de algum modo, para a boa utilização da madeira na construção e para a divulgação do seu interesse e potencial.
Esta coluna procurou tratar alguns aspetos que julguei merecerem atenção, ou por corresponderem a áreas em que se constata com frequência haver ainda lacunas de formação e de informação no meio técnico, no que se refere à madeira e suas aplicações na construção, ou por destacarem abordagens, técnicas ou materiais inovadores, o novo enquadramento normativo.
Seguindo o mote dado no meu primeiro texto – “Estruturas de madeira: tradição e modernidade” – a coluna procurou focar estas duas vertentes. Porque estão interligadas. Porque o saber evolui continuamente, permitindo-nos inovar, mas igualmente olhar de forma crítica as práticas tradicionais. E porque a inovação, além de ser motor de novas realizações, é igualmente suporte de intervenções seguras e sustentadas de reabilitação e salvaguarda do património edificado.
Os diversos textos publicados desde 2007 refletiram certamente uma visão pessoal. Contaram também com a preciosa colaboração de colegas com quem tenho tido a oportunidade, e o gosto, de trabalhar e a quem muito agradeço.159DE/NEMRevista Construção Magazin
Preliminary study of the acoustic behavior concerning an innovative prototype for indoor modular partitioning
No full textThis paper presents a preliminary acoustic study concerning the development of the first prototype of a
patented removable module for interior partitioning. It is a prefabricated, vertical element for division of
interior spaces that does not require the use of gutters or technical support. A set of such modules, linearly
disposed, will create a division, allowing the personalization of any indoor area, including open office spaces,
rooms, among others. The main characteristic that distinguishes this element from the existing solutions
available on the market is that its mobility relies exclusively on a set of integrated bearings at the base of each
module. Through an incorporated elevation system, the user can lower the module, move it to the desired
position and re-elevate it until pressed against the ledge of the ceiling, making it stable. In this sense, and
taking into account its acoustic behavior, several tests were made in the LNEC acoustics lab. Airborne sound
insulation tests for different typologies of the prototype were conducted, according to the applicable
standards EN ISO 354:2003, EN ISO 717-1:2013 and EN ISO 10140-2:2010. Some important conclusions
and analysis of the prototype viability were extracted.758pDED/NAICI201416 a 19 de Novembr
Quality Assessment of Vertical Angular Deviations for Photometer Calibration Benches
No full textLighting, both natural and electric, constitutes one of the most important aspects of the life ofhuman beings, allowing us to see and perform our daily tasks in outdoor and indoor environments. The safety aspects of Iighting are self-evident in areas such as road Iighting, urban Iighting and also indoor Iighting. The use of photometers to measure lighting leveIs requires traceability obtained in accredited laboratories, which must provide an associated uncertainty. It is therefore relevant to study the impact of known uncertainty sources Iike the vertical angular deviation of photometer calibration benches, in order to define criteria to its
quality assessment.7ppSeminário / IMEKO Joint Symposium TC1 - TC7 - TC13 "Measurement Science Behind Safety and Security"CIC/NQ
Rock joint roughness characterization and numerical modelling
No full textAs descontinuidades dos maciços rochosos influenciam o seu comportamento mecânico e hidráulico e consequentemente as obras neles construídas. Este trabalho descreve o desenvolvimento e aplicação de uma técnica de digitalização das superfícies de descontinuidades rochosas que recorre a uma mesa digitalizadora, visando contribuir para a compreensão dos mecanismos de contacto e desgaste. As superfícies numéricas obtidas são analisadas usando parâmetros geo-estatísticos que podem ser comparados com parâmetros semi-empíricos, como o JRC, permitindo quantificar a evolução da rugosidade após ensaios mecânicos de compressão ou deslizamento. Os resultados deste trabalho permitiram ainda a geração de descontinuidades que poderão ser usadas futuramente em modelos micromecânicos de partículas para simular o comportamento mecânico e hidráulico de descontinuidades.5-22pp132DT/NITGeotecni