Artigos de Revista

In its lifetime, a dam can be exposed to significant water level variations and seasonal environmental temperature changes. The structural safety control of a concrete dam is supported by monitoring activities and is based on models.In practice, the interpretation of recorded concrete dam displacements is usually based on HST (hydrostatic, seasonal, time) statistical models. These models are widely used and consider that the thermal effect can be represented by a seasonal function. The main purpose of this paper is to present an HTT (hydrostatic, thermal, time) statistical model to interpret recorded concrete dam displacements. The idea is to replace the seasonal function with the use of recorded temperatures that better represent the thermal effect on dam behavior.Two new methodologies are presented for constructing HTT statistical models, both based on principal component analysis applied to recorded temperatures in the concrete dam body. In the first method, principal component analysis is used to choose the thermometers for the construction of the HTT model. In the second method, the thermal effect is represented by the principal components of temperature of selected thermometers.The advantage of these methods is that the thermal effect is represented by real temperature measured in the concrete dam body. The HTT statistical models proposed are applied to the 110m high Alto Lindoso arch dam, and the results are compared with the HST displacement model.

A partir do estudo antropológico – desenvolvido no bairro da Mouraria, em Lisboa, onde se reflectiu sobre a articulação entre o campo de significações do bairro, os espaços e as experiências de distintos indivíduos, discute-se a tentativa de renovação de certos símbolos urbanos identitários, valores e representações, através do fomento de ideias como cidade plural, multicultural e/ou intercultural. O objectivo aqui é demonstrar que tais processos de reconstrução e reinvenção da imagem do bairro são também atravessados por contrariedades e desarmonias que importam conhecer, designadamente no âmbito da relação entre cidade e cidadania. No desenvolvimento do argumento desta reflexão, infere-se que as práticas de uso e apropriação dos espaços públicos interferem de forma decisiva no processo de construção de imagens identitárias locais que, entretanto, se inscrevem na paisagem urbana, fazendo também parte do conhecimento que se tem da cidade. Considerando que estas práticas se revelam através de alguma ‘visibilidade’, parte-se do princípio que o conhecimento dos processos de uso e apropriação do espaço, que contribuem para a construção de paisagens urbanas e culturais, pode ser importante no revelar da invisibilidade social em que se encontram muitos dos sujeitos identificados com a condição de imigrante.

Projected rates of global sea level rise and human pressures have increased attention to the potential for landformchange in estuaries. This paper assesses the status of the fetch-limited beaches in the Tagus estuary, one of the largestestuaries in Europe, with a focus on distinguishing active beaches from inactive vegetated banks and identifyingconditions under which they change state. A total of 26 beaches were identified in the inner estuary and 49 in thetributary basins on 2007 aerial photographs and compared with conditions on older photographs (1944-1958). Lengths,widths and maximum fetch distances for beaches were measured and site visits were made to determine their originsand present conditions. Beaches occur at eroding uplands or marshes or on spits extending from eroding uplands.Human-created beaches occur on spoil areas, within niches formed by structures and where vegetation is eliminated orprevented from colonizing (e.g. boat launches and recreational surfaces). Basin infilling, with increase in the elevationof low tide terraces and the formation of bars, is reducing wave energies, and some beaches are reverting to vegetatedbanks. Beaches that become vegetated banks because of human actions occur where use for boating or recreation isabandoned and where spits that form off spoil deposits reduce fetch distances upwind.

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La tentative de saisir la complexité de la question urbaine à travers le prisme de la diversité des êtres urbains et de leur inscription dans des entités culturelles ou sociales fixes ou figées, peut conduire à occulter de multiples aspects qui caractérisent à la fois leurs rapports à l

The evolution of numerical modelling in rock mechanics has made possible a more realistic representation of thebehaviour of rock masses, and a more reliable prediction of the response of rock engineering structures. Discontinuum modelling techniques, namely the discrete element method, based on the explicit representation of the rock mass discontinuous structure, have progressively acquired a broader role. In this lecture, the essential concepts and main features of these numerical techniques are discussed, with reference to their historical development. The use of these idealizations is exemplified by two areas in which they proved very effective. On one hand, the analysis of practical rock engineering problems, intended, for example, for safety assessment or monitoring interpretation. This type of application is illustrated herein by dam foundation analyses based on deformable block models.Asecond level of discontinuum modelling involves research aimed at the understanding of the fundamental behaviour of rock and rock masses. An example of this approach is the analysis of fracture phenomena with particle models, primarily of laboratory specimens, but being extended to larger scales. Critical issues identified in the effective application of these modelling tools are examined, as well as some foreseeable evolution trends.

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Abstract Salt decay is one of the most harmful and complex deterioration mechanisms of porous building materials in architectural heritage. Despite several decades of research, it is still insufficiently understood, which hampers the development of effective treatments and prediction models. One key aspect is the influence soluble salts have on the evaporative drying of porous materials. It is often observed, for example, that drying is slower for higher salt concentrations. However, there is still no consensus as to why it happens. In this article, we examine experimentally the drying kinetics of three natural stones impregnated with solutions of sodium chloride or sodium nitrate with different concentrations. The method consisted of the following sequence of determinations: capillary absorption, drying kinetics, vapour pressure and vapour conductivity. It also included a morphological analysis of the efflorescence formed during drying. We have concluded that the slower drying rate was mainly due to the reduced sorptivity that arises at higher salt concentrations. In the cases where compact salt crusts formed on the surface of the stone, therewas an additional reduction in the drying rate because these crusts obstructed vapour transport. However, in most cases, efflorescence was porous and had negligible obstructive effects. Efflorescence morphology is conditioned by well-determined causal factors, such as porosity, pore size and mineralogical structure of the stone, or the type of salt and its concentration. Here, it also revealed that it incorporated a component of unpredictability. This suggests that it may be necessary to move beyond purely deterministic approaches to salt decay.

The present work experimentally investigates the dynamics of unsteady gravitycurrents produced by lock-release of a saline mixture into a fresh water tank. Seven differentexperimental runs were performed by varying the density of the salinemixture in the lock andthe bed roughness. Experiments were conducted in a Perspex flume, of horizontal bed andrectangular cross section, and recorded with aCCD camera. An image analysis techniquewasapplied to visualize and characterize the current allowing thus the understanding of its generaldynamics and, more specifically, of the current head dynamics.The temporal evolution of bothhead length and mass shows repeated stretching and breaking cycles: during the stretchingphase, the head length and mass grow until reaching a limit, then the head becomes unstableand breaks. In the instants of break, the head aspect ratio shows a limit of 0.2 and the mass of the head is of the order of the initial mass in the lock. The average period of the herein calledbreaking events is seen to increase with bed roughness and the spatial periodicity of theseevents is seen to be approximately constant between runs. The rate of growth of the mass atthe head is taken as a measure to assess entrainment and it is observed to occur at all stagesof the current development. Entrainment rate at the head decreases in time suggesting this asa phenomenon ruled by local buoyancy and the similarity between runs shows independencefrom the initial reduced gravity and bed roughness.

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