Artigos de Revista

A oferta de produtos de madeira no mercado da construção tem vindo a crescer de forma clara na última década, multiplicando-se a variedade de espécies florestais utilizadas, os tipos de produtos comercializados e, paralelamente, as suas utilizações potenciais. O interesse dos utilizadores e, muito particularmente dos arquitectos, pela madeira prende-se, em grande medida, com o carácter ecológico e o conforto geralmente associados a este material. Interesse que é potenciado pela presente variedade de produtos de construção à base de madeira disponíveis, especialmente na forma de materiais de revestimento de piso e de paredes, para interiores e exteriores. A aplicação de placas de derivados de madeira em painéis de revestimento de fachadas exteriores tem vindo a ser realizada, no nosso País, envolvendo placas de contraplacado marítimo ou placas de laminados a alta pressão (HPL), vulgarmente designadas por placas fenólicas. O mercado tende a considerar o contraplacado como um produto tradicional e menos sofisticado (atendendo à experiência de uso no nosso País), e o HPL um produto sofisticado (face ao pouco conhecimento acerca do seu modo de produção) e inovador (pela ainda reduzida tradição de aplicação). No entanto, ambos são abrangidos pela marcação CE com base em normas harmonizadas (o contraplacado pela EN 13986:2004 e o HPL pela EN 438-7:2005). O desempenho destas placas tem sofrido alguns revezes, que se prendem na maioria das vezes com o desconhecimento da legislação aplicável e com a falta de ensaios de validação da qualidade do produto face à sua utilização (crítica, no caso de investimentos avultados).

N/A

A generalidade das estruturas correntes de madeira actualmente em serviço recorre a ligações por entalhe. Na ausência de elementos metálicos, a transmissão de esforços entre peças é feita principalmente por compressão e corte da madeira, o que limita a sua utilização a situações muito específicas. Elementos metálicos surgem frequentemente adicionados a algumas das ligações, nomeadamente onde é essencial assegurar a transmissão de esforços de tracção, sendo comum os esquadros metálicos, aplicados nas faces dos elementos que convergem na ligação, as braçadeiras, que cintam os elementos em torno da ligação, e as cavilhas, que os atravessam. Em Portugal, ligações de tipo tradicional com recurso a entalhe são encontradas correntemente em asnas de cobertura com vãos geralmente inferiores a 12 metros, verificando-se contudo uma grande diversidade no que se refere à qualidade de execução das respectivas ligações. A avaliação da segurança destas estruturas e a definição de eventuais acções de reparação e reforço levanta frequentemente dificuldades, na medida em que o funcionamento e o dimensionamento destas ligações são claramente dominados pelos técnicos envolvidos.

This study investigates the annual and inter-annual longshore transport at a high-energy dissipative beach (St. Trojan, SW Ole´ron Island, France), over the period 1997–2006. This study is divided in two parts: (1) a short-term study, based on field measurements carried out during, low, moderate and highenergy swell conditions, and permitting to calibrate a wave propagation model and both empirical longshore sediment transport formulas and a hydro-sedimentary numerical model; and (2) a long-term study, combining global optimization methods using WAVEWATCH III (WW3) model outputs and wave numerical modelling to define the nearshore wave climate and then to compute the annual and interannual longshore transport. A good agreement between the different methods was obtained and values for the annual longshore transport ranged from about 50,000720,000m3/yr to 140,000730,000m3/yr. The net annual longshore transport displayed an inter-annual variability, whereas values were always 3–10 times less than those proposed in previous studies. Such differences point out the necessity of calibrating empirical transport formulas and computing accurately the nearshore wave climate. The relatively low values for the net annual longshore transport were explained by a weak contribution of the most energetic swells, which systematically approach the shore with a frontal obliquity and also generate episodes of reverse transport. The methodology itself was also discussed, pointing out the limitations of this study but also the advantages of using WW3 data and simplified wave climates

Moisture is one of the most powerful causes of decay of historic buildings. A lack of understanding concerning the action of moisture and the resulting degradation mechanisms are often preventing efficient repair of ancient walls. Thus, there is a need to develop and systematise a methodology of diagnosis of defects due to moisture, taking into account the characteristics and properties of materials used on those walls. The use of in situ test methods, especially non-destructive methods, is an important tool, but those methods must be adapted to this particular use, calibrated and interrelated in a global approach. As a result of a Research Project developed at LNEC a methodology involving several phases is proposed, based on tests applied to several case studies and on the analysis of their results. This work synthesises the proposed methodology presenting examples of data combinations for the suggested techniques and its interpretation in order to characterise the state of conservation of renderings and to estimate their performance.

This trans-disciplinary work combines modeling and observational approaches and offers a unique dataset to study the behaviour of a wide estuary linear sandbank over different time-scales. The sandbank studied, the Longe de Boyard, lies in a macrotidal estuary environment off the French Atlantic coast. Side scan sonar data combined with shipek grab samples and numerical modeling of waves and tides revealed its short-term dynamics. Historical (1824) and present-day (2000 and 2003) bathymetric data combined with numerical simulations of waves and tides and tide-related sand transport in 1824, and seismic profiling, were then used to demonstrate the long-term evolution of the sandbank and how this correlates with the short-term dynamics. The geological evolution (centuries to millennia) was finally deduced from seismic stratigraphy combined with an analysis of vibrocore samples. Most of the long-term morphological changes in the ‘Longe de Boyard’ can be explained by the short-term dynamics involving sand transport convergence driven by both tides and waves. Seaward, the changes in the axial part of the bank correspond mainly to erosion and can be explained by wave and tide ravinment. Shoreward, sediment accretion is related to the convergence of tide-related sand transport during ebb and flood due to the dam-effect of the crest of the bank. The changes in the sandbank since 1824 can also be related to a decrease in the tidal channel cross section. The latter was the result of a 10% decrease in tidal currents and tidal prisms subsequent to the rapid sediment infill, and a related 20% reduction in the water volume of the estuary system where the sandbank lies. Seismic stratigraphy and cores showed that the modern sandbank consists of upper clinoforms made of fine sand built up over a core made of coarse sand and gravel related to high-energy environments. Hence, the Longe de Boyard is not only the result of sand convergence driven by both tides and waves but also integrates decreases in the tidal prism subsequent to sediment infilling of the surrounding estuaries on a century and millenia time-scale.

Purpose – The purpose of this paper is to discuss a method for assessing the condition of buildings. The method was developed in Portugal as part of a new Urban Tenancy Regime approved in 2006. Design/methodology/approach – The method was developed in six phases, namely: definition of objectives; analysis of existing instruments; formulation of the proposal; discussions with organisations in the rented sector; pilot; and technical presentations of the final version. Findings – The method is viable and adequate, since a balance was achieved between the accuracy of the results in view of their importance for the contractual relationship between landlord and tenant, and feasibility in terms of human and financial resources available for its implementation. Research limitations/implications – The method has been in use for two years. Further research is needed to confirm the accuracy of the results. Practical implications – The results are used to determine the maximum annual rent value and to summon landlords to carry out repairs if the state of the building falls short of the required standard of maintenance. In a broader perspective the method is also used to assess of rented stock condition of large property owners and, in an adapted form, to assess buildings viability and determine repair needs. Originality/value – This paper is relevant because it describes the assessment method; the previous methods for assessing the condition of Portuguese buildings were too simplistic and lacked the accuracy, transparency and independence required.

A erosão interna é uma das principais causas de acidentes e de roturas em barragens de aterro. Os modos de rotura deste tipo estão associados ao arrastamento de partículas de solo através da percolação no aterro da barragem ou na sua fundação. A erosão interna é uma expressão abrangente que engloba diferentes tipologias, conforme a sua iniciação fenomenológica, nomeadamente: erosão através de fuga concentrada, erosão regressiva, sofusão e erosão no contacto entre solos. Um processo de erosão interna que conduza à rotura de uma barragem de aterro desenvolve-se em quatro fases sequenciais fundamentais, designadas por: (i) iniciação da erosão, (ii) continuação da erosão ou filtração, (iii) progressão da erosão e (iv) formação de brecha. Neste documento identificam-se os principais factores que influenciam a probabilidade de ocorrência de cada fase de um processo de erosão interna.

Mediante o desafio de fomentar a relevância da investigação em sistemas de informação, sem por em causa o seu rigor, este artigo analisa os conceitos de rigor e de relevância da investigação, assim como as perspectivas existentes sobre as possibilidades de conjugação derigor e relevância em processos de investigação.Verificando-se que alguma da investigação mais rigorosa não atrai, tanto quanto seria desejável,o interesse de parte da sua audiência por falta de relevância, este artigo compila um conjunto derecomendações para que os investigadores em sistemas de informação desenvolvaminvestigação não só rigorosa mas também relevante. Considerando os objectivos doinvestigador, nomeadamente o nível de rigor e relevância pretendidos e os recursos disponíveispara o processo de investigação, este artigo discute o impacto da escolha por inovaçãoincremental, modular, arquitectural e radical nas perspectivas de exequibilidade de rigor e relevância. Assim, a discussão e as considerações finais deste trabalho deverão constituir contributo satisfatoriamente rigoroso e relevante para os investigadores em sistemas de informação.

Two years of offshore wave data and daily time exposure images from Trafalgar beach, a 2-km-long sandy beach located on the southwest coast of Spain that frequently exhibits rhythmic features, were used to (1) explore the variability of the beachface morphology and (2) determine environmental conditions associated with the different morphological states. The beachface morphology at three distinct alongshore sectors was analyzed and classified and five different morphological states were found that are related with the presence or absence of beach cusps and a berm: (1) large beach cusps, (2) small beach cusps, (3) low-tide terrace; (4) plane beach berm and (5) plane beach. The predominant beachface morphology is characterized by the presence of large beach cusps, and the main wave climate consisted of offshore significant wave heights ranging from 0.5–1 m and wave periods between 4 and 12 s. An alongshore variation of the morphology is found which might be related to the nearshore wave variability (SWAN wave model results). The morphologies are, in some cases, well-correlated with the daily offshore incident wave climate (described by the daily maximum significant wave height and the corresponding period), particularly for the moderate to high energy wave conditions. Small beach cusps appear under short period waves, whereas when the wave periods are longer the morphology tends to change to large beach cusps. This transition only occurs if the forcing is maintained as constant for a certain duration, which depends itself on the wave energy. It is concluded that correlations over 90% are only found for the highest wave energy conditions or under long wave periods. For the remainder, it is not possible to generally correlate the beachface morphology based only on the wave forcing because the previous morphological state cannot be ignored.