Papers

Sand transport models are often based on semi-empirical equilibrium transport formulae that relate sediment fluxes to physical properties such as velocity, depth and characteristic sediment grain sizes. In engineering applications, errors in these physical properties affect the accuracy of the sediment fluxes. The present analysis quantifies error propagation from the input physical properties to the sediment fluxes, determines which ones control the final errors, and provides insight into the relative strengths, weaknesses and limitations of four total load formulae (Ackers and White, Engelund and Hansen, van Rijn, and Karim and Kennedy) and one bed load formulation (van Rijn). The various sources of uncertainty are first investigated individually, in order to pinpoint the key physical properties that control the errors. Since the strong non-linearity of most sand transport formulae precludes analytical approaches, a Monte Carlo method is validated and used in the analysis. Results show that the accuracy in total sediment transport evaluations is mainly determined by errors in the current velocity and in the sediment median grain size. For the bed load transport using the van Rijn formula, errors in the current velocity alone control the final accuracy. In a final set of tests, all physical properties are allowed to vary simultaneously in order to analyze the combined effect of errors. The combined effect of errors in all the physical properties is then compared to an estimate of the errors due to the intrinsic limitations of the formulae. Results show that errors in the physical properties can be dominant for typical uncertainties associated with these properties, particularly for small depths. A comparison between the various formulae reveals that the van Rijn formula is more sensitive to basic physical properties. Hence, it should only be used when physical properties are known with precision. Keywords: Sediment transport models; Sensitivity analysis; Uncertainty analysis; Monte Carlo method

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The corrosion resistance under mechanical stress can be one of the most concerning types of localized corrosion for the application of stainless steel reinforcements in concrete. This paper will assess the stress corrosion cracking susceptibility, by the slow strain rate test method (SSRT), of three austenitic stainless steel alloys: one conventional Fe-Cr-Ni base alloy and two new composition Fe-Cr-Mn base alloys adequate to the manufacturing of ribbed bars for reinforcing concrete. The SSRT results show that only one of the austenitic Fe-Cr-Mn alloys is susceptible to stress corrosion cracking while the other shows a performance similar to that of the AISI 304 stainless steel alloy.

This work aims to contribute to a better understanding of the ionic strength effect on microcystin and natural organic matter (NOM) surrogate adsorption by analyzing the importance of adsorbate molecular size, and surface concentration. Adsorption kinetics and/or isotherms were performed on PAC Norit SA-UF for four microcystin variants (MC-LR,MC-LY,MC-LW,MCLF), and three NOM surrogates (salicylicacid(SA), tannicacid(TA), Aldrichhumicacid(AHA)) at different solution ionic strengths. Results showed that the ionic strength effect depends upon the adsorbate surface concentration, cation charge (monoordivalent), and adsorbate molecular size. Potassium seemed not to affect the MC-LR adsorption, while calcium enhanced MC-LR kinetics and adsorption capacity. K+ and, particularly, Ca2+ improved the adsorption kinetics of the other microcystin variants. For identical surface concentration and ionic strength, the impact of K+ and Ca2+ on NOM surrogates depended on the adsorbate molecular size: K+ effect was only observed for AHA, whereas Ca2+ caused no effect on SA adsorption, slightly enhanced TA adsorption, and greatly enhanced AHA adsorption. MC-LR isotherms with two salt concentrations (KCl or CaCl2) indicated that, for the studied range of equilibrium surface concentration (5.3–18.7mg/g), an enhanced adsorption regime prevails, and no transition regime was observed.

The protection performance of varnishes applied to two different wooden substrates (maritime pine and iroko) for outdoor exposure was investigated for eight different varnish systems (with and without colorants and two different light stabilizers). All were subjected to accelerated artificial weathering and natural weathering. Several test methods were used to evaluate the appearance and physical-chemical properties of the coatings during the degradation. The results obtained lead to the selection of the best varnish formulation for the protection of wood for exterior use and provide useful evaluation of the test methods employed.

As inovações tecnológicas, nomeadamente nas áreas das tecnologias e sistemas de informação e do conhecimento colocam à disposição da sociedade ferramentas para o desenvolvimento de sistemas que podem contribuir de forma significativa para apoiar as actividades do controlo de segurança de barragens, através, nomeadamente, da disseminação do conhecimento especializado, da automatização de processos, da formação técnica de novas equipas especializadas, entre outros. Este trabalho tem como principal objectivo apresentar uma proposta inovadora de modernização das actividades subjacente ao controlo de segurança de grandes barragens de betão com base em processos automatizados e com características inteligentes. Neste contexto, o Laboratório Nacional de Engenharia Civil (LNEC) promoveu, no início de 2004, o desenvolvimento do sistema GESTBARRAGENS, tendo como parceiros o Instituto de Engenharia de Sistemas e Computadores: Investigação e Desenvolvimento (INESC-ID) e a Companhia Portuguesa de Produção de Electricidade (CPPE/EDP).

Data quality tools aim at detecting and correcting data problems that affect the accuracy and efficiency of data analysis applications. We propose a classification of the most relevant commercial and research data quality tools that can be used as a framework for comparing tools and understand their funcionalities.

Some artificial accelerated methods are currently used and accepted in the prediction of polymer lifetimes. However, in order to evaluate the durability of these materials, it is indispensable to reproduce the natural weathering phenomena as closely as possible. To attain this target, it is fundamental to understand the role of the atmospheric agents in the photo-degradation. The importance of radiation and temperature in the degradation of polymers is universally recognised. However, there is a trend to underestimate other environmental agents, such as humidity and rain, which play an important part in the evolution of degradation in certain compounded polymers. The objective of this paper is to show the fundamental role of water in the mechanism of degradation of TiO2 pigmented PVC formulations, and compare the results from different exposure methods, considering the influence of this degradation agent.

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