Composição de betão de resistência melhorada ao fogo para aduelas de túneis : parte I

Relatório técnico 05-DEC/E-32Para a obtenção de um betão de ductilidade elevada e resistência melhorada ao fogo para aduelas de túneis, optou-se, entre outros, pela utilização de dois tipos de fibras. Um primeiro tipo de fibra, não metálica, que apresenta reduzido grau de polimerização e derrete na presença de temperaturas elevadas. Sob a acção do fogo, o desaparecimento desta fibra irá criar uma rede de micro canais que permite a saída do vapor de água do interior do betão. A inclusão deste tipo de fibra também reduz a propagação de fendas durante a fase de retracção plástica do betão. O outro tipo de fibra, metálica, tem o propósito de garantir o nível de ductilidade que se pretende para o betão, bem como reduzir a quantidade de armadura convencional a colocar nos elementos estruturais. O presente relatório começa com uma breve síntese do estado do conhecimento no âmbito de: incêndios em túneis, aspectos acerca do dimensionamento de aduelas para túneis, nomeadamente a inclusão de fibras metálicas e o comportamento do betão sob temperaturas elevadas (alterações das suas propriedades, cenários de fogo normalizados, classificação dos materiais e inspecção e avaliação de estruturas afectadas). Segue-se uma secção onde são reportados os ensaios preliminares efectuados com vista à selecção do tipo e dosagem de fibra não metálica a utilizar, bem como o tempo necessário para a estabilização da resistência residual do betão com o tempo após a exposição à simulação do efeito do fogo.To develop a high ductility concrete of enhanced fire resistance, two distinct types of fibers were used. The first one is a non-metallic fiber, with low degree of polymerization, that sublimes in the presence of high temperatures. Under the action of fire, these fibers create a network of micro channels for the escape of the water vapor. These fibers have also the purpose of decreasing the crack formation and crack propagation during the concrete plastic shrinkage phase. The other type of fibers, is made by steel, and has the purpose of providing high ductility to the concrete postcracking behaviour, as well as of replacing, totally of partially, conventional reinforcement applied in pre-casting concrete tunnel segments. A brief state-of-the-art is presented in the following topics: fire in tunnels; design of tunnel segments; the use of metallic fibers in this type of structural elements; concrete behavior under high temperatures (how material properties are affected, fire scenarios, fire classification for materials and inspection and evaluation of affected structures). A section of this document is dedicated to the description of the preliminary tests carried out to select a non-metallic fiber type and the content of this fiber. The period of time for the stabilization of the concrete compressive residual strength was also assessed

DNA-psoralen: single-molecule experiments and first principles calculations

The authors measure the persistence and contour lengths of DNA-psoralen complexes, as a function of psoralen concentration, for intercalated and crosslinked complexes. In both cases, the persistence length monotonically increases until a certain critical concentration is reached, above which it abruptly decreases and remains approximately constant. The contour length of the complexes exhibits no such discontinuous behavior. By fitting the relative increase of the contour length to the neighbor exclusion model, we obtain the exclusion number and the intrinsic intercalating constant of the psoralen-DNA interaction. Ab initio calculations are employed in order to provide an atomistic picture of these experimental findings.Comment: 9 pages, 4 figures in re-print format 3 pages, 4 figures in the published versio

Factores De Riesgo Para Incontinencia Urinaria En El Puerperio

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Fiber reinforced concrete of enhanced fire resistance for tunnel segments

In the last decades, technical and scientific efforts have been done to increase the concrete strength, based on the assumption that more economic, lightweight, durable and good looking structures can be built. This strength enhancement, however, has been obtained by increasing the compactness of the concrete internal structure, resulting concretes with a void percentage much lower than the values observed in concretes of current strength classes. Research and fire accidents have shown that the concrete failure of structures exposed to fire is as explosive as high is the concrete strength class, since the concrete brittleness increases with the concrete compressive strength. In the present work a fiber reinforced concrete of enhanced fire resistance was developed and its properties are characterized by experimental research. This concrete is intended to have enough resistance for the most structural engineering applications, while the performance of the fibrous reinforcement system was evaluated in terms of verifying its possibilities for replacing, partially or totally, conventional reinforcement used in concrete precast tunnel segments.The authors wish to acknowledge the support provided by the Portuguese Science and Technology Foundation (FCT) by means of the project POCTI/ECM/57518/2004 “FICOFIRE - High performance fiber reinforced concrete of enhanced fire resistance”, as well as the support of Spie Batignolles Company

FRCcalc - software for design of fiber reinforced concrete elements according to MC2010 recommendations

A new software, denominated FRCcalc, was developed for the analysis and design of fiber reinforced concrete (FRC) members based on the recommendations and design guidelines of MC2010. The software is guided for the analysis of FRC cross-sections with and without conventional steel reinforcements, submitted to bending and shear, in order to assess the ultimate and serviceability limit state safety verifications of structural members. A main feature of the software is the possibility to run a comparative analysis between FRC and reinforced concrete (RC) cross-sections from the technical aspects. Two examples of the analysis of FRC and RC cross-sections using FRCcalc are presented, having been explored the use of fiber reinforcement in members for increased structural performance and as a total or partial replacement of conventional steel reinforcement. Additionally, in order to appraise FRCcalc accuracy to evaluate the flexural response of FRC and RC cross-sections, a comparison with the results obtained with DOCROS software is presented, being DOCROS based on a layered model capable of attributing to each layer an aimed constitutive model, therefore adequate to predict the moment-curvature of cross sections composed of several types of cement, metallic and polymer materials.The first Author would like to acknowledge the grant SFRH/BDE/96381/2013 co-funded by CiviTest - Pesquisa de Novos Materiais para a Engenharia Civil, Lda. and by FCT - Portuguese Foundation for Science and Technology. The authors also acknowledge the support provided by the FCT project PTDC/ECM-EST/2635/2014

Innovative structural systems for industrial buildings using fiber reinforced concrete and material nonlinear FEM-Based models

Fibre Reinforced Concrete (FRC) can be very effective in precast pre-stressed high strength concrete structures, since shear reinforcement and passive longitudinal bars can be totally replaced by fibre reinforcement. To simulate adequately the fibre reinforcement benefits, material constitutive models, able of capturing the crack initiation and crack propagation need to be used, under the frame-work of FEM-based analysis. In the present work, the use of FRC was explored for the development of innovative structural systems for industrial buildings. The connections between structural precast elements were also simulated. The numerical simulations are described and the results are analyzed and discussed

Alterações bioquímicas durante a embebição de sementes de baraúna (Schinopsis brasiliensis Engl.).

O objetivo deste trabalho foi obter a curva de embebição e avaliar as alterações bioquímicas que ocorrem nas sementes de baraúna durante a germinação

Aplicação de microbetão para o reforço de elementos estruturais em betão armado danificados por ação de um fogo

No presente trabalho avalia-se a eficácia de uma técnica de reforço para elementos estruturais em betão armado afetados pela exposição a temperaturas elevadas e/ou fogo. Para tal, desenvolveu-se um programa experimental que incluiu a moldagem de catorze provetes prismáticos (150 x 150 x 600 mm 3 ) em betão de classe resistente corrente em estruturas de betão armado existentes no edificado português (C20/25). Após a exposição dos provetes a diferentes níveis de temperatura máxima (400ºC, 550ºC e 700ºC), estes foram reforçados com um microbetão auto-compactável (C40/50). O procedimento de reforço estrutural passa pela remoção do betão de recobrimento original das armaduras convencionais e aplicação de uma nova camada com a mesma espessura do microbetão auto-compactável de reforço. São avaliados os benefícios da aplicação do betão de reforço, bem como, da inserção adicional de armadura convencional de reforço ou fibras em aço