Desempenho de modelos analíticos de previsão da contribuição de materiais compósitos no reforço ao corte de vigas de betão armado

Na presente comunicação são apresentados alguns modelos analíticos para previsão da contribuição de materiais compósitos no reforço ao corte de vigas de betão armado recentemente introduzidos nos códigos de dimensionamento, sendo o seu desempenho aferido por comparação entre os valores estimados pelas formulações analíticas com os registados numa base de dados contendo informação referente a mais de 200 programas experimentais.Os autores manifestam os seus agradecimentos ao apoio prestado pela Fundação para a Ciência e Tecnologia (FCT) no projecto POCI/ECM/59033/2004. O primeiro autor agradece a bolsa UMINHO/POCI-59033/BI/05 concedida ao abrigo deste projecto

Novas perspectivas para o desenvolvimento de modelos de dimensionamento ao corte de vigas de betão armado reforçadas com FRP colado externamente

Com o presente artigo pretende-se apresentar uma base de dados (BD) contendo os registos relativos a mais de 250 vigas reforçadas ao corte com materiais poliméricos reforçados com fibras (FRP) e ensaiadas em diversos programas experimentais conduzidos por diferentes autores. O desempenho dos modelos de dimensionamento propostos pelo fib, ACI, e pelas Norma Italiana CNR-DT200 e Norma Australiana CIDAR é aferido comparando o comportamento observado experimentalmente com as previsões obtidas por via analítica. Tendo por base os resultados registados na BD, foi efectuado um estudo paramétrico com o objectivo de avaliar a influência no desempenho dos modelos de dimensionamento de diversos factores não explicitamente considerados nas formulações analíticas que os suportam. Os resultados são analisados, interpretados e apontadas as limitações encontradas nos modelos de dimensionamento em estud

Reliability analysis of shear strengthening EBR FRP models

This work presents a statistically oriented study aiming to assess the reliability of some of the most well known design models available for the prediction of the contribution of fiber reinforced polymer (FRP) systems applied according to the externally bonded reinforcing (EBR) technique for the shear strengthening of reinforced concrete (RC) beams. Relevant data was collected from experimental programs carried out in recent years in the context of the shear strengthening with FRP, and an extended database was obtained. Using this data, the performance of fib, ACI, Italian and Australian design guidelines was appraised by means of comparing the contribution of the FRP shear systems predicted by the analytical formulations with those registered experimentally. In general, the obtained results were not very promising, since a large scatter of the design safety factor was observed and, for some cases, the contribution of the FRP systems predicted by the design models was highly unconservative, which may be a serious concern as these formulations may be currently being used in design practice.The study reported in this paper forms a part of the research programme Cutinemo, supported by FCT, PTDC/ECM/73099/2006

Design models for shear strengthening of reinforced concrete beams with externally bonded FRP composites : a statistical vs reliability approach

Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/59033/200

CFRP group effect and interaction between stirrups and strips on the NSM-shear strengthening of RC beams

Available experimental research shows that the technique based on installing Carbon Fibre Reinforced Polymer (CFRP) strips into slits opened on the cover concrete of the beam’s lateral faces, designated as Near Surface Mounted (NSM), is very effective to increase the shear resistance of reinforced concrete (RC) beams. However, recent research has revealed that, in terms of NSM shear strengthening effectiveness, a detrimental effect can occur between existing steel stirrups and applied strips, as well as amongst the strips when the distance between strips, sf, is lower than a certain limit. In the present work, a test setup was developed and an experimental program was carried out to assess the influence of both sf and interaction between existing steel stirrups and strips on the shear strengthening of RC beams. The experimental program is described and the main results are presented and analyzed.(13-05-04-FDR-00031

Numerical simulation of continuous RC slabs strengthened using NSM technique

The effectiveness of the Near Surface Mounted (NSM) technique for the increase of the flexur-al resistance of reinforced concrete (RC) beams and slabs was already well proved. The NSM technique is es-pecially adapted to increase the negative bending moments of continuous (two or more spans) RC slabs. However, the influence of the NSM strengthening on the moment redistribution capability of RC structures should be investigated. Recently, an exploratory experimental program was conducted to assess the level of moment redistribution that can be obtained in two span RC slabs strengthened with NSM strips for negative bending moments. To help the preparation of an extensive experimental program in this domain, the values of the parameters of a constitutive model, implemented into a FEM-based computer program, were calibrated from the numerical simulation of these tests. The main aspects of the experimental program are presented, the numerical model is briefly described and the numerical simulations are presented and analyzed.The authors wish to acknowledge the support provided by the Empreiteiros Casais, S&P, Secil (Un-ibetao, Braga) Companies. The study reported in this paper forms a part of the research program CUTINEMO Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures supported by FCT, PTDC/ECM/73099/2006.The second author would like to acknowledge the National Council for Scientific and Technological Development(CNPq)Brazil for financial support for scholarship

Comparação de programas comerciais para dimensionamento de lajes em betão armado

Devido à evolução contínua de programas de cálculo, é impensável efectuar projectos de estabilidade nos dias de hoje sem o auxílio destas ferramentas. As dificuldades associadas à análise e dimensionamento automático de lajes em betão armado parecem representar um cenário de interesse significativo para a comunidade técnica. No presente trabalho comparam-se os resultados de três programas comerciais de cálculo de lajes em termos de deslocamentos, esforços e armadura. Para esse efeito são consideradas uma laje quadrada simplesmente apoiada, uma laje em L (descontinuidade geométrica) e uma laje fungiforme (descontinuidade de carga devido ao apoio isolado), apresentandose recomendações a adoptar na modelação. As possíveis estratégias de modelação para lajes contínuas fungiformes são discutidas, tendo em vista uniformizar os esforços associados a forças pontuais

Mechanisms underlying temperature extremes in Iberia: a Lagrangian perspective

The mechanisms underlying the occurrence of temperature extremes in Iberia are analysed considering a Lagrangian perspective of the atmospheric flow, using 6-hourly ERA-Interim reanalysis data for the years 1979–2012. Daily 2-m minimum temperatures below the 1st percentile and 2-m maximum temperatures above the 99th percentile at each grid point over Iberia are selected separately for winter and summer. Four categories of extremes are analysed using 10-d backward trajectories initialized at the extreme temperature grid points close to the surface: winter cold (WCE) and warm extremes (WWE), and summer cold (SCE) and warm extremes (SWE). Air masses leading to temperature extremes are first transported from the North Atlantic towards Europe for all categories. While there is a clear relation to large-scale circulation patterns in winter, the Iberian thermal low is important in summer. Along the trajectories, air mass characteristics are significantly modified through adiabatic warming (air parcel descent), upper-air radiative cooling and near-surface warming (surface heat fluxes and radiation). High residence times over continental areas, such as over northern-central Europe for WCE and, to a lesser extent, over Iberia for SWE, significantly enhance these air mass modifications. Near-surface diabatic warming is particularly striking for SWE. WCE and SWE are responsible for the most extreme conditions in a given year. For WWE and SCE, strong temperature advection associated with important meridional air mass transports are the main driving mechanisms, accompanied by comparatively minor changes in the air mass properties. These results permit a better understanding of mechanisms leading to temperature extremes in Iberia

Aplicação de novos materiais e de modelos de análise não linear material no desenvolvimento de sistemas estruturais pré-fabricados para edifícios industriais

No presente trabalho é descrita a investigação efectuada no âmbito do dimensionamento de viga pré-fabricada para vencer vãos de 20 m de coberturas de edifícios industriais, denominada VMC20. Para tal utilizou-se betão reforçado com fibras de aço e recorreu-se a métodos avançados de análise de estruturas

Fire behaviour of reinforced concrete slab strips strengthened with prestressed NSM-CFRP laminates

Carbon fibre reinforced polymer (CFRP) composites are now widely used to strengthen reinforced concrete (RC) structures. Among the strengthening systems available, near-surface mounted (NSM)-prestressed CFRP laminates offer several advantages, as they significantly increase the load carrying capacity and also the serviceability performance of RC structures. However, as for other CFRP systems, there is a concern about their behaviour at elevated temperature and under fire exposure due to the glass transition process undergone by their polymeric components. Nevertheless, the fire performance of NSM-prestressed-CFRP strengthening systems has not yet been investigated. This paper presents an experimental study about the fire resistance behaviour of RC slab strips strengthened with prestressed NSM-CFRP laminates; the slabs were simultaneously subjected to a mechanical (fire) load and the ISO 834 fire curve, and the influence of the following parameters on their fire resistance behaviour was assessed: (i) the prestress level (0 %, 25 % and 50 % of the CFRP tensile strength), and (ii) the presence of passive fire protection, comprising up to 48 mm thick calcium silicate (CS) boards. The results obtained showed that: (i) without fire protection, the strengthening system remained effective during a very low period of fire exposure, which significantly decreased with the prestress level, from 16 min (0 %) to less than 5 min (50 %); (ii) with fire protection, even with 50 % of prestress, the strengthening system remained effective for more than 120 min; and (iii) the “critical” temperatures in the anchorages of the strengthening systems were found to be about 2.5Tg, 2.0Tg and 1.5Tg, for the prestress levels of 0 %, 25 % and 50 %, respectively, with Tg being the glass transition temperature of the adhesive.The authors wish to acknowledge FCT (project FireComposite PTDC/ECM-EST/1882/2014 and CERIS project UIDB UIDB/04625/2020); Secil and Unibet˜ao for supplying the concrete; and S&P Clever Reinforcement for supplying the CFRP laminates and the epoxy adhesive. The first author also wishes to thank the financial support of FCT through the scholarship SFRH/BD/145256/2019