The predictive performance of design models for the punching resistance of SFRC slabs in inner column loading conditions

In the recent years steel fibre reinforced concrete (SFRC), in a volume percentage between 0.75 and 1.25, is being proposed to build slabs supported on piles and slabs supported on columns, where the unique conventional reinforcement is composed of some steel bars in the alignments of the columns/piles, designated as anti-progressive collapse bars. Punching resistance, however, can be a concern in this structural system. In fact, punching has a brittle failure character, and the prediction of the punching resistance is still a challenge, even in concrete slabs with traditional reinforcement systems. The difficulties on assessing the contribution of the reinforcement mechanisms of steel fibres for the flexural and shear resistance in the critical punching perimeter increase this complexity. The research carried out in this paper has the purpose of assessing the reliability of existing analytical models for the prediction of the punching resistance of SFRC slabs. For this purpose, a data-base of experimental tests with SFRC slabs failing in punching was built and the predictive performance of four analytical available models was assessed. In order to turn more practical the model that is more reliable from physical and mechanical point of views, the concepts proposed by Model Code 2010 for the characterization of the postcracking behaviour of FRC were introduced in this model

A model to simulate the contribution of fibre reinforcement for the punching resistance of RC slabs

In this paper analytical formulations are developed for the prediction of the punching resistance of flat slabs 17 of steel fibre reinforced concrete (SFRC) flexurally reinforced with steel bars. By performing statistical 18 analysis with a database that collects experimental results on the characterization of the post-cracking 19 behaviour of SFRC, equations are determined for the evaluation of the residual flexural tensile strength 20 parameters (fRi) from fundamental data that characterize steel fibres. The fRi strength parameters proposed by 21 CEB-FIP 2010 were used for the definition of the stress-crack width law (s-w) that simulates the fibre 22 reinforcement mechanisms in cement based materials. In the second part of the paper is described an 2 analytical formulation based on the concepts proposed by Muttoni and Ruiz, where 23 the s-w law is 24 conveniently integrated for the simulation of the contribution of steel fibres for the punching resistance of 25 SFRC slabs. By using a database composed of 154 punching tests with SFRC slabs, the good predictive 26 performance of the developed proposal is demonstrated. The good performance of this model is also 27 evidenced by comparing its predictions to those from other models.Fundação para a Ciência e a Tecnologia (FCT

An exact master equation for the system-reservoir dynamics under the strong coupling regime and non-Markovian dynamics

In this paper we present a method to derive an exact master equation for a bosonic system coupled to a set of other bosonic systems, which plays the role of the reservoir, under the strong coupling regime, i.e., without resorting to either the rotating-wave or secular approximations. Working with phase-space distribution functions, we verify that the dynamics are separated in the evolution of its center, which follows classical mechanics, and its shape, which becomes distorted. This is the generalization of a result by Glauber, who stated that coherent states remain coherent under certain circumstances, specifically when the rotating-wave approximation and a zero-temperature reservoir are used. We show that the counter-rotating terms generate fluctuations that distort the vacuum state, much the same as thermal fluctuations.Finally, we discuss conditions for non-Markovian dynamics

Avaliação do cálculo da resistência ao punçoamento centrado de lajes fungiformes reforçadas com fibras de aço : modelos teóricos

Desde 1979 que as fibras de aço vêm sendo estudadas como uma alternativa de reforço às estruturas de betão armado. No que diz respeito ao sistema estrutural de lajes fungiformes, os avanços conseguidos no campo da ciência dos materiais e das técnicas de construção já permitem a construção de estruturas onde as lajes são reforçadas praticamente apenas por fibras de aço. Para que este novo sistema construtivo possa competir com os métodos convencionais é necessário que os modelos teóricos que descrevem o complexo comportamento da ligação laje-pilar acompanhem a evolução destas técnicas construtivas. No entanto, ainda não existem regras de projeto que considerem a contribuição das fibras de aço na resistência ao punçoamento de lajes fungiformes. Com o intuito de contribuir para o aumento do conhecimento sobre o dimensionamento ao punçoamento centrado de lajes fungiformes de betão reforçado com fibras de aço (BRFA), o presente artigo apresenta e avalia o desempenho de quatro formulações semi-empíricas. Esse desempenho foi avaliado comparando-se os resultados previstos por cada modelo, Vteo, com as respostas experimentais, Vexp, de 154 lajes que compõem a base de dados (BD) construída para este efeito. As lajes da BD, além de terem rompido todas por punçoamento, também cobrem uma ampla faixa de resistência à compressão do betão, f c , de taxa de armadura de flexão, ρ, de altura útil das lajes, d, de percentagem volumétrica de fibras, Vf , e de esbelteza das fibras, L/D, em que L e D são o comprimento e o diâmetro da fibra. Além da avaliação da relação Vexp/Vteo, também foi avaliada a influência que os parâmetros f c , ρ, Vf e L/D exercem sobre a capacidade preditiva dos modelos considerados

Assessment of the effectiveness of steel fibre reinforcement for the punching resistance of flat slabs by experimental research and design approach

The present paper deals with the experimental assessment of the effectiveness of steel fibre reinforcement in terms of punching resistance of centrically loaded flat slabs, and to the development of an analytical model capable of predicting the punching behaviour of this type of structures. For this purpose, eight slabs of 2550 x 2550 x 150 mm3 dimensions were tested up to failure, by investigating the influence of the content of steel fibres (0, 60, 75 and 90 kg/m3) and concrete strength class (50 and 70 MPa). Two reference slabs without fibre reinforcement, one for each concrete strength class, and one slab for each fibre content and each strength class compose the experimental program. All slabs were flexurally reinforced with a grid of ribbed steel bars in a percentage to assure punching failure mode for the reference slabs. Hooked ends steel fibres provided the unique shear reinforcement. The results have revealed that steel fibres are very effective in converting brittle punching failure into ductile flexural failure, by increasing both the ultimate load and deflection, as long as adequate fibre reinforcement is assured. An analytical model was developed based on the most recent concepts proposed by the fib Mode Code 2010 for predicting the punching resistance of flat slabs and for the characterization of the behaviour of fibre reinforced concrete. The most refined version of this model was capable of predicting the punching resistance of the tested slabs with excellent accuracy and coefficient of variation of about 5%.The study presented in this paper is a part of the research project titled "SlabSys-HFRC - Flat slabs for multi-storey buildings using hybrid reinforced self-compacting concrete: an innovative structural system", with reference number of PTDC/ECM/120394/2010. The second author acknowledges the support provided by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) grant, and the grant provided by the project SlabSys. The authors would acknowledge the collaboration of Casais Company on the preparation of the moulds and flexural reinforcement, CiviTest on the design of the SFRSCC for the slabs, and Maccaferri, Secil (Unibetao), and Sika companies for the supplying of steel fibres, concrete and superplasticizers, respectively

Hepatotoxin microcystin-LR extraction optimization

Several cyanobacterial genera produce toxic secondary metabolites, the most well-known of which are the hepatotoxic microcystins (MCYSTs). Microcystin analyses in drinking water are a requirement of the Health Ministry (Regulation 518/2004) in Brazil, but this regulation does not establish which extraction and analytical method should be used; toxin quantification is usually carried out by ELISA (enzyme-linked immunosorbent assay) or HPLC (high performance liquid chromatography), the efficiency of which depends on the extraction method used. In this work a simple, fast and cheap method of extraction was developed for the isolation and identification of MCYSTs. For this, the strain Microcystis aeruginosa NPLJ-4, reported to be a MCYST-LR producer, was selected. Eight different treatments were tested to determine the best MCYST extraction. Samples were applied in LC-MS (liquid chromatography-mass spectrometry), ELISA and Q-TOF (quadrupole time-of-flight). The most efficient extraction was achieved by sonicating samples diluted in water. The proposed method permits rapid sample processing, and establishes an extraction method for both the analysis and identification of MCYST-LR and other variants.Vários gêneros de cianobactérias produzem metabólitos secundários tóxicos, entre eles as hepatotoxinas microcistinas. A análise de microcistinas em águas para abastecimento humano é uma exigência do Ministério da Saúde (Portaria 518/2004), mas essa portaria ainda não estabelece o método de extração e análise a serem usados e a quantificação da toxina é comumente realizada por ELISA ("enzyme-linked immunosorbent assay") ou HPLC (cromatografia líquida de alta eficiência), cuja eficiência depende do método de extração utilizado. Neste trabalho foi desenvolvido um método simples, rápido e barato de extração para o isolamento e identificação de microcistinas. Para isso, selecionou-se a linhagem Microcystis aeruginosa NPLJ-4 descrita como produtora de microcistina-LR. Oito diferentes tratamentos foram testados para determinar a melhor extração da toxina. As amostras foram analisadas por LC-MS (cromatografia líquida acoplada a espectrometria de massas), ELISA e Q-TOF ("quadrupole time-of-flight"). Os resultados mostraram que a melhor extração foi a que usou sonicação das amostras diluídas em água. O método proposto permite o processamento rápido das amostras e estabelece um método de extração para análise e identificação de microcistina-LR e outras variantes.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Numerical modelling of the punching behaviour of steel fibre reinforced self-compacting concrete flat slabs

Punching shear failure on flat reinforced concrete slabs of residential and commercial buildings is generally avoided by using transversal reinforcement and/or chapiters. The first option requires intense labour, mainly when densely flexural reinforcement exists in the potential punching failure region, with detrimental consequences in terms of costs of this construction solution. The second option has also extra costs due to the necessity of special arrangements of moulds for casting the chapiters. The interference of a chapiter on the flatness of the slab can also be a negative aspect from the architectonic point of view. The use of steel fibre reinforcement can be a solution to avoid both the conventional punching reinforcement and chapiters. Therefore, an experimental program was carried out to assess the potentialities of steel fibre reinforced self-compacting concrete (SFRSCC) for the punching resistance of flat slabs centrically loaded. This experimental program is described, and the main results are presented and analysed. To assess the potentialities of the Reissner-Mindlin FEM-based theory for modelling the behaviour of flat SFRSCC slabs submitted to punching loading configuration, new features were introduced in the out-ofplane shear constitutive law of the SFRSCC. These features are briefly described and the main focus was given on the modelling strategy adopted for simulating the punching tests.Fundação para a Ciência e a Tecnologia (FCT

Fontes de fósforo e uréia na suplementação mineral de bovinos em pastagem de Brachiaria humidicola na Ilha de Marajó.

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