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

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

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

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

Numerical simulation of the punching shear behaviour of self-compacting fibre reinforced flat slabs

This paper presents the numerical simulations of the punching behaviour of centrally loaded steel fibre reinforced self-compacting concrete (SFRSCC) flat slabs. Eight half scaled slabs reinforced with different content of hooked-end steel fibres (0, 60, 75 and 90 kg/m3) and concrete strengths of 50 and 70 MPa were tested and numerically modelled. Moreover, a total of 54 three-point bending tests were carried out to assess the post-cracking flexural tensile strength. All the slabs had a relatively high conventional flexural reinforcement in order to promote the occurrence of punching failure mode. Neither of the slabs had any type of specific shear reinforcement rather than the contribution of the steel fibres. The numerical simulations were performed according to the Reissner-Mindlin theory under the finite element method framework. Regarding the classic formulation of the Reissner-Mindlin theory, in order to simulate the progressive damage induced by cracking, the shell element is discretized into layers, being assumed a plane stress state in each layer. The numerical results are, then, compared with the experimental ones and it is possible to notice that they accurately predict the experimental force-deflection relationship. The type of failure observed experimentally was also predicted in the numerical simulations.This work is supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the project “SlabSys – HFRC – Flat slabs for multi-storey buildings using hybrid reinforced self-compacting concrete: an innovative structural system” PTDC/ECM/120394/2010

Diferentes aditivos para silagem de capim-elefante em propriedade de base familiar.

Este trabalho foi desenvolvido com o objetivo de avaliar a composição químico-bromatológica, o pH, o nitrogênio amoniacal e o processo fermentativo de silagens de capim-elefante (Pennisetum purpureum Schum.) conforme demonstrado: Controle - Capim-elefante (CE), Capim-elefante + 5% de farelo da vagem de algaroba (CEFVA), Capim-elefante + 5% farelo de milho (CEFM), capim-elefante + 5% melaço em pó (CEML), capim-elefante picado e emurchecido (CEPE) durante 24 horas. Os minissilos foram abertos 60 dias após fechamento e foi realizada a determinação de matéria seca (MS), da proteína bruta (PB), da fibra em detergente neutro (FDN), da fibra em detergente ácido (FDA), da hemicelulose (HEM), do pH e do nitrogênio amoniacal (N-NH3) e determinação dos ácidos graxos de cadeia curta. O tratamento com adição de farelo de milho apresentou menores valores de FDN, FDA e HEM. Exceto o CEPE, todos os tratamentos apresentaram valores ideais de pH. Os teores de N-NH3 das silagens sofreram variações significativas (P>0,05) no CEML e no CEPE. Os indicadores de qualidade de silagem e de características fermentativas, pH, N-NH3 e ácidos orgânicos evidenciaram que as silagens de capimelefante apresentaram resultados satisfatórios, com exceção do material picado e emurchecido, cabendo ao produtor decidir quanto à inclusão do aditivo.bitstream/item/114716/1/BPD115.pd

Estoque de serapilheira sobre o solo em plantios eucalipto e em vegetação de um cerrado sensu stricto em Paranoá, DF.

O objetivo desse estudo foi avaliar o estoque de serapilheira em florestas plantadas de eucalipto e nativa do cerrado sensu stricto no período chuvoso e seco. O estudo foi realizado no Núcleo Rural de Quebrada do Neres, Paranoá - DF

Targeting the Immune System with Plant Lectins to Combat Microbial Infections

The arsenal of drugs available to treat infections caused by eukaryotic and prokaryotic microbes has been declining exponentially due to antimicrobial resistance phenomenon, leading to an urgent need to develop new therapeutic strategies. Host-directed immunotherapy has been reported as an attractive option to treat microbial infections. It consists in the improvement of host defenses by increasing the expression of inflammatory mediators and/or controlling of inflammation-induced tissue injury. Although the in vitro antimicrobial and immunomodulatory activities of lectins have been extensively demonstrated, few studies have evaluated their in vivo effects on experimental models of infections. This review aims to highlight the experimental use of immunomodulatory plant lectins to improve the host immune response against microbial infections. Lectins have been used in vivo both prophylactically and therapeutically resulting in the increased survival of mice under microbial challenge. Other studies successfully demonstrated that lectins could be used in combination with parasite antigens in order to induce a more efficient immunization. Therefore, these plant lectins represent new candidates for management of microbial infections. Furthermore, immunotherapeutic studies have improved our knowledge about the mechanisms involved in host–pathogen interactions, and may also help in the discovery of new drug targets

Genome of the Avirulent Human-Infective Trypanosome—Trypanosoma rangeli

Background: Trypanosoma rangeli is a hemoflagellate protozoan parasite infecting humans and other wild and domestic mammals across Central and South America. It does not cause human disease, but it can be mistaken for the etiologic agent of Chagas disease, Trypanosoma cruzi. We have sequenced the T. rangeli genome to provide new tools for elucidating the distinct and intriguing biology of this species and the key pathways related to interaction with its arthropod and mammalian hosts.  Methodology/Principal Findings: The T. rangeli haploid genome is ,24 Mb in length, and is the smallest and least repetitive trypanosomatid genome sequenced thus far. This parasite genome has shorter subtelomeric sequences compared to those of T. cruzi and T. brucei; displays intraspecific karyotype variability and lacks minichromosomes. Of the predicted 7,613 protein coding sequences, functional annotations could be determined for 2,415, while 5,043 are hypothetical proteins, some with evidence of protein expression. 7,101 genes (93%) are shared with other trypanosomatids that infect humans. An ortholog of the dcl2 gene involved in the T. brucei RNAi pathway was found in T. rangeli, but the RNAi machinery is non-functional since the other genes in this pathway are pseudogenized. T. rangeli is highly susceptible to oxidative stress, a phenotype that may be explained by a smaller number of anti-oxidant defense enzymes and heatshock proteins.  Conclusions/Significance: Phylogenetic comparison of nuclear and mitochondrial genes indicates that T. rangeli and T. cruzi are equidistant from T. brucei. In addition to revealing new aspects of trypanosome co-evolution within the vertebrate and invertebrate hosts, comparative genomic analysis with pathogenic trypanosomatids provides valuable new information that can be further explored with the aim of developing better diagnostic tools and/or therapeutic targets