297 research outputs found
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
Shotgun Mitogenomics Provides a Reference Phylogenetic Framework and Timescale for Living Xenarthrans
Xenarthra (armadillos, sloths, and anteaters) constitutes one of the four major clades of placental mammals. Despite their phylogenetic distinctiveness in mammals, a reference phylogeny is still lacking for the 31 described species. Here we used Illumina shotgun sequencing to assemble 33 new complete mitochondrial genomes, establishing Xenarthra as the first major placental clade to be fully sequenced at the species level for mitogenomes. The resulting data set allowed the reconstruction of a robust phylogenetic framework and timescale that are consistent with previous studies conducted at the genus level using nuclear genes. Incorporating the full species diversity of extant xenarthrans points to a number of inconsistencies in xenarthran systematics and species definition. We propose to split armadillos in two distinct families Dasypodidae (dasypodines) and Chlamyphoridae (euphractines, chlamyphorines, and tolypeutines) to better reflect their ancient divergence, estimated around 42 million years ago. Species delimitation within long-nosed armadillos (genus Dasypus) appeared more complex than anticipated, with the discovery of a divergent lineage in French Guiana. Diversification analyses showed Xenarthra to be an ancient clade with a constant diversification rate through time with a species turnover driven by high but constant extinction. We also detected a significant negative correlation between speciation rate and past temperature fluctuations with an increase in speciation rate corresponding to the general cooling observed during the last 15 million years. Biogeographic reconstructions identified the tropical rainforest biome of Amazonia and the Guianan shield as the cradle of xenarthran evolutionary history with subsequent dispersions into more open and dry habitats.Fil: Gibb, Gillian C.. Universite de Montpellier; Francia. Massey Universit; Nueva ZelandaFil: Condamine, Fabien L.. University of Gothenburg; Suecia. Universite de Montpellier; Francia. University of Alberta; CanadáFil: Kuch, Melanie. McMaster University; CanadáFil: Enk, Jacob. McMaster University; CanadáFil: Moraes Barros, Nadia. Universidade Do Porto; Portugal. Universidade de Sao Paulo; BrasilFil: Superina, Mariella. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto de Medicina y Biología Experimental de Cuyo; ArgentinaFil: Poinar, Hendrik N.. McMaster University; CanadáFil: Delsuc, Frederic. Universite de Montpellier; Franci
Mineralização de bovinos no Estado do Amazonas. I. Levantamento dos teores minerais no complexo solo - planta - animal.
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
Immature development of Spodoptera dolichos (Fabricius) (Lepidoptera: noctuidae).
We provide detailed temporal and morphological parameters of the immature stages of Spodoptera dolichos (Fabricius) larvae fed on artificial diet under controlled conditions (25?±?1°C, 70?±?10% RH, and 14 h photophase). The viability of the egg, larval, pupal, and prepupal stages was 97.5%, 97.0%, 93.1%, and 98.9%, respectively. The average duration of the egg, larval, prepupal, and pupal stages was 5.0, 23.4, 3.2, and 21.5 days, respectively. Females took longer at the larval stage than males, with 10.5% of them having seven instars. The growth rate of female larvae that developed through six and seven instars was 1.72 and 1.54, respectively. Female pupae were significantly larger, exhibiting slower development than males
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