1,639 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
Absorbing-state phase transitions with extremal dynamics
Extremal dynamics represents a path to self-organized criticality in which
the order parameter is tuned to a value of zero. The order parameter is
associated with a phase transition to an absorbing state. Given a process that
exhibits a phase transition to an absorbing state, we define an ``extremal
absorbing" process, providing the link to the associated extremal
(nonabsorbing) process. Stationary properties of the latter correspond to those
at the absorbing-state phase transition in the former. Studying the absorbing
version of an extremal dynamics model allows to determine certain critical
exponents that are not otherwise accessible. In the case of the Bak-Sneppen
(BS) model, the absorbing version is closely related to the "-avalanche"
introduced by Paczuski, Maslov and Bak [Phys. Rev. E {\bf 53}, 414 (1996)], or,
in spreading simulations to the "BS branching process" also studied by these
authors. The corresponding nonextremal process belongs to the directed
percolation universality class. We revisit the absorbing BS model, obtaining
refined estimates for the threshold and critical exponents in one dimension. We
also study an extremal version of the usual contact process, using mean-field
theory and simulation. The extremal condition slows the spread of activity and
modifies the critical behavior radically, defining an ``extremal directed
percolation" universality class of absorbing-state phase transitions.
Asymmetric updating is a relevant perturbation for this class, even though it
is irrelevant for the corresponding nonextremal class.Comment: 24 pages, 11 figure
Avaliação da fadiga muscular pela mecanomiografia durante a aplicação de um protocolo de EENM
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
The Magnitude of Rapid Weight Loss and Rapid Weight Gain in Combat Sport Athletes Preparing for Competition: A Systematic Review
Combat sport athletes typically engage in a process called making weight, characterized by rapid weight loss (RWL) and subsequent rapid weight gain (RWG) in the days preceding competition. These practices differ across each sport, but no systematic comparison of the size of the changes in body mass exists. The aim was to determine the magnitude of RWL and RWG in combat sport athletes preparing for competition. The review protocol was preregistered with PROSPERO (CRD42017055279). In eligible studies, athletes prepared habitually with a RWL period ≤7 days preceding competition. An electronic search of EBSCOhost (CINAHL Plus, MEDLINE, and SPORTDiscus) and PubMed Central was performed up to July 2018. Sixteen full-text studies (total 4,432 participants; 156 females and 4,276 males) were included, providing data from five combat sports (boxing, judo, mixed martial arts, taekwondo, and wrestling). Three studies reported RWL and 14 studies reported RWG. Duration permitted for RWG ranged 3–32 hr. The largest changes in body mass occurred in two separate mixed martial arts cohorts (RWL: 7.4 ± 1.1 kg [∼10%] and RWG: 7.4 ± 2.8 kg [11.7% ± 4.7%]). The magnitude of RWG appears to be influenced by the type of sport, competition structure, and recovery duration permitted. A cause for concern is the lack of objective data quantifying the magnitude of RWL. There is insufficient evidence to substantiate the use of RWG as a proxy for RWL, and little data are available in females. By engaging in RWG, athletes are able to exploit the rules to compete up to three weight categories higher than at the official weigh-in
An overview of forest residues as promising low-cost adsorbents
Anthropogenic activities have severely affected biogeochemical cycles on a global scale, resulting in a drastic increase in environmental problems, intensified by wastewater generation containing high levels of pollutants. As it is known that water is precious yet limited, viable wastewater treatments must be developed. Adsorption is an environmentally friendly option, and it offers the possibility of resolving two problems simultaneously. Besides removing pollutants from water, many adsorbents can be produced using wooden forestry residues. Such materials are generally considered as waste, which leads to their direct disposal. In addition, there are types of wooden forestry waste that have little or no use for humankind, such as fallen leaves or rotten fruits. Therefore, the utilization of wooden forestry residues for preparing low-cost adsorbents is promising. In this review, we briefly approach adsorption advantages to wastewater treatment. Later on, we focus on several types of wooden forestry residues as alternative low-cost adsorbents. © 2021 International Association for Gondwana Research
On graviton non-Gaussianities during inflation
We consider the most general three point function for gravitational waves
produced during a period of exactly de Sitter expansion. The de Sitter
isometries constrain the possible shapes to only three: two preserving parity
and one violating parity. These isometries imply that these correlation
functions should be conformal invariant. One of the shapes is produced by the
ordinary gravity action. The other shape is produced by a higher derivative
correction and could be as large as the gravity contribution. The parity
violating shape does not contribute to the bispectrum [1106.3228, 1108.0175],
even though it is present in the wavefunction. We also introduce a spinor
helicity formalism to describe de Sitter gravitational waves with circular
polarization. These results also apply to correlation functions in Anti-de
Sitter space. They also describe the general form of stress tensor correlation
functions, in momentum space, in a three dimensional conformal field theory.
Here all three shapes can arise, including the parity violating one.Comment: 51 pages, v2: Corrected statement about parity violation in the
gravitational wave bispectrum. Some other changes and references adde
Fatty Acid Profile of Elephant Grass Pastures with Different Grazing Heights
Ruminant milk and meat are a source of CLA and omega-3 in the human diet and these fatty acids (FAs) have a beneficial effect on human health (Mcguire and Mcguire 2000). The increase in CLA and omega-3 in ruminant products is mainly related to proportion of C18:2 and C18:3 in the animal feed, like forage and to incomplete ruminal biohydrogenation (Bauman et al. 2000). Evaluation of FAs have been performed in temperate forage pastures, without the interaction of animal grazing, and presenting samples collected at ground level and at fixed re-growth intervals or seasons as the main sampling criteria. Therefore, the objective of this study was to evaluate the proportion of fatty acid in strata of elephant grass cv. Pioneiro with different grazing heights
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