37 research outputs found
Ultrastructure and complex polar architecture of the human pathogen Campylobacter jejuni
Campylobacter jejuni is one of the most successful food-borne human pathogens. Here we use electron cryotomography to explore the ultrastructure of C. jejuni cells in logarithmically growing cultures. This provides the first look at this pathogen in a near-native state at macromolecular resolution (∼5 nm). We find a surprisingly complex polar architecture that includes ribosome exclusion zones, polyphosphate storage granules, extensive collar-shaped chemoreceptor arrays, and elaborate flagellar motors
Deflection control for reinforced recycled aggregate concrete beams: Experimental database and extension of the fib Model Code 2010 model
Recycled aggregate concrete (RAC) has emerged as a viable solution for
solving some of the environmental problems of concrete production.
However, design guidelines for deflection control of reinforced RAC
members have not yet been proposed. This study presents a
comprehensive analysis of the applicability of the fib Model Code 2010
(MC2010) deflection control model to reinforced RAC beams. Three
databases of long-term studies on natural aggregate concrete (NAC) and
RAC beams were compiled and meta-analyses of deflection predictions
by MC2010 were performed. First, the MC2010 deflection control model
was tested against a large database of long-term tests on NAC beams.
Second, a database of RAC and companion NAC beams was compiled
and initial and long-term deflections were calculated using the MC2010
model. It was shown that deflections of RAC beams are significantly
underestimated relative to NAC beams. Previously proposed
modifications for MC2010 equations for shrinkage strain and creep
coefficient were used, and new modifications for the modulus of elasticity
and empirical coefficient β were proposed. The improved MC2010
deflection control model on RAC beams was shown to have equal
performance to that on companion NAC beams. The proposals presented
in this paper can help engineers to more reliably perform deflection
control of reinforced RAC members.This is the peer-reviewed version of the article:
N. Tošić, S. Marinković, and J. de Brito, ‘Deflection control for reinforced recycled aggregate concrete beams: Experimental database and extension of the fib Model Code 2010 model’, Structural Concrete, vol. 20, no. 6, pp. 2015–2029, 2019 [https://doi.org/10.1002/suco.201900035
Study of Composite Behavior of Reinforcement and Concrete in Tension
This paper aims to further the understanding of the interaction between reinforcement in tension and the surrounding cracked concrete. This is achieved using the elastic analysis of axisymmetric prisms reinforced with a single central bar. As a preliminary to the analyses, the behavior of axially reinforced prisms is described based on previous experiments. This preliminary analysis confirms that the elastic analysis adopted in this investigation is reasonable. Two analytical exercises are described: the first assumes no slip, plasticity, or internal cracking at the interface between the steel and the concrete; the second introduces internal cracking and debonding between ribs. The first analysis indicates that shear deformation of the surrounding concrete accounts for a substantial proportion of the surface crack width, and therefore that this form of deformation cannot be ignored in crack prediction formulae. The second analytical exercise shows that the internal cracking model described by Goto is appropriate