Use Of Slabs Research Articles

Assessment on the structural impact of the slabs with joists used in the reinforced concrete structures in Burundi

Introduction. This paper addresses the effect of reinforced concrete slabs with joists on the behavior of reinforced concrete buildings.
 
 Materials and methods. Firstly, models of 3-storey, 6-storey, 9-storey and 12-storey buildings were used to determine internal longitudinal forces in the most heavily loaded column on the ground floor and to identify the unloading action of slabs with joists. Secondly, natural periods of the structures were identified by solving the modal equation of vibration in reinforced concrete building models to identify the effect of the unloading action on the flexibility of a reinforced concrete building. Tables and diagrams were used to analyze and interpret the results.
 
 Results. For the ratio of 4.72 between the weight of one square meter of a reinforced concrete slab and the weight of joists used in one square meter of the slab, the unloading effect varies from 15.18 to 16.78 % and from 15.74 to 16.10 % in the columns, respectively, for the ultimate limit state and the serviceability limit state of a reinforced concrete building. The unloading action, induced by the slabs with joists, reduces the flexibility of a reinforced concrete building. Flexibility reductions are illustrated by reductions of the values of the natural periods from 6.74 to 6.98 % for the 3-storey building, from 5.77 to 6.74 % for the 6-storey building, from 5.36 to 6.56 % for the 9-storey building and from 4.26 to 7.84 % for the 12-storey building.
 
 Conclusions. The use of slabs with joists reduces the mass by 15 % and has an unloading effect on a reinforced concrete structure; it also boosts the building flexibility by 6 % and deteriorates the deformability due to the non-linear behaviour of concrete.

Sistema misto steel deck e suas aplicações na construção civil

O conceito de laje mista ou então laje com fôrma colaborante, surgiu nos Estados Unidos na década de 1950 e desde então passou a ser amplamente empregado, claramente em edificações metálicas de vários andares. Já no Brasil, começou a ser difundida na década de 1970 pela empresa Robtek (associação entre a empresa americana Robertson e a empresa brasileira Tekno). A laje steel deck ou laje colaborante ou mista como também é conhecida, é uma técnica usada na construção de lajes em edificações de vários portes. Uma laje composta basicamente por chapas ou telhas de aço galvanizado e uma camada de concreto. O uso da laje com formas colaborantes pode ser considerado em projetos de edifícios industriais; em lajes de escolas, rodoviárias; hospitais e órgãos públicos; terminais de aeroportos, passarelas ou pontes; cinemas e em shopping centers; edifícios de escritórios com vários andares. Elas podem usadas em estruturas de concreto e também estruturas metálicas. Esse tipo de laje está sendo muito utilizado, pois a velocidade de execução é muito maior, uma das principais características ditas por especialistas da área. Tanto em obras comerciais, residenciais ou industriais, esse tipo de laje geralmente é aplicada em obras onde há entrega em prazos curtos e a necessidade de racionalização dos processos construtivos.

Spatial transport of runaway electrons in axisymmetric tokamak plasmas

An implicit assumption made in the vast majority of studies of runaway electrons is that they are well confined to a given magnetic flux surface, thus allowing the use of slab or bounce averaged formulations that ignore the spatial transport of runaway electrons. While such an assumption is known to break down in the presence of strong 3D magnetic field perturbations, here we show that it can be violated even for an axisymmetric magnetic field under conditions representative of an actively mitigated disrupting plasma. Specifically, the low temperature and large impurity content typical of a post thermal quench plasma are shown to provide a drastic enhancement of the diffusive and convective transport of runaways electrons, where the convective component is found to be dominated by the Ware pinch. This inward convective flux allows runaway electrons to be displaced toward the plasma center, where they are eventually detrapped and reaccelerated, thus focusing populations of runaway electrons in the inner portion of the plasma. The resulting runaway electron distribution is shown to settle into a well-defined spatial eigenmode, whose form is often insensitive to the spatial distribution of the original seed population. The underlying transport processes responsible for determining the width and shape of the spatial runaway electron eigenmode are analyzed under a range of circumstances characteristic of a post thermal quench plasma.

Surface stress changes in the Ir(001)/H system: Density functional theory study

Density functional theory calculations of the surface energy and surface stress changes associated with the formation of the Ir(001)(5 \ifmmode\times\else\texttimes\fi{} 1)-hex clean-surface reconstruction and its transformation to a (5 \ifmmode\times\else\texttimes\fi{} 1)-added row (AR) structure in the presence of adsorbed atomic hydrogen have been performed and compared with experimental results. The calculations clearly show that the clean-surface (1 \ifmmode\times\else\texttimes\fi{} 1)-to-(5 \ifmmode\times\else\texttimes\fi{} 1)-hex reconstruction is not driven by a reduction in tensile surface stress. While the surface energy is reduced by this transformation, the surface stress increases; proper convergence of the calculated surface stress requires the use of slabs containing at least nine atomic layers, due to the substantial subsurface relaxations associated with the (5 \ifmmode\times\else\texttimes\fi{} 1)-hex phase. By contrast, the H-induced reconstruction leads to a calculated reduction in the tensile surface stress in the range 1.76--2.06 Nm${}^{\ensuremath{-}1}$ for an H coverage range of 0.6--0.8 ML, in excellent agreement with the experimentally determined value of 1.7 Nm${}^{\ensuremath{-}1}$.

Slab-based Faraday isolators and Faraday mirrors for 10-kW average laser power.

It is shown that the use of slabs instead of rods makes it possible to fabricate Faraday isolators and Faraday mirrors operating at a multikilowatt power. Analytical dependences of thermally induced depolarization in Faraday devices on radiation power and on slab aspect ratio have been obtained.

Concerted Use of Slab and Cluster Models in an ab Initio Study of Hydrogen Desorption from the Si(100) Surface

Slab and cluster models are used to study H2 desorption from a single dimer of the Si(100)−2 × 1 surface. The cluster models are constructed using geometries obtained from slab-model optimizations. The largest cluster model considered, Si89H62, contains eight surface dimers and gives reaction and activation energies for desorption nearly identical with the slab-model values when the same electronic structure method is used. The barrier for H2 desorption, calculated using the Si89H62 cluster model and the Becke3LYP functional, is 64.3 kcal/mol. When this result is corrected for the effects of basis set expansion and vibrational zero-point energy correction, the barrier decreases to about 61.0 kcal/mol, which is only 4.0 kcal/mol greater than the observed desorption barrier.

The in vivo orthodontic banding model for vital teeth and the in situ orthodontic banding model for hard-tissue slabs.

This paper presents the orthodontic banding model for vital teeth and the orthodontic in situ model for slabs of enamel, root surface, dentin, or other mineralized tissues such as shark enamel. The model for vital teeth is an in vivo model, since a crevice for plaque accumulation is created behind orthodontic bands on the buccal enamel surfaces of teeth in situ. Visible white-spot lesions are usually seen after a four-week banding period in the absence of fluoride. The microbiological flora developed behind the bands shows a similarity to that of natural caries. Microradiographic data show that the initial lesion is a softening of the enamel surface. Later, a subsurface lesion develops. A modification of the model has been developed for the use of slabs of mineralized tissues. In this model, slabs are mounted on a removable appliance. The slabs are covered with orthodontic banding material for plaque accumulation. Lesion development in enamel in the two model systems is almost identical. The benefit of the in vivo model is that caries development can be studied on vital teeth in young individuals. The model is independent of the patient's cooperation. No special diet is required, e.g., no sucrose rinsing. In the in situ model, slabs could be examined after one study period and then replaced for another period.

FIRST-PRINCIPLES CALCULATIONS OF THE ELECTRONIC STRUCTURE OF GRAIN BOUNDARIES

FIRST-PRINCIPLES CALCULATIONS OF THE ELECTRONIC STRUCTURE OF GRAIN BOUNDARIES