A usable web for long-stay hospitalised children

This paper analyses the problems that should be considered when designing a web site for disadvantaged children. We focus our research on long-stay hospitalised children who use the Internet to communicate with realities located outside their usual surroundings, especially with distance education related activities. We introduce a case study which focuses on the use of the Internet in some Italian hospitals and then we sketch out some guidelines for designing usable web sites for hospitalised children

Validation of international code-type concrete elastic modulus estimation methods

The elastic modulus of concrete is utilized in the design of reinforced concrete structures, including in predicting creep deformation. This elastic modulus can be estimated, using models contained in national design codes, by considering one or more properties (usually compressive strength). The proposed paper assesses the accuracy of eleven empirical elastic modulus estimation models, when compared with the actual values measured on a range of concretes under laboratory controlled conditions. The equations considered are those contained in BS 8110 (1985), SANS 10100 (2000), SANS 10100 (2000) Modified, ACI 209 (1992/2008), AS 3600 (1988, 2001 and 2009), CEB-FIP (1970, 1978 and 1990), EC 2 (2004), GL 2000 and 2004), GZ (1993) and RILEM Model B3 (1995). The test results indicated that the discrepancies between the measured and estimated values were only significant in the case of the SANS 10100 (2000) Modified method (P = 3,1 %) and the CEB-FIP (1970) method (P = 2 %). The most accurate methods were the SANS 10100 (2000) and AS (2009) which both yielded a coefficient of variation (ωj) of 9,3 %. The least accurate method was the CEB-FIP (1970) which yielded a coefficient of variation (ωj) of 22,7 %. Furthermore, the test results of this research were used to establish which factors influence the elastic modulus of concrete. It was found that the concrete density, the density of the included aggregate and the coarse aggregate content separately correlated significantly with the elastic modulus (P ≤ 3 %)

Evaluation of the creep coefficients of international concrete creep prediction models

Abstract: Creep of concrete is an important design consideration. National design codes therefore provide empirically based models for the estimation of creep deformation. Such models estimate a creep coefficient (φ) and an elastic modulus (E) of the concrete, both of which are used to predict the creep strain at any age. This paper assesses the accuracy of the creep coefficients (φ) predicted by fourteen “design code-type" models, with a view to ascertain whether the estimated φ or E is responsible for the inaccuracy of some of the models. The models considered are those contained in SANS 10100 (2000)/BS 8110 (1985), SANS 10100 (2000) Modified, ACI 209 (1992), AS 3600 (2001 & 2009), CEB-FIP (1970, 1978 & 1990), the Eurocode EC (2004), Gardener and Lockman (2000 & 2004), Gardener and Zhao (1993) and the RILEM B3 (1995) methods. Laboratory creep tests were conducted on concrete prisms covering a range of mixes. The measured φ values were statistically compared to those predicted by the models considered. The results indicated that, for the range of concretes tested, the CEB-FIP (1990) method yielded the most accurate predictions of creep coefficient, giving the lowest overall coefficient of variation (all) of 27,7 %. The least accurate method was the CEB-FIP (1978) which yielded an overall coefficient of variation (all) of 112,5 %. Furthermore, the accuracy of the predicted φ values correlated highly significantly (P = 0,001 %) with the accuracy of the predicted creep magnitudes. The results of this investigation led to recommending the SANS 10100 (2000)/ BS 8110 (1985) model for predicting creep coefficients for South African conditions

An investigation into the effects of early propping removal on the deflection of reinforced concrete beams

In today’s fast paced construction industry, there is an ever present need to increase productivity and to complete projects as quickly as possible. Reinforced concrete is a popular and widely used construction material. However it has the unfortunate drawback in that the concrete requires time to set and gain sufficient strength before loads may be applied and the formwork and props can be removed. It is therefore desirable to keep propping times to a minimum. If the propping is removed too early, there is a risk of the member deflecting excessively and exceeding the maximum allowable limits, or in severe cases it could even lead to a structural failure or collapse. The SANS 2001 code provides recommended propping times for beams and slabs, which can be used as a guideline by building contractors and structural designers. These propping times present a universal approach, which does not consider all the factors that affect deflection. This simplified approach may be considered to be conservative as shorter propping durations could be possible without a loss in performance. The aim of this dissertation is to look into the effects of early propping removal on the longterm deflections of concrete members. This was done by modelling the deflection of a typical reinforced concrete beam at different ages of loading, using three code-based deflection calculation methods. The codes that were used are the South African National Standard (SANS), Eurocode (EC2) and American Concrete Institute code (ACI 318). A detailed literature-based investigation was conducted to determine the factors which affect deflection in reinforced concrete members, as well as the theory behind the code-based deflection calculation procedures. This was followed by the modelling of deflections using the abovementioned methods. Three case studies were performed to determine the effects of early propping removal under different scenarios. The first case study only deals with the effects of early age loading on long-term deflection. As an added point of interest, two different concrete mixes were used, made with two different types of cement. The second case study compares the effect that different levels of relative humidity have on the long term deflection at early ages of loading. Lastly, the effects of concrete strength on long-term deflections at early ages of loading was modelled. The results of the first case study indicated that a reduction in propping time is possible without causing excessive deflections. In the second and third case study is was observed that both the relative humidity and concrete strength respectively have an effect on the long term deflection and therefore also influence the propping time. The study concluded that based on the obtained estimated deflection values using the codebased methods, the propping times provided in the SANS 2001 code may in certain applications be conservative. According to the results obtained from the code-based deflection calculation procedures, it is possible to reduce the propping duration. It was suggested that an alternative method should be developed which would allow structural designers to determine the required propping time more accurately

Application of a new natural carbonation prediction (NCP) model to evaluation of durability design factors - strength, cover, and cement type

Abstract : In this paper, durability design parameters that are typically specified in structural design codes, were evaluated for their impacts on service lifespan. These parameters comprising concrete strength, cover depth, and cement type, were used as input variables into the new natural carbonation prediction (NCP) model. The resulting changes on the predicted lifespans were then evaluated. It was found that 10 MPa increment in concrete strength increases the structures lifespan geometrically 2.5 to 5.0 times. Similarly, 10 mm increment in cover extends the service lifespan 2.0 to 2.5 times. Also CEM II concretes with 10 MPa higher strength over that of CEM I concretes, gave the same carbonation resistance as the latter. Understanding of the impacts of durability design parameters aided by practical service life models, contributes towards a rational approach for service life design of concrete structures

Influence of blended cements on rate of steel corrosion in reinforced concrete structures in a marine tidal zone

Thesis (Master: Engineering: Civil Engineering)--Central University of TechnologyTo minimise the impact of early deterioration of reinforced concrete (RC) structures in the marine environment, blended cements made using supplementary cementitious materials (SCMs) are used. However, the physical, chemical, and mineralogical composition of these materials varies, hence, there is variation in their performance. This study therefore investigated the influence of selected SCMs on the corrosion rate of RC structures in a marine tidal zone, in correlation with some influencing parameters of reinforcement corrosion such as cover depth, oxygen availability, and concrete resistivity. This was achieved through an automated cycle change system, simulating the natural tide change in the marine tidal zone. Accordingly, three binders (100%PC, 70%PC/30%FA, and 50%PC/50%SL), 2 water to binder ratios (w/b) (0.45 and 0.65), and 2 cover depths (20 mm and 40 mm) were used to manufacture corrosion specimens. A total of 12 specimens were cast, each reinforced with one high tensile mild steel to act as an anode and 2 stainless steels (316 grade) which served the function of cathode. The corrosion specimens were exposed to a simulated marine tidal zone in the laboratory, which consisted of 6 hours of cyclic wetting with 5% NaCl solution and 6 hours of air-drying for a period of 3 months. All corrosion specimens were connected to a data logger which measured the voltage across a 100-ohm resistor between the working and counter electrodes on a weekly basis. The resulting current was calculated as the corrosion rate indicator. The results of this experimental study indicate that, at the early age of RC structures in the marine tidal zone, the rate of reinforcement corrosion is mostly influenced by the concrete quality and concrete cover depth. The increase in concrete cover depth reduced the corrosion rate of all the specimens, irrespective of the w/b. This was because of the increased travel path for chlorides and oxygen. In addition, higher cover depth prolongs the drying rate of the concrete pore structure, causing low oxygen availability, especially at low w/b, and thus low corrosion risk. Furthermore, a higher w/b 0.65 was found to increase the corrosion risk of the specimens, especially at lower cover depth. Nevertheless, due to the denser microstructure of blended cement concretes, Portland cement (PC) exhibited the highest corrosion rate. Hence, it can be inferred that high w/b can be used in the application of blended cements, provided relatively higher cover depth is used. Blended cement concretes, overall, showed relatively high concrete resistivity compared to PC concretes. In relation to the refinement of the exposure classification used in SANS guidelines, the findings of this study support the notion of adopting the classification of RC structures with a concrete cover depth ≥ 30 mm in the same category as the submerged zone. However, a further laboratory investigation over a longer period of exposure is required to further clarify the corrosion performance of blended cement concretes in a marine tidal zone

Effect of Chain Stiffness on the Structure of Single-Chain Polymer Nanoparticles

Polymeric single-chain nanoparticles (SCNPs) are soft nano-objects synthesized by purely intramolecular cross-linking of single polymer chains. By means of computer simulations, we investigate the conformational properties of SCNPs as a function of the bending stiffness of their linear polymer precursors. We investigate a broad range of characteristic ratios from the fully flexible case to those typical of bulky synthetic polymers. Increasing stiffness hinders bonding of groups separated by short contour distances and increases looping over longer distances, leading to more compact nanoparticles with a structure of highly interconnected loops. This feature is reflected in a crossover in the scaling behaviour of several structural observables. The scaling exponents change from those characteristic for Gaussian chains or rings in $\theta$-solvents in the fully flexible limit, to values resembling fractal or `crumpled' globular behaviour for very stiff SCNPs. We characterize domains in the SCNPs. These are weakly deformable regions that can be seen as disordered analogues of domains in disordered proteins. Increasing stiffness leads to bigger and less deformable domains. Surprisingly, the scaling behaviour of the domains is in all cases similar to that of Gaussian chains or rings, irrespective of the stiffness and degree of cross-linking. It is the spatial arrangement of the domains which determines the global structure of the SCNP (sparse Gaussian-like object or crumpled globule). Since intramolecular stiffness can be varied through the specific chemistry of the precursor or by introducing bulky side groups in its backbone, our results propose a new strategy to tune the global structure of SCNPs.Comment: 20 pages, 17 figure

Kyste hydatique du foie révélé par sa fistulisation dans le thorax

Une patiente âgée de 28ans, sans antécédent pathologique particulier, avec notion de contact avec les chiens (hébergement d'un chien au domicile), accusait depuis 2 mois des douleurs basithoraciques droites avec gêne respiratoire. Dix jours avant son hospitalisation, le tableau s'est aggravé par l'apparition d'une toux sèche, une asthénie et une fièvre. L'examen clinique a révélé un syndrome d'épanchement basi thoracique droit. La patiente a bénéficié d'une radiographie thoracique de face (A), qui montrait un épanchement liquidien pleural droit de moyenne abondance sans foyer parenchymateux visible. Une tomodensitométrie thoracoabdominale a montré un épanchement liquidien pleural droit associé à une scissurite, l'épanchement communiquant par le biais d'une fistule avec une lésion arrondie, hypodense, bien limitée du dôme hépatique, renfermant une calcification périphérique et ne se rehausse pas après injection de produit de contraste (B). Le complément échographique réalisé a confirmé la présence de la lésion du dôme hépatique avec les caractères sémiologiques suscités (C). Biologiquement, on notait une discrète élévation de la VS à 15mm la première heure avec une sérologie hydatique positive. La patiente a bénéficié d'une chirurgie avec drainage de liquide pleural et fermeture de la fistule. L'évolution post opératoire était favorable. Le kyste hydatique est une parasitose due au développement de la forme larvaire d'échinococcus granulosus. L'hôte habituel est le chien, l'homme étant l'hôte intermédiaire. Toutes les localisations sont possibles. La fistulisation dans le thorax est beaucoup plus rare et varie de 2 à 5% selon les séries.Pan African Medical Journal 2015; 2