Experimental and Theoretical Investigation on the Shear Behaviour of High Strength Reinforced Concrete Beams Using Digital Image Correlation

In this chapter an experimental investigation is carried out on high strength concrete beams without transverse reinforcement and with transverse reinforcement. The beams were tested in bending under two concentrated loads using the technique of digital image correlation. In the test setup, the shear zone which is defined by the area of beam between the support point and the loading point was studied by the camera of high resolution. The Gom-Aramis software was used to record and analyse the numerical images by determination of the deformation of concrete in the compressed zone of the beam, to calculate the opening, the spacing and the length of the diagonal cracks. The experimental shear strength of the beams was compared with the theoretical values predicted by the different design codes, such as the American ACI 318, the British Standard BS 8110, the European Eurocode 2, the New Zealand NZS 3101 and the Indian Standard IS456. The results show that all the design codes underestimate the contribution of high strength concrete to the shear resistance of reinforced concrete beams, and greatly overestimate the contribution of transverse reinforcement. The European Eurocode 2 is the only one among the four code models that gives the best prediction of the ultimate shear strength of high strength concrete

Comportement du béton de chanvre en compression simple et cisaillement

International audience Dans la littérature, la plupart des mélanges chaux/chanvre étudiés montrent un comportement fragile et une très faible résistance mécanique. Les formulations sont généralement riches en liant et légèrement compactées. Jusqu'à présent, ce matériau n'est pas considéré comme un matériau porteur et est principalement utilisé comme isolant de remplissage, combiné avec des composants de structure en bois, en béton ou en maçonnerie. Le présent travail est une étude expérimentale du comportement du béton de chanvre à la compression et au cisaillement, afin d'évaluer la capacité porteuse et au contreventement de ce matériau bio-sourcé, tout en assurant de bonnes qualités d'isolation thermique. Deux séries de tests sont effectuées. Le premier est un test de compression uniaxiale dans chaque direction pour caractériser l'anisotropie mécanique du matériau. Le second permet de caractériser le comportement au cisaillement de différentes configurations de la composition. Les expériences réalisées montrent une ductilité élevée de ce matériau en cisaillement, ce qui confirme les résultats de la littérature sur les structures de paroi. Ces résultats sont très prometteurs, notamment pour des applications parasismiques.</p

Structural build-up of rigid fiber reinforced cement-based materials

International audienceThe structural build-up of rigid fiber reinforced cement-based materials is studied. It has recently been shown that the behaviour of fiber reinforced concrete depends on the orientation of the fibers that has to be optimized during casting. As a result, there is a great interest to study the rheology of fiber reinforced concrete. One of the most important characteristics of modern fresh concretes is the structural build-up which is involved in many recent issues of concrete casting. This characteristic depends on the cement pastes chemical activity. This present work shows that structural build-up modelling used for common concretes can be generalized to fiber reinforced concretes. It can be shown that, if the inclusions percolation threshold is not reached, the structural build-up rate Athix is amplified by the addition of fibers and aggregates. Finally, this amplification of the structuration is estimated using modelling initially developed for spherical inclusions and aggregates

Béton de chanvre : Effet du dosage en granulat sur les propriétés thermique et mécanique.

International audienceLa préfabrication d'éléments de construction composés de béton de chanvre, mélange chaux-chanvre, montre que leur compactage à l'état frais conduit à une amélioration notable de leur qualité à l'état sec : meilleures caractéristiques mécaniques et qualités de parement. Cette étude explore des domaines où le granulat est très fortement compacté, jusqu'à 500 kg/m3, pour évaluer la faisabilité de réaliser des éléments porteurs. Afin de mieux maîtriser ce processus de mise en oeuvre, une matrice cylindrique instrumentée a été utilisée pour étudier le comportement mécanique et les caractéristiques de différentes formulations. La teneur en eau du mélange, ressort comme un paramètre déterminant, puisqu'elle tend à augmenter le coefficient de frottement du matériau et par voie de conséquence, réduire l'efficacité du compactage. Ce procédé permet de substituer efficacement du liant (chaux + eau), qui présente l'inconvénient d'être la phase la plus conductrice thermiquement et d'avoir le plus d'impact sur l'environnement, par des granulats végétaux compressibles. En effet, de meilleures résistances mécaniques et des conductivités thermiques semblables sont obtenues, in fine sur des matériaux matures, avec moins de liant par volume unitaire et des dosages en granulats plus importants. Un tel procédé par compactage s'avère donc pertinent sur un plan qualitatif et environnemental

Granulation sèche des poudres : Influence des paramètres du procédé

National audienceDans un but d'optimisation du procédé de granulation sèche de poudres, une presse à rouleaux instrumentée a été développée. Une première campagne d'essais a permis de visualiser le profil des contraintes à la surface des rouleaux en fonction de l'angle de rotation, ainsi que l'allure des différents paramètres (couple, effort, entrefer) au cours de l'essai

Fresh concrete pumping arrest investigation for thixotropy by a CFD modelling apporach

Concrete pumping operations determine construction speed, finishing quality, durability and even structural integrity. When pumping operations cannot be continued, most problems occur due to complex time-dependent transformations. This causes significant industrial costs (e.g. material and delay). Since time-dependent aspects are currently not fully understood and cannot be predicted, a way to quantify time-dependent aspects is needed. Therefore, we make an attempt by numerical simulation by comparing thixotropic cases with different pumping arresting times. After an introduction to fresh concrete rheology and numerical modelling, ten representative thixotropy cases are analysed. Despite some unresolved numerical instabilities, the numerical framework allows to estimate pumping pressure peaks after resting time. The results evaluate a thixotropy model, which is generally applicable for less thixotropic SCC’s. It is clear that flow re-initiation after rest in concrete pumping is poorly understood. Numerical simulation could be one approach for further analysis and is potentially important for practice. Future work such as simulation of concrete mixers, pressure increase after pumping arrest, formwork pressure decay and leakage are therefore recommended

R&D managers’ adaptation of firms’ HRM practices

The heads of R&D departments are those most responsible for the adaptation of firms’ human resource management (HRM) practices to the idiosyncrasies of their departments. From their description, this paper analyzes the HRM practices in R&D departments and the adaptation achieved in four different firms. The data suggest that the main adaptations are produced primarily in recruiting and organizing the work of R&D personnel. In contrast to suggestions in the specialized literature, less adaptation is found in other HRM practices analyzed (managerial support and degree of delegation, compensation and career plans). Psychological theories of procedural justice and social comparison can improve our understanding of such results. The organizational structure affects the reference group for such comparisons and, consequently, the R&D managers’ capacity to adapt such practices. Based on these arguments, the delegation of HRM practices to R&D departments will enhance the degree of adaptation of such policiesPublicad

Simple scoring system to predict in-hospital mortality after surgery for infective endocarditis

BACKGROUND: Aspecific scoring systems are used to predict the risk of death postsurgery in patients with infective endocarditis (IE). The purpose of the present study was both to analyze the risk factors for in-hospital death, which complicates surgery for IE, and to create a mortality risk score based on the results of this analysis. METHODS AND RESULTS: Outcomes of 361 consecutive patients (mean age, 59.1\ub115.4 years) who had undergone surgery for IE in 8 European centers of cardiac surgery were recorded prospectively, and a risk factor analysis (multivariable logistic regression) for in-hospital death was performed. The discriminatory power of a new predictive scoring system was assessed with the receiver operating characteristic curve analysis. Score validation procedures were carried out. Fifty-six (15.5%) patients died postsurgery. BMI >27 kg/m2 (odds ratio [OR], 1.79; P=0.049), estimated glomerular filtration rate 55 mm Hg (OR, 1.78; P=0.032), and critical state (OR, 2.37; P=0.017) were independent predictors of in-hospital death. A scoring system was devised to predict in-hospital death postsurgery for IE (area under the receiver operating characteristic curve, 0.780; 95% CI, 0.734-0.822). The score performed better than 5 of 6 scoring systems for in-hospital death after cardiac surgery that were considered. CONCLUSIONS: A simple scoring system based on risk factors for in-hospital death was specifically created to predict mortality risk postsurgery in patients with IE