Stress-strain curve for the design of high-strength concrete elements

Although the great advances in concrete technology have led to the possibility of obtaining ready-mix concrete with compressive strength around 100 MPa, some national and international codes for concrete structures do not cover concrete strengths above 50 MPa. Many codes are under revision, but some of them (including the Brazilian Code) will still not include high strength concretes. Due to the different characteristics of higher strength concrete some design procedures traditionally used in normal strength concrete structures have to be changed. Different types of stress-train relationships for concrete have been proposed for the non-linear analysis of member behavior and for the ultimate state analysis of high strength concrete elements under combined flexure and axial load. In this work comparisons are made between proposed stress-strain curves and between the axial load-moment interaction diagrams based on these curves. Comparisons of test results with these diagrams, for columns subjected to eccentric compression, give an idea of the different degrees of safety obtained using those curves.

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Résumé Malgré les grands progrès de la technologie en matière de béton, qui ont rendu possible l'obtention de bétons résistant à une compression d'environ 100MPa, quelques codes nationaux et internationaux relatifs aux constructions en béton ne couvrent pas des résistance du béton supérieures à 50 MPa. Plusieurs codes sont en cours de révision, mais beaucoup (dont le code brésilien) ne s'intéressent toujours pas aux bétons à haute résistance. En raison des différentes caractéristiques des bétons à haute résistance, certains procédés de définition traditionnellement utilisés pour les constructions en béton normal doivent être modifiés. Différents types de relations contraintes—déformations ont été proposés pour le béton dans le cadre de l'analyse non-linéaire de son comportement et dans celui de l'analyse finale des éléments en béton armé en flexion combinée avec une charge axiale. Cet article compare les courbes contraintes—déformations proposées et les diagrammes interaction charge axiale—moment qui résultent de ces courbes. Les comparaisons effectuées entre les résultats expérimentaux et ces diagrammes, pour des colonnes soumises à des compressions excentriques viennent illuster les différents degrés de sécurité obtenus grace à ces courbes.

     

The effect of goal setting on group performance: A meta-analysis.

Updating and extending the work of O'Leary-Kelly, Martocchio, and Frink (1994), with this meta-analysis on goal setting and group performance we show that specific difficult goals yield considerably higher group performance compared with nonspecific goals (d = 0.80 ± 0.35, k = 23 effect sizes). Moderately difficult and easy goals were also associated with performance benefits relative to nonspecific goals, but these effects were smaller. The overall effect size for all group goals was d = 0.56 ± 0.19 (k = 49). Unexpectedly, task interdependence, task complexity, and participation did not moderate the effect of group goals. Our inventory of multilevel goals in interdependent groups indicated that the effect of individual goals in groups on group performance was contingent upon the focus of the goal: “Egocentric” individual goals, aimed at maximizing individual performance, yielded a particularly negative group-performance effect (d = –1.75 ± 0.60, k = 6), whereas “groupcentric” goals, aimed at maximizing the individual contribution to the group's performance, showed a positive effect (d = 1.20 ± 1.03, k = 4). These findings demonstrate that group goals have a robust effect on group performance. Individual goals can also promote group performance but should be used with caution in interdependent groups. Future research might explore the role of multilevel goals for group performance in more detail. The striking lack of recent field studies in organizational settings that emerged from our brief review of trends in group goal-setting research should be taken into account when designing future studies in this domain. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Empirical comparison of tree ensemble variable importance measures

Tree ensembles are becoming well-established as popular and powerful data modelling techniques. Tree ensemble models are essentially black box models, although their individual members may not be, and with their growing popularity, interest in the interpretation of tree ensemble models has also grown. This study presents variable importance measures associated with random forests, conditional inference forests and boosted trees, and employs a number of simulated data sets to compare these methods. Overall, variable importance indicators based on bagged conditional inference forests appear to strike a good balance between identification of significant variables and avoiding unnecessary flagging of correlated variables. Data preprocessing and interpretation by experts knowledgeable with a specific data set remain vital.     

Effect of Sodium Chloride, Acetic Acid, and Enzymes on Carotene Extraction in Carrots (Daucus carota L.)

ABSTRACT: Carrot root cores were cut off longitudinally and treated with NaCl (0.6 and 1.2 M ) and/or acetic acid (1.33%, 2.67%, and 4%) solutions. The extractability of the carotenes was estimated. Similarly, carrot cores were also treated with some degrading enzymes (carbohydrases, lipases, and proteases) alone or in combination to study the effect of the tissue rupture or the hydrolysis of possible complexes or interactions between carotenes and other components on the carotene extractability. The results showed that acetic acid increased the extractability of α- and β carotenes up to 99.8% and 94.6%, respectively, at a 4% acid concentration compared with the samples without any treatment. This increase was directly proportional to the acid concentration. An increase in extractability was also observed for NaCl, although the increases were not as high as in the previous case with values of 49% and 41.4% for α- and β-carotenes respectively at a 0.6 M concentration. The study of microstructural changes and extractability revealed that the enzymatic treatments could have broken some carotene complexes and interactions and altered the carbohydrate matrix structure, increasing to a certain extent the extractability of carotenes. It can be concluded then that pickling with 4% acetic acid is a good method to increase the extractability of α- and β-carotenes.     

Syntheses and biological activities of 1,4-iminoalditol derivatives as alpha-L-fucosidase inhibitors

A review dealing with 1,4-iminoalditol (hydroxylated pyrrolidine) derivatives as inhibitors of alpha-L-fucosidases including the different synthetic approaches for their preparation as well as their inhibitory properties is presented.     

Modification of epoxy–anhydride thermosets with a hyperbranched poly(ester amide). II. Thermal,dynamic mechanical,and dielectric properties and thermal reworkability

An epoxy–anhydride formulation used for the coating electrical devices was modified with a commercially available hyperbranched poly(ester amide), Hybrane S2200, to improve the thermal degradability of the resulting thermoset and, thus, facilitate the recovery of substrate materials after the service life of the component. The thermomechanical, mechanical, and dielectric properties and thermal degradability were studied and interpreted in terms of the composition and network structure of the cured thermosets. Although the crosslinking density was significantly reduced with the incorporation of S2200, the glass transition temperature of the fully cured material (T_g∞) of the modified thermoset was hardly affected because of the enhancement of H‐bonding interactions in the presence of S2200. Despite the different network structures, the combined dielectric and dynamic mechanical analysis revealed that the relaxation dynamics of both networks were very similar. In terms of application, improvements in the dielectric and mechanical properties were observed. The incorporation of S2200 accelerated the thermal decomposition of the material and, thus, facilitated the recovery of the valuable parts from the substrate at the end of the service life of the apparatus. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Microstructure and Phase Constitution Near the Interface of Explosively Welded Aluminum/Copper Plates

The microstructure changes and the phase constitution within the layers close to the bonding interface strongly influence the properties of bimetallic strips. In this work, the layers near the interface of explosively welded aluminum and copper plates were investigated by means of microscopic observations, mostly with the use of transmission electron microscopy (TEM) equipped with energy dispersive spectrometry (EDX). The study was focused on the identification of the intermetallic phases, the possible interdiffusion between the copper and the aluminum, and the changes in the dislocation structure of the parent plates. In macro-/mesoscale, the interfaces were outlined by a characteristic sharp transition indicating that there was no mechanical mixing between the welded metals in the solid state. In micro-/nanoscale, the layers adhering to the interface show typical deformed microstructure features, i.e., structure refinement, elongated dislocation cells, slip bands, and microtwins (in copper plate). The internal microstructure of the intermetallic inclusion is composed mostly of dendrites. The electron diffractions and TEM/EDX chemical composition measurements revealed three crystalline equilibrium phases of the γ-Al₄Cu₉, η-AlCu, and Θ-Al₂Cu type (the last one was dominant). However, most of the observed phases of the general Cu _m Al _n type (also crystalline) do not appear in the equilibrium Al-Cu phase diagram. Inside the intermetallic inclusions, no significant regularity in the phase distribution with respect to the parent sheets was observed. Therefore, it was concluded that the processes occurring in the melt determined their local chemical composition.