Shear Predictions of Eurocode EC2
The shear strength of reinforced concrete members is a function of shear capacity of concrete (Vc), which in turn depends on influencing parameters including concrete compressive strength (f’c), ratio of tension reinforcement (), shear span to depth ratio (a/d), size effect or depth factor (ξ), size of the aggregate in relation to the minimum size of the member (aggregate interlock aspects).Over the last several decades, researchers have tested reinforced concrete beams (without web reinforcement) over a range of variables limited by the breadth and depth of their experimental investigations and on the basis of their experimental results, have proposed empirical equations for predicting the shear capacity of normal and high strength-high performance concrete in reinforced concrete beams. In this paper a relational database using ACCESS software is developed and is populated with experimental results of 2145 shear critical reinforced concrete beams without web reinforcement using both normal as well as high strength –high performance concrete. An evaluation was also conducted to assess the predictive accuracy of shear design equation of Euro Code EC2. The results indicate for beams of normal as well as high strength concrete, the Euro Code EC2 design equation is adequate to accurately predict the shear capacity of reinforced concrete beams over the range of variables considered in this study.
Shear stress contributions and failure mechanisms of high strengh reinforced concrete beams
The problem of shear capacity of reinforced concrete members has engaged the attention of many researchers. Despite this, it has not yet been understood fully because of the fact that the behaviour of concrete structures under variable stresses is very complex. Moreover, little information is available regarding both the shear stress contribution of different elements and the failure mode mechanisms of high strength reinforced concrete (HSRC) members. In this paper an attempt has been made to discuss in some detail these aspects in the context of high strength reinforced concrete beams. In addition, new expressions have been developed to predict the ultimate shear stress of high strength reinforced concrete beams.RésuméLe problème de capacité de cisaillement des éléments en béton armé a toujours retenu l’attention de nombreux chercheurs. Malgré cela, on ne l’a pas encore complètement résolu, parce que le comportement des structures en béton soumises à différentes contraintes est très complexe. De plus, il existe peu d’informations sur la contribution des contraintes de cisaillement des différents éléments et les mécanismes de rupture des poutres en béton armé à haute ténacité. Dans cet article, nous entamons une discussion détaillée de ces aspects, dans le contexte des poutres en béton armé à haute ténacité qui subissent une défaillance critique du cisaillement. Nous y ajoutons également de nouvelles expressions développées pour prédire le taux de cisaillement critique de ces poutres.
Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material
Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.