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.
Where is Shear Reinforcement Required? Review of Research Results and Design Procedures
This paper presents a review of research on shear strength of reinforced concrete members without stirrups (shear reinforcement). A database of 1849 available experimental results from over the past 60 years is examined and these results are compared to predictions from current North American shear design procedures. Special attention is paid to the behavior of beams ranging from short span deep beams to members controlled by flexure. The findings from the review indicate that using the current ACI shear provisions to decide where shear reinforcement is required can be unconservative for members with larger effective depths, or higher stresses in the longitudinal reinforcement. Improvements to the ACI Code are proposed to mitigate these weaknesses. The AASHTO-LRFD and Canadian CSA sectional and strut-and-tie provisions are found to provide a more uniform level of safety for all member types. The results from this review can allow engineers to identify members in their own structure where a more conservative shear design procedure is appropriate.
Routine quantitative phase analysis of niobium-bearing lateritic ores
Routine quantitative analyses by Rietveld full-pattern fitting have been carried out on more than one thousand niobium ore samples originating from four pyrochlore deposits: Lueshe and Bingo (D.R. Congo), Mabounie (Gabon), and Sokli (Finland). The ore samples were characterized by a highly variable mineral content, the presence of mineral phases with a wide range of compositions and a high amorphous content. An analytical procedure was established which addressed several problems: creation of an appropriate crystallographic parameter database, specimen preparation, check for preferred orientation and measurement of the amorphous content by the internal standard method.