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.
A Comparative Analysis of Codes Prediction of Shear Resistance in Beams without Shear Reinforcement
Shear provisions in codes are based on empirical equations derived from experimental test results without any rational theory to explain its behavior. Some of these expressions, for example BS 8110, ACI 318 and Eurocode 2 takes into account the effect of reinforcement ratio, effective depth and concrete compressive strength while Canadian code considers the shear strength to be a function of concrete compressive strength only. The new Model code 2010 considers the shear strength of beams as a function of longitudinal strain in the web. This brings about disparity in shear strength prediction from different codes. This paper examines the accuracy of shear strength predictions in beams without shear reinforcement. The study involves a comparative analysis of shear strength predictions from five different codes: BS 8110, Eurocode 2, Canadian code, ACI code 318 and Model code 2010. A total of 435 experimental test results from database of shear critical beams in literature were used for the study. The results shows that Model code 2010 shear strength prediction is the most conservative among the five codes shear provisions considered in this study. This may be due to the assumed linear elastic state of the flexural reinforcement at the point of failure in shear. BS 8110 and Eurocode 2 predictions gave the least variation compared to other codes predictions. The highest number of unsafe shear strength predictions was obtained from Canadian code followed by prediction s from ACI 318.
Comparative study of in vitro flow characteristics between a human aortic valve and a designed aortic valve and six corresponding types of prosthetic heart valves.
A model of a pulsatile cardiovascular system is described including an electronic control, a hydraulic driving unit, a volume storage, a peripheral resistance and measuring equipment. Six different artificial heart valves, a designed aortic valve (Aachen pockett valve II) and a human aortic valve have been tested in the outflow position of the pump. Three of them are presently being used in clinical applications. Measurements of pressure and volume flow have been obtained for different frequencies n, pump volumes Vp and time ratios between pressure and suction phase. From the experimental results a comparative evaluation was deducted for different working conditions. In comparison to natural human aortic valve (NK) large volume flow is verified by the Aachen pocket valve II (AT), the Gott-Dagget value (GD), the Starr-Edwards valve (SE) and the Lillehei-Kaster valve (LK). The Gott-Daggett valve has the smallest back flow volume. The Smeloff-Cutter and in particular the Wada-Cutter valve have the largest regurgitation. This is to be expected since the Cutter valves are purposely so designed that they do not close tightly in order to avoid blood sedimentation. The human aortic valve, the Gott-Daggett valve and the Aachen pocket valve demonstrate the most favourable opening-closing characteristics. The human aortic valve achieves a negligible pressure loss, followed by the Björk-Shiley and the Lillehei-Kaster valve.