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Recently, the importance of high Strength concrete has appeared due to its application in manufacturing most of the concrete structures and members, as well as to its importance in the implementation of civilian facilities like bridge bases, skyscr apers and in implementing the columns and platforms which carry oil installations carried out in the oceans and seas. The research aims to design concrete mixtures with cylindrical resistors ( 55- 65- 75 Mpa) according to the American code AcI-211-4R-93 by using local and appropriate additions as well as explaining the method used in designing. Then, studying the transformation in stress strain curve – deformation (σ- ζ ) undergoing a simple pressure on the previous samples throughout the available devices. Then, it was compared to the charts obtained mathematically .Law behaviour of stress strain and deformation curve was rated, in addition to modulus of elasticity taken from the chart. Couple of results and recommendations related to the issue were concluded, those which were applied in praxis.
This research presents an experimental study about the effect of steel fibers on the main variables of stress- strain curve for high strength concrete on simple compression, which are: shape of stress- strain curve, ductility factor, energy absorpt ion capacity. For this purpose, series of cylinders concrete specimens were prepared in compressive strength (70 MPa). the steel fiber with aspect ratio of L/D =70 were added at the volume fractions of (0-1-1.5-2)%. The cylinders were tested under a monotonic loading at compression, and as a result of the tests, the total curve of stress- strain was obtained. The experimental results of research showed a positive effect of steel fibers on the behavior of high strength concrete, this effect increased with increasing volume fraction of steel fibers. It can be seen from stress-strain curve, whereas the slope of the ascending branch is not much affected. The descending branch of the stress- strain curve decreases by the increase in the fiber volume fraction. This means the ductility and toughness improve with the addition of steel fibers and as a result the behavior of high strength concrete has gone far away from being brittle as it is used to be.
This research presents an empirical study about the behavior of High Strength Concrete beams under the static cyclic loading. It determines the influence of cyclic loading on the moment capacity and deflection of HSC beams. A comparison of the mome nt capacity and deflection in both kinds of loading (monotonic and cyclic loading) were achieved. High Strength Concrete mixture was designed, based on the specifications of the American code ACI 211.4R-93. Thirty six concrete beams were prepared, nine of them were tested under monotonic loading and the rest of beams were tested under cyclic loading. The cyclic loading was performed for (5,10,15) cycles, at a range from zero to 65%, 75%, 85% of the minimum expected monotonic load. The results showed that the cyclic loading have positive effect on the flexural behavior of HSC members, whereas the moment capacity increased and the deflection decreased, especially at a range from zero to 75% of the minimum expected monotonic load, when the number of cycles was 5,10,15.
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