Size Effect in Compression of High Strength Fibre Reinforced Concrete Cylinders Subjected to Concentric and Eccentric Loads

Abstract

Tests results obtained as a part of a study of size-effects on the compressive behavior of axially and eccentrically loaded plain and fibre reinforced concrete members are presented. The specimens were geometrically similar, having circular cross-sections with diameters of 60 and 100 mm, and varying in length from 120 to 400 mm. Several types of fibres (steel and synthetic) were added to the high strength matrices at a constant volume percentage of 2 % to evaluate their influence on the behavior of the material and on the size effect. It was observed that for all types of specimens the failure loads exhibited a size effect. The nominal stress at maximum load decreased as the size of the specimens or the eccentricity of the external load increased, but the post peak behavior and the mode of failure of the specimens were not much affected by the specimen size when high volume fractions of fibres were utilized. IntroductionMost current design codes, which are based on limit state theory and justified by theory of plasticity, do not take into account size effects. In quasi-brittle materials, including concrete and rock, the observed load-deformation diagrams of members subjected to tension or compression are characterized by post-peak strain softening, which is due to the progressive development of damage in the form of microcracks which, after localization, lead to the final failure 1 . For this reason the description of the behavior of concrete is incorrect in terms of plasticity, and thus a size effect is observed. Recent developments in fracture mechanics have shown that the size effects which are observed in the failure of concrete structures are due to the concrete rather than the steel; this is true not only when the concrete fails in tension, (diagonal shear, bar pull-out, torsion, etc), but also when the concrete fails in compression, except when there are confining pressures that greatly exceed the uniaxial compression strength 2-4 . Recent studies 5-7 have shown that by adding sufficient quantities of randomly distributed short fibers of appropriate geometries to the matricesit is possible to improve the behavior of plain concrete and conventionally reinforced concrete in terms of both ductility and residual strength, especially in the case of high strength concrete. The active confinement due to the fibers because of their pull-out resistance ensures ductile behavior, reducing the quantity of lateral steel reinforcement required and thus reducing the size effect. Our aim here was to investigate the size effect in specimens having different aspect ratios, made of high Materials for Buildings and Structures. Edited by F. H. Wittmann

Fractal fragmentation theory for size effects of quasi-brittle materials in compression

“…In this section, a comparison is presented between the experimental results carried out by Campione and Mindless 28,29 and the theoretical predictions for the size effects on the dissipated energy density and on the compressive strength obtained respectively from the fractal laws of equations (7) and (8). The comparison regards geometrically similar cylindrical specimens with base diameters of 60, 100 and 150 mm and with fixed slenderness (height over diameter) equal to 2.…”

التحري التجريبي لبعض الخواص الميكانيكية للخرسانة المسلحة بأستخدام ألالياف الحديدية

“…The effect of steel fiber on the compressive strength of concrete has been discussed in many studies, and resulted that, the presence of the SF has slightly affect the compressive strength of concrete, but overall effect is negligible in many cases. Many researchers [10,11] have observed increases in the compressive strength of concrete ranging from (0 -15%) for up to 1.5 percent by volume of fibers. while other researchers observed that, the increase in the compressive strength range from negligible in most cases to 23 % for SFRC for up to 2.0 percent by volume of fiber [12].…”