Bond and fatigue characteristics of high-strength cement-based composites
Department of Civil and Environmental Engineering
Doctor of Engineering Science
Hsu, C.T. Thomas
Meegoda, Jay N.
The results of a series of tests on a variety of high strength cementitious composites yield a model from which an empirical equation of general normalized pull-out stress vs. pull-out displacement relationship is developed. A new variable named the "Brittleness Index" is defined and used in the proposed equation. Additionally, the concept of maximum strain is used to predict the fatigue life of high strength concrete.
Three sizes of deformed bars and two types of steel fibers with four different volume fractions were used to observe bond-slip and pull-out characteristics of high strength concrete. The results indicate that the maximum slippage of deformed bars is only about 10 of that observed in normal concrete. Consequently, the required development length may have to be longer for high strength concrete members as compared to normal concrete. For the fatigue characteristics study, standard 3x6 in. cylinders were tested at the rates of 6 and 12 Hz. in a closed-loop load-controlled system. The results show that as the compressive strength of the composites increases from 4000 to 11000 psi., the fatigue strength increases by 17 percents. The rate of loading does not significantly affect the S-N relationship, fatigue strength and fatigue limit of the high strength cement-based composites. The S-N curves of high strength concrete shows a faster decay rate than those of normal concrete. The maximum strain at any cycle under cyclic loading is always less than the maximum strain at failure under monotonic loading. Also observed is that the maximum strain-cycle relationship is linear. These results indicate that the design code for flexure of normal concrete cannot be applied to high strength concrete.
njit-etd1989-022 (329 pages ~ 9,823 KB pdf)
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Created August 2, 2011