tesi A. Caggiano.pdf - EleA@UniSA - Università degli Studi di Salerno

Chapter 2. Experimental characterization of steel fiber notched concrete beamsbe considered. Fiber reinforcements can substitute (also partially) the conventionalreinforcements at ultimate limit state if the above limits are fulfilled [UNI-11039-1,2003].2.4 Closing remarksThis chapter reports the results of a series of experimental tests aimed at investigatingthe behavior of FRC beams under four-point bending. Particularly, the proposedexperimental campaign focuses on investigating the possible influence of combiningtwo different types of fibers on the resulting properties of FRC. Thus, five combinationsof long/short hooked-end fibers have been considered in the concrete mixtures andtwo different amounts of steel fibers have been employed for each of them.The following observations emerged by analyzing the experimental results:• the first-crack strength and the whole post-cracking behavior have mainly beeninfluenced by the amount of fibers: crack-softening response has been observedfor all specimens with ρ f = 0.5%, whereas a rather plastic behavior characterizesthe post-cracking response of specimens with ρ f = 1.0%;• a slight influence of fiber combination has been observed in terms of first-crackstrength: this parameter has been almost irrelevant in the case of low amountof fibers, while results in a slightly more regular trend in the case of ρ f = 1.0%fibers;• the ductility indices determined for all specimens point out that no clear influencecan be recognized to fiber combination in affecting the overall response ofFRC in the post-cracking regime.As a matter of fact, the very low influence of fiber combination on the observed FRCbehavior is the key conclusion of the experimental activity in this thesis. However, itis worth highlighting that this cannot be considered as a general conclusion, as thetwo “different” fibers have been characterized by the same material, similar geometricdetails (i.e., hooked-ends) and rather close values of aspect ratios. Thus, the possiblesynergistic effect of combining different types of fibers should be investigated by consideringtwo (or more) kinds of really “more different” fibers (i.e., in terms of materials,geometric and detailing).42