The effect of low-volume fiber and micro fiber type on the punching strength of RC flat slab systems

While flat slab systems have advantages such as being aesthetic and useful, reducing formwork costs, and placing concrete more easily, it is known that flat slab systems may also experience collapses due to the punching effect. Within the scope of this thesis, an experimental study program was carried out to test large-scale slab column connection elements containing different punching measures (control without any punching measure, shear wedge, single fiber, double and triple hybrid fiber SCC) in order to increase the punching resistance performance of slabs formed without beams. For this purpose; 7 SCC mixtures were designed, including one fiber-free SCC (for control and shear wedge samples), one SCC with only macro steel fibers, and three binary and two triple hybrid fiber SCC mixtures containing macro and different types of micro fibers (6 mm and 13 mm micro steel fibers and polypropylene (PP) fiber). For these designed non-fibrous and fibrous SCC mixtures, slump flow, J-ring and V-funnel workability tests were carried out based on EFNARC 2005. Then, samples were produced from the obtained mixtures for compression, splitting tensile and bending tensile strength tests, and after curing for 7, 28 and 56 days, the mentioned strength tests were performed on these samples. Then, a total of 8 large-scale floor-column connection elements were produced from non-fibrous and fibrous SCC mixtures, whose fresh and hardened concrete properties were determined. After 56 days of curing, the large-scale floor-column connection elements were tested with displacement control using a large frame test setup. Using the load-deflection data obtained from the test, the load-carrying capacity, load-deflection behavior, toughness and ductility values of the samples were calculated, as well as the crack distributions in the lower part of the samples were drawn. In conclusion, it was found that the punching strength, toughness and ductility index values of the slab-column connection elements produced from, in a total of 0.75% by volume, binary hybrid steel fiber reinforced mixtures containing 6 mm and 13 mm micro steel fiber were the best among all samples. Keywords: Low volume hybrid fiber reinforcement, micro fiber type, self-compacting concrete, punching strength, large-scale slab-column connection element, shear wedge.