Influence of polypropylene fibers on the flexural behavior of reinforced concrete slabs with different opening shapes and sizes

The effect of polypropylene fibers (PF) on the flexural behavior of reinforced concrete one-way slabs with opening was investigated in this paper. The evaluated parameters included four different PF volume percentages (0, 0.3, 0.6, and 0.9%), with and without opening, two opening shapes (square and circular), and three opening sizes (100, 150, and 200 mm). Three groups of tested slabs were casted: without opening, with square opening, and circular opening, resulting in a total of 28 slabs. The behavior of each slab was evaluated in terms of the cracking load, ultimate capacity, initial and yielding stiffness, deflection ductility, and energy ductility. In addition, the steel and concrete strains, crack opening, and mode of failure were measured and monitored. The minimum design load capacities were calculated theoretically based on the sectional analysis and compared with the tested ones. The results showed that the use of PF at percentages greater than 0.6% significantly enhanced the performance parameters of the slabs with small opening size (2% opening ratio) and provided acceptable enhancement for slabs with large opening size (8% opening ratio). Therefore, the PF can be optimized to substitute the conventional steel reinforcement of slabs with small openings, especially circular openings.