Abstract. This paper presents findings from an experimental study that was focused on evaluating the use of Forta-Ferro (𝐹𝐹) and Polyvinyl Alcohol (𝑃𝑉𝐴) fibers on the response of moderate and special ductility beams under load cycles. For this reason, eight full-scale specimens, identical in geometry, were subjected to gradual cyclic loading. The specimens included two plain concrete beams with medium and special ductility, three beams with medium ductility and stirrup spacing of one-quarter the effective depth ( 𝑑/4 ) and three beams with special ductility, and stirrup spacing of one-half the effective depth ( 𝑑/2), strengthened with 𝐹𝐹 and 𝑃𝑉𝐴 fibers separately. The use of fibers was aimed at reducing the amount of shear reinforcement in flexural members. Here, the variation of parameters including the maximum strength, ultimate strength, stiffness, ductility, damage index, energy dissipation, and equivalent damping was studied. Utilizing 𝐹𝐹 and 𝑃𝑉𝐴 fibers improved the performance in beams with moderate ductility when compared to those beams with special ductility. Therefore, in special ductility beams, fibers can be used instead of crossties and in moderate ductility beams, fibers can be added to reduce the ratio of shear reinforcement. Furthermore, increasing the stirrup spacing in the moderate ductility beams from 𝑑/4 to 𝑑/2 and adding 0.6% 𝐹𝐹 or 1.5% 𝑃𝑉𝐴 fibers resulted in behavior similar to those of the moderate ductility beam.
