Besides the common modes of failure including compressive, tensile, and bending in concrete structures,
cracking and failure due to the shear is also considered as a significant and hazardous mode of failure. The shear
failure mode can be observed in structural elements such as deep beams, locations having high point loads,
connection cores of beams and concrete columns, short columns, punching shear in slabs and foundations, etc.
However, the direct shear strength of the fiber-reinforced concretes has seen limited studied. Hereupon, this
study aims to experimentally investigate the influences of the type, length, and various volumetric fractions of
the steel fiber (SF) and polypropylene (PP) fiber on the compressive strength, the tensile strength, and specifically
on the direct shear strength of the fiber-reinforced concretes. To this end, four different mixture design
schemes of the plain concrete were examined by adding PP and SF with lengths of 3 cm, 5 cm, and their half-half
combination with volumetric fractions of 0.5 %, 1 %, and 1.5 % to measure the compressive strength (the cubic
sample), the tensile strength (the cylindrical sample), and the direct shear strength (the prismatic sample) of the
concrete specimens. In addition, the plain concrete specimens as the witness specimens were built to compare
with fiber-reinforced ones. The experiments were not only performed for 20–25 MPa concrete strength category,
but were also executed for 25–30 MPa. The constructed concrete specimens were exhaustively surveyed in terms
of the contribution of the fibers, the failure patterns in various specimens, the force-displacement diagrams in
shear, the maximum displacement in specimens, the aspect ratio of the fibers, and the shear ductility index in
various specimens. The obtained results indicated that, with increasing the length and volumetric fraction of the
fibers (i.e., the aspect ratios), the compressive, tensile, and direct shear strengths have been subsequently
aug