Influence of polypropylene fibers on the shear strength of rc beams without stirrups

Abstract

Reinforced concrete (RC) beams with light transverse reinforcement are vulnerable to shear failure during seismic response. The codes require the use of a certain amount of transverse reinforcement to resist the expected total shear demand to prevent brittle shear failure at plastic hinge regions. Some codes ignore the contribution of concrete to shear strength when the shear demand due to seismic effects is above a certain level. This research studied the contribution of concrete to shear strength of beams reinforced with longitudinal bars and polypropylene fibers (PPF). The beams including two reference and two macro-synthetic polypropylene fibers reinforced concrete (PPFRC) beams tested under concentrated loads at mid-span to determine the shear strength. The variable parameters are volume fraction of polypropylene fibers (Vf) and shear span-to-depth ratio (a/d). Deflection of the beam and the cracking pattern were monitored during the test at different stages of the monotonic loading until failure. When the beams with a/d = 2.5 and 3.5 are compared, it is concluded that the contributions of PPF to the shear strength at ultimate state are 0.39 MPa and 0.34 MPa, respectively, in case of the beams with volume fractions of PPF equal to 1.0%. It is observed that the contribution of PPF to shear strength decreases with the increasing a/d. It can also be stated that the dissipated energies under the area of load-deflection curve by the PPFRC beams are 341 and 226 times the energy dissipated by a/d = 2.5 and a/d = 3.5 reference beams, respectively.