Flexural performance of highly reinforced composite beams with ultra -high performance fiber reinforced concrete layer

Abstract

The study aimed to obtain the composite beams with high flexural capacity by using the high compressive strength and deformation capacity of Ultra -High Performance Fiber Reinforced Concrete (UHPFRC). For this purpose, the composite RC beams consisting of UHPFRC layer in the compressive side and Normal Strength Concrete (NSC) in the tensile side were produced and the four -point bending tests were carried out on the beams. By making parametric study for the ratio of tensile reinforcements (ranging from 1.8% to 5.0%), highest ratio where sufficient ductility can be acquired in the beams were determined. Two different thicknesses (one -fifth of the beam height/one-third of the beam height) of UHPFRC layer were applied in the compressive side of the composite beams in order to determine the appropriate thickness. The flexural behavior characteristics (ducti- lity, capacity, stiffness) of the composite beams were evaluated by comparing the pure NSC beams (reference beams) with the same properties. With the use of UHPFRC in the compressive side of the beams, significant advantages have been acquired in ductility, flexural capacity and stiffness compared to the NSC beams. However, the main advantage of the composite application was that it allows the use of very high amount of tensile reinforcement in the beam. The study indicated that it was possible to increase tensile reinforcement ratio of the composite beams up to 5% without using compressive reinforcement. Thus, the ductile composite beams with high flexural capacity were produced with the use of economical amount of UHPFRC. The UHPFRC layer thickness of one-third of the beam height was appropriate for the overall flexural performance at this type of composite beam.