Shear Behavior of Steel Fiber Reinforced Prestressed Concrete Beams

Prestressed concrete girders are the main superstructure elements in many bridge structures. Shear failures in these girders are undesirable due to brittle failure and little warning time. To prevent shear controlled brittle failure, it is normal practice to increase the amount of transverse reinforcement in flexural members. However, past studies have revealed that even higher transverse reinforcement ratios (i.e. > 4%) may not be able to eliminate shear failure in some cases. Moreover, the increased reinforcement makes it more difficult to place and consolidate the concrete. This research program aimed to investigate the feasibility of replacing traditional shear reinforcement in prestressed concrete beams with steel fibers. A total of 14 rectangular and 8 I-shaped prestressed concrete beams were investigated after subjecting them to two-point loading test. The beams were casted with steel fiber ratios ranging from 0.75% to 2.00%. Experimental results revealed that the inclusion of steel fibers in concrete mix improved the shear strength of rectangular and I shaped prestressed beams. It was observed that on adding 1% fibers, the shear strength of I-beams enhanced by 23%. Moreover, in some cases, the addition of steel fibers also caused the shear failure mode to shift to flexural failure mode without traditional shear reinforcement. Furthermore, the cracking behavior and ultimate strength were also improved.  However, at high fiber dosages, balling of the fibers was observed and the load capacity decreased compared to beams with lower fiber contents.