Effect of Steel Fibers on the Strength and Failure Modes of Reinforced Concrete Beams with Circular Openings in the Shear Zone

Abstract

Transverse openings in the shear zone of reinforced concrete beams, without taking prior precautions, generate stress concentrations around these openings, reducing the capacity of the beams and thus favoring brittle failure modes. This study investigates the use of steel fibers to address this issue.

A series of three-point bending tests was conducted on nine beams with dimensions of 100x200x1000 mm, incorporating Ø63 mm transverse openings in the high-shear zone. In addition to the flexural and shear reinforcements, these beams, both with and without openings, were strengthened with hooked steel fibers type FIBERTEK A at rates of 0.2%, 0.4%, 0.6%, and 0.8%.

The test results indicated that the steel fibers significantly enhance the performance of beams with openings. It allows the beams to maintain their ultimate bending capacity despite the presence of openings, achieving significant improvements compared to the reference beam: a 34.69% increase in first crack load, a 39% increase in ultimate capacity, and a 56% increase in absorbed energy. Additionally, increasing the fiber content makes it possible to shift the shear failure mode from frame-type to beam-type.