Shear Strength of Beams Made Using Hybrid Fiber–Engineered Cementitious Composites

This paper reports the results of an experimental investigation of the shear behavior of beams made using hybrid fiber–engineered cementitious composites (HFECC). The paper specifically deals with the shear behavior of beams made using strain hardening engineered cementitious composites that incorporate relatively low volume ratios (Vf≤2%) of discontinuous, randomly distributed hybrid fibers (steel and polyethylene) and how the strain hardening characteristics of the fiber composite impact the shear behavior of the beam. A total of 21 beams reinforced with longitudinal steel bars and with various combinations of polyethylene (PE) and steel (ST) fibers were tested in a three-point loading setup at a shear span to depth ratio of 3. The total volume fraction of the fibers in the composites ranged from 0 to 2%, and the matrix was either cementitious paste or cementitious mortar. The beams were tested in controlled deformations to enable capturing the postpeak behavior. It is shown that HFECC made using cementitious paste was effective in increasing the shear strength by up to 8 times relative to the nonfibrous matrix. In addition, the ductility, multiple cracking behavior, and shear strain capacity of the beams were considerably improved. Improvements were also observed in the HFECC beams made with cementitious mortar but to a lesser extent, in which the shear strength increased up to 3 times relative to the nonfibrous matrix. The results also showed that when used in HFECC, the PE fibers were nearly as effective as steel fibers in increasing the shear strength. The addition of fibers allowed the beams to reach or exceed their calculated flexural capacity in spite of the relatively large longitudinal reinforcement ratio used. A fiber volume of 1% is shown to be an adequate minimum shear reinforcement for beams with compressive strengths ranging from 40 to 65 MPa, irrespective of the hybridization ratio and the binding matrix.