Overview of Torsion Tests on Fiber-Reinforced Concrete Beams

The article presents the results of laboratory tests published in dozens of publications. These tests focused on reinforced concrete beams with additional dispersed reinforcement that were loaded with torsional moments. The results of cracking and ultimate stress were presented depending on various factors influencing the beam's load-bearing capacity, i.e., the degree of fiber reinforcement V_f, the angle of rotation θ, the compressive strength of the concrete f_c, the fiber slenderness l/d, the degree of conventional reinforcement ρ_tot, the proportions of the cross-section h/b, and the slenderness of the tested element. The frequency of occurrence of the aforementioned factors in the tests was also statistically analyzed. Additionally, the influence of fibers on the factors determining the torsional load-bearing capacity was examined. It has been shown that fibers can significantly contribute to increasing the torsional load-bearing capacity of beams and can even be characterized by a twofold increase. It has also been observed that despite the increased load-bearing capacity, beams with fibers are often characterized by lower torsional stiffness. Additionally, it has been found that fibers provide the greatest increase in load-bearing capacity for concretes with compressive strengths in the range of 25-45 MPa and for square cross-sections (b/h = 1.0). In addition, fibers can lead to the formation of torsional cracks at higher reinforcement factors (V_f). However, in terms of cooperation with conventional reinforcement, fibers are of little importance in transferring torsional stresses in the case of beams with a high conventional reinforcement factor ρ_tot > 3%.