Ohybová zkouška pro výstižnější stanovení tahové pevnosti vláknobetonu

Two configurations are currently used to determine the tensile strength of fiber reinforced concrete: simply supported beams of square cross section loaded either by two forces at thirds of spans (four-point bending test) or by one force at the midspan where the specified cross section is weakened on the tensile side by a notch (three-point bending test). Based on elementary formulas, the tensile strength of fiber reinforced concrete is then determined. Considering the unacceptability of these formulas to capture the 3D problem and, in particular, for the three-point bending test, also because of significant singularities at the notch and the degree of statistical uncertainty in determining the actual position of the weakest area of the test specimen, such a test does not respect the real stress distribution in the tensile area which is changing in the process of load increase. The proposed adjustment of the test specimen eliminates these fundamental drawbacks by removing the singular areas of the specimen and leaving only the cross-sectional areas where only uniaxial stress state may be assumed. The results obtained by this methodology are presented, statistically evaluated and compared with the currently used procedures.