Issue 35

S. Tarasovs et alii, Frattura ed Integrità Strutturale, 35 (2016) 271-277; DOI: 10.3221/IGF-ESIS.35.31 275 3-point bending test (Fig. 2a) 2h Height , cm 7.5 2b Width, cm 7.5 2w Length, cm 30 2a 0 Initial crack length, cm 2 2l Support separation, cm 28 4-point bending test (Fig. 2b) 2h Height, cm 15 2b Width, cm 15 2w Length, cm 60 2a 0 Initial crack length, cm 4 2l Support separation, cm 45 2x Load separation, cm 15 Table 2 : Geometrical parameters of the specimen. 0 500 1000 1500 2000 2500 3000 3500 0.E+00 2.E-05 4.E-05 6.E-05 8.E-05 1.E-04 COD, mm Load, N Experiment FEM Figure 7 : Load-crack opening displacement diagram of a three point bending test for plain concrete beam. Numerical and experimental curves. R ESULTS OF NUMERICAL SIMULATIONS s an example the wedge splitting test [14] will be simulated using proposed approach. The specimen’s size is 20  20  30 cm with initial crack depth equal 15 cm. Previous studies show [15], that due to vibration during specimen’s preparation stage, the fibers tend to be aligned horizontally and there are much less vertical fibers. This deviation from uniform random distribution creates anisotropy of the fracture toughness of the fiber reinforced concrete. As a result, the crack may grow in unexpected direction and simple models are unable to predict such behavior. Fig. 8 shows two possible modes of failure of plain concrete and fiber reinforced concrete. The plain concrete has isotropic fracture toughness and crack typically grow downward, as it is expected. In the fiber reinforced concrete the horizontal cracks are more favorable, and in some situations the crack may turn and grow toward the side of the specimen. To prevent such behavior, deeper initial notch and/or side grooves can be used. Proposed numerical model was used to simulate the failure of notched fiber reinforced concrete specimen in 4-point bending tests (Fig. 9). The results of simulation are shown in Fig. 10, compared with experimental curves. The numerical results show substantially higher reinforced concrete strength, which can be explained by the fibers interaction and non- uniform distribution of fibers in the specimen. The numerical model does not take into account the interaction between individual fibers: when fibers are located too close to each other, the total pull-out force could be less, than the sum of forces of individual fibers, which was measured in single fiber pull-out test. A