# Hybrid Fibres as Shear Reinforcement in High-Performance Concrete Beams with and without Openings
## 3 Experimental Results and Discussion
### Strains  
The major strains in the concrete and hybrid fibre concrete in the beams without/with openings, together with the location of longitudinal sections and measurement areas for the beams in the ARAMIS system are shown in Figures 11 and 12. The major strain curves were made in longitudinal sections A-A and B-B located respectively in the tension and complex stress state area in the mid-span of beams B1 \(\div\) B3. In beams BO1 \(\div\) B03 with the openings, the longitudinal sections A-A, B-B and C-C are located in the shear span in the area of complex stress state. An additional longitudinal section  
Figure 10: Comparison of beam (**a**) ultimate deflection and (**b**) ductility factor.  
Figure 9: Comparison of beam toughness.  
C-C is located at half the height of these beams. Based on the non-contact measurements of strains, the essential differences in the concrete and fibre concrete strain distributions may be observed.  
The major strains in the longitudinal sections of the tested beams depends on the type of reinforcement, the fibre volume content and the openings in the shear span. The mean strain values in the B1, B2 and B3 beams at the service load near the tensile edge (in section A-A) determined on the basis of statistical analysis are 0.22, 0.17 and 0.39%, respectively, and near the compressive edge (in section B-B) they are 0.061, 0.043 and 0.058%. The mean strains of beams B1-B3 at the maximum load are respectively 2.12, 0.28 and 2.28% (in section A-A) and 0.111, 0.043 and 0.043% (in section B-B). The major strains at the bottom of the beams without fibres and with the highest fibre content increased approximately 10 and 6 times. On the other hand, at the upper edge the strains increased almost two-fold in the reinforced bar and decreased by 35% in the beam with the highest fibre content. Figure 13 shows the comparison of the major strain images for the B1 and B3 beams at the constant deflection of 10 mm. It can be noticed that the highest strain of beam B3 is about 28% lower than the highest strain of beam B1 without fibres.  
Figure 11: Major strains of concrete beam (B1) and hybrid fibre concrete beams (B2, B3): (**a**) at service load, and (**b**) at maximum load.  
The major strains of beams B1 \(\div\) B3 at maximum load are illustrated in Figure 14. The highest values of strains in the B1 and B3 beams are observed near the widest crack and are equal to 12.2 and 22%, respectively. Nevertheless, the greatest measured strain of the B2 beam is much lower and amounted to 1.4%. In this case, however, the greatest strain occurred in the shear span, outside the measuring field. The mean strains at service and maximum load of the BO1, BO2 and BO3 beams with openings are 0.3%, 0.15%, 0.14% and 3.11%, 2.02%, 0.25% in section A-A, respectively, and 0.12%, 0.08%, 0.12% and 0.14, 0.16, 0.12% in section B-B, and 0.2, 0.08, 0.1% and 0.71%, 0.13%, 0.19% in section C-C. The lowest values of strain at the tensile edge of the beam are noted in the BO3 beam with the highest fibre content.  
Figure 12: Major strains of concrete beam (BO1) and hybrid fibre concrete beams (BO2, BO3) with openings: (**a**) at service load, and (**b**) at maximum load.  
Figure 13: Comparison of major strains for B1 and B3 beams in measurement area, at deflection of 10 mm.  
In the strain images of the BO beams at maximum load shown in Figure 14, it can be noticed that diagonal cracks propagate from the support to the upper edge of the opening in fibre beams BO3 and BO2, which is reflected in about 3.5-5.5 times lower mean strains in the longitudinal section C-C in the beam mid-height compared to the BO1 beam with stirrups and without fibres. The reasons are to be found in another work mechanism of FRC beams with openings in which the development of diagonal cracks is inhibited by fibres constituting the only reinforcement of the shear zone additionally weakened by the hole.