# Hybrid Fibres as Shear Reinforcement in High-Performance Concrete Beams with and without Openings
## 3 Experimental Results and Discussion
### Load-Deflection Curves and Cracking Behaviour
#### 3.1.5 Cracking Patterns and Failure Modes  
The cracks of all the tested beams at different loading stages are illustrated in detail in Figure 6. The crack shapes and their corresponding load levels are drawn. The first crack in the B beams always appeared in the middle zone, due to the high moment applied in this zone. Cracks in the BO beams were first observed below the openings. Diagonal cracks appeared at the mid-height of the B beams within the clear shear span in the direction of the main strut as the load increased to 78-85% (for the beams with fibres) and 53% (for the traditionally reinforced beam) of the ultimate load. In the next stages of loading, diagonal cracks propagated rapidly toward the cylindrical support and the outside edge of the loaded point. Their widths increased in the centre of the shear span, while diagonal cracks developed across the natural shear splitting line. Moreover, other diagonal cracks, parallel to the first crack were observed in the traditionally RC beam without fibres. Diagonal cracks in the BO beams were first observed below the corners of the opening. The diagonal cracking load of the BO beams with fibres was in the range of 49-91% of the ultimate load. On the other hand, the diagonal crack in the traditionally RC beam with openings appeared as the load increased to 46% of the ultimate load. It can be noticed that the openings had a significant impact on the cracking load. When the beams with fibres had openings the cracking load was increased. The cracks and location of the concrete crushing in the compression zone that appeared in the post-yield strain hardening stage were marked in blue. It was observed that in a fibre-free beam BO1 a larger number of cracks and a larger crushing area were formed in this loading stage. As given in Table 6, the final patterns of all the cracks were created in the beams at loading levels ranging between 125.6-163.9%, 92.1-100.2%, 75.4-98.4% and 94.2-123% for the cracking, yielding, maximum and ultimate loading stages, respectively. The applied load means the load at which the final patterns of all the cracks were created. Furthermore, the service load was determined as the experimental maximum load multiplied by 0.6 based on [PERSON] et al. [63]. The widest crack appeared accidentally in the zone of operation of the fixed moment in the B beams and under the openings of the BO beams. On the other hand, the widest crack in the BO beams occurred near the openings. Figure 6: \(Cont.\)Figure 6: Crack patterns for beams. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Beam**} & \multicolumn{6}{c}{**Loading Stages**} & \multicolumn{6}{c}{**Percentage Loading**} \\ \cline{2-10}  & **Applied** & **Service Load** & **Yield Load** & **Maximum** & **Ultimate** & **Applied/Service** & **Applied/Yield** & **Applied/Maximum** & **Applied/Ultimate** \\  & **Load (N)** & **(N)** & **(kN)** & **Load (kN)** & **Load (kN)** & **Load (\%)** & **Load (\%)** & **Load (\%)** & **Load (\%)** & **Load (\%)** \\ \hline B1 & 350.0 & 238.2 & 350.9 & 397.0 & 317.6 & 146.9 & 99.7 & 88.2 & 110.2 \\ B2 & 290.0 & 176.9 & – & – & 294.8 & 235.8 & 163.9 & – & 98.4 & 123.0 \\ B3 & 430.0 & 279.9 & 432.5 & 466.5 & 373.2 & 153.6 & 99.4 & 92.2 & 115.2 \\ B01 & 305.0 & 242.8 & 331.3 & 404.6 & 323.7 & 125.6 & 92.1 & 75.4 & 94.2 \\ B02 & 390.0 & 271.6 & 414.1 & 452.7 & 362.2 & 143.6 & 94.2 & 86.1 & 107.7 \\ B03 & 415.0 & 277.4 & 414.3 & 462.4 & 369.9 & 143.6 & 100.2 & 89.7 & 112.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Applied load to service, yield, maximum and ultimate load ratios. The loading stages and failure modes of the beams are shown in Table 5 and Figure 7. In general, the high-performance FRC beams tested in this study exhibited failure modes similar to the identical beams without fibres. Obviously, the highest percentage of steel and polypropylene fibres (B3, BO3) transformed the failure mode into a more ductile one.