# Concrete Beams Reinforced with High Strength Rebar in Combination with External Steel Tape
## 3 Results and Discussion
### Process of Cracking  
The formation of normal cracks in the experimental samples causes the violation of the homogeneity of stresses and strains of concrete. The processes of formation and opening of cracks are accompanied by a sharp increase in deformations and deflections. Therefore, the value of the bending moment corresponding to the break on the graph of the deformation and strain development was taken as the moment of crack formation. In this study, this conventional break point was determined with linear interpolation of two adjacent points from the predicted location of the graph sections. The load-bearing capacity of bended beams was carried out according to the ultimate limit state. Therefore, the basic value for comparative analysis is the value of maximum bending momentM\({}_{\text{dr2}}\), which corresponds to the conditional yield point in high-strength rebar. Cracks in the middle part of the beams B-I-I and B-I-2 (with 1e10 A1000 steel bar (0.785 cm\({}^{2}\)) and 6.56 cm\({}^{2}\) of tape reinforcement) appeared at loading, equal to 0.14 M\({}_{\text{dr2}}\) (see Table 3). These cracks immediately spread to the height of 0.2-0.3 of the total height of the beam. Cracks in beams B-II-1 and B-II-2 ( with 2e10 A1000 steel bars (1.57 cm\({}^{2}\)) and 3.68 cm\({}^{2}\) of tape reinforcement) appeared at loading, equal to 0.15 M\({}_{\text{dr2}}\). The height of the cracks reached the value of 0.13-0.3 of the beam's height. In beams B-III-1 and B-III-2 (with 3e10 A1000 steel bars (2.355 cm\({}^{2}\))), the cracks were indicated at loading equal to 0.2 M\({}_{\text{dr2}}\). The cracks' height was 0.13-0.25 of the total height of the beam. Beams B-IV-1 and B-IV-2 with only external steel tape reinforcement of 9.12 cm\({}^{2}\) total area. First cracks appeared at loading 0.16 M\({}_{\text{dr2}}\). A comparison of experimental and theoretical moments of crack formation is given in Table 2.  
Higher values of high-strength rebar percentage correspond to higher moments of crack formation. This can be explained by the fact that the reduction of the tape reinforcement area reduces the stress in the places where the anchors are welded, which facilitate mor even redistribution of stresses in the zone of maximum bending moment. However, in steel-concrete beams B-IV the moment of the formation of cracks is the highest, which is explained by the highest percentage of reinforcement. The deviation between experimental and theoretical results according to DBN B.2.6-98:2009 [46] for beams with A1000 class rebar in combination with S275 tape ranges from 14.2% to 23.5%. Experimental results of the moments of crack formation for different samples are given in Table 3. Graphs of strains development are presented on the Figure 6. Beams B-I-1 and B-I-2; B-II-1 and B-II-2; B-III-1 and B-III-2; and B-IV-1 and B-IV-2 formed the twin pairs to confirm the validity of the data. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Notation of the Beams**} & \multicolumn{3}{c}{**Beginning of Crack Formation**} \\ \cline{2-4}  & **Experimental M\({}^{\text{exp}}\)\({}_{\text{crcr}}\), kN \(\times\) m** & **According to DBN V.2.6-98:2009** & **(M\({}^{\text{exp}}\)\({}_{\text{crcr}}\) – M\({}^{\text{DBN}}\))/M\({}^{\text{exp}}\)\({}_{\text{crcr}}\), \%** \\ \hline B-I-1 & 6.9 & & 14.2 \\ B-I-2 & 7.15 & 5.92 & 17.2 \\ B-II-1 & 8.00 & & 23.5 \\ B-II-2 & 7.46 & & 18.0 \\ B-III-1 & 6.42 & & 18.1 \\ B-III-2 & 5.6 & 5.26 & 6.1 \\ B-IV-1 & 8.08 & & 11.9 \\ B-IV-2 & 7.92 & 7.12 & 10.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of moments corresponding to crack formation. Beams B-I-1 and B-I-2; B-II-1 and B-II-2; B-III-1 and B-III-2; B-IV-1 and B-IV-2, which were the twin pairs, had exactly the same parameters (reinforcement ratio and amount of each type of the reinforcement).