## 4 Results
### State of Deformation Analyses of Reinforced Concrete Beams Strengthened with CFRP Strips  
In the experiments, deformations were measured at selected measurement points located on the composite strip, middle reinforcing bar, and top and side surfaces of the concrete in the compressed zone in the middle of the beam span (Figure 3). The values of strains of composite strips and reinforcing bars in the middle of the beam span for different load levels are presented in Table 4. Table 4 is illustrated in Figures 6 and 7, which show the quantitative relationship between the strip and reinforcing steel strains for individual beams for the load P = 60 kN and for the beam failure moment. Table 4 shows that the initiation of the destruction of all beams took place in the reinforcing bars in the central zone of beams due to the steel yielding (\(\epsilon_{\rm pl}\) = 2.5%). The rapid increase in the deformation of reinforcing bars on the central sections of the beams resulted in an immediate increase in the deformation of composite strips on these sections. The maximum strains of the composite strip with the failure of the beams ranged from 4.58% for the beam loaded before the strengthening with the strip (Bow type) to 6.45% for the beam strengthened with the strip from the beginning of loading (Bz type). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Beam**} & \multirow{2}{*}{**Ultimate Load**} & \multirow{2}{*}{**Mean Ultimate Load**} & \multirow{2}{*}{**Max. Deflection at Failure**} & **Mean max.** \\  & & [kN] & [kN] & [cm] & **Deflection at Failure [cm]** \\ \hline
1 & Br-2 & 97.13 & & 4.06 & \\
2 & Br-3 & 95.85 & & 4.32 & \\
3 & Bz-1 & 124.25 & & 2.78 & \\
4 & Bz-2 & 126.57 & & 2.83 & \\
5 & Boow-2 & 118.59 & & 2.60 1  & & \\
6 & Boow-3 & 120.50 & & 2.68 1  & & 2.64 1  \\
7 & Bow-1 & 116.39 & & 2.90 & \\
8 & Bow-2 & 114.84 & & 2.76 & \\
9 & Bopp-1 & 117.39 & & 2.84 & \\
10 & Bopp-2 & 116.02 & & 2.91 & 2.88 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Values of ultimate load and maximum deflections during failure for laboratory-tested beams. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Beam**} & \multirow{2}{*}{**Load-Carrying Capacity**} & \multirow{2}{*}{**Max. Deflection at Failure**} \\  & & & [-] & [-] \\ \hline
1 & Br & 1 & 1 \\
2 & Bz & 1.30 & 0.67 \\
3 & Boow & 1.24 & 0.63 1  \\
4 & Bow & 1.20 & 0.68 \\
5 & Bopp & 1.21 & 0.69 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Relative values of ultimate load and maximum deflections during failure for laboratory-tested beams. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Br** & **Bz** & **Bow** & **Bow** \\ \hline Results of FEM & 95.00 & 124.00 & 118.00 & 116.00 & 115.00 \\ Results of experiments & 96.48 & 125.40 & 119.60 & 115.60 & 116.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Ultimate load received using FEM analysis and experiments [kN]. 75% of the design capacity of the reinforced concrete beam (Bow and Bopw beams) show that the greater the overload of the beams before strengthening, the greater the use of the CFRP strip strength at the time of their failure. The load levels at which the reinforcing steel reaches the yield limit are summarized for all beams in Table 5. The table also gives the relative values of loads causing the reinforcing steel yielding in the beams strengthened with the CFRP strips in relation to the load at which the steel was yielding in the beams with no strengthening (the value of 1 for beams without any strengthening is the reference level). Increasing the relative levels of loads causing the steel yielding in beams strengthened with CFRP strips is one of the most important criteria for assessing the effectiveness of RC beams with composite strips. This criterion determines the range of safe operation of RC beams, which would be damaged without the CFRP strengthening as a result of exceeding the yield limit of the steel in tension.