## 2 Experimental Work
### Test Results and Discussion
#### 2.2.2 Effect of Steel Plate Thickness on Concrete and Steel Strains  
Figure 6 shows the strain development during the loading of the beams. The positioning of the strains is such that the concrete strains are on the top surfaces of the beams in the longitudinal direction, whereas the steel plate and longitudinal reinforcement strains are in the bottom rebar. After spalling, a very brittle response was exhibited by the CB at a normal strain, as shown in Figure 6a, however, the BCSP beams with bolted steel plates experienced a remarkable increase in bending capacity in the compression zone, even at large strains. Here, the steel plates contributed to the ductile behavior of the \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Specimens** & **P\({}_{\textbf{C}}\)** & **P\({}_{\textbf{C}}\) \%** & \(\Delta\)** & **P\({}_{\textbf{Spall}}\)** & **P\({}_{\textbf{Spall}}\)** \%** & **P\({}_{\textbf{Vield}}\)** & **\(\Delta_{\textbf{spall}}\)** & **\(\Delta_{\textbf{yield}}\)** & **P\({}_{\textbf{Peak}}\)** \%** & **\(\Delta_{\textbf{mem}}\)** \\
**Designation** & **(kN)** & **Increase** & **(mm)** & **(kN)** & **Increase** & **(kN)** & **(mm)** & **(mm)** & **(kN)** & **Increase** & **(mm)** \\ \hline
**CB** & 71.5 & - & 1.87 & 356 & - & - & 8.33 & - & 375.5 & - & 10.8 \\ \hline
**BCSP-6** & 247 & 245.5 & 3.48 & 521 & 46.3 & - & 8.2 & - & 652.3 & 73.7 & 11.7 \\ \hline
**BCSP-10** & 362 & 406.3 & 3.73 & 635 & 78.4 & - & 6.9 & - & 837.6 & 123 & 12.5 \\ \hline
**BCSP-15** & 460 & 543.5 & 3.99 & - & - & 935.3 & - & 10.2 & 935.3 & 149 & 15.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Measured values of the load types of all of the over-reinforced concrete beam specimens. Figure 5: Modes of failure and crack patterns of all of the specimens: (**a**) CB; (**b**) BCSP-6; (**c**) BCSP-10 and (**d**) BCSP-15. concrete. The large compressive strains led to an increase in material stiffness, and the lateral expansion of the beam was reduced. This resulted in an increase in the compressive ductility. The front elevation of each beam is presented in Figure 6, which illustrates the strain distributions in the cross section at both spalling and peak loads. Beyond P\({}_{\text{spall}}\) loading, the concentration of the strain is introduced towards the middle of the span of the beam, due to the emergence of a plastic hinge region. This phenomenon can be observed in the BCSP-6 beam, since the strains in its compressive reinforcement increased more than the average strain on the top surface, from P\({}_{\text{spall}}\) to P\({}_{\text{peak}}\). The load-strain behavior for the concrete (\(\epsilon_{\text{c-avg}}\)) beams is also shown in Figure 6a. The average concrete strain was found to be 0.0026, based on a linear regression analysis of the loading data until spalling (i.e., the crushing of the concrete cover). A full failure of the cross section was observed for the CB shortly after the spalling load was applied. This failure was very brittle in nature. Linear regression was not fit to determine the average concrete strain for the steel plate for the BCSP-6, BCSP-10, and BCSP-15 beams. The concrete strains at failure for these beams were found to be 0.003, 0.0035 and 0.0038, respectively. These values are consistent with the assumed maximum compressive strain values of 0.003 and 0.0035, according to the ACI and CSA [28; 36], respectively. For these beams, the tension reinforcement strains from the tests at a spalling load exhibited elastic behavior without failure until the peak load was reached. After the crushing of the beam, the tension reinforcement yielded, as shown in Figure 6. At higher strains of the BCSP beams on the steel bars, the beams withstood more loading. This means that the beams can carry higher loads without failure at the same strain as the steel bar. At much higher applied loads, yielding of the steel plates occurred, which was localized under the flexural loading area.