# Experimental Testing of Reinforced Concrete Deep Beams Designed by Strut-And-Tie Method
## 5 Results and Discussion
For walls W1 and W2, the crack distributions obtained by experimental tests, Figure 22a,d, did not correspond to the crack arrangement determined in the model FEM A, and at wall W3 the crack arrangement corresponded approximately, Figure 22g. Also, the results of the mid-span deflection, Figure 24, showed differences in the behavior of the model FEM A in comparison with experimental results, for all three specimens. For the walls W1 and W2 the differences are smaller, while for the wall W3 they are larger. The reason for this behavior of the member is the interaction between the steel frame and the walls during the test. The consequence is the achievement of lower values of stresses and strains at the same load level compared to Strut-and-Tie models applied for the design. According to the above-mentioned, the model FEM A was expanded and the model FEM B was formed. In addition to the tested specimens, the latter contains a steel frame and its contact with the ground and wooden spacers, Figure 22c,f,i, and was used for further analyzes. The distributions of tensioned damage obtained by model FEM B analyzes are shown in Figure 22c,f,i, at the maximum load level. Distribution of cracks in tested elements is in accordance with the distribution of damage determined by model FEM B analysis, although it was observed that the arrangement of the cracks, especially the appearance of the first cracks, was influenced by the arrangement of the spacers for fixing the reinforcement. The dimensions of the spacers are such that they extend over the entire thickness of the specimen, so that the holes in concrete volume were formed in their places to initiate the cracks at the beginning. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Memb.**} & **Load Level [First Crack]** & \multirow{2}{*}{**Crack Direction**} & **First Crack Width** & **Max Load Level** & **Crack Width at Max** & \multirow{2}{*}{**Total Number of Cracks**} \\  & **[N]** & & & **[mm]** & **[NN]** & **[mm]** \\ \hline W1 & \(2\times 90\) & inclined & 0.75 & \(2\times 150\) & 4.0 & 5 \\ W2 & \(2\times 90\) & vertical & 1.2 & \(2\times 150\) & 7.0 & 3 \\ W3 & \(2\times 70\) & inclined & 0.4 & \(2\times 150\) & 1.5 & 7 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Crack widths depending on load level. Figure 21: Crack and failure pattern: (**a**) tested member W3 at maximum load, (**b**) schematic view. Based on the measured mid-span deflection at measuring points D1, D3, and D5 (Figures 11-13), a relative mid-span deflection was calculated at the measuring point D3. The diagrams of the relative mid-span deflections of the W1, W2, and W3 members are shown in Figure 23. It can be concluded that the mid-span deflection of the W3 specimen at each load intensity is smaller than the mid-span deflections of the other specimens. At the load level of \(2\times 100\) kN the mid-span deflections of specimens W1 and W2 are approximately the same and larger by about 37% when compared to the mid-span deflection of the W3 specimen. At the load level of \(2\times 150\) kN, which is close to the maximum load intensity for all three specimens, the mid-span deflection of the specimen W1 is approximately 20%, and of the specimen W2 is approximately 60% higher than the mid-span deflection of the W3 specimen. It can be concluded that the bending rigidity of the W3 specimen is higher than those of the specimens W1 and W2. It can also be concluded that specimens W1 and W2 have approximately the same mid-span deflections up to the load level of \(2\times 100\) kN, and at the load level of \(2\times 150\) kN, the mid-span deflection of the specimen W1 is by approximately 36% smaller than the one of the specimen W2. It is observed that the deflection change trend determined experimentally and by model FEM B analysis is the same for all three walls individually.