# Experimental Testing of Reinforced Concrete Deep Beams Designed by Strut-And-Tie Method
## 5 Results and Discussion  
During the testing of the reinforced concrete member W1, the first cracks appeared at the load level of 2 \(\times\) 90 kN, with the layout and widths as shown in Figure 19, (cracks in Phase I). At the load of 2 \(\times\) 105 kN, new cracks appeared and the widths of the existing cracks increased (cracks in Phase II). Figure 18: Model FEM B of the reinforced concrete W1 specimen with wooden spacers and the steel frame. By further load intensity increasing, no new cracks appeared, but the existing cracks continued to propagate in both length and width (cracks in Phase III, at the load intensity of \(2\times 115\) kN). At the maximum load level of \(2\times 150\) kN, only the increase in the width of the existing cracks was registered (cracks in Phase IV). According to the failure pattern (circled cracks in red color, Figure 19), the weak regions of the specimen were the inclined cracks between the supports and the holes. In the specimen W2, the first crack was formed at the load level of \(2\times 90\) kN. The position and width of this crack are shown in Figure 20, (crack in Phase I). By increasing the load level during Phase II (at load intensity of \(2\times 100\) kN), the new cracks appeared and the propagation of the width of the existing crack was seen. In Phase III (load level of \(2\times 120\) kN), the new cracks appeared and the existing cracks showed an increase in length and width. Similarly, further increasing of the load intensity caused new crack appearances while the existing cracks showed continuous propagation of their length and width (cracks in Phase IV, at a load level of \(2\times 150\) kN). The maximum load level for the specimen W2 was \(2\times 150\) kN. The failure pattern (circled cracks in red color, Figure 20) shows that the weak regions of the specimen were the vertical mid-span crack and the inclined crack between the right support and the hole. At the load level of \(2\times 70\) kN, the first cracks appeared in the reinforced concrete specimen W3 (the crack in Phase I), Figure 21. As the load intensity increased, the width increase and length propagation of the existing cracks occurred (the crack in Phase II at the load level of \(2\times 80\) kN and the crack in Phase III at the load level of \(2\times 90\) kN). At the load level of \(2\times 110\) kN, new cracks appeared (cracks in Phase IV). By further increasing the load intensity, new cracks appeared and the existing cracks continued to propagate in length and width (cracks in Phase V at the load level of \(2\times 140\) kN). Further increase of the load intensity resulted in the appearance of new cracks, as well as in propagation and  
Figure 19: Crack and failure pattern: **(a)** tested member W1 at maximum load, **(b)** schematic view. Figure 20: Crack and failure pattern: **(a)** tested member W2 at maximum load, **(b)** schematic view. width increase of the existing cracks (cracks in Phase V at the load level of \(2\times 140\) kN). The maximum load level for the specimen W3 is \(2\times 150\) kN with crack patterns and widths in Phase VI, as shown in Figure 21. Based on the failure pattern (circled cracks in red color, Figure 21) the weak regions of the specimen were inclined cracks between the supports and the holes, the inclined crack in the upper zone of the right hole and the vertical crack near the right hole. In the W1 and W2 members, the first cracks occurred at a load level of \(2\times 90\) kN, while in the member W3 they occurred at a load level of \(2\times 70\) kN, which is summarized in Table 7. Regardless of the amount of embedded reinforcement, which is placed only in the directions of tensioned Strut-and-Tie elements of models obtained from the software \"ST method\", the size of the formed cracks did not cause the disintegration of the members. In reality, they could carry more than the maximum applied load. In the model FEM A, crack arrangements shown in Figure 22b,e,h, corresponded to the adopted forms of the Strut-and-Tie models for design.