# Experimental Testing of Reinforced Concrete Deep Beams Designed by Strut-And-Tie Method
## 5 Results and Discussion
The displacement values at designed loads of \(2\times 100\) kN obtained by numerical analysis are greater than those obtained by experimental testing for walls W1 and W2 and these differences are  
Figure 22: Shapes of the Strut-and-Tie models from “ST method” program for members W1, W2, and W3 and crack patterns obtained by: the experiment (**a**,**d**,**g**), model FEM A analysis (**b**,**e**,**h**), and model FEM B analysis (**c**,**f**,**i**). It is observed that the trend of dependence between loads and strains, measured and numerically determined, is approximately the same for all three measuring sites and for all three specimens, before the appearance of the first crack, i.e., up to a load level of approximately \(2\times 60\) kN in the numerical model. Subsequently, significant differences between numerical and experimentally determined results for measurement sites C4 and C6 occur. In contrast, for the measuring position site C5, whose direction roughly corresponds to the direction of the strut, the same trend of dependence between load and strain even after reaching the first crack is maintained. At the maximum load intensity during the test, the maximum measured compression strains were observed at the measuring points C4-C5-C6 and did not exceed 0.15%o in all three specimens. Although the results of crack distribution and mid-span deflection determined in the FEM B model were close to the test results, the results for strains in concrete differ significantly, i.e., the model proved to be insufficiently reliable for estimating these values in the tested members. The maximum values of the tensile strains in the reinforcement at the mid-span of the lower edge of the member are: 0.27%o (at the measuring point S8 of the specimen W1, Figure 11), 1.35%o (at the measuring point S4 of the member W2, Figure 12), and 1.1%o (at the measuring point S6 of the member W3, Figure 13). At other measuring points, in the member W1, the measured maximum value of the tensile strain did not exceed 1.8%o, the maximum value of the tensile strain measured in the member W2 was not greater than 1.25%o, while for the specimen W3, the measured maximum tensile strain value did not exceed 0.16%o. The maximum values of the tensile strains in the reinforcement at the measuring points S8, S4, and S6 of specimens W1, W2, and W3 respectively, did not reach the ultimate limit strain values. The reason is in the fact that the steel frame with its rigidity reduced stresses and deformations in the member. The member is designed in the software \"ST method\" under the assumption of a static simple beam system. However, during the test, because of the interaction between the frame and the specimen, the spreading between the points at the contact of the frame and the specimen (Figure 14, zones circled in red) was partially prevented because of the stiffness of the frame. This phenomenon will be explained for specimen W2, and the other samples behaved analogously. Based on experimentally measured strains at half the height of the \"U\" profile (Figure 14, zones circled in red color, and Figure 28), the values of normal force, bending moment, and transverse force were determined. At designed loads of \(2\times 100\) kN, the normal force, bending moment, and transverse force were--129.91 kN, 7.36 kNm, and 17.24 kN, respectively. By experimental measurement of strains in the reinforcement along the lower edge of the member (measuring point S3/S4, Figure 12), the axial force in the reinforcement was calculated, which at a load value of \(2\times 100\) kN is 11.77 kN. The axial force in the tie, along the lower edge of the support, of the Strut-and-Tie model for design, determined in the program \"ST method\", is 33 kN. The difference between this axial force and the axial force calculated on the basis of experimental results is \(33-11.77=21.23\) kN.