## 3 Comparison of the Experiments with Analytical Models and Discussion of the Results
### Discussion and Interpretation of the Results  
For the analysis of the results, the test specimen TS\({}_{\text{Ref}}\) is discussed first. In addition to the results, Table 4 shows the ratio of the measured torsional moment in relation to the calculated results, with the deviation of only 1% demonstrating a particularly good agreement. This confirms the force redistribution from the longitudinal bars (which began to yield first) to the stirrups, accompanied by the inclination of the compression struts from  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Test Specim** & \( \begin{array}{c}T_{max,experiment}\\ \text{(kNm)}\end{array} \) & \( \begin{array}{c}M_{experiment}\\ \text{(kNm)}\end{array} \) & \( \begin{array}{c}V_{max,experiment}\\ \text{(kN)}\end{array} \) & \(\begin{array}{c}\text{\boldmath$\Theta$ ($  
45\({}^{\circ}\) to the calculated 54.6\({}^{\circ}\). It is important to note that the failure did not occur at the place with the highest bending moment--the restraint (M = 161 kN)--but rather at a distance of 1.20 m (M = 96 kN). The rationale for this behavior, as described below, is of utmost relevance for the further understanding of the load-bearing behavior of TSjoint. According to [PERSON] et al. [16; 17; 20], it is not sufficient for one side of a box girder to have reached its torsional load capacity to lead to a failure of the entire girder, as the load-bearing reserves of the remaining sides of the box girder are activated. This theorem was proven by [PERSON] and [PERSON] [16; 17; 20] by comparing girders with bending reinforcement on one side with ones with distributed reinforcement around the cross-section. Additional load reserves in the girder with bending reinforcement, with regard to torsion, were determined, allowing for an increase in load beyond the theoretically possible, according to the truss model. Coming back to TSRef, with equal longitudinal reinforcement around the cross-section, other load reserves must have been active in order for the girder not to fail at the restraint. A plausible explanation could be the vertical compressive stress in the webs, resulting from two sources: the downward tensioning of the middle diaphragm simulating the vertical forces of the prestressing, and the reaction forces resulting from the concrete compression struts at the restraint. As these compressive stresses decrease with increasing distance from the restraint, a failure in the field occurs in accordance with the truss model. With regard to TSjoint, the field section is considered first, i.e., the area where the effectiveness of the longitudinal reinforcement in the webs can be assumed (TSjoint w/web-reinf.). Table 4 shows that failure due to yielding of the reinforcement can be expected at 700 kNm. As the test specimen failed at 680 kNm due to shear failure in the joint, this value was not reached. The question still arises as to how such high values could be achieved at all if the longitudinal reinforcement ends directly at the restraint and, thus, is not supposed to be effective. The exact same explanation as for TSRef must be considered. The vertical compressive stress must have been sufficient to strengthen the webs at the restraint to an extent of making it equal to the field section. In addition, the vertical compressive stress reduced the required anchorage length for the longitudinal reinforcement abutting the joint, making it fully effective after a short distance. However, the exact influence of the compressive stresses will have to be determined in further experimental investigations in order to make a definite statement. A possible test setup could be the placement of the joint directly in the field area. Similar tests, but with the joint reaching across the entire cross-section (i.e., including the bottom and top plates), are presented by [PERSON] [25].