## 1 Introduction
### Basic Concept of the Experimental Program  
The experimental investigations considered two large-scale test specimens, resulting in four possible torsion tests with the selected test setup. Both test specimens had a total length of 9.20 m, cross-sectional dimensions of 1.30 m by 1.00 m (height to width), and a wall thickness of 100 mm. The basic concept of the experimental investigations was to conduct a torsion test with a static system (Figure 2a,b) of a cantilever with a length of 4.60 m (corresponding to half the length of the test specimens), allowing two tests per test specimen. By applying the torsional load at the end of the test specimen (cantilever end) and creating a restraint in the middle to absorb the applied load, it was possible to leave the other half of the test specimen undamaged. Through modification of the test setup or rotation of the test specimen, a second torsion test was then performed on the undamaged half. Figure 2: _Cont._  
One of the two test specimens was a hollow box girder with continuous longitudinal torsion reinforcement without joints in the webs (named TS\({}_{\text{Ref}}\); shown in Figure 2a,c), while the other represented the unique connection between the hollow box girder and the pier segment of the novel bridge construction method (named TS\({}_{\text{Joint}}\); shown in Figure 2b,d). Figure 2: Overview, dimensions, and reinforcement layout of the two test specimens: (**a**) static system, dimensions, and cross-section of TS\({}_{\text{Ref}}\); (**b**) static system, dimensions, and cross-section of TS\({}_{\text{Joint}}\); (**c**) reinforcement details for TS\({}_{\text{Ref}}\), showing the bottom slab, webs, and middle diaphragm. Yellow: \(\OUR 08\) continuous longitudinal reinforcement in bottom slab and webs, cyan: \(\OUR 010\) stirrups; (**d**) reinforcement details for TS\({}_{\text{Joint}}\), showing the bottom slab, webs, and middle diaphragm. Yellow: \(\OUR 08\) continuous longitudinal reinforcement in the bottom slab and longitudinal reinforcement abutting the joint in the webs; green: \(\OUR 012\) continuous longitudinal reinforcement in the bottom slab; cyan: \(\OUR 010\) stirrups. The test bodies were fitted with a total of three diaphraggrams with a thickness of 0.25 m each; while the outer two were necessary for the safe introduction of the torsional loads, the middle diaphragm was required for the restraint, which was achieved by applying a large vertical force to counteract the initiated loads. In the case of TS\({}_{\text{Point}}\), the middle diaphragm--with a height of 1.10 m and width of 1.00 m--additionally represented the pier segment of the LT-bridge construction method, with the unreinforced joints situated between the webs and the middle diaphragm itself. The bottom and top slabs of TS\({}_{\text{Point}}\) were cast continuously over the whole length of 9.20 m. The webs, bottom slab, and deck slab of TS\({}_{\text{Ref}}\), on the other hand, were cast continuously over the whole length of 9.20 m, which was made possible by reducing the width of the middle diaphragm to 0.80 m.  
According to [PERSON] et al. [18], post-tensioning tendons can be considered as reinforcement in terms of torsional resistance if they are bonded; however, careful considerations have to be made regarding the external post-tensioning used in the new construction method. Considering this fact, it was decided to omit the post-tensioning for the time being, which also led to a simpler test procedure and a more conclusive evaluation of the results. The effects of external post-tensioning will be evaluated in a further test series. Due to the anchoring of the post-tensioning tendons at the pier segment, vertical compressive stresses occur, which also locally influence the webs and, thus, the joint. This vertical pressure was automatically generated in the test program when the vertical loads on the middle diaphragm (representing the pier segment) were applied for the creation of the restraint.