## 5 Experimental Investigations
### Transverse Load-Bearing Behavior of Cross-Beams for Construction State
#### 5.1.1 Specimens and Test Set-Up  
Two beams were produced by Alfred Trepka GmbH (Ober-Grafendorf, Austria), each of which was tested at both ends, resulting in a total of four bending tests. The height \(h\) and width \(b\) of the members were 430 and 220 mm, respectively. The length \(l\) of each beam was 8000 mm. Each of the four tests was labeled with an identifying code. The first four characters describe the loop spacing in mm, either 100 or 200 mm (S100/S200). The following four to five characters correspond to the anchorage length of the loops, either 95 or 295 mm (AL95/AL295). The test set-up is shown in Figure 13. The distance between the support and the loading point of the cantilever was \(a_{\mathrm{v}}=3000\) mm. Uplifting was prevented by two tension rods at the opposite support. Figure 12: Experimental investigations: Transverse load bearing-behavior of cross-beams for construction state (red); Longitudinal load-bearing behavior of beams cast in several steps (blue). An illustration of the cross-section above the support is shown in Figure 14. The longitudinal reinforcement and the stirrups were identical in both beams. The top longitudinal reinforcement consisted of four continuous bars of \(\mathcal{O}\)26 mm. The four bars were combined into two-bar bundles. The lower bar was fully embedded in concrete, and half of the diameter of the second bar directly above protruded from the upper edge of the member. The bottom longitudinal reinforcement consisted of four continuous bars of \(\mathcal{O}\)20 mm. These bottom bars were enclosed by the shear reinforcement \(\mathcal{O}\)10 mm, which consisted of two-legged stirrups, equally spaced at a distance of 100 mm. The shear reinforcement of \(\mathcal{O}\)10 mm was installed at a distance of 100 mm and consisted of two-legged stirrups. The stirrups were led out of the beam at the top and bent around the upper longitudinal reinforcement, resulting in two overlapping legs at the top of the bar. The overlapping distance was 60 mm. In order to exert as little influence as possible on the additional loops, the legs of the stirrups were not closed. The reinforcement was designed in such a way that a flexural failure in the region of the support is ensured. In this way, it was possible to investigate whether the protruding  
Figure 14: Cross-section above the support (all dimensions in mm). (**a**) Drawing of the cross-section; (**b**) Photo of the top of the beam. Figure 13: Test set-up for experimental investigations on cross-beams (all dimensions in mm). reinforcement can be loaded to the yield stress. Therefore, sufficient shear reinforcement was provided and a high shear-to-span ratio \(\lambda=7.19\) was chosen. A high shear-to-span ratio \(\lambda\) is equivalent to an increase in the acting bending moment with a constant shear force and avoids direct compression struts leading into the support. According to [PERSON] [27], this ratio has a remarkable influence on the shear capacity. It can also be considered as a bending-moment-to-shear force ratio. Through experimental studies [27], the range between \(2.0\leq\lambda\leq 4.0\) was found to be particularly at risk for shear failure for beams without sufficient shear reinforcement. .1.2 Theoretical Considerations Regarding the Mechanical Operating Principle of the Additional Loops  
The mechanical background of bonding between concrete and reinforcement has already been described in great detail [28; 29]. The mechanical model consists of three-dimensional tension rings and compression struts, which are in equilibrium. The compression struts, emanating radially from the ribs of the rebar, form a tension ring running radially around the reinforcing bar. In the instance of unconfined concrete, these tensile stresses must be absorbed by the concrete alone. If the ultimate tensile stress resistance of the plain concrete is exceeded, this leads to sudden and brittle premature splitting failure with associated spalling of the concrete cover, if any.