## 2 Shear Tests on Cross-Frames in Lightweight Segments
### Discussion  
#### 2.3.1 Double Wall Elements  
KAP-Steel-Connectors  
The load-deformation diagram in Figure 7a shows an almost linear behaviour in the laboratory tests until the KAP-sticks as well as the KAP-waves began to buckle.  
The finite element analysis confirmed not only the ultimate load, but also showed, that the wave is responsible for a major part of the load bearing capacity. This can be seen by comparing the results curve from the model without sticks to the complete model. The load deformation diagram also shows that the finite element analysis slightly overestimates the stiffness from the laboratory tests.  
The buckled KAP-wave and buckled KAP-sticks in the lower part of the specimen in Figure 7b,c after failure were the same for all specimens and did not cause any damage to the surrounding concrete.  
Lattice Girders 05 mm and 09 mm Diagonals  
The load deformation diagrams in Figure 8a,b show that until the buckling of the compressed diagonals, the behaviour was almost linear. In the diagram in Figure 8b, three of the four tested connecting elements are plotted due to problems at the deformation measurement of element V8_Lat9_4. As can be seen in Table 5, the load was in the same range as the other three lattice girders.  
The results from the finite element parameter study (Figure 8a,b) on imperfections show the reduction in load bearing capacity and stiffness with increasing magnitude of imperfection. The best fit to the experiment was obtained at an imperfection of 4 mm for the 5 mm diagonals and at 5 mm for the 9 mm diagonals.  
Table 2 shows the range of magnitude of imperfections, measured at two lattice girders. Superimposing deformations in the two directions shows that the results from the FE-simulations are plausible.  
However, it must be considered that not all bars have the same pre-deformation and therefore behave more rigidly or softly, resulting in different stresses in the bars.  
Figure 8c shows a 9 mm diagonals specimen after failure. Up to a deformation of approximately 10 mm, no damage was observed at the interface between the concrete and the lattice girder. After reaching the maximum load, the specimen was pushed further, deforming the already buckled steel bars, followed by a failure of the concrete panel (pull-out of the individual reinforcement bars of the lattice girder). This behaviour can be explained by a failure of the compressed bars, while the tensioned diagonals  
Figure 7: Test results KAP-steel-connector double wall elements: (**a**) load-deformation diagram with results from laboratory tests (black and grey) and FEA-simulations (blue and red); (**b**) specimen post failure in the laboratory test; (**c**) finite element specimen post failure, deformation superelevated two times.  
were still under tension. The pull-out failure occurred at three of the four tested lattice girders with 9 mm diagonals and at very large deformations long after the ultimate load. This failure mode was also observed in the simulations for the 9 mm diagonals without imperfections (Figure 8b). At the 5 mm diagonals, no damage at the concrete next to the lattice girders could be observed, showing that the compressed bars have a fixed-fixed boundary condition.  
Figure 8: Test results \(\mathcal{O}\)5 mm and \(\mathcal{O}\)9 mm lattice girder double wall elements: (**a**) \(\mathcal{O}\)5 mm lattice girder double wall elements: load-deformation diagram with results from laboratory tests (black and grey) and FEA-simulations (blue and purple); (**b**) \(\mathcal{O}\)9 mm lattice girder double wall elements: load-deformation diagram with results from laboratory tests (black and grey) and FEA-simulations (blue and purple); (**c**) specimen post failure in the laboratory test; (**d**) finite element specimen post failure, deformation superelevated two times.