## 3 Push-Off Tests on Joints between Segments
### Discussion of Failure Cause by Non-Linear FEM-Analysis  
The non-linear FEM analysis was performed using ABAQUS FEA with the previously introduced material and parameters (Table 3). The interface parameters were calibrated by the test results of the plain grouted joint. The simulations can fully reproduce the achieved test loads (Table 7). Moreover, the load carrying behaviour is represented quite accurately with some lack in the post-peak behaviour of the keyed and grooved joints (Figure 15). Pronounced plateaus at load-peak were observed in the experiments, which could not be covered in the simulations. These plateaus could be explained by delamination processes of these rough interfaces, accompanied by an early shear deformation, both of which were observed in the experiments. These computing time intensive delamination processes were not integrated in the FE-model of this investigation. The comparison between the cracking pattern of the tests and the simulations is shown in Figure 16.  
Figure 15: Load-deformation diagrams compared to simulation results for (**a**) dry joint; grout 1: (**b**) plain; (**c**) groove; (**d**) keyed and for grout 2: (**e**) plain; (**f**) grooved, respectively.  
The failure in the plain grouted joint is defined by overcoming the frictional capacity plus an adhesive portion according to the shear-friction model of the fib Model Code 2010 and Eurocode 2. After reaching this load level, delamination occurs, accompanied by shear deformation, which leads to a single inclined crack in the grout located approximately at the middle of the joint. In the end, the grout is fully separated, with the rest of the material still attached to the opposite concrete blocks in simulations and testing (Figure 16a). The bearable load drops to the level of the test with dry surface, which could be explained by the fact that the grout slides as a quasi-negative profile on the dry surface. The simulations also showed this failure surface.  
After overcoming this preliminary shear friction, the shear displacement leads to an activation of shear keys at the specimen with the keyed surface. When this happens, the formation of concrete compression struts occurs (Figure 16b). The load increase is then limited by a diagonal cracking initiated at the contact point of the upper shear key on the specimen half with load introduction (Figure 16b). The same crack can be found on the lower shear key on the specimen half with the load-bearing point. Finally, the grout part is also separated in the middle in tests and simulations.  
The grooved joint can be interpreted as a rougher surface that acts along the plain surface. Thus, the bearing portions of both surfaces could be aggregated. Until this load level is reached, only a slight shear deformation occurs (Figure 14a). When this load level is surpassed, the separation between concrete block and grout leads to a grind down of the ribs (Figure 16c) and also to a separation of this grouted pillar and the plain grout at various locations in the joint. Only in test VO was a different cracking pattern with an almost linear separation of the pillar observed, resulting in a lower transferable force (Table 7).  
Figure 16: Typical cracking pattern for different joint types: (**a**) VG (plain); (**b**) VL (keyed); (**c**) VN (grooved). Comparison to the FEM results: (**d**) plain, (**e**) keyed, (**f**) grooved.