## 2 Experimental Investigations
### Test Results
\[\left(\frac{P_{S}}{P_{S,R}}\right)^{k}+\left(\frac{P_{T}}{P_{T,R}}\right)^{k} \leq 1.0 \tag{1}\]  
While in case of \(e_{r}=0\) mm, with ensured py-out failure regardless of the load's direction, a quadratic interaction formula can be applied to the design, pull-out is characterized by premature failure at load levels below the linear interaction between tensile and shear load-bearing capacity. This is demonstrated in diagram (a), red ellipse. Diagram (b) includes specimens with \(e_{r}=16\) mm in both uncracked and cracked concrete. On axis X, the reduction of the pure shear load-bearing capacity can be identified in case of py-out failure owing to the cracks separating the py-out cone into several smaller segments. The degradation of the concrete's condition leads to a reduction of the load-bearing capacity by approx. 26%. Since for load directions above 22.5\({}^{\circ}\) solely pull-out failure occurred, it is not possible to identify the effect of cracks in the concrete in case of py-out failure. Nevertheless, the load-bearing capacity of the specimens was also slightly lower in cracked concrete for pull-out failure as demonstrated in diagram b by the blue and orange dotted lines. Diagram (c) contains results from CLASSEN ([19]). The latter demonstrates the validity of the linear interaction between the pure shear and the pure tensile load-bearing capacity when positioning the concrete dowel reinforcement bars within the steel dowels' recess without securing the bars directly at the steel surface (\(0\) mm \(<e_{r}=8\) mm). Finally, diagram (d) includes results of varying crack width for the load directions 0\({}^{\circ}\) and 45\({}^{\circ}\). For pure shear loading, py-out failure was decisive and the load-bearing capacity was reduced with increasing crack width as demonstrated earlier in [22; 33]. For a load direction of 45\({}^{\circ}\) only pull-out failure was observed. Here, the concrete's condition only influences the load-bearing capacity marginally. While the py-out cone is separated by the cracks, thus leading to a reduced concrete surface available for the tensile load transfer, the mechanisms of the load reduction are different in case of pull-out failure. Here, the load-bearing capacity is influenced negatively by the tensile stresses in the concrete required for the crack initiation and not by the resulting cracks. The anchoring effect of the steel dowel in the concrete is decreased as the concrete within the steel dowel's recesses is being \"pulled-out\" by the forces necessary to create the cracks. While tensile forces in the composite dowels should be avoided in case of puzzle-shaped connectors, securing the reinforcement bars of the concrete dowels at the surface of the steel dowel's recesses leads to good load-bearing behaviour (avoidance of pull-out failure) and sufficient resistance against tensile loading. The shear-tension interaction Formula (1) may then be used with the value \(k=2\) for the exponent. While a value of \(k=1\) can be used in case of the bars being positioned within the steel dowel's recesses without touching the steel dowel's surface (\(e_{r}>0\) mm), it is difficult to secure such conditions on construction sites. Additionally, the effort required for securing \(e_{r}=0\) mm would only be marginally higher. Thus, it is suggested to consider the latter (\(e_{r}=0\) mm) as soon as tensile loading is expected on the dowels. Better suited dowel shapes with bigger steel recesses and thus better anchoring capabilities (such as the clothoid-shaped dowels (CL)) should be preferred as soon as tensile loads are expected by design.