## 4 Conclusions  
This contribution discusses the impact of test conditions on the behavior of timber-concrete composite (TCC) connections. In the first test series C1, Wirth FT connectors with one screw per side were used as TCC connectors for 20 symmetrical push-out tests. This type of TCC connector allowed for the variation in torque levels of the screws, enabling the investigation of different pressure levels between the timber and concrete. Within these studies, the interlayer between the timber and concrete was varied, including direct contact, plastic foil only, and two plastic foils with Vaseline between the timber and concrete. In addition, the number of applied load cycles was varied, and stiffness values were derived for each cycle. Tests with direct contact generally showed higher stiffness values when the screws were subjected to higher levels of torque. In the tests involving plastic foil and plastic foil and Vaseline between the timber and concrete, the increase in stiffness values occurred in smaller steps within a lower range. All push-out test series that used two plastic foils together with Vaseline as an interlayer showed equal and nearly constant stiffness values of the connection for all the different screw torque levels.  
Furthermore, two test series, C20 and C21, with notched connections were conducted. Each test series consisted of five specimens: one series was manufactured as inclined test specimens with one notch and one test series was manufactured as symmetrical push-out test specimens with two notches. Despite the differences in test setups, all tests within both series showed the same final failure mode and only slightly different maximum load-carrying capacities. For all tests, the final failure mode occurred as ductile timber compression failure in front of the loaded edge of the notch. This failure mode is typical for the chosen geometry of the timber length in front of the loaded edge of the notch and was also observed in several symmetrical push-out tests conducted in [13] or other similar tests in [20]. However, all tests in both series showed an adhesive friction break-off between the direct contact of timber and concrete. Therefore, it was not possible to derive and compare stiffness values. However, based on the overall behaviors (final failure mode and load-carrying capacity) of the two different test series and considering the results of [13], it can be assumed that both test setups are suitable for characterizing the shear behavior.  
Conceptualization, S.M., A.M.P.G.D. and U.K.; Validation, S.M., J.A.A.C., A.M.P.G.D. and U.K.; Formal analysis, S.M. and J.A.A.C.; Investigation, S.M., J.A.A.C., A.M.P.G.D. and U.K.; Resources, S.M., J.A.A.C. and A.M.P.G.D.; Writing--original draft, S.M. and J.A.A.C.; Writing--review & editing, S.M., J.A.A.C., A.M.P.G.D. and U.K.; Supervision, A.M.P.G.D. and U.K.; Project administration, A.M.P.G.D. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
\begin{table}
\begin{tabular}{c c} \hline
**Test No.** & \(\mathbf{F_{\text{max}}}\)**/**Notch [kN]** \\ \hline C20.1 & 137.2 \\ C20.2 & 128.2 \\ C20.3 & 129.7 \\ C20.4 & 128.5 \\ C20.5 & 132.9 \\ \hline MV & 131.1 \\ CoV & 2.9\% \\ \hline C21.1 & 119.0 \\ C21.2 & 96.8 \\ C21.3 & 93.2 \\ C21.4 & 108.2 \\ C21.5 & 102.0 \\ \hline MV & 103.8 \\ CoV & 10\% \\ \hline \end{tabular}
\end{table}
Table 6: Summary of the maximum load-carrying capacity \(F_{\text{max}}\) per notch of test series C20 and C21.