## 2 Experimental Program
### Type of Contact Surface and Load Procedure  
Test series C1 involved static and cyclic (non-destructive) shear tests under various conditions. The test conditions considered variations in the contact interface between the  
Figure 4: Fabrication process: (**a**,**d**) notch with screw of test series C20 and C21; (**b**,**e**) formwork with reinforcement of test series C20 and C21; (**c**,**f**) final specimens with concrete of test series C20 and C21. concrete and timber, the level of tightening of the screws, and the number of load cycles. These variations were possible because of the selected connection system, which was developed for use in prefabricated composite systems and allows for assembly, disassembly, and torque adjustment. This allowed the concrete elements to be used multiple times within the test series. The three contact interface types were (i) direct contact (DC), (ii) one plastic foil as an interlayer (P), and (iii) Vaseline between two plastic foils as an interlayer (PV) (see Figure 5 and Table 2). A plastic foil with a thickness of 0.2 mm and a density ranging from 920 to 930 kg/m\({}^{3}\) was selected. The thickness of two plastic foils and Vaseline was less than 0.5 mm and can therefore be neglected. In test series C1, two loading procedures were conducted: cyclic and static (see Table 2). The stiffness of the connection was determined for each load cycle and torque level through cyclic tests. Tests were conducted using a manual torque wrench to tighten the screws, with torques levels of 30 Nm, 60 Nm, and 80 Nm for two, three, ten, and one hundred load cycles (see Table 3). \(F_{\text{est}}\) (the estimated maximum load) was calculated based on initial tests or estimated based on similar tests conducted in [20]. The ETA-13/0029 [18] recommends a minimum torque of 20 Nm for tightening screws. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Series No.**} & \multicolumn{2}{c}{**Interface between**} & \multirow{2}{*}{**Test Procedure**} & \multirow{2}{*}{**No. of Specimens**} \\  & & **Timber and Concrete** & & \\ \hline \multirow{3}{*}{C1.x} & Direct contact & & & \\  & Plastic foil & Static and cycle & & \\  & Plastic + Vaseline & & & \\ \hline \multirow{3}{*}{C20} & Direct contact & Static & & \\ \cline{1-1}  & Direct contact & Static & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Interface and test procedure type for test series. Figure 5: Interface types in test series C1: (**a**) direct contact (DC); (**b**) one plastic foil (P); (**c**) two plastic foils and Vaseline (PV); (**d**) detail of the application of Vaseline. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Test Series** & **Load Protocol** & **Load Procedure** & \(F_{\text{est}}\) [kN] & **Speed** \\ \hline C1.x & See Table 4 & Load controlled & 50.0 & 0.1667 kN/s \\ \hline \multirow{3}{*}{C20} & \multirow{3}{*}{Static} & Displacement & \multirow{3}{*}{110.0} & \multirow{3}{*}{0.50 mm/min} \\  & & controlled & & \\ \hline \multirow{3}{*}{C21} & \multirow{3}{*}{Static} & Displacement & \multirow{3}{*}{220.0} & \multirow{3}{*}{0.50 mm/min} \\  & & controlled & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: General overview of applied load protocols. The tests were conducted according to the parameters outlined in Table 4, which includes all evaluated parameters. For example, specimen C1.6 was tested in a direct contact surface test with three load cycles for each applied torque level (see Figure 6). Figure 7 illustrates the load procedure used for ten load cycles. However, two failure tests were conducted at the end of the test series to determine the load capacity after applying the cyclic tests. Torque levels were applied after the load was removed at the end of each set of cycles. The load protocols, static and cyclic, have been defined on the basis of the EN 26891 [23] load protocol. The load protocol definition is dependent on the estimated maximum load, Fest, which is typically obtained through bibliography or preliminary tests.