# Study of Innovative Connector for Steel-Concrete Composite Structures
## 4 Discussion  
The summary of the results from the experimental tests of the fasteners is presented in Table 11. The average value of the breaking load \(P_{S,Rk}\) of the fastener in model no. 2, which was built using fasteners in the form of the corrugated sheet with a thickness of 1.00 mm and 4 nails, obtained experimentally is 47.50 kN. Reducing the number of nails by 50%, i.e., from 4 to 2, resulted in reducing the average breaking load \(P_{S,Rk}\) of the fastener by 35%, because the average breaking load of the fastener in model no. 3 in which fasteners made of 1.0 mm thick corrugated sheet and 2 nails were used, and experimentally obtained to be 30.83 kN. However, increasing the sheet thickness from 1.00 to 1.25 mm, i.e., by 25% (while maintaining 2 nails), resulted in a return of the average breaking load \(P_{S,Rk}\) of the connector by only 11%, because the average breaking load \(P_{S,Rk}\) of the connector in model 4, in which fasteners were made of corrugated sheet metal with a thickness of 1.25 mm and 2 nails, obtaining the value of 34.17 kN. Comparing the weight of the adopted fastener, which is affected by the thickness of the sheet and the number of nails, as well as taking into account the labor consumption of driving two and four nails, the fastener from model no 3, which was made of 1.00 mm thick corrugated sheet and two nails, was considered the most effective. It cannot be said that \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Model of Connector** & **2** & **3** & **4** \\ \hline Average value of the breaking load of the fastener \(P_{S,Rk}\), kN & 47.50 & 30.83 & 34.17 \\ Characteristic load capacity of the fastener \(P_{Rk}\), kN & 40.50 & 27.00 & 29.25 \\ Design resistance of the connector \(P_{Rk}\), kN & 38.00 & 24.67 & 27.33 \\ Slip capacity \(\delta_{\text{s}ik}\), mm & 7.70 & 10.77 & 14.40 \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Summary of the results from the experimental tests of fasteners. Figure 14: Slip–force diagram to determine the slip of fastener for (**a**) sample 2A (1.00 mm thick sheet and 4 nails); (**b**) sample 3A (1.00 mm thick sheet and 2 nails); and (**c**) 4C samples (1.25 mm thick sheet and 2 nails). this is the best solution, because the selection of fasteners in composite structures always depends on the acting load. Therefore, in places where a greater load capacity is required, it was decided that a better solution was to increase the number of nails to four than to increase the thickness of the sheet. This is supported by the fact that the fastener with four nails carries a 35% higher load than the fastener with 2 nails but increasing the sheet thickness from 1.00 to 1.25 mm results in the increase in load by only 11%. It should be remembered that the labor consumption of using a thicker sheet metal is practically nil compared to shooting 50% more fasteners. However, in one structural member, it is possible to use fasteners with two and four nails in such a way as to optimize the fasteners and increase the number of nails only locally, in areas where greater load capacity is required. Among all analyzed connector models, the maximum deviation from the average value is equal to 5.3%. This value was considered mean, because EN 1994-1-1 [20] allows deviations of up to 10%. The reason for the deviation of the results of individual samples from the average value are inaccuracies in the execution of materials, components of the samples (I-beam, sheet metal, nails) and inaccuracies in the execution of the samples subjected to the shear test. Ductile connectors are characterized by sufficient deformability to justify the perfectly plastic behavior of the connection in the considered structure. As shown in Table 11, all analyzed fasteners were considered ductile as they had the characteristic slip capacity \(\delta_{uk}\) of at least 6.0 mm. The connector in model no. 2 showed the lowest slip capacity, because it is 7.70 mm. Reducing the number of nails from four to two resulted in a 29% increase in slip, because in model no. 3, it was 10.77 mm.