## 2 Pocket-Type Connections in System Scaffolding  
Both pocket-type and wedge-type connections are commonly used connection styles for system scaffolding in Korea. Figure 1 and Table 1 show the structural shapes of the pocket-type connections used in this study, their specific dimensions, and their average measured values. During the connection fabrication process, there may be differences between the connection members' specifications and the actual measured values; therefore, the actual values for each member were measured, and the results are shown in Table 1. The averages of the measured values were found by randomly selecting and analyzing 20 of the 60 specimens that were used in this study. The error rate of the average measured value compared to the specifications was within \(-0.3\%\) to \(2.6\%\). Figure 1: Shapes and dimensions of pocket-type connection: (**a**) Shapes and names of parts; (**b**) Abbreviations of detailed dimensions; (**c**) Connected shape. The vertical members and horizontal members of pocket-type connections are connected by inserting a pin that is welded to the end of the horizontal member steel pipe into the pocket on the vertical member, and this is followed by striking with a hammer. Figure 1 shows the pocket part where four pockets are welded to the vertical member. Each pocket connection acts independently of the other pocket connections so that the number of horizontal members inserted into the pockets has almost no effect on the rotational stiffness of the other connections. Therefore, this study focused on the connection rotational stiffness of a configuration in which only one vertical member and one horizontal member were connected, and the number of connected horizontal members was not considered to be a variable that affects the rotational stiffness. Table 2 shows the material and mechanical properties of the steel pipes, pockets, and pins that make up the pocket-type connection. The Mill Test Certificate, which guarantees the quality of the steel, was used to find the yield strength, tensile strength, and elongation percentage of each component. Instead of the coupon test to obtain the stress-strain curve, the Mill Test Certificate was used to show the material properties of used steel members since it is not easy to cut a specimen to test a coupon test from considered connection specimens. The average value of 12 certificates was used for the pocket material, and the average value of nine results was used for the pin material. The Mill Test Certificate received from a steel manufacturer was issued according to ISO 1047/EN 10204 3.1. The material properties of the system scaffolding with the pocket-type connections used in this study meet Korea's performance standards for members used in system scaffolding [18]. The mill sheet certificates for the vertical member steel pipes and horizontal member steel pipes include the results of tests performed on products that were fabricated as steel sheets (raw material) rather than steel pipes. As such, it was determined that the results in the mill sheet certificates reflected any changes in yield strength, etc., that may have occurred during the process of fabricating the steel sheets into steel pipes. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Part**} & \multirow{2}{*}{**Specifications (mm)**} & \multicolumn{3}{c}{**Actual Measurement**} \\ \cline{3-5}  & & **Mean (mm)** & **SD (mm)** & **Error (\%)** \\ \hline HD & 42.9 & 42.91 & 0.12 & 0.0 \\ Ht & 1.8 & 1.82 & 0.04 & 1.1 \\ Pin-t & 9 & 8.97 & 0.08 & \(-\)0.3 \\ Pin-T & 29 & 29.10 & 0.27 & 0.3 \\ Pin-H & 60 & 60.51 & 0.10 & 0.8 \\ Pin-B & 23 & 23.35 & 0.07 & 1.5 \\ VD & 48.6 & 48.69 & 0.09 & 0.2 \\ Vt & 2.3 & 2.36 & 0.12 & 2.6 \\ Pocket-t & 3 & 3.05 & 0.06 & 1.7 \\ Pocket-T & 31 & 31.14 & 0.11 & 0.5 \\ Pocket-H & 40 & 40.22 & 0.21 & 0.5 \\ Pocket-B & 27 & 27.19 & 0.19 & 0.7 \\ Pocket-W & 18 & 18.17 & 0.08 & 0.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Detailed dimensions of pocket-type connection.