## 3 On-Site Investigation and Specimen Design
### Results of the On-Site Investigation  
This field investigation served as a preliminary investigation to gather essential data for future shaking table tests on vertical hydrogen storage vessels. The primary objective was to investigate the installation conditions, as well as the configuration and dimensions of the foundations of vertical hydrogen storage vessels currently deployed in real-world settings. To achieve this goal, a series of activities were carried out, including visits to representative regions in Korea where vertical hydrogen storage vessels are installed, along with the collection of information through on-site assessments and the examination of relevant documents. Figure 3 compares the support structure types and anchor specifications of the target structures installed in each region. In the case of the target structure installed in Gangneung (as shown in Figure 3a), the column shape for support was constructed with H-beams (300 mm \(\times\) 300 mm \(\times\) 10 mm \(\times\) 15 mm) with a height of 980 mm, and the storage vessel was supported by three of these columns. The height from the top of the storage vessel to the foundation concrete was measured to be 8500 mm, and the size of the supporting concrete was measured as 750 \(\times\) 650 \(\times\) 440 mm\({}^{3}\). The anchors connecting the structure to the support were D30 pre-installed set anchors, with a total of six anchors, two per support point. In the case of the target structure installed in Samcheok (as shown in Figure 3b), the column shape for support was constructed with L-angle steel (75 mm \(\times\) 75 mm \(\times\) 9 mm) and had a height of 965 mm, with a total of four columns supporting the storage vessel. The height from the top of the storage vessel to the concrete was measured as 4000 mm, and the supporting concrete had a panel-shaped single piece with dimensions of 1650 \(\times\) 1650 \(\times\) 50 mm\({}^{3}\). The anchors connecting the structure to the support were D20 pre-installed set anchors, with a total of four anchors, one per support point. In the case of the target structure installed in Ulsan (as shown in Figure 3c), the column shape for support was constructed with square-shaped steel (220 mm \(\times\) 220 mm \(\times\) 10 mm) with a height of 800 mm, and the storage vessel was supported by three of these columns. The height from the top of the storage vessel to the foundation concrete was measured as 8000 mm, and the size of the supporting concrete was 470 \(\times\) 440 \(\times\) 240 mm\({}^{3}\). The anchors connecting the structure to the support were D30 pre-installed set anchors, with a total of 12 anchors, four per support point. Table 1 compares the measured values of the foundation concrete strength of the target structures installed in each region, as obtained using Schmidt hammer testing [30]. Figure 2: Outline of the on-site investigation. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Field Investigation Value for Concrete Compressive Strength (MPa)**} \\ \multirow{2}{*}{**Case No.**} & \multicolumn{2}{c}{**Gangneung**} & \multicolumn{2}{c}{**Samcheok**} & \multicolumn{2}{c}{**Ulsan**} \\  & \multicolumn{2}{c}{**Rebound**} & \multicolumn{2}{c}{**Correction**} & \multicolumn{2}{c}{**Rebound**} & \multicolumn{2}{c}{**Correction**} & \multicolumn{2}{c}{**Rebound**} & \multicolumn{2}{c}{**Correction**} \\  & **Hardness** & **Value** & **Hardness** & **Value** & **Hardness** & **Value** & **Hardness** & **Value** \\ \hline  
AVG. & N/A & 39 & N/A & 30 & N/A & 37 \\ SD & N/A & 1.5 & N/A & 2.9 & N/A & 1.4 \\ CV & N/A & 3.8 & N/A & 9.6 & N/A & 3.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Review of the non-destructive strength of the substructure concrete in each region. Figure 3: The configuration and support system of the target structures installed in each region (unit: mm): (a) Gangneung, (b) Samcheok, and (c) Ulsan.