## 3 Experimental Program
### Specimen Details
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Specimen**} & **Retrofitting** & **Eccentric** & **Sliding Slot** & **Point at Which the Steel Link Begins** \\  & & **Method** & **Distance (mm)** & **Length (mm)** & **to Resist Load** \\ \hline
1 & NE-10 & & 0 & \\ \hline
2 & E130-10 & & 130 & 10 & Shear crack initiation \\ \hline
3 & NE-5 & & 0 & \\ \hline
4 & E65-5 & & 65 & 5 & Flexural crack initiation \\ \hline
5 & E130-5 & & 130 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Details of the specimens. Figure 4: Notation of specimens. experimental results are presented in Figure 5. The 28-day compressive strength of the concrete used in fabricating the column was found to be 24.3 MPa, while for the foundation, it was 30.8 MPa. The yield strengths of the steel plate and reinforcing bar, determined through experimentation, were 275.4 MPa and 401 MPa, respectively. The RSL was specifically designed to retrofit only the plastic hinge length of the reinforced concrete columns. This length, when subjected to cyclic loading, was estimated using the formula proposed by [PERSON] and [PERSON] [22] as in Equation (1). \[\updownarrow_{\text{p}}=0.08\updownarrow+0.022\text{d}_{\text{b}}f_{\text{y}} \tag{1}\]  
Here, \(\updownarrow_{p}\) is the plastic hinge length, \(\updownarrow\) is the height of the column, \(d_{b}\) is the diameter of the longitudinal bar, and \(f_{\text{y}}\) is the yield strength of the longitudinal reinforcement. In previous research [18] involving cyclic loading tests, the plastic hinge lengths predicted by Equation (1) were similar to the experimentally observed plastic hinge regions in reinforced concrete columns. This confirmation led to the use of the equation to calculate the plastic hinge length in the present study, which was 338 mm. To facilitate fabrication and construction, the section 375 mm from the base of the column was identified as the anticipated plastic hinge region and retrofitted with the RSL. The components of the RSL method, the steel link and steel plate, were made using steel with a yield strength of 275 MPa. The steel link was designed as a lightweight square hollow section to simplify replacement, with dimensions of 20 mm in width and 1.5 mm in thickness. The length of the steel link was based on the RSL retrofitting length, which matched the plastic hinge length of the reinforced concrete column. To enable installation of the steel link at a 45-degree angle within the plastic hinge region, its length was 455 mm. The steel plate used to connect the structural members was 200 mm wide, 250 mm deep, and 10 mm thick, with an 8-mm-thick hinge welded to the bottom plate. The steel link was secured to the bottom plate's sliding slot using 10-mm-diameter high-tensile strength bolts. The steel plate was attached to both the column and the foundation with 16-mm-diameter chemical anchors. The details of the test specimen are shown in Figure 6.  
The RSL system was retrofitted to the reinforced concrete columns using the process shown in Figure 7. The replacement of a damaged RSL system after an earthquake is carried out in the reverse order of this construction process. If the structural members are not significantly damaged, it may be sufficient to replace only the steel link without needing to replace the steel plate. Figure 5: Material properties: (**a**) concrete and (**b**) steel and rebar. Figure 6: Details of the specimen [mm]: (**a**) RC column and (**b**) RSL system. Figure 7: Construction process: (**a**) surface treatment, (**b**) drilling, (**c**) joining the steel plate to the structural element with chemical anchors, and (**d**) connecting the steel link to the steel plate. 1. Surface treatment of the retrofitting location for the RSL system. 2. Drilling into the reinforced concrete column and beam. 3. Joining the steel plate to the reinforced concrete column and beam using chemical anchors. 4. Securing the steel link to the steel plate with high-tensile strength bolts.