## 4 Experimental Results and Analysis
### Strain  
The main distinction between the RSL retrofitting method and conventional bracing techniques lies in the movement of the steel link, attached to the bottom plate with high-tensile bolts within a sliding slot, laterally in response to lateral displacements acting on the column. Within the permissible displacement of the sliding bolt, the steel link behaves elastically. When this permissible displacement is exceeded and an excessive load is applied, the steel link is buckled. Consequently, the behavior of the RSL method varies with the sliding slot length, which can be adjusted to enable the RSL to function effectively as a structural fuse. In this study, the behavior of the steel link was analyzed experimentally by observing the strain distribution at different drift ratios using gauges attached to the steel link. The gauges were aligned along the length of the steel link, but the analysis focused on the gauge positioned in the middle, where the highest strain was recorded. This analysis is depicted in Figure 15. The yield strength of the steel link was 275 MPa, and its yield strain was 1375 \(\mu\varepsilon\). The deformation behavior of the steel link demonstrated a pattern across various eccentric distances and sliding slot lengths. The steel link underwent lateral movement within the sliding slot, initiating load resistance once the displacement exceeded the sliding slot length,  
Figure 14: Torsional moment–twist envelopes. eventually reaching the slot end. In specimens with a 5 mm sliding slot, load resistance was anticipated to begin at a drift ratio of 0.75%. The analysis showed that deformation in the steel link commenced at a 1% drift ratio and yielded at 2.2%. For specimens with a 10 mm sliding slot, resistance to load started at a drift ratio of 1.4%, with deformation occurring at this point and yielding observed at 2.75%. Specimens with a 5 mm slot yielded earlier and exhibited a higher final strain compared to those with a 10 mm slot. The strain in the steel link increased with the eccentric distance, a phenomenon attributed to the increased torsion exerted on the specimens. The visual inspection of the steel link revealed a buckling point at a drift ratio of 2.2% for the 5 mm slot and 2.75% for the 10 mm slot, accompanied by a noticeable increase in strain observed before these points. Given the tendency of reinforced concrete columns to exhibit brittle behavior after the longitudinal reinforcement yields, with rapid crack propagation in the concrete, it becomes crucial to identify the yield point of the longitudinal reinforcement. Figure 16 illustrates the strain distribution along the height of the longitudinal reinforcement from the base of the column. Across all specimens, the strain in the longitudinal reinforcement increased from the middle to the bottom of the column, reaching its peak at the bottom. The yield strain for the longitudinal reinforcement of deformed bars with a yield strength of 400 MPa corresponds to 2000 \(\upmu\varepsilon\). The RSL method is specifically designed to retrofit the expected plastic hinge regions of reinforced concrete columns. Normally, the strain in the longitudinal reinforcement of columns sharply increases at the bottom. However, in RSL-retrofitted specimens, cracking and deformation were dispersed toward the middle of the column, resulting in an even distribution of strain along the column height. In specimens with a 5 mm sliding slot, the longitudinal reinforcement in specimens with eccentric distances of 0 and 65 mm yielded at drift ratios of 2.75% and 2.2%, respectively, with an eccentric distance of 130 mm. For the 10 mm slot, specimens with eccentric distances of 0 and 130 mm yielded at drift ratios of 3.5% and 2.75%, respectively. All specimens exhibited an increase in strain in the upper of the column with increasing eccentric distance, likely attributed to increased torsion. Figure 15: Strain of the steel link.