## 4 Experimental Results and Analysis  
### Crack Propagation and Failure Modes  
Figure 9 illustrates the propagation of cracks in each test specimen on side 2. Flexural cracks at the bottom of the column emerged in all specimens when the drift ratio reached  
Figure 8: Test setup: (**a**) concept of the experiment, (**b**) loading protocol, and (**c**) photograph of the test setup. 0.75%. As the load intensified, shear cracks developed and extended, eventually leading to concrete spalling at the bottom of the column. The experimental plan aimed to conclude the tests when the load dropped to 80% or less of the maximum after reaching the peak load, a point reached by all specimens at a drift ratio of 4.5%. The key initiation points for primary cracks in each specimen are summarized in Table 2. When comparing crack patterns among specimens with different eccentric distances, specimens NE-5 and E65-5, both featuring a sliding slot length of 5 mm and eccentric distances of 0 mm and 65 mm, respectively, exhibited similar patterns. In both cases, flexural cracks were distributed evenly throughout the column with an increasing drift ratio. Shear cracks manifested at a drift ratio of 2.2%, leading to concrete spalling in the first cycle at a drift ratio of 4.5%, concluding the experiment. Specim E130-5, with a sliding slot length of 5 mm and an eccentricity of 130 mm, showed shear cracks at a lower drift ratio of 1.75%. These cracks concentrated at the bottom of the column, resulting in concrete spalling at a drift ratio of 3.5%, prompting the conclusion of the experiment at 4.5%. Specimen NE-10, featuring a sliding slot length of 10 mm and no eccentricity, exhibited shear cracks at a drift ratio of 2.2%, with concrete spalling observed at the column's bottom at a drift ratio of 4.5%. Similarly, in specimens with a 10 mm sliding slot length and an increased eccentricity of 130 mm, there was an acceleration in crack propagation. In these cases, shear cracks emerged at a drift ratio of 1%, with concrete spalling observed at a drift ratio of 3.5%. The point at which the steel links began to resist load was visually inspected, as shown in Figure 10. Regardless of eccentricity, the steel links in specimens with a 5 mm sliding slot length commenced load resistance at a drift ratio of 1% and experienced buckling at 2.2%. Similarly, for specimens with a 10 mm sliding slot length, the steel links began resisting the load at a drift ratio of 1.4% and buckled at 2.75%, showing a consistent response across eccentricities. The point at which the steel links started resisting loads influenced the number and width of shear cracks in the reinforced concrete columns. The difference in the load-resisting initiation points resulted in fewer shear cracks in specimens with a 5 mm sliding slot length compared to those with a 10 mm length. Figure 9: Crack propagation: (**a**) NE-10, (**b**) E130-10, (**c**) NE-5, (**d**) E65-5, and (**e**) E130-5. Cracks significantly impacting the failure of the test specimens were shear cracks originating at the bottom of the columns. Therefore, Table 3 presents the crack patterns observed at the bottom of the columns from side 1 at the point of failure. While the initiation of flexural cracks was identical for all specimens, the onset of shear cracks varied with the length of the sliding slot and eccentric distance. An increase in eccentric distance and a sliding slot length of 10 mm, as opposed to 5 mm, led to the earlier development of shear cracks. The effect of eccentric distance on the timing of shear crack initiation is attributed to the increased torsion on the specimen as the eccentric distance increases, resulting in an increase in the number and width of cracks and a rapid propagation of existing flexural cracks into shear cracks. The effect of sliding slot length on the crack propagation pattern, considered at the design stage, was validated through the experimental results, affirming the conceptual validity of the RSL system's retrofitting strategy.