## 2 Experimental Programs
### Damage to Longitudinal Reinforcements  
In this study, we focused on the reinforcement damage in Case-2 within small-diameter and high-density bar arrangements. Figure 8a shows the strain history of the longitudinal reinforcement on both the north and south sides at the base of the column. Figure 8b,c show the history of horizontal load versus longitudinal reinforcement strain at the same location. From (a) and (b), the south-side longitudinal reinforcement appears to exhibit almost elastic deformation. However, from (a) and (c), the north-side longitudinal reinforcement experiences plasticization up to 20,000 \(\upmu\) after yielding during the first loading at 1.0% Drift and remains in the strain region of approximately +4000 \(\upmu\) (tension) until the loading reaches 2.5% Drift. The extent of plasticization of the longitudinal reinforcement differs drastically between the south and north sides, and this may be due to the bonding failure of the southern steel bars from the beginning, resulting in stress not being well transmitted to the reinforcements, resulting in the reinforcements being in an elastic deformation state. However, since the southern reinforcement is almost unable to bear the load, stress concentration occurs in the northern reinforcement, resulting in significant plastic deformation.  
Additionally, as shown in (c), the relationship between the horizontal load and longitudinal strain of the north-side reinforcement shifts to the compression side (negative) from 3.0% Drift onwards, and the horizontal load-bearing capacity gradually decreases as the deformation increases. As the loading progressed, it was observed that the longitudinal reinforcement in the corner began to buckle at 3.5% Drift, as shown in Figure 9a-c. At 4.5% Drift, the sound of the longitudinal reinforcement breaking was confirmed, and a sudden drop in load-bearing capacity was observed, leading to the termination of the experiment.  
Similarly to Figure 8, the history of horizontal load versus longitudinal reinforcement strain at 100 mm and 200 mm above the column base is shown in Figure 10 for 0.25% to 3.0% Drift. Focusing on the height of 100 mm above the column base, the damage is less severe than at the column base. However, significant plasticization occurs on the north-side longitudinal reinforcement (with strain exceeding 10,000 \(\upmu\)), and residual strain is also observed.  
Figure 7: Stiffness Degradation History.  
On the other hand, the plastic deformation of the south-side longitudinal reinforcement is considerably smaller than that of the north-side, as in the case of the column base, and the difference in damage levels between the north and south sides is significant. For the longitudinal reinforcement strain at the height of 200 mm above the column base, the damage level is smaller compared to the column base and 100 mm height position, but the difference in deformation between the north and south sides is almost negligible.  
Figure 8: Damage to Axial Reinforcements at Base of Columns. (**a**) Strain History. (**b**) Load-Strain History on South Side. (**c**) Load-Strain History on North Side.  
Figure 9: Damage at Column Base Location (Case-2). (**a**) 2.0%Drift of NW. (**b**) 2.5%Drift of NW. (**c**) 3.5%Drift of WS.