## 3 FEA Results without Bond-Slip
### Discussion of Analysis Results without Bond-Slip  
In summary, the horizontal load-displacement relationship and envelope at the load point were obtained from the analysis of the model that assumes fully bonded between the longitudinal reinforcement and concrete are shown in Figure 20. Since the geometrical nonlinearity of the reinforcement was not considered, the analysis results of the basic model Case-1 could not reproduce in load-bearing capacity drop due to the spalling of the covering concrete and buckling of the longitudinal reinforcement of the Case-1 specimen from 4.0% Drift, however, it successfully reproduced the maximum and minimum horizontal forces up to 3.5% Drift before the reinforcement buckled. And for Case-2, as in Case-1, although the maximum and minimum horizontal forces were reproduced up to 2.0% Drift on the  
Figure 19: Menegotto-Pinto Model. Figure 17: Hysteresis for Maekawa model. (**a**) Maekawa Crack Curve. (**b**) JSCE Softening Model. Figure 18: Stress Reduction Factor due to Lateral Cracking. front side and 2.5% Drift on the reverse side, the subsequent drop in load capacity was not reproduced. For both specimens, the second and fourth-quadrant load-displacement histories of the horizontal load-displacement relationship were significantly inflated compared to the experimental results. The result showed an overestimation of the energy absorption capacity of the RC column since the reverse S-shaped curve observed due to stiffness changes during unloading and reloading was not reproduced. At the first cycle of 3.5% Drift when the maximum positive displacement is reached, the crack contour diagrams of the analysis are shown in Figure 21. For both specimens, the damage is concentrated from the boundary to a height of 200 mm, which is generally consistent with the damaged area during the experiment. The analysis results of Case-1, horizontal cracks appear at the tension edge and extend to the compression edge, but the horizontal cracks have not penetrated yet. The cracks at the compressive edge are mainly distributed in the longitudinal reinforcement direction. On the other hand, in the analysis results of Case-2 with closely spaced reinforcement, the horizontal cracks at the boundary have penetrated wholly, and the damage level is higher than in Case-1. Moreover, the analysis results of the Case-2 specimen with small-diameter and high-density arrangements, and the horizontal load-longitudinal reinforcement strain history for are shown in Figure 22. In the experimental results shown in Figure 8 (strain history at the 0 mm position), the south-side reinforcement exhibited almost elastic deformation. In contrast, in this analysis case, both the north and south-side longitudinal reinforcements have yielded. Although the load-displacement relationship is generally consistent, it can be concluded that the damage condition of the longitudinal reinforcement has not been reproduced accurately. Figure 21: Crack contour diagrams(0–200 mm, 3.5%Drift). Figure 20: Examples of Force–Displacement Responses without Bond-Slip. (**a**) Case-1(EXP vs. ANA). (**b**) Case-2 (EXP vs. ANA). In summary, the study aims to analyze the behavior of reinforced concrete columns under various loading conditions by using the model with the assumption of the complete fixation between longitudinal reinforcement and concrete. Some limitations were observed while the results successfully reproduced the maximum and minimum horizontal forces up to a certain level of Drift for both Case-1 and Case-2 specimens. Specifically, the analysis could not accurately reproduce the decrease in load-bearing capacity of the Case-1 specimen due to the spalling of the covering concrete and buckling of the longitudinal reinforcement, and the load-bearing capacity drop of the Case-2 specimen due to bond failure. Additionally, the analysis overestimated the energy absorption capacity of the RC columns, as it could not reproduce the reverse S-shaped curve observed in the experiment induced by bond-slip.