# Seismic Performance Assessments of RC Frame Structures Strengthened by External Precast Wall Panel
## 5 Verifications of the Analysis Model
### Failure Mode and Element Behavior  
The behavior of the column member was analyzed in detail to verify whether the analytical method presented in this study properly evaluates the failure mode of the specimen. Figure 16 shows the pushover analysis, the moment-curvature relationship and the shear force-shear strain relationship of the column member of Specim FB. The moment-curvature relationship of the column shown in Figure 16b revealed that the moment of the column increased gradually and, after reaching the flexural strength (\(M_{n}\)), the column exhibited ductile behavior. On the other hand, in the shear force-shear strain relationship of Figure 16c, the shear force did not reach the shear strength (\(V_{n}\)), and the shear strain was recovered with a decrease in shear force at 0.7% drift ratio. The results of Specimens FBC and FPB, shown in Figures 17 and 18, also confirmed that, similar to the characteristics shown in Figure 16, flexure-dominant behavior occurred, and shear was found to behave in the elastic region. These results indicate that, after reaching the flexural strength (\(M_{n}\)), the column exhibits ductile behavior and the precast walls suffer failure. These behavior patterns are consistent with the test results and this leads to the conclusion that the proposed analysis method can adequately predict the failure mode of the columns. Figure 15: Measured and estimated cumulative energy dissipation: (**a**) Specim FB; (**b**) Specim FBC; (**c**) Specim FPB. Figure 16: Flexural and shear behavior of column element in Specim FB: **(a)** pushover; **(b)** flexural behavior; **(c)** shear behavior. Figure 17: Flexural and shear behavior of column element in Specim FBC: **(a)** pushover; **(b)** flexural behavior; **(c)** shear behavior. Figure 9 shows that the overall behaviors of Specimens FB and FBC were similar. However, the curvature analysis results of the columns shown in Figures 16b and 17b demonstrate that, under the same lateral displacement conditions, the curvature was larger in Specim FBC than in Specim FB. These results were similar to the test results, in that the column damage was greater in Specim FBC, in which high-strength anchor bolts were connected to both the beam and column. At a 2.0% drift ratio, Specim FPB showed a curvature similar to that of Specim FB, but when the drift ratio was 2.7%, it showed a similar degree of curvature to that of Specim FBC. As can be identified from the test results, the column damage was smaller than that of Specim FBC, thereby helping to achieve superior deformation capacity. Figures 19-21 show the force-displacement responses of major elements in Specimens FB, FBC and FPB. Since the column of the frame structure shown in Figure 19a was modeled as a nonlinear beam-column element, it was represented by global lateral displacement and global lateral force. On the other hand, the longitudinal and diagonal elements of the wall shown in Figure 19b,c were represented as the axial displacement and axial force, respectively. This was because they were modeled as truss elements. Figure 19a shows that Specim FB exhibited frame behavior that was similar to that of Specim FC, and showed a characteristic after the ultimate load in which the load decreased slowly with an increase in displacement. In relation to the longitudinal element of Figure 19b, there was a rapid increase in displacement along with the yielding of reinforcement on the tension side, while elastic behavior occurred on the compression side. Since the diagonal element shown in Figure 19c is a concrete element without reinforcement, it does not resist tension well, but does resist high loads in  
Figure 18: Flexural and shear behavior of column element in Specim FPB: (**a**) pushover; (**b**) flexural behavior; (**c**) shear behavior. compression. In addition, as the strength decreased after reaching the maximum compressive strength, it reached strain softening, unlike the longitudinal element.