# Seismic Performance Assessments of RC Frame Structures Strengthened by External Precast Wall Panel
## 3 Experimental Results  
### Behavior of Test Specimens  
Figures 7 and 8 show the crack patterns and photographs of test specimens after failure. For Specim FC, the strength was reduced to 78% of the maximum load, as the cover peeled off at the top of the column after the first load cycle at 2.0% drift ratio. The test was then terminated in accordance with laboratory safety regulations. Specimen FBC achieved 90% of the maximum load at 2.0% drift ratio, but underwent failure as the load rapidly decreased during loading in the negative  
Figure 5: Test setup. Figure 6: Loading steps. direction. This occurred after loading in the positive direction with a drift ratio of 2.0%. For Specim FBC, as the EPCWs were connected to both the columns and the beam, significant crack damage was observed in the vicinity of the anchor bolts installed at the bottom of the columns, as shown in Figures 7b and 8b. Specim FB, in which the EPCW was connected only to the beam, underwent separation between the frame and the EPCW as the concrete peeled off at the EPCW-foundation connections at a 2.0% drift ratio. In terms of Specim FB, the crack widths observed from the columns were smaller, while those observed from the walls were larger, compared to those of Specim FBC. For Specim FB, the strength was reduced to 65% of the maximum load at the third cycle with a drift ratio of 2.0%, and the test was terminated after the loading of the third cycle. In Specim FB, where the EPCW was connected only to the beam with anchor bolts, relatively small damage was observed in the columns, as shown in Figures 7c and 8c, compared to Specim FBC. In Specim FPB, to which two EPCWs were applied near the column in the form of wing walls, there was no significant decrease in the load, even at 2.0% drift ratio, and the test was terminated after loading at up to 3% drift in the positive direction. The load at 3.0% drift ratio was 94% of the maximum load, showing stable behavior without a significant decrease in load. Specim FPB observed less damage in RC frames compared to other specimens, as shown in Figures 7d and 8d. When the conventional infill wall-strengthening method is used for the purpose of increasing the strength, the lateral stiffness and strength are greatly improved, but the lateral deformation capacity tends to significantly decrease. In addition, if the shear strength ratio of the infill wall to the existing RC frame is large, shear failure of the column may occur [7,8] which, when seismic strengthening is performed, is not a desirable failure mode. In the EPCW method proposed in this study, there was no reduction in lateral deformation capacity after strengthening, compared to the frame structures before the deformation capacity is increased. Figure 8: Photographs of specimens after failure: (**a**) Specimen FC; (**b**) Specimen FBC; (**c**) Specim FB; (**d**) Specimen FPB. strengthening. In addition, in all specimens, the failure of the walls occurred prior to the shear failure of the column. These results suggest that efficient seismic strengthening has been achieved. Figure 9 shows the load-displacement curves of Specimens FC, FBC, FB and FPB. The pinching effect was not significant in all specimens. Figure 9a shows that the maximum load of Specim FC was 54.6 kN in the positive direction, and -51.7 kN in the negative direction. In both the positive and the negative directions, the maximum load occurred at 1.0% drift ratio, and there was then a gradual decrease in load. Figure 9b shows that the maximum load of Specim FBC was 240.1 kN in the positive direction, and \(-\)272.1 kN in the negative direction. Specim FBC showed a maximum load in the positive direction at 1.0% drift ratio, and a maximum load in the negative direction at 1.5% drift ratio. The maximum load of Specim FBC was 4.4 and 5.26 times higher in the positive and negative directions, than that of Specim FC. Figure 9c shows that Specim FB showed its maximum load at 1.0% drift ratio. It was measured at 238.9 kN in the positive direction, and \(-\)216.9 kN in the negative direction.