## 2 Experimental Preparations
### Experimental Results  
The ultimate strength characteristics, which depend on three main variables of a curved plate (flank angle, slenderness ratio, aspect ratio), were investigated. When the arc length (b) was constant, a small radius means that curved plate bent more, with a large flank angle. The radii selected for the plates, and the equivalent flank angles are as follows: 11.45\({}^{\circ}\) (R = 2000 mm), 5.72\({}^{\circ}\) (R = 4000 mm), and 2.86\({}^{\circ}\) (R = 8000 mm). Figure 6a shows compressive load versus displacement curve when the thickness is 6 mm and aspect ratio is 2. From this graph, it is confirmed that a curved plate with the highest flank angle has the highest ultimate strength when compared with the curved plates having other flank angles. In addition, the slope of the load-displacement curve after reaching the ultimate strength decreased rapidly when compared to the corresponding curve of a flat plate. This means that once the strength of the curved plate has reached its maximum value, its load-carrying capacity reduces rapidly. This phenomenon is more gradual when the flank angle of the curved plate decreases. Figure 5: Buckling collapse test for curved plates. Figure 6b shows the comparison of the results of ultimate strengths with curved and flat plates. In this figure, a clear difference is observed in the ultimate strength distribution of the curved plates near the flank angle of 5\({}^{\circ}\). The ultimate strength of curved plates with a flank angle near or lower than 5\({}^{\circ}\) (2.86\({}^{\circ}\), 5.72\({}^{\circ}\)) is lower than that of flat plates, while the ultimate strength of curved plates with a flank angle higher than 5\({}^{\circ}\) (11.45\({}^{\circ}\)) is greater than that of flat plates. In order words, the ultimate strength for a curved plate with a small flank angle (less than 5\({}^{\circ}\)) is lower than that of a flat plate under longitudinal compressive loading condition. These results were reconfirmed through another study, which verified that the increase in the ultimate strength is greater when the curvature is higher. [PERSON] et al. [8] reported that the curvature increases the elastic buckling resistance of the curved plates. Thus, the higher the curvature, the higher the effect. In addition, the curvature also changes the shape of bucking: the number of half-waves increases with the curvature. In addition to the ultimate strength, the buckling mode is distinguished based on flank angle 5\({}^{\circ}\), as shown in Figure 7. When the flank angle is more than 5\({}^{\circ}\), buckling takes place with three longitudinal half-waves. With a decrease in the flank angle, the buckling mode is changed from one longitudinal half-wave to two longitudinal half-waves when the flank angle is zero. These characteristics related to the buckling mode are similar to those of the flat plates (two longitudinal half-waves) as the aspect ratio decreases. Figure 8 shows the effect of flank angle, slenderness ratio, and aspect ratio on the ultimate strength of curved plates based on the results of our experimental investigation. In Figure 8a, the average values of the experimental results for each condition are indicated using a solid line. From the figure, it can be confirmed that an increase in the flank angle causes an increase in the ultimate strength of curved plates. However, in the case of the  
Figure 6: (**a**) Compressive load versus displacement curves of curved plates and (**b**) comparison of ultimate strengths of curved and flat plates. Figure 7: Collapse mode of curved plates after testing (a/b = 2.0, t = 6 mm): (**a**) C01, (**b**) C02, (**c**) C03, and (**d**) F01. slanderness ratio, the ultimate strength displays an unusual trend; the ultimate strength of relatively thin plates (t = 7 mm) is higher than that of relatively thick plates (t = 8 mm). This tendency is more prominent when the a/b ratio is 1.5 or when the flank angle is 11.45\({}^{\circ}\) (See Figure 8c).