## 4 Overview of Pseudo-Dynamic Testing and Result Analysis
### Experimental Results and Analysis  
Both the test specimen with no reinforcement applied (PD-FR) and the test specimen retrofitted with the NBSD-based WSCS (PD-NBSD) were subjected to pseudo-dynamic testing and then tested for any cracks and breakage. Moreover, the resultant load-displacement curves (restoring force), temporal hysteresis loops with respect to the displacement, and maximum seismic response were analyzed to determine and compare the seismic retrofitting effect of PD-FR and PD-NBSD. In this test frame retrofitted with NBSD (PD-NBSD-WSCS), fine initial flexural cracks started to occur at the lower part of the columns at around 1.88 s (3.5 mm) when the input seismic ground motion was set to 200 cm/s\({}^{2}\) (Figures 16 and 19a). Subsequently, at 2.61 s (12.7 mm), these flexural cracks increased in number, but their size remained limited. At 6.33 s (23.9 mm), where the maximum seismic response occurred, fine flexural cracks also occurred. The pseudo-dynamic testing was conducted for a period of 10 s. The results showed that PD-NBSD retrofitted with NBSD was subject to only fine flexural cracks in contrast to PD-FR with no reinforcement applied, which underwent a shear failure, when the input seismic ground motion was 200 cm/s\({}^{2}\). Figure 14: Cracks and ultimate failure of test frame with no reinforcement applied (PD-FR) (200 cm/s\({}^{2}\)): (a) flexural cracks at around 2.4 s (18.2 mm), (b) flexural and shear cracks at around 2.89 s (38.9 mm), (c) shear cracks and maximum displacement at around 3.46 s (70.2 mm), and (d) shear failure and maximum displacement at the final stage of the test. Figure 15: Cracks of test frame with no reinforcement applied (PD-FR) at the final stage (200 cm/s\({}^{2}\)). Figure 16: Cracks and ultimate state of test frame retrofitted with NBSD-WSCS (PD-NBSD-WSCS) (200 cm/s\({}^{2}\)): (**a**) flexural cracks at around 1.88 s (3.5 mm), (**b**) flexural cracks at around 2.61 s (12.7 mm), (**c**) flexural cracks at around 6.33 s (23.9 mm), and (**d**) patterns at the final stage (10 s). Figure 17: Cracks and ultimate state of test frame retrofitted with NBSD-WSCS (PD-NBSD-WSCS) (300 cm/s\({}^{2}\)): (**a**) flexural and shear cracks at around 2.75 s (37 mm), (**b**) flexural and shear cracks at around 3.31 s (46.6 mm), (**c**) flexural and shear cracks at around 3.7 s (49 mm), and (**d**) patterns at the final stage (10 s). Figure 18: Cracks and ultimate state of test frame retrofitted with NBSD-WSCS (PD-NBSD-WSCS) (400 cm/s\({}^{2}\)): (**a**) flexural and shear cracks at around 2.88 s (75.1 mm), (**b**) flexural and shear cracks at around 3.38 s (85.2 mm), (**c**) flexural and shear cracks at around 3.7 s (85.6 mm), and (**d**) patterns at the final stage (10 s). When the input seismic ground motion was increased to 300 cm/s\({}^{2}\) (Figures 17 and 19b), the number of flexural cracks was larger at 2.75 s (37.0 mm) compared to when the input seismic ground motion was 200 cm/s\({}^{2}\). From 3.7 s (49.0 mm) on, where the maximum seismic response occurred, small flexural cracks continued to occur, and it was found that these flexural cracks determined the failure mode of the frame. In the test frame with no reinforcement applied, as shown in Figures 14 and 15 above, a typical shear failure was observed, but PD-NBSD developed in the present study was found to undergo flexural failure; the failure mode shifted from shear to flexural. When the input seismic ground motion was set to 400 cm/s\({}^{2}\), which simulated the occurrence of a large-scale earthquake, as shown in Figures 18 and 19c, more flexural cracks were observed at 2.88 s (75.1 mm) compared to when the input seismic ground motion was 300 cm/s\({}^{2}\), and, at the same time, shear cracks occurred but to a limited extent. At 3.38 s (85.2 mm), where the maximum seismic response occurred, both flexural and shear cracks increased in width and number, and the ultimate failure mode was determined by flexural shear cracks.