## 3 Seismic Shaking Table Tests
### Results of Shaking Table Tests  
#### 3.5.1 Seismic Isolation Characteristics and Performance  
To investigate the seismic isolation characteristics of the lead inserted small-sized LRB developed for an individual nuclear facility component seismic isolation, the test results for the representative design basis earthquake level of PGA = 0.3 g are presented in Figure 5. From the spectrum responses of Figure 5b corresponding to the test results of acceleration time history responses shown in Figure 5a, we can see that the peak spectral frequency band around 10 Hz in the input shaking table motion is significantly shifted to the 2.6 Hz in the dummy mass response, which is slightly higher than the 2.3 Hz of the design seismic isolation frequency in Table 2. From this result, it can be confirmed that the LRB on development in this study has one of the typical seismic isolation characteristics that can assure the seismic isolation performance for the nuclear facility components generally having around 10 Hz dynamic frequencies.  
Figure 5: Test results for safe shutdown earthquake (PGA = 0.3 g): (**a**) Acceleration time histories; (**b**) Corresponding response spectrum.  
Figure 11: Test results of acceleration time history response (TEST ID: OPT-2B-3, PGA = 0.1 g): (**a**) S1; (**b**) S2; (**c**) S3.  
Figure 10: Test results of acceleration time history response (TEST ID: OPT-2B-2, PGA = 0.3 g): (**a**) S1; (**b**) S2; (**c**) S3.  
Figure 9: Test results of acceleration time history response (TEST ID: OPT-2B-1, PGA = 0.5 g): (**a**) S1; (**b**) S2; (**c**) S3.  
As clearly shown in the above test results of the acceleration time history responses, the seismically-isolated structures reveal the seismic isolation performance as expected from the frequency shift effect presented in Figure 5b of results of the response spectrum, which are for the shaking table and the dummy mass.  
Figure 14 presents the comparison of the spectral peak values between seismically-isolated structures and the non-isolated structures calculated from the above acceleration time history responses. As shown in the figure, we can see that the LRB gives better seismic isolation performance as the input earthquake levels increase.  
From the above acceleration seismic responses, the results of the shaking table tests of the lead inserted small-sized LRB are summarized as follows;  
Figure 14: Comparison of spectral peak values calculated from the test results: (**a**) S1; (**b**) S2; (**c**) S3.  
Figure 12: Test results of acceleration time history response (TEST ID: OPT-2C-1, PGA = 0.3 g): (**a**) S1; (**b**) S2; (**c**) S3.  
Figure 13: Test results of acceleration time history response (TEST ID: OPT-2C-2, PGA = 0.6 g): (**a**) S1; (**b**) S2; (**c**) S3.  
It is confirmed that the fabricated lead inserted small-sized LRB gives a consistent seismic isolation performance through the repeated shaking table tests with different sets of the fabricated LRB as intended in the test matrix to check the reproducibility of LRB;
2. Contrary to concerns about the lead plug after experiencing larger earthquakes, the lead inserted small-sized LRB reveals adequate seismic isolation performance in subsequent shaking table tests;
3. In particular, the seismic isolation performance in a frequency range of 9 to 20 Hz, which corresponds to the resonance frequency band of most nuclear facility components, is confirmed as expected in the LRB design;
4. When the input earthquake level is small, such as PGA = 0.1 g, the amplitude of the cyclic shear displacement of LRB occurs is also small and the initial stiffness effects of the lead plug increase the seismic isolation frequency. As a result, the seismic isolation performance is relatively reduced.
5. In the test results of the PGA = 0.6 g in Figure 13, LRB failure occurred after 13 s due to exceeding the LRB shear strain limits of 600% (120 mm), which has been confirmed in previous quasi-static tests [21].