## 4 Sine Sweep Testing
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & \multicolumn{3}{c}{**Peak Acceleration at the Top of**} \\  & \multicolumn{3}{c}{**the Tested Model (m/s\({}^{2}\))**} \\ \cline{2-4}
**Dynamic Excitation** & **Fixed-Base Model Model with PBs** & **Reduction (\%)** \\ \hline
1940 El Centro earthquake & 11.39 & 6.98 & 38.7 \\ NS component, original record with PGA = 3.070 m/s\({}^{2}\) & 15.59 & 10.47 & 32.8 \\ \hline
1989 Loma Prieta earthquake & & & \\ Corralitos station, NS component, scaled record with PGA = 3.158 m/s\({}^{2}\) & 13.82 & 8.27 & 40.2 \\ \hline
1994 Northridge earthquake & & & \\ Santa Monica station, EW component, scaled record with PGA = 4.332 m/s\({}^{2}\) & 8.73 & 7.74 & 11.3 \\ \hline
2002 Polkowice mining tremor & & & \\ NS component, original record with PGA = 1.634 m/s\({}^{2}\) & 3.53 & 2.18 & 38.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Results of the seismic tests for the single-storey structure model. The shaking table tests confirm very high effectiveness of the prototype base isolation system made of PBs in improving dynamic behaviour by reducing structural vibrations, thus enhancing structural safety and reliability. The inspection of Tables 1 and 2 demonstrates that, due the application of the isolation devices, the peak lateral accelerations recorded at the top of the tested structures were reduced by approximately 11-39% and 12-57% for the single-storey and two-storey structure models, respectively. It should also be noted that only peak lateral accelerations are compared, which may result in such large intervals in reduction levels. When full time-acceleration records are compared, the reduction level due to application of the PBs varies from 35% to more than 50%. As expected, the reduction level strongly depends on the amplitude-frequency characteristics of the ground motion. More specifically, the smaller the difference between the predominant frequency of the ground motion and the natural frequency of the tested model structure, the lower the reduction level. Furthermore, it should also be underlined that the amplitude-frequency characteristics of mining tremors are quite different from those that are observed in the case of seismic events. Earthquake excitations are generally characterized by high amplitudes and predominant frequencies varying usually from 1 to 5 Hz, whereas mining tremors exhibit lower amplitudes but slightly higher predominant excitation frequencies, which are usually around 5 Hz or higher. Moreover, different earthquakes themselves are also characterized by different frequency content. This is the reason why the reduction in lateral accelerations is so different for various seismic excitations. For example, in the case of the single-storey structure model, the reduction in the peak acceleration is only 11.3% for the Northridge earthquake, while it is as large as 40.2% for the Loma Prieta earthquake (see Table 1). A similar situation also concerns the results of the seismic tests for the two-storey structure model, which has substantially different dynamic properties compared to the single-storey structure model. In this case, the smallest reduction in the peak acceleration (equal to 28.1%) has been obtained for the Loma Prieta earthquake, while the largest one (as large as 56.8%) has been observed for the San Fernando earthquake (see Table 2). Nevertheless, the results obtained explicitly confirm high effectiveness of the prototype PBs in reducing structural vibration during seismic excitations as well as mining tremors.