What characteristics of ground motions influence the selection of the appropriate isolator type in a base isolation system?

Several characteristics of ground motions influence the selection of the appropriate isolator type in a base isolation system. Key characteristics include the frequency content, the amplitude (or intensity), and the duration of the ground motions. The frequency content, often represented by the site-specific response spectrum, determines the range of frequencies that the isolators must be effective at filtering out. Sites with a high proportion of low-frequency ground motions may require isolators with a longer period shift capability. The amplitude, typically quantified by peak ground acceleration (PGA) or spectral acceleration (Sa), determines the required displacement capacity of the isolators. Higher amplitude ground motions will induce larger displacements in the isolators, requiring them to be able to accommodate these displacements without failure. The duration of the ground motions influences the energy dissipation requirements of the isolators. Longer duration earthquakes impart more energy into the system, requiring the isolators to dissipate more energy to control the building's response. For example, lead-rubber bearings are often selected for sites with moderate ground motion intensities and durations, while friction pendulum systems may be more suitable for sites with high ground motion intensities or long durations.