Relative Transmissibility to Control Isolator Displacement Under Earthquakes

A solution to the large base displacement problem in isolated buildings under seismic load is sought. This is based on the notion of relative transmissibility of mechanical vibrations. A second and important novelty is the application of a new spectral characterization, as narrow band, of ground displacement. In situations where the large isolator displacement is a concern, the proposal can work as a base-isolation design procedure. A standard isolated structural model is employed to demonstrate that the base displacement level can be reduced to well under the ground displacement one, which results in a positive comparison with previous passive and active control solutions; in fact, the design aim is a competitive ½ ratio for both displacements. Nevertheless, it is also demonstrated that these good reduction levels are possible at the expense of a large damping ratio.