The dynamic responses of a set of elastic six storey shear structures mounted on a bilinear hysteretic Base Isolation (B.I.) System and forced by a wide range of different 'types’ and 'strengths’ of real and simulated earthquakes, are studied. The responses of the same set of structures, without the Base Isolation System, to the same range of earthquakes are also computed for comparative purposes. It is found that for the B.I. system investigated, not only are
the maximum shear forces in an isolated structure reduced to, on average, 0.2 of their values without B.I., but also that the maximum shear responses of isolated structures can be closely estimated from a wide variety of different parameters, selected from ground motion and elastic response spectrum data of the forcing earthquakes. Ninety-five percent confidence intervals are determined for the linear least squares regression relations between structure responses and earthquake parameters. For the isolation system considered the maximum displacement across the isolation system during an earthquake is shown to be very closely correlated with the maximum structure shear force.