ABSTRACT
The RBRL isolators support the isolated load-eg a museum artefact. They also accommodate differential horizontal motion between the isolated load and the ground, thus decoupling it from strong horizontal ground motion in the event of an earthquake. Since the risk of such motion in any horizontal direction is the same, and in any single event the motion has approximately isotropic content in all horizontal directions, it is desirable that the behaviour of the system is horizontally isotropic. It would thus appear natural to use balls rolling on a planar track to accommodate the relative motion and decouple the isolated load from horizontal force, and such a system has been tried in Mexico. However, it would be impractical
• to achieve adequate tolerances on the tracks to ensure uniform loads for an array of balls or
• to level them well enough to avoid rolling under the influence of gravity.
