Patent ID: 8484911

Claim:
In a sliding pendulum seismic isolation system for protecting a structure from earthquake ground motions, said isolation system having concave spherical surfaces and sliders that support the structure, and where said sliders slide along said concave spherical surfaces resulting in a lifting of the supported structure consistent with a specified effective pendulum length, wherein the improvement comprises: a configuration of two or more independent sliding pendulum mechanisms configured so as to function consecutively in series for lateral displacements in the same direction, at least one of said pendulum mechanisms having a specified friction coefficient that is lower than the specified friction coefficient of another of said sliding pendulum mechanisms, said independent sliding pendulum mechanisms configured to become consecutively active or inactive in series at increasing amplitudes of lateral displacement in the same direction, and said independent pendulum mechanisms configured such that the effective pendulum length of the isolation system in the direction of motion changes when the sliding pendulum mechanisms become active or inactive.