Base Isolation of Rocking Systems: A Rotation-Based Design Procedure

When subjected to earthquakes some elements or structures behave like rocking rigid bodies. Art objects, computer servers and electrical equipment are frequently included in this category. This study is motivated by the need to protect these non-structural elements from earthquakes and base isolation technology was proven to be a viable option for this purpose. The dynamic model of a rocking rigid block placed on a base isolation device is summarized here. Then, a rotation-based procedure to design this type of protection system for rigid rocking bodies is proposed, and the main steps are illustrated. The procedure is aimed at designing base isolation devices for rocking bodies, in order to activate a specified maximum rotation during the code-level earthquake event. The presented rotation-based procedure is particularly suitable for large structure / objects, as long as small oscillations are acceptable. Indeed, as the block size increases, the capacity of the system also increases. The main advantage of this procedure is that the maximum displacement of the isolator can be reduced compared to the case where rotations are not allowed, hence rocking motion is not initiated. Despite this advantage, the design procedure allows the rigid body to rock and, thus, to impact the base.