Seismic isolation

Seismic isolation reduces the transfer of earthquake motion from the ground to a structure, commonly by placing flexible bearings or sliding interfaces between its foundation and superstructure.

Base isolation: A structural technique that separates a building’s superstructure from ground motion using flexible or sliding devices. It is the most common building-scale form of seismic isolation.
Ground motion: The movement of the ground, especially as recorded during an earthquake. It is the input that isolation devices are designed to decouple from the structure.
San Francisco City Hall: A civic building in California retrofitted with base isolation after damage in the 1989 Loma Prieta earthquake. Its retrofit illustrates how isolation can protect a major existing public building.
Earthquake-resistant structure: A structure designed to limit damage or collapse under earthquake forces through strength, ductility, or other measures. It may resist ground motion directly rather than reduce its transfer through an isolation interface.
Lead-rubber bearing: A laminated rubber-and-steel bearing with a lead core that provides flexibility, damping, and recentering force. Its yielding lead core dissipates energy while the rubber layers permit horizontal movement.
Seismic wave: An elastic disturbance that travels through Earth or along its surface after an earthquake or other source. Different wave types and frequencies produce different demands on isolated structures.
U.S. Court of Appeals for the Ninth Circuit Building: A courthouse in San Francisco designed with a base-isolation system to reduce earthquake forces. It is a prominent application of isolation in a new government building.
Energy dissipation device: A structural component that reduces vibration by converting mechanical energy into heat or another form. Dampers dissipate energy within a structure, while isolation primarily reduces motion transmitted from the ground.
Friction pendulum system: A sliding isolation device in which a curved surface makes a supported structure move like a pendulum. Its sliding interface lengthens the vibration period and dissipates energy through friction.
Structural dynamics: The study of how structures move and respond to time-varying forces. Isolation design predicts how a building’s motion changes under earthquake loading.

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