Seismic Isolation Bearings

Seismic Isolation Bearings 

Seismic isolation is a technology that protects the structure from the destructive effects of an earthquake. The seismic isolation bearings decouples the structure from the ground and provides it with damping. This decoupling allows the building to behave more flexibly which improves its response to an earthquake. The added damping allows the earthquake energy to be absorbed by the isolation systems and therefore reduces the energy transferred to the structure. Seismic isolation is physically achieved by placing the structure on isolators. The isolators are laterally flexible elements, yet they are able to carry the vertical loads of the stucture. Since the isolators are more flexible than the structure, most of the lateral movements occur in the isolators. As a result the isolated structure experiences less motion and reduced forces.

Seismic isolation provides superior performance compared to a traditional structural design. It reduces the forces and displacements in the structure by up to 75%. The isolation system accomplishes this by deforming laterally during the earthquake. After the earthquake this results in a functional structure with little or no damage.

How does isolation provide cost savings?

In bridges, the foundation design is based on elastic forces. Isolation reduces elastic forces by up to 75%; this translates into direct cost savings in the foundation.

In buildings, Isolation provides cost savings over the life of the structure. An isolated building will be essentially undamaged in an earthquake. By comparison a conventional building’s structure and contents will be damaged. The occupants will also experience interruption of their businesses sometimes for weeks or even months.

What type of structures are isolation candidates?

• Hospitals, Bridges and Emergency Centers that require operation during and immediately after an earthquake.
• Structures with valuable contents or operations such as data centers, communmications facilities, high-tech manufacturing facilities and museums.
• Buildings with high occupancy such as low to medium-rise residences and office buildings.
• Historical Buildings

Performance of Seismic Isolation Bearings

The USC Hospital was isolated and remained operational throughout the 1994 Northridge Earthquake. There was no damage to the USC Hospital. In contrast the Los Angeles County Medical Center located less than a mile away suffered $400 million of damage and was not operational after the earthquake.

The Stanford Linear Accelerator in Palo Alto California was unscathed by the 1989 Loma Prieta earthquake. Elsewhere on campus damage was reported to be approximately $160 million.

The Eel River Bridge in Humboldt County, California, was isolated and experienced accelerations of 0.55g in the 1992 Petrolia Earthquake. The bridge displaced 9 inches laterally and sustained no damage.