In earthquake engineering, seismic (or base) isolation includes the development of bearings whose primary purpose is to isolate the ground motion of earthquakes from the larger supported structure or superstructure in order to reduce inertia loads and internal stresses. To protect against damaging vibration effects of earthquake shaking, modern base isolation technologies are used in some buildings (including the San Francisco International Airport), more widely in highway bridges where research has pushed development (e.g.: HITEC Summary Report or AASHTO Guidelines) and will soon be applied to much mission-critical infrastructure (such as nuclear power plants). Seismic isolation is used in the USA and worldwide. (For further reading see: JM Kelly, ‘History of Base Isolation’ chapters in Wiley e-book or similar in CRCnetbase).
In seismic isolation applications, the horizontal flexibility of the isolation system increases the fundamental period of the supported structure and reduces inertial forces, often enabling the secondary systems to be designed for smaller forces and displacements. (See: NZ Science Learning media). Seismic isolation systems typically use either spring or elastomeric bearings from various manufacturers around the globe. Elastomeric bearings are engineered principally of laminated natural rubber, high damping rubber similar to the type of bearing used in this UC Berkeley building for example, neoprene as seen in this bridge bearing, lead core with laminated rubber layers or in similar metal core designs. In addition to elastomeric and spring-based bearings, steel sliding bearings (sometimes with Teflon coatings) are increasingly common.
An ambitious application of base isolation technology for the protection of multi-family residences is the design and construction of the Kamikuzawa-Juhtaku near Tokyo (often referred to as the
Kamikuzawa Condominiums, design completed by March, 2000 and pictured here courtesy of UCB Professor J. M. Kelly). This design features seismically isolated ‘artificial ground’ (effectively large and very stiff slabs of reinforced concrete resting on 242 bearings – three types of isolation bearings are used; 148 very large lead-rubber bearings, 109 sliding bearings, 48 smaller, ball bearing devices) supporting 21 apartment buildings in a community project. The site dimensions are about 125 m wide and 250 m in length. The project provides, 53,297 m2 of floor space and weighs approximately 111,600 tons above the seismic isolators. The condominiums are in use today.