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Base isolation, also known as seismic base isolation or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially decouple a superstructure from its substructure resting on a shaking ground thus protecting a building or non-building structure's integrity.
Base isolation is one of the most powerful tools of earthquake engineering pertaining to the passive structural vibration control technologies. It is meant to enable a building or non-building structure to survive a potentially devastating seismic impact through a proper initial design or subsequent modifications. In some cases, application of base isolation can raise both a structure's seismic performance and its seismic sustainability considerably. Contrary to popular belief base isolation does not make a building earthquake proof.
Base isolation system consists of isolation units with or without isolation components, where:
- Isolation units are the basic elements of a base isolation system which are intended to provide the mentioned decoupling effect to a building or non-building structure.
- Isolation components are the connections between isolation units and their parts having no decoupling effect of their own.
By their response to an earthquake impact, all isolation units may be divided into two basic categories: shear units and sliding units. The first evidence of architects using the principle of base isolation for earthquake protection was discovered in Pasargadae, a city in ancient Persia, now Iran: it goes back to 6th century BC. It works by having a wide and deep stone and mortar foundation, smoothed at the top, upon which a second foundation is built of wide, smoothed stones which are linked together, forming a plate that slides back and forth over the lower foundation in case of an earthquake, leaving the structure intact.
This technology can be used both for new structural design and seismic retrofit. In process of seismic retrofit, some of the most prominent U.S. monuments, e.g. Pasadena City Hall, San Francisco City Hall, Salt Lake City and County Building or LA City Hall were mounted on Base Isolation Systems. It required creating rigidity diaphragms and moats around the buildings, as well as making provisions against overturning and P-Delta Effect.
Base isolation is also used on a smaller scale - sometimes down to a single room in a building. Isolated raised-floor systems are used to safeguard essential equipment against earthquakes. The technique has been incorporated to protect statues and other works of art - see, for instance, Rodin's Gates of Hell at the National Museum of Western Art in Tokyo's Ueno Park.
Research on Base Isolation 
Through the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES), researchers are studying the performance of base isolation systems. The project, a collaboration among researchers at University of Nevada, Reno; University of California, Berkeley; University of Wisconsin, Green Bay; and the University at Buffalo, SUNY is conducting a strategic assessment of the economic, technical, and procedural barriers to the widespread adoption of seismic isolation in the United States. NEES resources have been used for experimental and numerical simulation, data mining, networking and collaboration to understand the complex interrelationship among the factors controlling the overall performance of an isolated structural system. This project involves shaking table and hybrid tests at the NEES experimental facilities at the University of California, Berkeley, and the University at Buffalo, aimed at understanding ultimate performance limits to examine the propagation of local isolation failures (e.g., bumping against stops, bearing failures, uplift) to the system level response. These tests, including a full-scale, three-dimensional test of an isolated 5-story steel building on the E-Defense shake table in Miki, Hyogo, Japan, will help fill critical knowledge gaps, validate assumptions regarding behavior and modeling, and provide essential proof-of-concept evidence regarding the importance of isolation technology.
See also 
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- Earthquake engineering structures
- Geotechnical engineering
- Seismic retrofit
- Shock absorber
- Shock mount
- Vibration isolation
- Los Angeles City Hall
- Pressman, Andy (2007). Architectural graphic standards. John Wiley and Sons. p. 30. ISBN 978-0-471-70091-3.
- Webster, Anthony C. (1994). Technological advance in Japanese building design and construction. ASCE Publications. p. 70. ISBN 978-0-87262-932-5.
- Datta, T. K. (2010). Seismic Analysis of Structures. John Wiley and Sons. p. 369. ISBN 978-0-470-82462-7.
- http://www.youtube.com/watch?v=ZqlXp3czrrM[unreliable source?]
- Lead Rubber Bearing being tested at the UCSD Caltrans-SRMD facility, YouTube[unreliable source?]
- Hybrid Simulation of Base Isolated Structures, YouTube[unreliable source?]
- Seismic isolation in buildings to be a practical reality: Behavior of structure and installation technique
- Seismic Isolation Projects in Japan
- Reitherman, Robert (2012). Earthquakes and Engineers: An International History. Reston, VA: ASCE Press. ISBN 9780784410622.
- nees@berkeley project highlight: NEES TIPS Seismic Isolation Hybrid Simulation, http://www.youtube.com/watch?v=Uh6l5Jqtp0c