Base isolation
Encyclopedia
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Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
forces. It is a collection of structural elements which should substantially decouple a superstructure
Superstructure
A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships...
from its substructure resting on a shaking ground thus protecting a building
Building
In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...
or non-building structure's integrity.
Base isolation is the most powerful tool of earthquake engineering
Earthquake engineering
Earthquake engineering is the scientific field concerned with protecting society, the natural and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels...
pertaining to the passive structural vibration control
Vibration control
In earthquake engineering, vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures.All seismic vibration control devices may be classified as passive, active or hybrid where:...
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
Sustainability
Sustainability is the capacity to endure. For humans, sustainability is the long-term maintenance of well being, which has environmental, economic, and social dimensions, and encompasses the concept of union, an interdependent relationship and mutual responsible position with all living and non...
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 base isolation system which are intended to provide the mentioned decouplingDecouplingThe term "decoupling" is used in many different contexts.-Economic growth without environmental damage:In economic and environmental fields, decoupling is becoming increasingly used in the context of economic production and environmental quality. When used in this way, it refers to the ability of...
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 architect
Architect
An architect is a person trained in the planning, design and oversight of the construction of buildings. To practice architecture means to offer or render services in connection with the design and construction of a building, or group of buildings and the space within the site surrounding the...
s using the principle of base isolation for earthquake protection was discovered in Pasargadae
Pasargadae
Pasargadae , the capital of Cyrus the Great and also his last resting place, was a city in ancient Persia, and is today an archaeological site and one of Iran's UNESCO World Heritage Sites.-History:...
, a city in ancient Persia, now Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...
: 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
Seismic retrofit
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers,...
. In process of seismic retrofit
Seismic retrofit
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers,...
, some of the most prominent U.S. monuments, e.g. Pasadena City Hall
Pasadena City Hall
Pasadena City Hall, completed in 1927, serves as the central location for city government in the City of Pasadena and it is a significant example of the City Beautiful movement of the 1920s.-History:...
, San Francisco City Hall
San Francisco City Hall
San Francisco City Hall, re-opened in 1915, in its open space area in the city's Civic Center, is a Beaux-Arts monument to the City Beautiful movement that epitomized the high-minded American Renaissance of the 1880s to 1917. The structure's dome is the fifth largest in the world...
, Salt Lake City and County Building
Salt Lake City and County Building
The Salt Lake City and County Building, usually called the "City-County Building", is the seat of government for Salt Lake City, Utah. The historic landmark formerly housed offices for Salt Lake County government as well, hence the name.- History :...
or LA City Hall were mounted on Base Isolation Systems. It required creating rigidity diaphragms
Diaphragm (structural system)
In structural engineering, a diaphragm is a structural system used to transfer lateral loads to shear walls or frames primarily through in-plane shear stress...
and moat
Moat
A moat is a deep, broad ditch, either dry or filled with water, that surrounds a castle, other building or town, historically to provide it with a preliminary line of defence. In some places moats evolved into more extensive water defences, including natural or artificial lakes, dams and sluices...
s around the buildings, as well as making provisions against overturning and P-Delta Effect
P-Delta Effect
In structural engineering, the P-Δ or P-Delta effect refers to the abrupt changes in ground shear, overturning moment, and/or the axial force distribution at the base of a sufficiently tall structure or structural component when it is subject to a critical lateral displacement.The P-Delta effect is...
.
See also
- Earthquake engineering structuresEarthquake engineering structuresEarthquake-resistant structures are designed and constructed to withstand various types of hazardous earthquake exposures at the sites of their particular location....
- Geotechnical engineeringGeotechnical engineeringGeotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but is also used by military, mining, petroleum, or any other engineering concerned with construction on or in the ground...
- Seismic retrofitSeismic retrofitSeismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers,...