Floating raft is a land-based building
foundation that protects it against settlement and
liquefaction
In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics.
It occurs both naturally and artificially. As an example of t ...
of soft soil from seismic activity. It was a necessary innovation in the development of
tall buildings
A skyscraper is a tall continuously habitable building having multiple floors. Most modern sources define skyscrapers as being at least or in height, though there is no universally accepted definition, other than being very tall high-rise buil ...
in the wet soil of
Chicago
Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...
in the 19th century, when it was developed by
John Wellborn Root
John Wellborn Root (January 10, 1850 – January 15, 1891) was an American architect who was based in Chicago with Daniel Burnham. He was one of the founders of the Chicago School style. Two of his buildings have been designated National Hist ...
who came up with the idea of interlacing the concrete slab with steel beams. The earliest precursor to the modern version may be the concrete rafts developed for the building of
Millbank Prison
Millbank Prison or Millbank Penitentiary was a prison in Millbank, Westminster, London, originally constructed as the National Penitentiary, and which for part of its history served as a holding facility for convicted prisoners before they were p ...
in 1815 by
Robert Smirke.
For a floating raft foundation – or simply "floating foundation" – the foundation has a volume such that, if that volume filled with soil, it would be equal in weight to the total weight of the structure.
When the soil is so soft that not even
friction piles will support the
building load, these types of foundation are the final option and makes the building behave like a boat: obeying
Archimedes' principle
Archimedes' principle states that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially, is equal to the weight of the fluid that the body displaces. Archimedes' principle is a law of physics fun ...
, buoyed up by the weight of the earth displaced in creating the foundation.
Buildings with a floating raft system
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Jin Mao Tower
The Jin Mao Tower (; Shanghainese:'' Cinmeu Dagho''; lit. ‘Golden Prosperity Building’), also known as the or , is a , 88-story (93 if counting the floors in the spire) landmark skyscraper in Lujiazui, Pudong, Shanghai, China. It contains a ...
(1999) in
Shanghai
Shanghai, Shanghainese: , Standard Chinese pronunciation: is a direct-administered municipality and the most populous urban area in China. The city is located on the Chinese shoreline on the southern estuary of the Yangtze River, with the ...
, China
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Rönesans Rezidans (2012) in
Antakya
Antakya (), Turkish form of Antioch, is a municipality and the capital Districts of Turkey, district of Hatay Province, Turkey. Its area is . Prior to the devastating 2023 Turkey–Syria earthquakes, 2023 earthquakes, its population was recorded ...
, Turkey
See also
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Buoyancy
Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...
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Building construction
Construction are processes involved in delivering buildings, infrastructure, industrial facilities, and associated activities through to the end of their life. It typically starts with planning, financing, and design that continues until the a ...
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Foundations (buildings and structures)