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Concrete shell

Concrete shell

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A concrete shell, also commonly called thin shell concrete structure, is a structure composed of a relatively thin shell of concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

, usually with no interior column
Column
A column or pillar in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below. For the purpose of wind or earthquake engineering, columns may be designed to resist lateral forces...

s or exterior buttress
Buttress
A buttress is an architectural structure built against or projecting from a wall which serves to support or reinforce the wall...

es. The shells are most commonly flat plates and dome
Dome
A dome is a structural element of architecture that resembles the hollow upper half of a sphere. Dome structures made of various materials have a long architectural lineage extending into prehistory....

s, but may also take the form of ellipsoids or cylindrical
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...

 sections, or some combination thereof. The first concrete shell dates back to the 2nd century.

Uses


Most concrete shell structures are buildings, including storage facilities, commercial buildings, and residential homes. Concrete shell construction techniques are well suited for complex curves and are also used to build boat hulls
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...

 (called ferroconcrete). Historically, it was used by the British to create the Mulberry Harbour
Mulberry harbour
A Mulberry harbour was a British type of temporary harbour developed in World War II to offload cargo on the beaches during the Allied invasion of Normandy....

s for the 1944 D-Day
D-Day
D-Day is a term often used in military parlance to denote the day on which a combat attack or operation is to be initiated. "D-Day" often represents a variable, designating the day upon which some significant event will occur or has occurred; see Military designation of days and hours for similar...

 invasion of Normandy
Normandy
Normandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...

.

Advantages


Like the arch
Arch
An arch is a structure that spans a space and supports a load. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures.-Technical aspects:The...

, the curved shapes often used for concrete shells are naturally strong structures, allowing wide areas to be spanned without the use of internal supports, giving an open, unobstructed interior. The use of concrete as a building material reduces both materials cost and construction costs, as concrete is relatively inexpensive and easily cast into compound curves. The resulting structure may be immensely strong and safe; modern monolithic dome
Monolithic dome
A monolithic dome is a structure cast in a one-piece form. The form may be permanent or temporary and may or may not remain part of the finished structure....

 houses, for example, have resisted hurricanes and fires, and are widely considered to be strong enough to withstand even F5 tornado
Tornado
A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...

es.

Disadvantages


Since concrete is a porous material, concrete domes often have issues with sealing. If not treated, rainwater can seep through the roof and leak into the interior of the building. On the other hand, the seamless construction of concrete domes prevents air from escaping, and can lead to buildup of condensation on the inside of the shell. Shingling or sealants are common solutions to the problem of exterior moisture, and dehumidifier
Dehumidifier
A dehumidifier is typically a household appliance that reduces the level of humidity in the air, usually for health reasons. Humid air can cause mold and mildew to grow inside homes, which pose various health risks. Very humid climates or air make some people extremely uncomfortable, causing...

s or ventilation can address condensation.

Historic concrete shells


The oldest known concrete shell, the Pantheon in Rome
Pantheon, Rome
The Pantheon ,Rarely Pantheum. This appears in Pliny's Natural History in describing this edifice: Agrippae Pantheum decoravit Diogenes Atheniensis; in columnis templi eius Caryatides probantur inter pauca operum, sicut in fastigio posita signa, sed propter altitudinem loci minus celebrata.from ,...

, was completed about AD 125, and is still standing. It has a massive concrete dome 43m in diameter, with an oculus at its centre. A monolithic structure, it appears to have been sculpted in place by applying thin layers on top of each other in decreasing diameter. Massively thick at the bottom and thinning (with aerated volcanic pumice as part of the concrete mix) at the top, the Pantheon is a remarkable feat of engineering.

Modern concrete shell construction


Modern thin concrete shells, which began to appear in the 1920s, are made from thin steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 reinforced concrete, and in many cases lack any ribs or additional reinforcing structures, relying wholly on the shell structure itself.

Shells may be cast in place, or pre-cast off site and moved into place and assembled. The strongest form of shell is the monolithic shell, which is cast as a single unit. The most common monolithic form is the dome, but ellipsoids and cylinders (resembling concrete Quonset hut
Quonset hut
A Quonset hut is a lightweight prefabricated structure of corrugated galvanized steel having a semicircular cross section. The design was based on the Nissen hut developed by the British during World War I...

s / Nissen hut
Nissen hut
A Nissen hut is a prefabricated steel structure made from a half-cylindrical skin of corrugated steel, a variant of which was used extensively during World War II.-Description:...

s) are also possible using similar construction methods.

Geodesic dome
Geodesic dome
A geodesic dome is a spherical or partial-spherical shell structure or lattice shell based on a network of great circles on the surface of a sphere. The geodesics intersect to form triangular elements that have local triangular rigidity and also distribute the stress across the structure. When...

s may be constructed from concrete sections, or may be constructed of a lightweight foam with a layer of concrete applied over the top. The advantage of this method is that each section of the dome is small and easily handled. The layer of concrete applied to the outside bonds the dome into a semi-monolithic structure.

Monolithic domes are cast in one piece out of reinforced concrete and date back to the 1960s. Advocates of these domes consider them to be cost-effective and durable structures, especially suitable for areas prone to natural disasters. They also point out the ease of maintenance of these buildings. Monolithic domes can be built as homes, office buildings, or for other purposes.

The Seattle Kingdome was the world's first (and only) concrete-domed multi-purpose stadium. It was completed in 1976 and demolished in 2000. The Kingdome was constructed of triangular segments of reinforced concrete
Reinforced concrete
Reinforced concrete is concrete in which reinforcement bars , reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. It was invented by French gardener Joseph Monier in 1849 and patented in 1867. The term Ferro Concrete refers only to concrete that is...

 that were cast in place. Thick ribs provide additional support.

See also

  • Thin-shell structure
    Thin-shell structure
    Thin-shell structures are light weight constructions using shell elements. These elements are typically curved and are assembled to large structures...

  • Pier Luigi Nervi
    Pier Luigi Nervi
    Pier Luigi Nervi was an Italian engineer. He studied at the University of Bologna and qualified in 1913. Dr. Nervi taught as a professor of engineering at Rome University from 1946-61...

  • Eduardo Torroja
    Eduardo Torroja
    Eduardo Torroja y Miret, was a Spanish structural engineer, pioneer in the design of concrete-shell structures. His first large project was the Tempul cable-stayed aqueduct in 1926, Guadalete, Jerez de la Frontera, in which he used prestressed girders, and he made his name with the concrete...

  • Félix Candela
    Félix Candela
    Félix Candela Outeriño was a Spanish architect known for his significant role in the development of Mexican architecture and structural engineering. Candela’s major contribution to architecture was the development of thin shells made out of reinforced concrete...

  • Seaplane Hangars in Seaplane Harbour , Estonian Maritime Museum
    Estonian Maritime Museum
    The Estonian Maritime Museum is located in the Fat Margaret tower in the old town of Tallinn. The museum presents history of ships and navigation in Estonia and related to Estonia...

     in Tallinn
    Tallinn
    Tallinn is the capital and largest city of Estonia. It occupies an area of with a population of 414,940. It is situated on the northern coast of the country, on the banks of the Gulf of Finland, south of Helsinki, east of Stockholm and west of Saint Petersburg. Tallinn's Old Town is in the list...

    , Estonia
    Estonia
    Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...

    , ex-Peter the Great's Naval Fortress
    Peter the Great's Naval Fortress
    Peter the Great's naval fortress or the Tallinn-Porkkala defence station was a Russian fortification line, which aimed to block access to the Russian capital Saint Petersburg via the sea. The plans for the fortress included heavy coastal artillery pieces along the northern and southern shores of...


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