Prefabrication
Overview
 
Prefabrication is the practice of assembling components of a structure
Structure
Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...

 in a factory
Factory
A factory or manufacturing plant is an industrial building where laborers manufacture goods or supervise machines processing one product into another. Most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production...

 or other manufacturing
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

 site, and transport
Transport
Transport or transportation is the movement of people, cattle, animals and goods from one location to another. Modes of transport include air, rail, road, water, cable, pipeline, and space. The field can be divided into infrastructure, vehicles, and operations...

ing complete assemblies or sub-assemblies to the construction
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...

 site where the structure is to be located. The term is used to distinguish this process from the more conventional construction practice of transporting the basic material
Material
Material is anything made of matter, constituted of one or more substances. Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term "material" is used more narrowly to refer to substances or components with certain physical properties that are used as inputs to...

s to the construction site where all assembly is carried out.

The term prefabrication also applies to the manufacturing of things other than structures at a fixed site.
Encyclopedia
Prefabrication is the practice of assembling components of a structure
Structure
Structure is a fundamental, tangible or intangible notion referring to the recognition, observation, nature, and permanence of patterns and relationships of entities. This notion may itself be an object, such as a built structure, or an attribute, such as the structure of society...

 in a factory
Factory
A factory or manufacturing plant is an industrial building where laborers manufacture goods or supervise machines processing one product into another. Most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production...

 or other manufacturing
Manufacturing
Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

 site, and transport
Transport
Transport or transportation is the movement of people, cattle, animals and goods from one location to another. Modes of transport include air, rail, road, water, cable, pipeline, and space. The field can be divided into infrastructure, vehicles, and operations...

ing complete assemblies or sub-assemblies to the construction
Construction
In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of human multitasking...

 site where the structure is to be located. The term is used to distinguish this process from the more conventional construction practice of transporting the basic material
Material
Material is anything made of matter, constituted of one or more substances. Wood, cement, hydrogen, air and water are all examples of materials. Sometimes the term "material" is used more narrowly to refer to substances or components with certain physical properties that are used as inputs to...

s to the construction site where all assembly is carried out.

The term prefabrication also applies to the manufacturing of things other than structures at a fixed site. It is frequently used when fabrication
Fabrication (metal)
Fabrication as an industrial term refers to building metal structures by cutting, bending, and assembling. The cutting part of fabrication is via sawing, shearing, or chiseling ; torching with handheld torches ; and via CNC cutters...

 of a section of a machine or any movable structure is shifted from the main manufacturing site to another location, and the section is supplied assembled and ready to fit. It is not generally used to refer to electrical or electronic components of a machine, or mechanical parts such as pumps, gearboxes and compressors which are usually supplied as separate items, but to sections of the body of the machine which in the past were fabricated with the whole machine. Prefabricated parts of the body of the machine may be called 'sub-assemblies' to distinguish them from the other components.

The process and theory of prefabrication

An example from house-building illustrates the process of prefabrication. The conventional method of building a house is to transport brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

s, timber
Timber
Timber may refer to:* Timber, a term common in the United Kingdom and Australia for wood materials * Timber, Oregon, an unincorporated community in the U.S...

, cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

, sand
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

, 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...

 and construction aggregate
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...

, etc. to the site, and to construct the house on site from these materials. In prefabricated construction
Prefabricated buildings
Prefabricated building is a type of building that consists of several factory-built components or units that are assembled on-site to complete the unit.- Prefabricated Housing :"Prefabricated" may refer to buildings built in components Prefabricated building is a type of building that consists of...

, only the foundations
Foundation (architecture)
A foundation is the lowest and supporting layer of a structure. Foundations are generally divided into two categories: shallow foundations and deep foundations.-Shallow foundations:...

 are constructed in this way, while sections of wall
Wall
A wall is a usually solid structure that defines and sometimes protects an area. Most commonly, a wall delineates a building and supports its superstructure, separates space in buildings into rooms, or protects or delineates a space in the open air...

s, floors and roof
Roof
A roof is the covering on the uppermost part of a building. A roof protects the building and its contents from the effects of weather. Structures that require roofs range from a letter box to a cathedral or stadium, dwellings being the most numerous....

 are prefabricated (assembled) in a factory (possibly with window and door frames included), transported to the site, lifted into place by a crane
Crane (machine)
A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...

 and bolted
Screw
A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

 together.

Prefabrication is used in the manufacture of ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s, aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 and all kinds of vehicle
Vehicle
A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....

s and machine
Machine
A machine manages power to accomplish a task, examples include, a mechanical system, a computing system, an electronic system, and a molecular machine. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work...

s where sections previously assembled at the final point of manufacture are assembled elsewhere instead, before being delivered for final assembly.

The theory behind the method is that time and cost is saved if similar construction tasks can be grouped, and assembly line
Assembly line
An assembly line is a manufacturing process in which parts are added to a product in a sequential manner using optimally planned logistics to create a finished product much faster than with handcrafting-type methods...

 techniques can be employed in prefabrication at a location where skilled labour is available, while congestion at the assembly site, which wastes time, can be reduced. The method finds application particularly where the structure is composed of repeating units or forms, or where multiple copies of the same basic structure are being constructed. Prefabrication avoids the need to transport so many skilled workers to the construction site, and other restricting conditions such as a lack of power, lack of water, exposure to harsh weather or a hazardous environment are avoided. Against these advantages must be weighed the cost of transporting prefabricated sections and lifting them into position as they will usually be larger, more fragile and more difficult to handle than the materials and components of which they are made.

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History

Prefabrication has been used since ancient times. For example, it is claimed that the world's oldest known engineered road
Road
A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...

way, the Sweet Track
Sweet Track
The Sweet Track is an ancient causeway in the Somerset Levels, England. It was built in 3807 or 3806 BC and has been claimed to be the oldest road in the world. It was the oldest timber trackway discovered in Northern Europe until the 2009 discovery of a 6,000 year-old trackway in Belmarsh Prison...

 constructed in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 around 3800 BC
39th century BC
-Events:* The Post Track, an ancient causeway in the Somerset Levels, England, is built, ca. 3838 BC. It is one of the oldest engineered roads discovered in Northern Europe....

, employed prefabricated timber sections brought to the site rather than assembled on-site.

Sinhalese kings of ancient Sri Lanka
Sri Lanka
Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...

 have used prefabricated buildings technology to erect giant structures, which dates back as far as 2000 years, where some sections were prepared separately and then fitted together, specially in the Kingdom
Monarchy
A monarchy is a form of government in which the office of head of state is usually held until death or abdication and is often hereditary and includes a royal house. In some cases, the monarch is elected...

 of Anuradhapura
Anuradhapura
Anuradhapura, , is one of the ancient capitals of Sri Lanka, famous for its well-preserved ruins of ancient Lankan civilization.The city, now a UNESCO World Heritage Site, lies 205 km north of the current capital Colombo in Sri Lanka's North Central Province, on the banks of the historic...

 and Kingdom of Polonnaruwa
Polonnaruwa
The second most ancient of Sri Lanka's kingdoms, was first declared the capital city by King Vijayabahu I, who defeated the Chola invaders in 1070 AD to reunite the country once more under a local leader.-History:While Vijayabahu's victory and shifting of Kingdoms to the more strategic Polonnaruwa...



The method was widely used in the construction of prefabricated housing in the 20th century, such as in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 to replace houses bombed during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. Assembling sections in factories saved time on-site and reduced cost. However the quality was low, and when such prefabricated housing was left in use for longer than its designed life, it acquired a certain stigma..

The Crystal Palace
The Crystal Palace
The Crystal Palace was a cast-iron and glass building originally erected in Hyde Park, London, England, to house the Great Exhibition of 1851. More than 14,000 exhibitors from around the world gathered in the Palace's of exhibition space to display examples of the latest technology developed in...

, erected in London
London
London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

 in 1851, was a highly visible example of iron and glass prefabricated construction; it was followed on a smaller scale by Oxford Rewley Road railway station
Oxford Rewley Road railway station
Oxford Rewley Road railway station was a railway station serving the city of Oxford, England, located immediately to the north of what is now Frideswide Square on the site of the Saïd Business School. It was the terminus of the Buckinghamshire Railway, which was worked, and later absorbed, by the...

.

Current uses

The most widely-used form of prefabrication in building and civil engineering
Civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...

 is the use of prefabricated 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...

 and prefabricated 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...

 sections in structures where a particular part or form is repeated many times. It can be difficult to construct the formwork
Formwork
Formwork is the term given to either temporary or permanent molds into which concrete or similar materials are poured. In the context of concrete construction, the falsework supports the shuttering moulds.-Formwork and concrete form types:...

 required to mould concrete components on site, and delivering wet concrete to the site before it starts to set requires precise time management. Pouring concrete sections in a factory brings the advantages of being able to re-use moulds and the concrete can be mixed on the spot without having to be transported to and pumped wet on a congested construction site. Prefabricating steel sections reduces on-site cutting and welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

 costs as well as the associated hazards.

Prefabrication techniques are used in the construction of apartment
Apartment
An apartment or flat is a self-contained housing unit that occupies only part of a building...

 blocks, and housing developments with repeated housing units. The quality of prefabricated housing units had increased to the point that they may not be distinguishable from traditionally-built units to those that live in them. The technique is also used in office blocks, warehouses and factory buildings. Prefabricated steel and glass sections are widely used for the exterior of large buildings.

Prefabrication saves engineering time on the construction site in civil engineering projects. This can be vital to the success of projects such as bridges and avalanche galleries, where weather conditions may only allow brief periods of construction.Prefabricated bridge elements and systems offer bridge designers and contractors significant advantages in terms of construction time, safety, environmental impact, constructibility, and cost. Prefabrication can also help minimize the impact on traffic from bridge building. Additionally, small, commonly-used structures such as concrete pylons are in most cases prefabricated.

Radio towers for mobile phone and other services often consist of multiple prefabricated sections. Modern lattice towers and guyed masts are also commonly assembled of prefabricated elements.

Prefabrication has become widely used in the assembly of aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 and spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....

, with components such as wings and fuselage sections often being manufactured in different countries or states from the final assembly site. However this is sometimes for political rather than commercial reasons - e.g. Airbus
Airbus
Airbus SAS is an aircraft manufacturing subsidiary of EADS, a European aerospace company. Based in Blagnac, France, surburb of Toulouse, and with significant activity across Europe, the company produces around half of the world's jet airliners....


Advantages of prefabrication

  1. Self-supporting ready-made components are used, so the need for formwork, shuttering and scaffolding is greatly reduced.
  2. Construction time is reduced and buildings are completed sooner, allowing an earlier return of the capital invested.
  3. On-site construction and congestion is minimized.
  4. Quality control can be easier in a factory assembly line setting than a construction site setting.
  5. Prefabrication can be located where skilled labour is more readily available and costs of labour, power, materials, space and overheads are lower.
  6. Time spent in bad weather or hazardous environments at the construction site is minimized.
  7. Less waste may

Disadvantages

  1. Careful handling of prefabricated components such as concrete panels or steel and glass panels is required.
  2. Attention has to be paid to the strength and corrosion-resistance of the joining of prefabricated sections to avoid failure of the joint.
  3. Similarly, leaks can form at joints in prefabricated components.
  4. Transportation costs may be higher for voluminous prefabricated sections than for the materials of which they are made, which can often be packed more efficiently.
  5. Large prefabricated sections require heavy-duty cranes and precision measurement and handling to place in position.
  6. Larger groups of buildings from the same type of prefabricated elements tend to look drab and monotonous.
  7. Local jobs are lost

See also

  • Prefabricated home
    Prefabricated home
    Prefabricated homes, often referred to as prefab homes, are dwellings manufactured off-site in advance, usually in standard sections that can be easily shipped and assembled....

  • Prefabricated buildings
  • 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...

     and concrete perpend
  • Panelák
    Panelák
    is a colloquial term in Czech and Slovak for a panel building constructed of pre-fabricated, pre-stressed concrete, such as those extant in Czech Republic and elsewhere in the former Soviet bloc...

  • Tower block
    Tower block
    A tower block, high-rise, apartment tower, office tower, apartment block, or block of flats, is a tall building or structure used as a residential and/or office building...

  • Concrete pylon
  • St Crispin's School — an example of a prefabricated school building
  • Nonsuch House
    Nonsuch House
    The four-story Nonsuch House on London Bridge, completed in 1579, is the earliest documented prefabricated building. It was originally constructed in the Netherlands, taken apart and shipped to London in pieces in 1578, where it was reassembled. Each timber was marked so that it could be...

    , first prefabricated building

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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