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65-407: The bridges are post tensioned cast-in-place concrete box girder bridges . Each bridge has two lanes of travel on a 39-foot deck. The bridge has roughly 7,500 travelers per day. The bridges were completed in 1988. The highway was not completed until 1992, when Highway 36 was rerouted onto I-72 and the older Florence Bridge began carrying Illinois Routes 100 and 106 . This article about

130-467: A corrosion -inhibiting grease , usually lithium based. Anchorages at each end of the tendon transfer the tensioning force to the concrete, and are required to reliably perform this role for the life of the structure. Unbonded post-tensioning can take the form of: For individual strand tendons, no additional tendon ducting is used and no post-stressing grouting operation is required, unlike for bonded post-tensioning. Permanent corrosion protection of

195-437: A structure in a factory or other manufacturing site, and transporting complete assemblies or sub-assemblies to the construction site where the structure is to be located. Some researchers refer it to “various materials joined together to form a component of the final installation procedure“. The most commonly cited definition is by Goodier and Gibb in 2007, which described the process of manufacturing and preassembly of

260-575: A bridge in Illinois is a stub . You can help Misplaced Pages by expanding it . This article relating to the Interstate Highway System is a stub . You can help Misplaced Pages by expanding it . Post-tensioned concrete Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" ( compressed ) during production, in a manner that strengthens it against tensile forces which will exist when in service. It

325-508: A broad range of structural, aesthetic and economic requirements. Significant among these include: a minimum number of (intrusive) supporting walls or columns; low structural thickness (depth), allowing space for services, or for additional floors in high-rise construction; fast construction cycles, especially for multi-storey buildings; and a low cost-per-unit-area, to maximise the building owner's return on investment. The prestressing of concrete allows "load-balancing" forces to be introduced into

390-407: A certain number of building components, modules, and elements before their shipment and installation on construction sites. The term prefabrication also applies to the manufacturing of things other than structures at a fixed site. It is frequently used when fabrication of a section of a machine or any movable structure is shifted from the main manufacturing site to another location, and the section

455-413: A factory (possibly with window and door frames included), transported to the site, lifted into place by a crane and bolted together. Prefabrication is used in the manufacture of ships , aircraft and all kinds of vehicles and machines where sections previously assembled at the final point of manufacture are assembled elsewhere instead, before being delivered for final assembly. The theory behind

520-609: A proof-loaded, redundant and monitorable pressure-containment system. Nuclear reactor and containment vessels will commonly employ separate sets of post-tensioned tendons curved horizontally or vertically to completely envelop the reactor core. Blast containment walls, such as for liquid natural gas (LNG) tanks, will normally utilize layers of horizontally-curved hoop tendons for containment in combination with vertically looped tendons for axial wall pre-stressing. Heavily loaded concrete ground-slabs and pavements can be sensitive to cracking and subsequent traffic-driven deterioration. As

585-419: A protective sleeve or duct which is either cast into the concrete structure or placed adjacent to it. At each end of a tendon is an anchorage assembly firmly fixed to the surrounding concrete. Once the concrete has been cast and set, the tendons are tensioned ("stressed") by pulling the tendon ends through the anchorages while pressing against the concrete. The large forces required to tension the tendons result in

650-620: A railway bridge constructed 1946 in the UK . By the 1960s, prestressed concrete largely superseded reinforced concrete bridges in the UK, with box girders being the dominant form. In short-span bridges of around 10 to 40 metres (30 to 130 ft), prestressing is commonly employed in the form of precast pre-tensioned girders or planks. Medium-length structures of around 40 to 200 metres (150 to 650 ft), typically use precast-segmental, in-situ balanced-cantilever and incrementally-launched designs . For

715-508: A result, prestressed concrete is regularly used in such structures as its pre-compression provides the concrete with the ability to resist the crack-inducing tensile stresses generated by in-service loading. This crack-resistance also allows individual slab sections to be constructed in larger pours than for conventionally reinforced concrete, resulting in wider joint spacings, reduced jointing costs and less long-term joint maintenance issues. Initial works have also been successfully conducted on

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780-532: A significant permanent compression being applied to the concrete once the tendon is "locked-off" at the anchorage. The method of locking the tendon-ends to the anchorage is dependent upon the tendon composition, with the most common systems being "button-head" anchoring (for wire tendons), split-wedge anchoring (for strand tendons), and threaded anchoring (for bar tendons). Tendon encapsulation systems are constructed from plastic or galvanised steel materials, and are classified into two main types: those where

845-503: A single tendon duct, with the exception of bars which are mostly used unbundled. This bundling makes for more efficient tendon installation and grouting processes, since each complete tendon requires only one set of end-anchorages and one grouting operation. Ducting is fabricated from a durable and corrosion-resistant material such as plastic (e.g., polyethylene ) or galvanised steel, and can be either round or rectangular/oval in cross-section. The tendon sizes used are highly dependent upon

910-444: A specific part of the project or to the whole of it. The efficiency and speed in the execution times of these works offer that, for example, in the case of the educational sector, it is possible to execute the projects without the cessation of the operations of the educational facilities during the development of the same. Prefabrication saves engineering time on the construction site in civil engineering projects. This can be vital to

975-592: Is a highly versatile construction material as a result of it being an almost ideal combination of its two main constituents: high-strength steel, pre-stretched to allow its full strength to be easily realised; and modern concrete, pre-compressed to minimise cracking under tensile forces. Its wide range of application is reflected in its incorporation into the major design codes covering most areas of structural and civil engineering, including buildings, bridges, dams, foundations, pavements, piles, stadiums, silos, and tanks. Building structures are typically required to satisfy

1040-418: Is fed into a greasing chamber and then passed to an extrusion unit where molten plastic forms a continuous outer coating. Finished strands can be cut-to-length and fitted with "dead-end" anchor assemblies as required for the project. Both bonded and unbonded post-tensioning technologies are widely used around the world, and the choice of system is often dictated by regional preferences, contractor experience, or

1105-423: Is most commonly used for the fabrication of structural beams , floor slabs , hollow-core slabs, balconies , lintels , driven piles , water tanks and concrete pipes . Post-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned after the surrounding concrete structure has been cast. The tendons are not placed in direct contact with the concrete, but are encapsulated within

1170-436: Is often also referred to as off-site construction. These can be described as component (or sub-assembly) systems, panelised systems, volumetric systems, and modular systems. Below these categories different branches, or technologies are being developed. There are a vast number of different systems on the market which fall into these categories and with recent advances in digital design such as building information modeling (BIM),

1235-437: 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

1300-428: Is that once the initial compression has been applied, the resulting material has the characteristics of high-strength concrete when subject to any subsequent compression forces and of ductile high-strength steel when subject to tension forces . This can result in improved structural capacity and/or serviceability compared with conventionally reinforced concrete in many situations. In a prestressed concrete member,

1365-459: Is the most popular structural material for bridges, and prestressed concrete is frequently adopted. When investigated in the 1940s for use on heavy-duty bridges, the advantages of this type of bridge over more traditional designs was that it is quicker to install, more economical and longer-lasting with the bridge being less lively. One of the first bridges built in this way is the Adam Viaduct ,

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1430-486: Is the protection afforded to the end-anchorage assemblies of unbonded tendons or cable-stay systems, as the anchorages of both of these are required to retain the prestressing forces. Failure of any of these components can result in the release of prestressing forces, or the physical rupture of stressing tendons. Modern prestressing systems deliver long-term durability by addressing the following areas: Several durability-related events are listed below: Prestressed concrete

1495-434: Is the use of prefabricated concrete and prefabricated steel sections in structures where a particular part or form is repeated many times. It can be difficult to construct the formwork 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

1560-417: Is undertaken for three main purposes: to protect the tendons against corrosion ; to permanently "lock-in" the tendon pre-tension, thereby removing the long-term reliance upon the end-anchorage systems; and to improve certain structural behaviors of the final concrete structure. Bonded post-tensioning characteristically uses tendons each comprising bundles of elements (e.g., strands or wires) placed inside

1625-400: Is used in various industries and construction sectors such as healthcare, retail, hospitality, education, and public administration, due to its many advantages and benefits over traditional on-site construction, such as reduced installation time and cost savings. Being used in single-story buildings as well as in multi-story projects and constructions. Providing the possibility of applying it to

1690-816: The Kingdom of Anuradhapura and Polonnaruwa . After the great Lisbon earthquake of 1755 , the Portuguese capital, especially the Baixa district, was rebuilt by using prefabrication on an unprecedented scale. Under the guidance of Sebastião José de Carvalho e Melo, popularly known as the Marquis de Pombal , the most powerful royal minister of D. Jose I , a new Pombaline style of architecture and urban planning arose, which introduced early anti-seismic design features and innovative prefabricated construction methods, according to which large multistory buildings were entirely manufactured outside

1755-405: The application, ranging from building works typically using between 2 and 6 strands per tendon, to specialized dam works using up to 91 strands per tendon. Fabrication of bonded tendons is generally undertaken on-site, commencing with the fitting of end-anchorages to formwork , placing the tendon ducting to the required curvature profiles, and reeving (or threading) the strands or wires through

1820-456: The assembly of aircraft and spacecraft , 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, such as for Airbus . Off-site fabrication is a process that incorporates prefabrication and pre-assembly. The process involves the design and manufacture of units or modules, usually remote from

1885-412: The authorities of building codes or standards, but rather exist to promote the understanding and development of prestressed concrete design, codes and best practices. Rules and requirements for the detailing of reinforcement and prestressing tendons are specified by individual national codes and standards such as: Prefabrication Prefabrication is the practice of assembling components of

1950-468: The availability of alternative systems. Either one is capable of delivering code-compliant, durable structures meeting the structural strength and serviceability requirements of the designer. The benefits that bonded post-tensioning can offer over unbonded systems are: The benefits that unbonded post-tensioning can offer over bonded systems are: Long-term durability is an essential requirement for prestressed concrete given its widespread use. Research on

2015-514: The city, transported in pieces and then assembled on site. The process, which lasted into the nineteenth century, lodged the city's residents in safe new structures unheard-of before the quake. Also in Portugal, the town of Vila Real de Santo António in the Algarve , founded on 30 December 1773, was quickly erected through the use of prefabricated materials en masse. The first of the prefabricated stones

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2080-402: 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 costs as well as the associated hazards. Prefabrication techniques are used in the construction of apartment blocks, and housing developments with repeated housing units. Prefabrication is an essential part of

2145-433: The concrete volume (internal prestressing) or wholly outside of it (external prestressing). While pre-tensioned concrete uses tendons directly bonded to the concrete, post-tensioned concrete can use either bonded or unbonded tendons. Pre-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned prior to the concrete being cast. The concrete bonds to the tendons as it cures , following which

2210-404: The concrete wall to form a series of hoops, spaced vertically up the structure. When tensioned, these tendons exert both axial (compressive) and radial (inward) forces onto the structure, which can directly oppose the subsequent storage loadings. If the magnitude of the prestress is designed to always exceed the tensile stresses produced by the loadings, a permanent residual compression will exist in

2275-964: The design and construction of prestressed concrete structures. In the United States, such organizations include the Post-Tensioning Institute (PTI) and the Precast/Prestressed Concrete Institute (PCI). Similar bodies include the Canadian Precast/Prestressed Concrete Institute (CPCI), the UK's Post-Tensioning Association, the Post Tensioning Institute of Australia and the South African Post Tensioning Association. Europe has similar country-based associations and institutions. These organizations are not

2340-413: The ducting. Following concreting and tensioning, the ducts are pressure-grouted and the tendon stressing-ends sealed against corrosion . Unbonded post-tensioning differs from bonded post-tensioning by allowing the tendons permanent freedom of longitudinal movement relative to the concrete. This is most commonly achieved by encasing each individual tendon element within a plastic sheathing filled with

2405-426: The durability performance of in-service prestressed structures has been undertaken since the 1960s, and anti-corrosion technologies for tendon protection have been continually improved since the earliest systems were developed. The durability of prestressed concrete is principally determined by the level of corrosion protection provided to any high-strength steel elements within the prestressing tendons. Also critical

2470-399: The end-anchoring of the tendons is released, and the tendon tension forces are transferred to the concrete as compression by static friction . Pre-tensioning is a common prefabrication technique, where the resulting concrete element is manufactured off-site from the final structure location and transported to site once cured. It requires strong, stable end-anchorage points between which

2535-451: The form of post-tensioned anchors drilled into the dam's concrete structure and/or the underlying rock strata. Such anchors typically comprise tendons of high-tensile bundled steel strands or individual threaded bars. Tendons are grouted to the concrete or rock at their far (internal) end, and have a significant "de-bonded" free-length at their external end which allows the tendon to stretch during tensioning. Tendons may be full-length bonded to

2600-428: The improved quality. However, tradition often favors building by hand in many countries, and the image of prefab as a "cheap" method only slows its adoption. However, current practice already allows the modifying the floor plan according to the customer's requirements and selecting the surfacing material, e.g. a personalized brick facade can be masoned even if the load-supporting elements are timber. Today, prefabrication

2665-751: The industrialization of construction. 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. Detached houses, cottages, log cabin, saunas, etc. are also sold with prefabricated elements. Prefabrication of modular wall elements allows building of complex thermal insulation , window frame components, etc. on an assembly line , which tends to improve quality over on-site construction of each individual wall or frame. Wood construction in particular benefits from

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2730-622: The internal stresses are introduced in a planned manner so that the stresses resulting from the imposed loads are counteracted to the desired degree. Prestressed concrete is used in a wide range of building and civil structures where its improved performance can allow for longer spans , reduced structural thicknesses, and material savings compared with simple reinforced concrete . Typical applications include high-rise buildings , residential concrete slabs , foundation systems , bridge and dam structures, silos and tanks , industrial pavements and nuclear containment structures . First used in

2795-404: The late nineteenth century, prestressed concrete has developed beyond pre-tensioning to include post-tensioning , which occurs after the concrete is cast. Tensioning systems may be classed as either monostrand , where each tendon's strand or wire is stressed individually, or multi-strand , where all strands or wires in a tendon are stressed simultaneously. Tendons may be located either within

2860-476: The lightness of the panels reduced the cost of foundations and assembly on site. Coloured concrete grey and with flat roofs, prefab houses were uninsulated and cold and life in a prefab acquired a certain stigma, but some London prefabs were occupied for much longer than the projected 10 years. The Crystal Palace , erected in London in 1851, was a highly visible example of iron and glass prefabricated construction; it

2925-432: The longest bridges, prestressed concrete deck structures often form an integral part of cable-stayed designs . Concrete dams have used prestressing to counter uplift and increase their overall stability since the mid-1930s. Prestressing is also frequently retro-fitted as part of dam remediation works, such as for structural strengthening, or when raising crest or spillway heights. Most commonly, dam prestressing takes

2990-674: The materials and components of which they are made. Prefabrication has been used since ancient times. For example, it is claimed that the world's oldest known engineered roadway , the Sweet Track constructed in England around 3800 BC , employed prefabricated timber sections brought to the site rather than assembled on-site. Sinhalese kings of ancient Sri Lanka 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

3055-406: The method is that time and cost is saved if similar construction tasks can be grouped, and assembly line 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

3120-471: The other components. An example from house-building illustrates the process of prefabrication. The conventional method of building a house is to transport bricks , timber , cement , sand , steel and construction aggregate , etc. to the site, and to construct the house on site from these materials. In prefabricated construction , only the foundations are constructed in this way, while sections of walls , floors and roof are prefabricated (assembled) in

3185-479: 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

3250-553: The strands is provided by the combined layers of grease, plastic sheathing, and surrounding concrete. Where strands are bundled to form a single unbonded tendon, an enveloping duct of plastic or galvanised steel is used and its interior free-spaces grouted after stressing. In this way, additional corrosion protection is provided via the grease, plastic sheathing, grout, external sheathing, and surrounding concrete layers. Individually greased-and-sheathed tendons are usually fabricated off-site by an extrusion process. The bare steel strand

3315-579: The structure to counter in-service loadings. This provides many benefits to building structures: Some notable building structures constructed from prestressed concrete include: Sydney Opera House and World Tower , Sydney; St George Wharf Tower , London; CN Tower , Toronto; Kai Tak Cruise Terminal and International Commerce Centre , Hong Kong; Ocean Heights 2 , Dubai; Eureka Tower , Melbourne; Torre Espacio , Madrid; Guoco Tower (Tanjong Pagar Centre), Singapore; Zagreb International Airport , Croatia; and Capital Gate , Abu Dhabi UAE. Concrete

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3380-754: 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

3445-475: The surface of the tendons is critical to the pre-tensioning process, as it determines when the tendon anchorages can be safely released. Higher bond strength in early-age concrete will speed production and allow more economical fabrication. To promote this, pre-tensioned tendons are usually composed of isolated single wires or strands, which provides a greater surface area for bonding than bundled-strand tendons. Unlike those of post-tensioned concrete (see below),

3510-432: The surrounding concrete or rock once tensioned, or (more commonly) have strands permanently encapsulated in corrosion-inhibiting grease over the free-length to permit long-term load monitoring and re-stressability. Circular storage structures such as silos and tanks can use prestressing forces to directly resist the outward pressures generated by stored liquids or bulk-solids. Horizontally curved tendons are installed within

3575-465: The task of integrating these different systems into a construction project is becoming increasingly a "digital" management proposition. The prefabricated construction market is booming. It is growing at an accelerated pace both in more established markets such as North America and Europe and in emerging economies such as the Asia-Pacific region (mainly China and India). Considerable growth is expected in

3640-546: The tendon element is subsequently bonded to the surrounding concrete by internal grouting of the duct after stressing ( bonded post-tensioning); and those where the tendon element is permanently de bonded from the surrounding concrete, usually by means of a greased sheath over the tendon strands ( unbonded post-tensioning). Casting the tendon ducts/sleeves into the concrete before any tensioning occurs allows them to be readily "profiled" to any desired shape including incorporating vertical and/or horizontal curvature . When

3705-418: The tendons are stretched. These anchorages form the ends of a "casting bed" which may be many times the length of the concrete element being fabricated. This allows multiple elements to be constructed end-to-end in the one pre-tensioning operation, allowing significant productivity benefits and economies of scale to be realized. The amount of bond (or adhesion ) achievable between the freshly set concrete and

3770-406: The tendons are tensioned, this profiling results in reaction forces being imparted onto the hardened concrete, and these can be beneficially used to counter any loadings subsequently applied to the structure. In bonded post-tensioning, tendons are permanently bonded to the surrounding concrete by the in situ grouting of their encapsulating ducting (after tendon tensioning). This grouting

3835-662: The tendons of pre-tensioned concrete elements generally form straight lines between end-anchorages. Where "profiled" or "harped" tendons are required, one or more intermediate deviators are located between the ends of the tendon to hold the tendon to the desired non-linear alignment during tensioning. Such deviators usually act against substantial forces, and hence require a robust casting-bed foundation system. Straight tendons are typically used in "linear" precast concrete elements, such as shallow beams, hollow-core slabs ; whereas profiled tendons are more commonly found in deeper precast bridge beams and girders. Pre-tensioned concrete

3900-677: The use of precast prestressed concrete for road pavements, where the speed and quality of the construction has been noted as being beneficial for this technique. Some notable civil structures constructed using prestressed concrete include: Gateway Bridge , Brisbane Australia; Incheon Bridge , South Korea; Roseires Dam , Sudan; Wanapum Dam , Washington, US; LNG tanks , South Hook, Wales; Cement silos , Brevik Norway; Autobahn A73 bridge , Itz Valley, Germany; Ostankino Tower , Moscow, Russia; CN Tower , Toronto, Canada; and Ringhals nuclear reactor , Videbergshamn Sweden. Worldwide, many professional organizations exist to promote best practices in

3965-491: The wall concrete, assisting in maintaining a watertight crack-free structure. Prestressed concrete has been established as a reliable construction material for high-pressure containment structures such as nuclear reactor vessels and containment buildings, and petrochemical tank blast-containment walls. Using pre-stressing to place such structures into an initial state of bi-axial or tri-axial compression increases their resistance to concrete cracking and leakage, while providing

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4030-450: The work site, and the installation at the site to form the permanent works at the site. In its fullest sense, off-site fabrication requires a project strategy that will change the orientation of the project process from construction to manufacture to installation. Examples of off-site fabrication are wall panels for homes, wooden truss bridge spans, airport control stations . There are four main categories of off-site fabrication, which

4095-486: Was followed on a smaller scale by Oxford Rewley Road railway station . During World War II , prefabricated Cargo ships , designed to quickly replace ships sunk by Nazi U-boats became increasingly common. The most ubiquitous of these ships was the American Liberty ship , which reached production of over 2,000 units, averaging 3 per day. The most widely used form of prefabrication in building and civil engineering

4160-591: Was laid in March 1774. By 13 May 1776, the centre of the town had been finished and was officially opened. In 19th century Australia a large number of prefabricated houses were imported from the United Kingdom. The method was widely used in the construction of prefabricated housing in the 20th century, such as in the United Kingdom as temporary housing for thousands of urban families "bombed out" during World War II . Assembling sections in factories saved time on-site and

4225-440: Was patented by Eugène Freyssinet in 1928. This compression is produced by the tensioning of high-strength "tendons" located within or adjacent to the concrete and is done to improve the performance of the concrete in service. Tendons may consist of single wires , multi-wire strands or threaded bars that are most commonly made from high-tensile steels , carbon fiber or aramid fiber . The essence of prestressed concrete

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