View source for Prestressed concrete

{{short description|Form of concrete used in construction}}
[[File:PrestressedConcrete-en1.png|thumb|upright=1.35|alt=six figures showing forces and resulting deflection of beam|Comparison of non-prestressed [[Beam (structure)|beam]] (top) and prestressed concrete beam (bottom) under load: {{olist
    |Non-prestressed beam without load
    |Non-prestressed beam with load
    |Before concrete solidifies, tendons embedded in concrete are tensioned
    |After concrete solidifies, tendons apply compressive stress to concrete
    |Prestressed beam without load
    |Prestressed beam with load
}}]]
'''Prestressed concrete''' is a form of [[concrete]] used in construction. It is substantially "prestressed" ([[Compression (physics)|compressed]]) during production, in a manner that strengthens it against tensile forces which will exist when in service.<ref name="LinTY">{{cite book|last1=Lin|first1=T.Y.|last2=Burns|first2=Ned H.|title=Design of Prestressed Concrete Structures|date=1981|publisher=John Wiley & Sons|location=New York, US|isbn=0-471-01898-8|edition=Third|url=http://www.slideshare.net/ankitd1094/design-of-prestressed-concrete-structures-tylin-50801288|access-date=24 August 2016|archive-date=8 February 2017|archive-url=https://web.archive.org/web/20170208031221/http://www.slideshare.net/ankitd1094/design-of-prestressed-concrete-structures-tylin-50801288|url-status=live}}</ref><ref name="FIB31">{{cite book|last1=Federation Internationale du Beton|title=fib Bulletin 31: Post-tensioning in Buildings|date=February 2005|publisher=FIB|isbn=978-2-88394-071-0|url=http://www.civil.ist.utl.pt/~cristina/EBAP/book_63505_fib31.pdf|access-date=26 August 2016|archive-date=8 February 2017|archive-url=https://web.archive.org/web/20170208014104/http://www.civil.ist.utl.pt/~cristina/EBAP/book_63505_fib31.pdf|url-status=dead}}</ref>{{rp|3–5}}<ref name="ACI-CT13">{{cite web|last1=American Concrete Institute|title=CT-13: ACI Concrete Terminology|url=https://www.concrete.org/topicsinconcrete/topicdetail/prestressed|website=American Concrete Institute|publisher=ACI|access-date=25 August 2016|location=Farmington Hills, Michigan US|archive-date=11 December 2016|archive-url=https://web.archive.org/web/20161211061649/https://www.concrete.org/topicsinconcrete/topicdetail/prestressed|url-status=live}} Post-tensioned concreted is "structural concrete in which internal stresses have been introduced to reduce potential tensile stresses in the concrete resulting from loads."</ref> It was patented by [[Eugène Freyssinet]] in 1928.<ref>{{cite book| last = Billington| first = David| title = The Tower and the Bridge| publisher = Princeton University Press| location = Princeton| year = 1985| isbn = 0-691-02393-X| url = https://archive.org/details/towerbridgenewar00bill}}</ref> 

This compression is produced by the [[Tension (physics)|tensioning]] of high-strength "tendons" located within or adjacent to the concrete and is done to improve the performance of the concrete in service.<ref name="Warner-1">{{cite book |last1=Warner |first1=R. F. |last2=Rangan |first2=B. V. |last3=Hall |first3=A. S. |last4=Faulkes |first4=K. A. |title=Concrete Structures |date=1988 |publisher=Addison Welsley Longman |location=South Melbourne, Australia |isbn=0-582-80247-4 |pages=8–19}}</ref> Tendons may consist of single [[wire]]s, multi-wire [[Wire rope|strands]] or threaded bars that are most commonly made from [[high-tensile steel]]s, [[carbon fiber]] or [[aramid fiber]].<ref name="LinTY"/>{{rp|52–59}} The essence of prestressed concrete 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 (physics)|tension forces]]. This can result in improved structural capacity and/or [[Serviceability (structure)|serviceability]] compared with conventionally [[reinforced concrete]] in many situations.<ref name="WarnerB">{{cite book |last1=Warner |first1=R. F. |last2=Faulkes |first2=K. A. |title=Prestressed Concrete |date=1988 |publisher=Longman Cheshire |location=Melbourne, Australia |isbn=0-582-71225-4 |pages=1–13 |edition=2nd}}</ref><ref name="FIB31"/>{{rp|6}} In a prestressed concrete member, 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 [[Span (engineering)|spans]], reduced structural thicknesses, and material savings compared with simple [[reinforced concrete]]. Typical applications include [[Tower block|high-rise buildings]], residential [[concrete slab]]s, [[Foundation (engineering)|foundation systems]], [[bridge]] and [[dam]] structures, [[silo]]s and [[water tanks|tanks]], [[Hardstand|industrial pavements]] and [[Containment building|nuclear containment structures]].<ref name="PTI-Apps">{{cite book |last1=Post-Tensioning Institute |title=Post-Tensioning Manual |url=https://archive.org/details/posttensioningma00inst |url-access=limited |date=2006 |publisher=PTI |location=Phoenix, AZ US |isbn=0-9778752-0-2 |pages=[https://archive.org/details/posttensioningma00inst/page/n18 5]–54 |edition=6th}}</ref>

First used in the late nineteenth century,<ref name=LinTY /> prestressed concrete has developed beyond [[Prestressed concrete#Pre-tensioned concrete|pre-tensioning]] to include [[Prestressed concrete#Post-tensioned concrete|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.<ref name="WarnerB" /> Tendons may be located either ''within'' 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==
[[File:Sofortiger-Verbund-en.png|left|thumb|upright=1.3|alt=three figures; darker green slab is pre-tensioned in lighter green casting bed|Pre-tensioning process]]
Pre-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned ''prior'' to the concrete being cast.<ref name="LinTY" />{{rp|25}} The concrete bonds to the tendons as it [[Concrete#Curing|cures]], following which the end-anchoring of the tendons is released, and the tendon [[Tension (physics)|tension forces]] are transferred to the concrete as compression by [[static friction]].<ref name="WarnerB" />{{rp|7}}

[[File:AASHTO Girder.jpg|thumb|upright|alt=Form for concrete I-beam with tendons in lower portion|Pre-tensioned bridge girder in precasting bed, with single-strand tendons exiting through the [[formwork]]]]
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 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.<ref name="WarnerB" /><ref>{{cite web |last1=Tokyo Rope Mfg Co Ltd |title=CFCC Pre-tensioning Manual |url=http://www.maine.gov/mdot/contractors/projects/2014/019283.00-kittery/pm019283.00.pdf |website=MaineDOT |access-date=19 August 2016 |archive-date=8 February 2017 |archive-url=https://web.archive.org/web/20170208073207/http://www.maine.gov/mdot/contractors/projects/2014/019283.00-kittery/pm019283.00.pdf |url-status=live}}</ref>

The amount of bond (or [[adhesion]]) achievable between the freshly set concrete and 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.<ref name="WarnerB" />

[[File:SpannbetonFertigdecke Montage.jpg|thumb|left|alt=Crane manoeuvres concrete plank|Pre-tensioned, precast [[hollow-core slab]]  being placed]]
Unlike those of post-tensioned concrete (see below), the tendons of pre-tensioned concrete elements generally form straight lines between end-anchorages. Where "profiled" or "harped" tendons<ref>"Tendons having one or more deviations from a straight line, either vertically or horizontally, between the ends of the structure"</ref> 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.<ref name="LinTY" />{{rp|68–73}}<ref name="WarnerB" />{{rp|11}} 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 slab]]s; whereas profiled tendons are more commonly found in deeper precast bridge beams and girders.

Pre-tensioned concrete is most commonly used for the fabrication of structural [[Beam (structure)|beams]], [[Concrete slab|floor slabs]], hollow-core slabs, [[balcony|balconies]], [[lintel]]s, driven [[Deep foundation|piles]], [[water tanks]] and concrete [[Pipe (fluid conveyance)|pipes]].
{{Clear}}

==Post-tensioned concrete==
<!-- Courtesy note per [[WP:RSECT]]: [[Post-tensioned concrete]] links here -->

[[File:Post-Tensioned Concrete.svg|thumb|right|alt=four diagrams showing loads and forces on beam|Forces on post-tensioned concrete with profiled (curved) tendon]]
[[File:Stressing_anchorage.jpg|thumb|upright|alt=A dozen parallel cables are individually anchored to an assembly.|Post-tensioned tendon anchorage; four-piece "lock-off" wedges are visible holding each strand]]
Post-tensioned concrete is a variant of prestressed concrete where the tendons are tensioned ''after'' the surrounding concrete structure has been cast.<ref name="LinTY" />{{rp|25}}

The tendons are not placed in direct contact with the concrete, but are encapsulated within 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 a significant permanent compression being applied to the concrete once the tendon is "locked-off" at the anchorage.<ref name="LinTY"/>{{rp|25}}<ref name="WarnerB"/>{{rp|7}} 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), [[Wedge (mechanical device)|split-wedge]] anchoring (for strand tendons), and [[Screw thread|threaded]] anchoring (for bar tendons).<ref name="LinTY"/>{{rp|79–84}}

[[File:Go Between Bridge construction (2).jpg|thumb|left|alt=A T-shaped section of bridge being constructed over a river|Balanced-cantilever bridge under construction. Each added segment is supported by post-tensioned tendons]]
Tendon encapsulation systems are constructed from plastic or [[galvanised]] steel materials, and are classified into two main types: those where the tendon element is subsequently bonded to the surrounding concrete by internal [[grout]]ing 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 [[Grease (lubricant)|greased]] sheath over the tendon strands (''unbonded'' post-tensioning).<ref name="LinTY"/>{{rp|26}}<ref name="WarnerB"/>{{rp|10}}

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 the tendons are tensioned, this profiling results in [[Reaction (physics)|reaction]] forces being imparted onto the hardened concrete, and these can be beneficially used to counter any loadings subsequently applied to the structure.<ref name="FIB31"/>{{rp|5–6}}<ref name="WarnerB"/>{{rp|48}}{{rp|9–10}}

===Bonded post-tensioning===
[[File:Prestress Post Tension Anchor.jpg|thumb|left|alt=a detached anchor displaying tendon lock-offs|Multi-strand post-tensioning anchor]]
In bonded post-tensioning, tendons are permanently bonded to the surrounding concrete by the ''[[in situ]]'' [[grout]]ing of their encapsulating ducting (after tendon tensioning). This grouting 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 analysis|structural behaviors]] of the final concrete structure.<ref name="Aalami">{{cite journal|last1=Aalami|first1=Bijan O.|title=Unbonded and bonded post-tensioning systems in building construction|journal=PTI Technical Notes|date=5 September 1994|issue=5|url=http://www.post-tensioning.org/Uploads/technote5.pdf|access-date=23 August 2016|publisher=Post-Tensioning Institute|location=Phoenix, Arizona US|archive-date=23 November 2016|archive-url=https://web.archive.org/web/20161123041522/http://www.post-tensioning.org/Uploads/technote5.pdf|url-status=live}}</ref>

Bonded post-tensioning characteristically uses tendons each comprising ''bundles'' of elements (e.g., strands or wires) placed inside 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.<ref name="FIB31"/>{{rp|7}} The tendon sizes used are highly dependent upon 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 the ducting. Following concreting and tensioning, the ducts are [[pressure grouting|pressure-grouted]] and the tendon stressing-ends sealed against [[corrosion]].<ref name="WarnerB"/>{{rp|2}}

===Unbonded post-tensioning===
{{multiple image
|align=right
|total_width=200
|direction=vertical
|image1=Post-Tensioning-Cables-2.jpg
|alt1=prepared concrete forms with grid of tendons and ducts
|image2=Post-Tensioning-Cables-8.jpg
|alt2=after removal of forms, tendons visible emerging from ducts
|footer=Unbonded slab post-tensioning. (Above) Installed strands and edge-anchors are visible, along with prefabricated coiled strands for the next pour. (Below) End-view of slab after stripping forms, showing individual strands and stressing-anchor recesses.
}}

Unbonded post-tensioning differs from bonded post-tensioning by allowing the tendons permanent freedom of [[Geometric terms of location|longitudinal]] movement relative to the concrete. This is most commonly achieved by encasing each individual tendon element within a plastic sheathing filled with a [[corrosion]]-inhibiting [[Grease (lubricant)|grease]], usually [[lithium]] based. Anchorages at each end of the tendon transfer the [[Tension (physics)|tensioning]] force to the concrete, and are required to reliably perform this role for the life of the structure.<ref name="Aalami"/>{{rp|1}}

Unbonded post-tensioning can take the form of:
* Individual strand tendons placed directly into the concreted structure (e.g., buildings, ground slabs)
* Bundled strands, individually greased-and-sheathed, forming a single tendon within an encapsulating duct that is placed either within or adjacent to the concrete (e.g., restressable anchors, external post-tensioning)

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 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.<ref name="Aalami"/>{{rp|1}}

Individually greased-and-sheathed tendons are usually fabricated off-site by an [[extrusion]] process. The bare steel strand 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.

===Comparison between bonded and unbonded post-tensioning===
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 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.<ref name="Aalami" />{{rp|2}}

The benefits that bonded post-tensioning can offer over unbonded systems are:
* Reduced reliance on end-anchorage integrity. Following tensioning and grouting, bonded tendons are connected to the surrounding concrete along their full length by high-strength [[grout]]. Once cured, this grout can transfer the full tendon tension force to the concrete within a very short distance (approximately 1 metre). As a result, any inadvertent severing of the tendon or failure of an end anchorage has only a very localised impact on tendon performance, and almost never results in tendon ejection from the anchorage.<ref name="FIB31"/>{{rp|18}}<ref name="Aalami"/>{{rp|7}}
* Increased [[Strength of materials|ultimate strength]] in [[Bending|flexure]]. With bonded post-tensioning, any flexure of the structure is directly resisted by tendon [[Deformation (engineering)|strains]] at that same location (i.e. no strain re-distribution occurs). This results in significantly higher [[Tension (physics)|tensile]] strains in the tendons than if they were unbonded, allowing their full [[Yield (engineering)|yield strength]] to be realised, and producing a higher ultimate load capacity.<ref name="FIB31"/>{{rp|16–17}}<ref name="WarnerB" />{{rp|10}}
* Improved crack-control. In the presence of concrete [[Properties of concrete#Cracking|cracking]], bonded tendons respond similarly to conventional reinforcement ([[rebar]]). With the tendons fixed to the concrete at each side of the crack, greater resistance to crack expansion is offered than with unbonded tendons, allowing many design codes to specify reduced reinforcement requirements for bonded post-tensioning.<ref name="Aalami"/>{{rp|4}}<ref name="Adapt">{{cite journal |last1=Aalami |first1=Bijan O. |title=Nonprestresed Bonded Reinforcement in Post-Tensioned Building Design |journal=ADAPT Technical Publication |date=February 2001 |issue=2–01 |url=http://www.adaptsoft.com/resources/ADAPT_P201_Nonpre-Bonded-PT-Bldg-Dsgnr.pdf |access-date=2016-08-25 |archive-date=2017-02-08 |archive-url=https://web.archive.org/web/20170208013955/http://www.adaptsoft.com/resources/ADAPT_P201_Nonpre-Bonded-PT-Bldg-Dsgnr.pdf |url-status=live}}</ref>{{rp|1}}
* Improved fire performance. The absence of strain redistribution in bonded tendons may limit the impact that any localised overheating has on the overall structure. As a result, bonded structures may display a higher capacity to resist fire conditions than unbonded ones.<ref name="Bailey">{{cite journal |last1=Bailey |first1=Colin G. |last2=Ellobody |first2=Ehab |title=Comparison of unbonded and bonded post-tensioned concrete slabs under fire conditions |journal=The Structural Engineer |date=2009 |volume=87 |issue=19 |url=https://www.istructe.org/journal/volumes/volume-87-(published-in-2009)/issues/issue-19/articles/comparison-of-unbonded-and-bonded-posttensioned-co |access-date=22 August 2016 |archive-date=2016-09-17 |archive-url=https://web.archive.org/web/20160917225506/https://www.istructe.org/journal/volumes/volume-87-(published-in-2009)/issues/issue-19/articles/comparison-of-unbonded-and-bonded-posttensioned-co |url-status=live}}</ref>

The benefits that unbonded post-tensioning can offer over bonded systems are:
* Ability to be [[prefabricated]]. Unbonded tendons can be readily prefabricated off-site complete with end-anchorages, facilitating faster installation during construction. Additional [[lead time]] may need to be allowed for this fabrication process. 
* Improved site [[productivity]]. The elimination of the post-stressing grouting process required in bonded structures improves the site-labour productivity of unbonded post-tensioning.<ref name="Aalami"/>{{rp|5}}
* Improved installation [[flexibility]]. Unbonded single-strand tendons have greater handling flexibility than bonded ducting during installation, allowing them a greater ability to be deviated around service penetrations or obstructions.<ref name="Aalami"/>{{rp|5}}
* Reduced [[concrete cover]]. Unbonded tendons may allow some reduction in concrete element thickness, as their smaller size and increased corrosion protection may allow them to be placed closer to the concrete surface.<ref name=FIB31/>{{rp|8}}
* Simpler replacement and/or adjustment. Being permanently isolated from the concrete, unbonded tendons are able to be readily de-stressed, re-stressed and/or replaced should they become damaged or need their force levels to be modified in-service.<ref name="Aalami"/>{{rp|6}}
* Superior overload performance. Although having a lower ultimate strength than bonded tendons, unbonded tendons' ability to redistribute strains over their full length can give them superior pre-collapse [[ductility]]. In extremes, unbonded tendons can resort to a [[catenary]]-type action instead of pure flexure, allowing significantly greater [[Deformation (engineering)|deformation]] before structural failure.<ref name="Bondy">{{cite journal |last1=Bondy |first1=Kenneth B. |title=Two way post-tensioned slabs with bonded tendons |journal=PTI Journal |date=December 2012 |volume=8 |issue=2 |page=44 |url=http://www.kenbondy.com/images/ProfessionalArticles/130129-Journal_Reprint-Bondy-Two-Way_PT_Slabs_with_Bonded_Tendons.pdf |access-date=2016-08-25 |publisher=Post-Tensioning Institute |location=US |archive-date=2016-08-28 |archive-url=https://web.archive.org/web/20160828205253/http://www.kenbondy.com/images/ProfessionalArticles/130129-Journal_Reprint-Bondy-Two-Way_PT_Slabs_with_Bonded%20Tendons.pdf |url-status=live}}</ref>

==Tendon durability and corrosion protection==
Long-term durability is an essential requirement for prestressed concrete given its widespread use.
Research on the durability performance of in-service prestressed structures has been undertaken since the 1960s,<ref name="Szilard">{{cite journal|last1=Szilard|first1=Rudolph|title=Survey on the Durability of Prestressed Concrete Structures|journal=PCI Journal|date=October 1969|pages=62–73|url=http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1969/DOI_Articles/jl-69-october-7.pdf|access-date=7 September 2016|archive-date=16 September 2016|archive-url=https://web.archive.org/web/20160916113911/http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1969/DOI_Articles/jl-69-october-7.pdf|url-status=live}}</ref> and anti-corrosion technologies for tendon protection have been continually improved since the earliest systems were developed.<ref name="Podolny">{{cite journal|last1=Podolny|first1=Walter|title=Corrosion of Prestressing Steels and its Mitigation|journal=PCI Journal|volume=37|issue=5|date=September 1992|pages=34–55|url=http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1992/DOI_Articles/jl-92-september-october-4.pdf|access-date=7 September 2016|doi=10.15554/pcij.09011992.34.55|s2cid=109223938 |archive-date=16 September 2016|archive-url=https://web.archive.org/web/20160916113840/http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1992/DOI_Articles/jl-92-september-october-4.pdf|url-status=live}}</ref>

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 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:
* Tendon grouting (bonded tendons)<br/>Bonded tendons consist of bundled strands placed inside ducts located within the surrounding concrete. To ensure full protection to the bundled strands, the ducts must be pressure-filled with a [[Corrosion inhibitor|corrosion-inhibiting]] grout, without leaving any voids, following strand-tensioning.
* Tendon coating (unbonded tendons)<br/>Unbonded tendons comprise individual strands coated in an anti-corrosion grease or wax, and fitted with a durable plastic-based full-length sleeve or sheath. The sleeving is required to be undamaged over the tendon length, and it must extend fully into the anchorage fittings at each end of the tendon.
* Double-layer encapsulation<br/>Prestressing tendons requiring permanent [[Deformation monitoring|monitoring]] and/or force adjustment, such as [[Cable-stayed bridge|stay-cables]] and re-stressable dam anchors, will typically employ double-layer corrosion protection. Such tendons are composed of individual strands, grease-coated and sleeved, collected into a strand-bundle and placed inside encapsulating [[polyethylene]] outer ducting. The remaining void space within the duct is pressure-grouted, providing a multi-layer polythene-grout-plastic-grease protection barrier system for each strand.
* Anchorage protection<br/>In all post-tensioned installations, protection of the end-anchorages against corrosion is essential, and critically so for unbonded systems.

Several durability-related events are listed below:
* Ynys-y-Gwas bridge, West Glamorgan, Wales, 1985<br/>A single-span, [[Segmental bridge|precast-segmental]] structure constructed in 1953 with longitudinal and transverse post-tensioning. [[Corrosion]] attacked the under-protected tendons where they crossed the ''in-situ'' joints between the segments, leading to sudden collapse.<ref name="Podolny"/>{{rp|40}}
* Scheldt River bridge, Melle, Belgium, 1991<br/>A three-span prestressed [[Cantilever bridge|cantilever structure]] constructed in the 1950s. Inadequate [[concrete cover]] in the side [[abutment]]s resulted in tie-down cable [[corrosion]], leading to a progressive failure of the main bridge span and the death of one person.<ref>{{cite book|last1=De Schutter|first1=Geert|title=Damage to Concrete Structures|date=10 May 2012|publisher=CRC Press|isbn=978-0-415-60388-1|pages=31–33|url=https://books.google.com/books?id=38LLBQAAQBAJ&q=melle+bridge+belgium&pg=PA31|access-date=7 September 2016|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417194438/https://books.google.com/books?id=38LLBQAAQBAJ&q=melle+bridge+belgium&pg=PA31|url-status=live}}</ref>
* [[Highways Agency|UK Highways Agency]], 1992<br/>Following discovery of tendon corrosion in several bridges in England, the Highways Agency issued a moratorium on the construction of new internally grouted post-tensioned bridges and embarked on a 5-year programme of inspections on its existing post-tensioned bridge stock. The moratorium was lifted in 1996.<ref>{{cite book|last1=Ryall|first1=M. J.|last2=Woodward|first2=R.|last3=Milne|first3=D.|title=Bridge Management 4: Inspection, Maintenance, Assessment and Repair|date=2000|publisher=Thomas Telford|location=London|pages=170–173|url=https://books.google.com/books?id=vSZAnyWpzDcC&q=uk+highways+agency+moratorium+post-tensioning+bridges&pg=PA170|access-date=7 September 2016|isbn=978-0-7277-2854-8|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417204757/https://books.google.com/books?id=vSZAnyWpzDcC&q=uk+highways+agency+moratorium+post-tensioning+bridges&pg=PA170|url-status=live}}</ref><ref>{{cite web|last1=CARES|title=Post-Tensioning Systems|url=http://www.ukcares.com/certification/post-tensioning-systems|website=www.ukcares.com|publisher=CARES|access-date=7 September 2016|archive-date=11 June 2016|archive-url=https://web.archive.org/web/20160611025353/http://ukcares.com/certification/post-tensioning-systems|url-status=live}}</ref>
* Pedestrian bridge, [[Charlotte Motor Speedway#Bridge collapse|Charlotte Motor Speedway]], North Carolina, US, 2000<br/>A multi-span steel and concrete structure constructed in 1995. An unauthorised [[Concrete#Admixtures|chemical]] was added to the tendon grout to speed construction, leading to corrosion of the prestressing strands and the sudden collapse of one span, injuring many spectators.<ref>{{cite web|last1=NACE|title=Corrosdion Failures: Lowe's Motor Speedway Bridge Collapse|url=http://www.nace.org/CORROSION-FAILURES-Lowes-Motor-Speedway-Bridge-Collapse.aspx|website=www.nace.org|publisher=NACE|access-date=7 September 2016|archive-url=https://web.archive.org/web/20160924051847/http://www.nace.org/CORROSION-FAILURES-Lowes-Motor-Speedway-Bridge-Collapse.aspx|archive-date=24 September 2016|url-status=dead}}</ref>
* [[Hammersmith Flyover]] London, England, 2011<br/>Sixteen-span prestressed structure constructed in 1961. Corrosion from road [[De-icing#Roadways|de-icing salts]] was detected in some of the prestressing tendons, necessitating initial closure of the road while additional investigations were done. Subsequent repairs and strengthening using external post-tensioning was carried out and completed in 2015.<ref name=ednbeccy>{{cite news|url=https://www.bbc.co.uk/news/uk-england-london-20533457|title=TfL report warned of Hammersmith Flyover collapse risk|publisher=BBC News, London|author=Ed Davey and Rebecca Cafe|date=3 December 2012|access-date=3 December 2012|archive-date=3 December 2012|archive-url=https://web.archive.org/web/20121203013407/http://www.bbc.co.uk/news/uk-england-london-20533457|url-status=live}}</ref><ref>{{cite web|last1=Freyssinet|title=Extending the Life of Hammersmith Flyover|url=http://www.freyssinet.com/freyssinet/wfreyssinet_en.nsf/sb/repair.extending-the-life-of-hammersmith-flyover---second-step-of-the-strengthening-works|website=www.freyssinet.com|publisher=Freyssinet|access-date=7 September 2016|archive-date=15 September 2016|archive-url=https://web.archive.org/web/20160915155635/http://www.freyssinet.com/freyssinet/wfreyssinet_en.nsf/sb/repair.extending-the-life-of-hammersmith-flyover---second-step-of-the-strengthening-works|url-status=live}}</ref>
* Petrulla Viaduct ("Viadotto Petrulla"), Sicily, Italy, 2014<br/>One span of a 12-span viaduct collapsed on 7 July 2014, causing 4 injuries,<ref>{{cite news|url=https://qds.it/16684-giu-il-viadotto-petrulla-panico-sulla-statale-626-htm/ |title=Giù il viadotto Petrulla, panico sulla Statale 626 |date=8 July 2014}}</ref> due to corrosion of the post-tensioning tendons.
* [[Ponte Morandi|Genoa bridge collapse]], 2018. The Ponte Morandi was a cable-stayed bridge characterised by a prestressed concrete structure for the piers, pylons and deck, very few stays, as few as two per span, and a hybrid system for the stays constructed from steel cables with prestressed concrete shells poured on. The concrete was only prestressed to 10 MPa, resulting in it being prone to cracks and water intrusion, which caused corrosion of the embedded steel.
* Churchill Way flyovers, [[Liverpool]], England<br/>The flyovers were closed in September 2018 after inspections revealed poor quality concrete, tendon corrosion and signs of structural distress. They were demolished in 2019.<ref>{{cite web|url=https://www.liverpool.gov.uk/parking-roads-and-travel/getting-around-liverpool/road-improvements/better-roads/better-roads-schemes/completed-schemes/churchill-way-flyovers-deconstruction-scheme/|title=Churchill Way Flyovers Deconstruction Scheme|access-date=8 April 2021|archive-date=9 April 2021|archive-url=https://web.archive.org/web/20210409234446/https://www.liverpool.gov.uk/parking-roads-and-travel/getting-around-liverpool/road-improvements/better-roads/better-roads-schemes/completed-schemes/churchill-way-flyovers-deconstruction-scheme/|url-status=live}}</ref>

==Applications==
Prestressed concrete 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.<ref name="LinTY"/>{{rp|12}} 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.<ref name="PTI-Apps"/>

===Building structures===
Building structures are typically required to satisfy 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 the structure to counter in-service loadings. This provides many benefits to building structures:
* Longer spans for the same structural depth<br/>Load balancing results in lower in-service deflections, which allows spans to be increased (and the number of supports reduced) without adding to structural depth.
* Reduced structural thickness<br />For a given span, lower in-service deflections allows thinner structural sections to be used, in turn resulting in lower floor-to-floor heights, or more room for building services.
* Faster stripping time<br/>Typically, prestressed concrete building elements are fully stressed and self-supporting within five days. At this point they can have their formwork stripped and re-deployed to the next section of the building, accelerating construction "cycle-times".
* Reduced material costs<br />The combination of reduced structural thickness, reduced conventional reinforcement quantities, and fast construction often results in prestressed concrete showing significant cost benefits in building structures compared to alternative structural materials.

Some notable building structures constructed from prestressed concrete include: [[Sydney Opera House]]<ref name="SOH">{{cite web|last1=Australian Society for History of Engineering and Technology|title=An Engineering Walk around the Sydney Opera House|url=http://ashet.org.au/images/Opera-House.pdf|website=ashet.org.au|publisher=ASHET|access-date=1 September 2016|archive-date=8 February 2017|archive-url=https://web.archive.org/web/20170208014406/http://ashet.org.au/images/Opera-House.pdf|url-status=live}}</ref> and [[World Tower]], Sydney;<ref name="WorldTower">{{cite web|last1=Martin|first1=Owen|last2=Lal|first2=Nalean|title=Structural Design of the 84 Storey World Tower in Sydney|url=http://global.ctbuh.org/resources/papers/download/1649-structural-design-of-the-84-storey-world-tower-in-sydney.pdf|website=ctbuh.org|publisher=Council on Tall Buildings and Urban Habitat|access-date=1 September 2016|archive-date=14 April 2016|archive-url=https://web.archive.org/web/20160414020438/http://global.ctbuh.org/resources/papers/download/1649-structural-design-of-the-84-storey-world-tower-in-sydney.pdf|url-status=live}}</ref> [[St George Wharf Tower]], London;<ref name="Tower">{{cite web|title=The Tower, One St. George Wharf, London, UK|url=http://www.cclint.com/tower-st-george|website=cclint.com|publisher=CCL|access-date=1 September 2016|archive-date=30 April 2021|archive-url=https://web.archive.org/web/20210430221204/https://www.cclint.com/tower-st-george|url-status=live}}</ref> [[CN Tower]], Toronto;<ref name="CN">{{cite journal|last1=Knoll|first1=Franz|last2=Prosser|first2=M. John|last3=Otter|first3=John|title=Prestressing the CN Tower|journal=PCI Journal|volume=21|issue=3|date=May–June 1976|pages=84–111|url=http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1976/DOI_Articles/jl-76-may-june-6.pdf|doi=10.15554/pcij.05011976.84.111|access-date=2 September 2016|archive-date=15 September 2016|archive-url=https://web.archive.org/web/20160915190533/http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1976/DOI_Articles/jl-76-may-june-6.pdf|url-status=live}}</ref> [[Kai Tak Cruise Terminal]]<ref name="KaiTak">{{cite web|last1=VSL|title=Kai Tak Cruise Terminal Building - Hong Kong|url=http://www.vslvietnam.com/References/jobreport.php?getfile=JR2847.pdf&name=VSL_____(2847).pdf|website=vslvietnam.com|publisher=VSL|access-date=1 September 2016|archive-date=14 September 2016|archive-url=https://web.archive.org/web/20160914095625/http://www.vslvietnam.com/References/jobreport.php?getfile=JR2847.pdf&name=VSL_____(2847).pdf|url-status=live}}</ref> and [[International Commerce Centre]], Hong Kong;<ref name="ICC">{{cite web|last1=ARUP|title=International Commerce Centre (ICC)|url=http://www.arup.com/projects/international_commerce_center_hong_kong|website=www.arup.com|publisher=ARUP|access-date=2 September 2016|archive-date=4 September 2016|archive-url=https://web.archive.org/web/20160904202806/http://www.arup.com/projects/international_commerce_center_hong_kong|url-status=live}}</ref> [[Ocean Heights 2]], Dubai;<ref name="Ocean">{{cite web|last1=CM Engineering Consultants|title=Ocean Heights 2, Dubai UAE|url=http://www.cmecs.co/Projects?item=2|website=www.cmecs.co|publisher=CMECS|access-date=1 September 2016|archive-date=24 September 2016|archive-url=https://web.archive.org/web/20160924054337/http://www.cmecs.co/Projects?item=2|url-status=live}}</ref> [[Eureka Tower]], Melbourne;<ref name="Eureka">{{cite web|last1=Design Build Network|title=Eureka Tower, Melbourne Victoria Australia|url=http://www.designbuild-network.com/projects/eureka/|website=www.designbuild-network.com|publisher=Design Build Network|access-date=1 September 2016|archive-date=13 February 2012|archive-url=https://web.archive.org/web/20120213040847/http://www.designbuild-network.com/projects/eureka/|url-status=live}}</ref> [[Torre Espacio]], Madrid;<ref name="Espacio">{{cite journal|last1=Martinez|first1=Julio|last2=Gomez|first2=Miguel|title=Torre Espacio. Building Structure|journal=Hormigon y Acero|date=July 2008|volume=59|issue=249|pages=19–43|url=http://e-ache.com/modules/pd-downloads/visit.php?cid=1&lid=12|access-date=1 September 2016|location=Madrid, Spain|issn=0439-5689|archive-date=8 February 2017|archive-url=https://web.archive.org/web/20170208014249/http://e-ache.com/modules/pd-downloads/visit.php?cid=1&lid=12|url-status=live}}</ref> Guoco Tower (Tanjong Pagar Centre), Singapore;<ref name="Connaect2016">{{cite journal|last1=BBR Network|title=Reaching for the Skies|journal=Connaect|date=2016|volume=10|page=51|url=http://www.bbrnetwork.com/fileadmin/bbr_network/PDFs/CONNAECTs/CONNAECT_2016.pdf|access-date=2 September 2016|archive-date=22 September 2016|archive-url=https://web.archive.org/web/20160922200652/http://www.bbrnetwork.com/fileadmin/bbr_network/PDFs/CONNAECTs/CONNAECT_2016.pdf|url-status=live}}</ref> [[Zagreb International Airport]], Croatia;<ref name="Connaect2016-1">{{cite journal|last1=BBR Network|title=Gateway to South Eastern Europe|journal=Connaect|date=2016|volume=10|pages=37–41|url=http://www.bbrnetwork.com/fileadmin/bbr_network/PDFs/CONNAECTs/CONNAECT_2016.pdf|access-date=2 September 2016|archive-date=22 September 2016|archive-url=https://web.archive.org/web/20160922200652/http://www.bbrnetwork.com/fileadmin/bbr_network/PDFs/CONNAECTs/CONNAECT_2016.pdf|url-status=live}}</ref> and [[Capital Gate]], Abu Dhabi UAE.<ref name="Capital">{{cite journal|last1=Schofield|first1=Jeff|title=Case Study: Capital Gate, Abu Dhabi|journal=CTBUH Journal|date=2012|issue=11|url=http://global.ctbuh.org/resources/papers/download/21-case-study-capital-gate-abu-dhabi.pdf|access-date=2 September 2016|archive-date=30 July 2016|archive-url=https://web.archive.org/web/20160730000725/http://global.ctbuh.org/resources/papers/download/21-case-study-capital-gate-abu-dhabi.pdf|url-status=live}}</ref>

<gallery class="center" heights="120px" text-align:"left"="" perrow="5">
File:International Commerce Centre.jpg|[[International Commerce Centre|ICC tower]], Hong Kong<br/>''484m 2010''
File:Guoco Tower, Singapore, under construction - 20141006.jpg|Guoco Tower, Singapore<br/>''290m 2016''
File:Aerial view of the Sydney Opera House.jpg|[[Sydney Opera House]]<br/>''1973''
File:Kai Tak Cruise Terminal in June 2014.jpg|[[Kai Tak Cruise Terminal|Kai Tak Terminal]]<br/>Hong Kong ''2013''

File:World Tower 2014-08-22.jpg|[[World Tower]], Sydney<br/>''230m 2004''
File:Ocean Heights Dubai Marina.jpg|[[Ocean Heights 2]], Dubai<br/>''335m 2016''
File:Eureka Tower LC.JPG|[[Eureka Tower]], Melbourne<br/>''297m 2006''
File:Torre Espacio (Madrid) 06.jpg|[[Torre Espacio]], Madrid<br/>''230m 2008''
File:Capital Gate.jpg|[[Capital Gate]], Abu Dhabi<br/>''18° lean 2010''
</gallery>

===Civil structures===
====Bridges====
Concrete is the most popular structural material for bridges, and prestressed concrete is frequently adopted.<ref>{{cite journal |first1=Man-Chung |last1=Tang |author1-link=Man-Chung Tang |title=Evolution of Bridge Technology |journal=IABSE Symposium Proceedings |date=2007 |page=7 |url=http://www.ciccp.es/ImgWeb/Castilla_y_Leon/Ingenier%C3%ADa-Humanismo/Evolution_of_bridge_technology.pdf |access-date=2016-09-05 |archive-date=2016-09-17 |archive-url=https://web.archive.org/web/20160917041304/http://www.ciccp.es/ImgWeb/Castilla_y_Leon/Ingenier%C3%ADa-Humanismo/Evolution_of_bridge_technology.pdf |url-status=live}}</ref><ref name="Hewson">{{cite book |last1=Hewson |first1=Nigel R. |title=Prestressed Concrete bridges: design and Construction |date=2012 |publisher=ICE |isbn=978-0-7277-4113-4 |url=https://books.google.com/books?id=WXKbZwEACAAJ |access-date=2016-09-02 |archive-date=2021-04-17 |archive-url=https://web.archive.org/web/20210417201235/https://books.google.com/books?id=WXKbZwEACAAJ |url-status=live}}</ref> 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.<ref>{{cite book |author=R. L. M'ilmoyle |title=Railway Age |chapter-url=https://books.google.com/books?id=aXFCAQAAIAAJ&pg=RA10-PA56 |volume=123 |publisher=Simmons-Boardman Publishing Company |date=20 September 1947 |pages=54–58 |chapter=Prestressed Concrete Bridge Beams Being Tested in England |access-date=2018-08-25 |archive-date=2021-04-17 |archive-url=https://web.archive.org/web/20210417201238/https://books.google.com/books?id=aXFCAQAAIAAJ&pg=RA10-PA56 |url-status=live}}</ref><ref>{{cite web |url=http://www-civ.eng.cam.ac.uk/cjb/4d8/public/history.html |title=History of Prestressed Concrete in UK |publisher=[[Cambridge University]] |date=2004 |access-date=25 August 2018 |archive-url=https://web.archive.org/web/20180825180324/http://www-civ.eng.cam.ac.uk/cjb/4d8/public/history.html |archive-date=2018-08-25 |url-status=dead}}</ref> One of the first bridges built in this way is the [[Adam Viaduct]], a railway bridge constructed 1946 in the [[UK]].<ref>{{NHLE |num=1061327 |desc=Adam Viaduct |access-date=2018-08-25}}</ref> By the 1960s, prestressed concrete largely superseded reinforced concrete bridges in the UK, with [[Box girder bridge|box girders]] being the dominant form.<ref>{{cite web |url=https://www.cbdg.org.uk/history.asp|website=Concrete Bridge Development Group |title=History of Concrete Bridges |access-date=2024-02-22}}</ref>

In short-span bridges of around {{convert|10|to|40|m|ft|-1}}, prestressing is commonly employed in the form of precast pre-tensioned [[girder]]s or planks.<ref name="MRWA">{{cite web |last1=Main Roads Western Australia |title=Structures Engineering Design Manual |url=https://www.mainroads.wa.gov.au/Documents/SE_Design_Manual_3_8_11.PDF |website=www.mainroads.wa.gov.au |publisher=MRWA |access-date=2016-09-02 |pages=17–23 |archive-date=2016-09-16 |archive-url=https://web.archive.org/web/20160916212247/https://www.mainroads.wa.gov.au/Documents/SE%20Design%20Manual%203_8_11.PDF |url-status=live}}</ref> Medium-length structures of around {{convert|40|to|200|m|ft|round=50}}, typically use precast-segmental, ''in-situ'' [[Cantilever bridge|balanced-cantilever]] and [[Incremental launch|incrementally-launched designs]].<ref>{{cite book |last1=LaViolette |first1=Mike |title=Bridge Construction Practices Using Incremental Launching |date=December 2007 |publisher=AASHTO |page=Appendix A |url=http://onlinepubs.trb.org/onlinepubs/archive/NotesDocs/20-07(229)_FR.pdf |access-date=7 September 2016 |archive-date=30 November 2016 |archive-url=https://web.archive.org/web/20161130190333/http://onlinepubs.trb.org/onlinepubs/archive/NotesDocs/20-07(229)_FR.pdf |url-status=live}}</ref> For the longest bridges, prestressed concrete deck structures often form an integral part of [[Cable-stayed bridge|cable-stayed designs]].<ref>{{cite journal |last1=Leonhardt |first1=Fritz |title=Cable Stayed Bridges with Prestressed Concrete |journal=PCI Journal |volume=32 |issue=5 |date=September 1987 |pages=52–80 |url=https://www.pci.org/Design_Resources/Guides_and_Manuals/References/Bridge_Design_Manual/JL-87-September-October_Cable_Stayed_Bridges_with_Prestressed_Concrete |doi=10.15554/pcij.09011987.52.80 |access-date=2016-09-07 |archive-url=https://web.archive.org/web/20160916234355/https://www.pci.org/Design_Resources/Guides_and_Manuals/References/Bridge_Design_Manual/JL-87-September-October_Cable_Stayed_Bridges_with_Prestressed_Concrete/ |archive-date=2016-09-16 |url-status=dead}}</ref>

====Dams====
Concrete dams have used prestressing to counter uplift and increase their overall stability since the mid-1930s.<ref>{{cite journal|last1=Roemermann|first1=A. C.|title=Prestressed Concrete Dams: 1936–1964|journal=PCI Journal|volume=10|date=February 1965|pages=76–88|url=http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1965/DOI_Articles/JL-65-FEBRUARY-4.pdf|access-date=2 September 2016|doi=10.15554/pcij.02011965.76.88|archive-date=16 September 2016|archive-url=https://web.archive.org/web/20160916100247/http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1965/DOI_Articles/JL-65-FEBRUARY-4.pdf|url-status=live}}</ref><ref name="Brown">{{cite journal|last1=Brown|first1=E. T.|title=Rock-engineering design of post-tensioned anchors for dams - A review|journal=Journal of Rock Mechnanics and Geological Engineering|date=February 2015|volume=7|issue=1|pages=1–13|doi=10.1016/j.jrmge.2014.08.001|doi-access=free|bibcode=2015JRMGE...7....1B }}</ref> Prestressing is also frequently retro-fitted as part of dam remediation works, such as for structural strengthening, or when raising crest or spillway heights.<ref name="Catagunya">{{cite web|last1=Institution of Engineers Australia|title=Catagunya Dam Tasmania|url=https://www.engineersaustralia.org.au/portal/system/files/engineering-heritage-australia/nomination-title/Catagunya_Dam.pdf|website=www.engineersaustralia.org.au|publisher=IEAust|access-date=2 September 2016|archive-date=14 September 2016|archive-url=https://web.archive.org/web/20160914132637/https://www.engineersaustralia.org.au/portal/system/files/engineering-heritage-australia/nomination-title/Catagunya_Dam.pdf|url-status=live}}</ref><ref>{{cite journal|last1=Xu|first1=Haixue|last2=Benmokrane|first2=Brahim|title=Strengthening of existing concrete dams using post-tensioned anchors: A state-of-the-art review|journal=Canadian Journal of Civil Engineering|date=1996|volume=23|issue=6|pages=1151–1171|url=https://www.researchgate.net/publication/237191178|access-date=2 September 2016|doi=10.1139/l96-925|archive-date=29 June 2021|archive-url=https://web.archive.org/web/20210629082836/https://www.researchgate.net/publication/237191178_Strengthening_of_existing_concrete_dams_using_post-tensioned_anchors_A_state-of-the-art_review|url-status=live}}</ref>

Most commonly, dam prestressing takes 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 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.<ref name="Cavill">{{cite journal|last1=Cavill|first1=Brian|title=Very High capacity Ground Anchors Used in Strengthening Concrete Gravity Dams|journal=Conference Proceedings|date=20 March 1997|page=262|publisher=Institution of Civil Engineers|location=London UK}}</ref>

====Silos and tanks====
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 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 the wall concrete, assisting in maintaining a watertight crack-free structure.<ref name="Priestley">{{cite journal|last1=Priestley|first1=M. J. N.|title=Analysis and Design of Prestressed Circular Concrete Storage Tanks|journal=PCI Journal|date=July 1985|pages=64–85|url=http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1985/DOI_Articles/jl-85-july-august-5.pdf|access-date=5 September 2016|doi=10.15554/pcij.07011985.64.85|archive-date=16 September 2016|archive-url=https://web.archive.org/web/20160916112233/http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1985/DOI_Articles/jl-85-july-august-5.pdf|url-status=live}}</ref><ref name="Ghali">{{cite book|last1=Ghali|first1=Amin|title=Circular Storage Tasnks and Silos|date=12 May 2014|publisher=CRC Press|isbn=978-1-4665-7104-4|pages=149–165|edition=Third|url=https://books.google.com/books?id=RYjNBQAAQBAJ&q=silo+tank+design+prestressed+concrete&pg=PA217|access-date=5 September 2016|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417194356/https://books.google.com/books?id=RYjNBQAAQBAJ&q=silo+tank+design+prestressed+concrete&pg=PA217|url-status=live}}</ref><ref name="Gilbert">{{cite book|last1=Gilbert|first1=R. I.|last2=Mickleborough|first2=N. C.|last3=Ranzi|first3=G.|title=Design of Prestressed Concrete to AS3600-2009|date=17 Feb 2016|publisher=CRC Press|edition=Second|url=https://books.google.com/books?id=8tSYCgAAQBAJ&q=silo+tank+design+prestressed+concrete|access-date=5 September 2016|isbn=978-1-4665-7277-5|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417194425/https://books.google.com/books?id=8tSYCgAAQBAJ&q=silo+tank+design+prestressed+concrete|url-status=live}}</ref>{{rp|61}}

====Nuclear and blast====
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 a proof-loaded, redundant and monitorable pressure-containment system.<ref name="Bangash">{{cite book|last1=Bangash|first1=M. Y. H.|title=Structures for Nuclear Facilities – Analysis, Design and Construction|date=2011|publisher=Springer|location=London|isbn=978-3-642-12560-7|pages=36–37|url=https://books.google.com/books?id=SOF6ZQfxulUC&q=nuclear+vessels+prestressed+concrete&pg=PA333|access-date=5 September 2016|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417194354/https://books.google.com/books?id=SOF6ZQfxulUC&q=nuclear+vessels+prestressed+concrete&pg=PA333|url-status=live}}</ref><ref name="Gerwick">{{cite book|last1=Gerwick|first1=Ben C.|title=Construction of Prestressed Concrete Structures|date=13 Feb 1997|publisher=John Wiley & Sons|location=New York|isbn=0-471-53915-5|pages=472–494|edition=Second|url=https://books.google.com/books?id=w1Ay2s9FtgoC&q=nuclear+containment+prestressed+concrete&pg=PA473|access-date=5 September 2016|archive-date=17 April 2021|archive-url=https://web.archive.org/web/20210417203921/https://books.google.com/books?id=w1Ay2s9FtgoC&q=nuclear%2Bcontainment%2Bprestressed%2Bconcrete&pg=PA473|url-status=live}}</ref><ref name="Raju">{{cite book|last1=Raju|first1=Krishna|title=Prestressed Concrete|publisher=Tata McGraw Hill|location=New Delhi|isbn=0-07-063444-0|edition=Fourth|url=http://clghub.com/wp-content/uploads/2016/07/Prestressed-Concrete.pdf|access-date=5 September 2016|date=2006-12-01|archive-date=11 September 2016|archive-url=https://web.archive.org/web/20160911184704/http://clghub.com/wp-content/uploads/2016/07/Prestressed-Concrete.pdf|url-status=live}}</ref>{{rp|585–594}}

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.

====Hardstands and pavements====
Heavily loaded concrete ground-slabs and pavements can be sensitive to cracking and subsequent traffic-driven deterioration. As 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.<ref name="Raju"/>{{rp|594–598}}<ref>{{cite web|title=Building Post-Tensioned Slabs on Grade|url=http://www.concreteconstruction.net/how-to/building-post-tensioned-slabs-on-grade_o|website=www.concreteconstruction.net|publisher=Concrete Construction|access-date=5 September 2016|archive-date=18 September 2016|archive-url=https://web.archive.org/web/20160918110855/http://www.concreteconstruction.net/how-to/building-post-tensioned-slabs-on-grade_o|url-status=live}}</ref>  Initial works have also been successfully conducted on 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.<ref>{{cite book|last1=Merritt|first1=David|last2=Rogers|first2=Richard|last3=Rasmussen|first3=Robert|title=Construction of a Precast Prestressed Concrete Pavement Demonstration Project on Interstate 57 near Sikeston, Missouri|date=March 2008|publisher=US DOT Federal Highway Administration|url=https://www.fhwa.dot.gov/pavement/concrete/pubs/hif08009/hif08009.pdf|access-date=5 September 2016|archive-date=15 September 2016|archive-url=https://web.archive.org/web/20160915234455/http://www.fhwa.dot.gov/pavement/concrete/pubs/hif08009/hif08009.pdf|url-status=live}}</ref>

Some notable civil structures constructed using prestressed concrete include: [[Sir Leo Hielscher Bridges|Gateway Bridge]], Brisbane Australia;<ref name="Gateway">{{cite web|last1=Connall|first1=John|last2=Wheeler|first2=Paul|last3=Pau|first3=Andrew|last4=Mihov|first4=Miho|title=Design of the Main Spans, Second Gateway Bridge, Brisbane|url=http://www.cmnzl.co.nz/assets/sm/3553/61/0037-Wheeler.pdf|website=www.cmnzl.co.nz|access-date=2 September 2016|archive-date=17 September 2016|archive-url=https://web.archive.org/web/20160917020811/http://www.cmnzl.co.nz/assets/sm/3553/61/0037-Wheeler.pdf|url-status=live}}</ref> [[Incheondaegyo|Incheon Bridge]], South Korea;<ref name="Incheon">{{cite web|last1=DYWIDAG|title=Incheon Bridge, Seoul, South Korea|url=https://www.dywidag-systems.at/en/projects/project-details/article/incheon-bridge-seoul-south-korea.html|website=www.dywidag-systems.a|publisher=DYWIDAG|access-date=2 September 2016|archive-date=10 August 2016|archive-url=https://web.archive.org/web/20160810063321/https://www.dywidag-systems.at/en/projects/project-details/article/incheon-bridge-seoul-south-korea.html|url-status=live}}</ref> [[Roseires Dam]], Sudan;<ref name="Roseires">{{cite web|title=SRG Remote Projects|url=http://www.srglimited.com.au/images/files/brochures/srg-remote-projects-brochure-2015-07-e.pdf|website=www.srglimited.com.au|publisher=SRG Limited|access-date=6 September 2016|page=10|archive-date=26 February 2017|archive-url=https://web.archive.org/web/20170226050940/http://www.srglimited.com.au/images/files/brochures/srg-remote-projects-brochure-2015-07-e.pdf|url-status=live}}</ref> [[Wanapum Dam]], Washington, US;<ref>{{cite journal|last1=Eberhardt|first1=A.|last2=Veltrop|first2=J. A.|title=1300-Ton-Capacity Prestressed Anchors Stabilize Dam|journal=PCI Journal|volume=10|issue=4|date=August 1965|pages=18–43|url=http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1965/DOI_Articles/JL-65-AUGUST-2.pdf|access-date=6 September 2016|doi=10.15554/pcij.08011965.18.36|archive-date=16 September 2016|archive-url=https://web.archive.org/web/20160916101504/http://www.pci.org/uploadedFiles/Siteroot/Publications/PCI_Journal/1965/DOI_Articles/JL-65-AUGUST-2.pdf|url-status=live}}</ref> [[South Hook LNG terminal|LNG tanks]], South Hook, Wales; [[Norcem Brevik|Cement silos]], Brevik Norway; [[Itz Valley Autobahn Bridge (Coburg)|Autobahn A73 bridge]], Itz Valley, Germany; [[Ostankino Tower]], Moscow, Russia; [[CN Tower]], Toronto, Canada; and [[Ringhals Nuclear Power Plant|Ringhals nuclear reactor]], Videbergshamn Sweden.<ref name="Bangash"/>{{rp|37}}

<gallery class="center" heights="120px" text-align:"left"="" perrow="5">
File:Gateway Bridge aerial4.JPG|[[Sir Leo Hielscher Bridges|Gateway Bridge]]<br/>Brisbane, Aust.
File:Incheon Grand Bridge.jpg|[[Incheondaegyo|Incheon Bridge]]<br/>South Korea
File:Itztalbruecke 2005-07-24.jpg|[[Itz Valley Autobahn Bridge (Coburg)|Autobahn A73]]<br/>Itz Valley, Germany
File:Ostankino Tower, 2015.JPG|[[Ostankino Tower]]<br/>Moscow, Russia
File:Toronto - ON - Toronto Harbourfront7.jpg|[[CN Tower]]<br/>Toronto, Canada
File:Norcem Brevik fra sjøen.JPG|[[Norcem Brevik|Norcem silos]]<br/>Brevik, Norway
File:Roseires Dam.jpg|[[Roseires Dam]]<br/>Ad Damazin, Sudan
File:Wanapum Dam from West Shore - downstream 10360031.jpg|[[Wanapum Dam]]<br/>Washington, US
File:Gas storage tanks at LNG terminal - geograph.org.uk - 1025438.jpg|[[South Hook LNG terminal|LNG tanks]]<br/>South Hook, Wales
File:Ringhals.JPG|[[Ringhals Nuclear Power Plant|Ringhals nuclear plant]]<br/>Videbergshamn, Sweden
</gallery>

==Design agencies and regulations==
Worldwide, many professional organizations exist to promote best practices in 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).<ref>[https://web.archive.org/web/19961220081344/http://www.pci.org/ Precast/Prestressed Concrete Institute]</ref> Similar bodies include the Canadian Precast/Prestressed Concrete Institute (CPCI),<ref>{{Cite web |url=http://www.cpci.ca/ |title=Canadian Precast/Prestressed Concrete Institute |access-date=12 September 2016 |archive-date=5 May 2021 |archive-url=https://web.archive.org/web/20210505153327/http://www.cpci.ca/ |url-status=live }}</ref> the UK's Post-Tensioning Association,<ref>{{Cite web |url=http://www.posttensioning.co.uk/ |title=Post-Tensioning Association |access-date=12 September 2016 |archive-date=19 September 2016 |archive-url=https://web.archive.org/web/20160919213154/http://www.posttensioning.co.uk/ |url-status=live }}</ref> the Post Tensioning Institute of Australia<ref>{{Cite web |url=http://www.ptia.org.au/ |title=Post Tensioning Institute of Australia |access-date=12 September 2016 |archive-date=25 September 2016 |archive-url=https://web.archive.org/web/20160925000347/http://www.ptia.org.au/ |url-status=live }}</ref> and the South African Post Tensioning Association.<ref>{{Cite web |url=http://www.sapta.co.za/ |title=South African Post Tensioning Association |access-date=12 September 2016 |archive-date=25 May 2016 |archive-url=https://web.archive.org/web/20160525015459/http://sapta.co.za/ |url-status=live }}</ref> Europe has similar country-based associations and institutions.

These organizations are not the authorities of [[building code]]s 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:
*European Standard [[EN 1992]]-2:2005 – [[Eurocode]] 2: Design of Concrete Structures;
* US Standard [[American Concrete Institute#ACI318|ACI318]]: Building Code Requirements for Reinforced Concrete; and
* [[Standards Australia|Australian Standard]] AS 3600-2009: Concrete Structures.

==See also==
{{Commons category|Prestressed concrete}}
{{columns-list|colwidth=30em|
* [[Cable stayed bridge]]
* [[Dyckerhoff & Widmann]] AG (Dywidag)
* [[Eugène Freyssinet]]
* [[Freyssinet Test Arch]]
* [[Glossary of prestressed concrete terms]]
* [[PC strand]]
* [[Prestressed structure]]
* [[Properties of concrete]]
* [[Segmental bridge]]
}}

==References==
{{Reflist}}

==External links==
* [http://www.sedhc.es/biblioteca/actas/CIHC1_130_Marrey%20B.pdf The story of prestressed concrete from 1930 to 1945: A step towards the European Union]
*[https://purl.fdlp.gov/GPO/gpo41564 Guidelines for Sampling, Assessing, and Restoring Defective Grout in Prestressed Concrete Bridge Post-Tensioning Ducts] [[Federal Highway Administration]]
* [http://www.arct.cam.ac.uk/Downloads/ichs/vol-2-1719-1740-anaya.pdf Historical Patents and the Evolution of Twentieth Century Architectural Construction with Reinforced and Pre-stressed Concrete]

{{Concrete navbox}}
{{Authority control}}
{{Use dmy dates|date=April 2017}}

[[Category:Building materials]]
[[Category:Concrete buildings and structures]]
[[Category:Reinforced concrete]]
[[Category:Structural engineering]]

[[fr:Béton#Béton précontraint]]
[[sv:Armerad betong#Spännarmerad betong]]