Glossary of prestressed concrete terms

This page is a glossary of Prestressed concrete terms.

A
actual extension: See measured extension.

anchor: anchorage: A rigid component, commonly constructed of cast iron, located at the end of a tendon and that directly transfers a tendon's force to the surrounding concrete.

anchor block: A rigid, usually circular, component placed over a bundle of prestressing strands at the end of a tendon, and that transfers the strand forces directly to the anchor component via tapered wedges located within its internal conical recess.

anchor centreline height: The positional dimension setting the height of an end-anchorage, usually measured vertically up from the formwork surface to the mid-depth of the anchor component.

anchor friction: The loss of prestressing force in the tendons due to friction generated by the strands sliding against the anchorage assembly during the tensioning operations.

anchor recess: A formwork blockout or recess former fitted to the edge formwork of a post-tensioned concrete member, and that creates a temporary void space external to the prestressing anchor to allow the anchor block or similar to be fitted after formwork stripping.

anchor set: See wedge set.

anchorage assembly: An assembly of components located at the end of a tendon and commonly comprising any employed combination of the anchor, anchor block, banana block, barrels, wedges, ducting transition, grouting tubes and anti-burst reinforcement.

anchorage zone: The region at the end of a tendon in the immediate vicinity of the anchorage, in which the most concentrated force transfer occurs between the anchor and the surrounding concrete.

anti-burst reinforcement: Unstressed reinforcement provided in the anchorage zones around individual tendons and/or grouped anchorages, which resists the secondary stresses created in the concrete from the applied prestressing forces.

B
banana: banana block: A short, curved anchor block sometimes fitted to a mono-strand stressed tendon, and that transfers the strand forces to the anchor via tapered wedges located within its internal conical recesses.

bar: See threaded bar.

barrel: A cylindrical component fitted over a single prestressing strand at an anchorage, and that transfers the strand force to the anchor via tapered wedges located within its internal conical recess. A set of barrels can be used with a mono-strand stressed tendon as an alternative to an anchor block.

block: See anchor block.

bond: The adhesion of concrete or grout to prestressing strands, wires or bars, or to unstressed reinforcement, either through friction or mechanical interlock.

bond strength: The resistance to separation of hardened concrete or grout from prestressing strands, wires or bars, or from unstressed reinforcement. Typically measured in the same units as concrete compressive strength.

bonded length: The length of that part of a prestressing tendon that is, or is to be, bonded to the surrounding concrete, either directly or via internal grouting of the tendon's ducting.

bonded tendon: bonded prestressing: A prestressing tendon that is, or is to be, permanently connected to the surrounding concrete along the full length between its end anchorages. Such connection may be directly, or via internal grouting of the tendon's ducting.

bripak: A portable frame structure commonly employed on site to support coils of prestressing strand and to facilitate the safe unloading of continuous lengths of strand into tendons or ducting.

bursting stresses: Localised stresses produced by prestressing forces in the anchorage zone of a prestressed member, and that tend to promote tensile rupture in the region immediately inboard of the anchorage.

C
cable: See tendon.

cable stay: See stay cable.

circular prestressing: An arrangement of prestressing where the tendons form partial or full sections of (usually horizontal and circular) arcs between end anchorages. Commonly used for the prestressing of tanks, silos and pipes.

conventional reinforcement: See unstressed reinforcement.

coupler: A rigid component, commonly constructed from cast iron, which is located at the end of a tendon and transfers the tendon force from the end of one tendon segment to another.

cut-off: See tendon cut-off.

D
de-bond: Prevent the bond of a prestressing tendon to the surrounding concrete.

de-bonded length: The length of that part of a prestressing tendon that is to remain permanently unbonded from the surrounding concrete.

dead end anchorage: A "passive" end anchorage of a prestressing tendon that does not have any jacking operations undertaken at that end.

de-stress: To release the prestressing forces within a tendon, usually in a controlled manner.

deviation point: deviator: A device or structural element that permanently deviates a tendon's profile at a location, for the purposes of producing a reactionary force against the concrete when the tendon is stressed. Used in pre-tensioned elements, and in external prestressing.

drape: See tendon drape.

draped tendon: Tendons that are profiled predominately to a curved profile between support points.

draw-in: See wedge draw-in.

duct: ducting: Encapsulating tube-like component, usually constructed from galvanised steel or polythene, which creates a void space within the concrete and surrounds the strands, wires or bar of a post-tensioned tendon.

duct chair: See tendon chair.

duct friction: The stress loss in a prestressing tendon resulting from friction between the tendon and duct during tensioning.

duct joiner: A component that securely connects separate segments of post tensioning ducting, commonly used when joining precast concrete segments in a prestressed structure.

dummy strand: A short length of prestressing strand pre-installed into ducting during concreting to maintain duct integrity. Occasionally used at some jointing arrangements.

E
eccentricity: The distance between the centre of gravity of the concrete cross-section and the centroid of its prestressing element(s), at any point along the member.

elastic modulus: See Young's Modulus.

elongation: See tendon extension.

end block: An end section of a prestressed member that houses one or more anchorage assemblies, and is often locally enlarged to reduce the applied anchorage stresses.

extension: See tendon extension.

external post-tensioning: Post-tensioning comprising tendons placed externally to the concrete structure, but connected to it at the end anchorages and profile-deviation points.

F
final stress: The final tensioning operation undertaken during post-tensioning, resulting in the design prestress level being established within the member.

flat duct: Ducting with an oval or "stadium" cross sectional shape. Such ducting is usually extruded (if plastic), or constructed from flat metal strip folded and joined with a longitudinal seam. Commonly used for mono-strand bonded tendons.

flat tendon: A prestressing tendon installed with no vertical or horizontal curvature. It forms a straight line between end anchorages.

friction loss: The loss of prestressing force in a tendon resulting from all frictional sources. The total friction loss in a tendon is the sum of duct friction loss and anchor friction loss.

full prestressing: Prestressing to a stress level such that, under design loads, no tensile stresses exist in the precompressed tensile zone of the member. Can be compared to partial prestressing.

G
grouting: The process of filling post-tensioning ducts with grout after tensioning.

grout tube: Tubular components connected to anchors or ducting through which grout is pumped and/or air is bled, during the process of grouting.

H
harped tendon: Tendons that are profiled predominately having lengths of straight tendon between points of significant angular deviation. Commonly employed in pre-tensioned elements, where the angular deviations are created by hold-down points in the casting bed.

high point: See tendon high point.

hoop tendon: A horizontally-curved tendon forming part or all of a circle, typically installed in vertically-spaced layers up the height of a prestressed tank or silo to resist hoop tensions generated by the stored contents.

I
initial stress: The first tensioning operation undertaken during post-tensioning, typically applied as soon as the concrete at the anchorage locations has attained sufficient strength to resist the resulting anchorage zone stresses.

J
jack: See stressing jack.

jack ram: The active hydraulic cylinder of a stressing jack, being the cylinder that extends from the body of the jack as the tendon strain increases.

jacking force: The prestressing force applied by the stressing jack to the tendons during tensioning.

L
lift-off load: The force required to be applied to an already-tensioned anchor block to lift it free of its associated anchor or bearing plate. This value represents the magnitude of prestressing force within the tendon at that point in time.

live end anchorage: A "active end anchorage of a prestressing tendon that has jacking operations undertaken at that end.

load balancing: A prestressed concrete design method in which the prestressing forces exerted upon the member act to balance a given proportion of the service loads that the member will be subjected to.

longitudinal prestressing: Prestressing forces acting along the longitudinal axis of the member.

low point: See tendon low point.

M
Macalloy bar: See threaded bar.

measured extension: The measured tendon elongation produced by tensioning operations on that tendon.

minimum prestress level: The (generally long-term) minimum level of residual prestressing stress within a member following tensioning and the actions of all time-dependent losses.

mono-strand: A prestressing system utilising tendons with single strands, or tendons able to be tensioned using a mono-strand jack.

mono-strand jack: A tensioning jack that applies force to a single tendon strand at a time.

multi-strand: A prestressing system utilising tendons with multiple strands, and are tensioned using a multi-strand jack.

multi-strand jack: A tensioning jack that applies force to a more than one tendon strand at a time.

O
offset: The eccentricity within a post-tensioning tendon between the centreline of the duct component and the centreline of the strand bundle.

onion dead end: A form of dead-end anchorage utilising strand "onions" or "bulbs" on the ends of each prestressing strand.

P
P/A level: The level of compressive stress present within an element due to prestressing forces. Derived from the prestressing force at that location divided by the cross-sectional area.

partial prestressing: Prestressing to a stress level such that, under design loads, tensile stresses are allowed to exist in the pre-compressed tensile zone of the member. Can be compared to full prestressing.

preload: A quantity of initial prestressing force applied to a tendon or structural element, prior to subsequent operations being undertaken.

pre-tensioning: pre-tensioned: A method of prestressing concrete where the tendons are tensioned before the concrete is placed.

post-tensioning: post-tensioned: A method of prestressing concrete where the tendons are tensioned after the concrete has attained a specified minimum strength or age.

prestress level: The level of compressive stress created within a prestressed concrete member as a result of prestressing.

prestressing: The introduction of internal stresses into structural concrete via tensioned tendons, to reduce potential tensile stresses in the concrete from applied loads.

primary grouting: The first, or only, stage of grouting for post-tensioned tendons. Multiple stages of grouting may be employed for doubly-encapsulated tendons such as re-stressable ground anchors.

profile: See tendon profile.

profiled tendon: A tendon that has been draped or harped to give it a non-flat profile between end anchorages.

pump: A device to provide hydraulic pressure for the operation of stressing jacks. Also a device to provide a supply of pressurised grout for the grouting of bonded tendons.

R
ram: See jack ram.

re-stressable: A prestressing tendon that can be re-tensioned, often permanently, following having been tensioned to its full design load.

round duct: Ducting with a circular cross sectional shape. Such ducting is usually extruded (if plastic), or constructed from flat metal strip helically-wound with a continuous helical seam. Common;ly used for multi-strand bonded and unbonded tendons.

S
secondary grouting: A second stage grouting operation for post-tensioned tendons, following the primary grouting of the duct. Usually associated with doubly-encapsulated tendons such as re-stressable ground anchors.

sheathing: material encasing prestressing steel in unbonded tendons to prevent it bonding to the surrounding concrete, to contain the anti-corrosion coating on the steel, and to provide corrosion protection.

spalling stresses: Localised stresses produced by prestressing forces in the anchorage zone of a prestressed member, which tend to promote tensile rupture in the region(s) midway between spaced anchorages.

stay cable: A external, double-encapsulated, unbonded tendon of bundled strands or wires, used for the support of deck structures on cable-stayed bridges.

stool: See stressing stool.

strand: High-strength (usually) steel wires wound helically around a centre wire, typically in a 7-wire arrangement.

strand bundle: The collection of prestressing strands within a single multi-strand tendon.

strand onion: A permanent deformation in the wires of a strand at one end, resulting in an open "bulb" arrangement of the wires so as to permit enhanced bonding of the strand

strand pusher: A device to forcefully push prestressing strand, utilised in the installation of strand into the ducting of post-tensioning tendons.

strand shears: A device, often hydraulic, to sever the excess length of strand protruding from an anchorage following tensioning.

stressing: See tensioning.

stressing jack: A device that tensions prestressed concrete tendons.

stressing stool: A device interposed between the stressing jack and the concrete member during tensioning operations, to allow manipulation of the anchor block and seating wedges. Often used during lift-off testing.

swage: A sturdy fitting surrounding a strand clamped onto the strand by compressive deformation. Once fitted, the force required to move the swage along the strand should be greater than the strand's breaking load.

swaged dead end: A form of dead-end anchorage utilising swages placed on each strand of the tendon, with all swages bearing onto a common dead-end bearing plate.

T
tendon: A complete assembly of a prestressing element, comprising one or more tensioned elements (bar, strand, wire, etc) that apply compression to surrounding concrete, along with any associated components such as ducting, anchorages, etc required to enclose and anchor these tensioned elements.

tendon chair: A component that positions and hold a tendon above the concrete formwork to make it comply with its required profile.

tendon cut-off: tendon cutting: The removal of excess tendon length from the end of a tendon following tensioning and lock-off.

tendon drape: The magnitude of vertical curvature of a profiled tendon between any two high points of its profile, usually given as the averaged vertical distance to the low point from the high points.

tendon elongation: tendon extension: The increase in length of a prestressing tendon due to the application of tensioning force.

tendon height: The vertical distance of a tendon from the member's soffit formwork. Usually measured to the underside of the duct or sheathing.

tendon high point: The maximum height of a tendon's profile (usually) over a support location, such a column, wall, pier, etc. Usually measured from the concrete soffit formwork to the underside of the tendon duct or sheathing.

tendon length: The distance between end anchorages of a tendon.

tendon low point: The minimum height of a tendon's profile between two consecutive high points, or high point and end anchorage, and commonly occurring in the midspan region of the element. Usually measured from the concrete soffit formwork to the underside of the tendon duct or sheathing..

tendon number: The identifying number given to a specific tendon within the set of tendons installed into the structure.

tendon profile: The physical path taken by a tendon between its end anchorages.

tendon spacing: The distance, horizontally or vertically as appropriate, between individual tendons within a set of parallel tendons when installed. Usually measured between tendon centrelines.

tendon termination: termination: The intentional severing and remediation of an already-installed and stressed post-tensioned tendon, such as to allow modifications to be made to an existing prestressed structure.

theoretical extension: The calculated tendon elongation predicted to result from stressing operations on that tendon.

threaded bar: A long, slender structural element, usually made from continuously threaded high-strength steel, and employed as a prestressing tendon.

time dependent losses: The loss of force in a prestressing tendon that occurs over time as the result of shrinkage, creep and relaxation actions.

transfer length: The distance required to fully transfer the bonded tendon's prestressing force to the surrounding concrete solely by bond.

transfer strength: The concrete compressive strength required to be achieved before force can be applied to the member from the jacking system.

transverse prestressing: Prestressing forces acting transversely to the longitudinal axis of the member.

U
unbonded tendon: unbonded prestressing: A tendon in which the tensioned element (strand, wire, etc) is unbonded from, and permanently free to move relative to, the surrounded concrete.

unstressed reinforcement: Bars, wires, strands, fibres or similar elements directly embedded into the concrete matrix such that they resist forces applied to it.

V
vertical prestressing: Prestressing forces acting in the vertical direction, or along the vertical axis of the member. Often employed in prestressed tanks, cores and tensioned columns.

W
wedge: wedges: Tapered high-strength steel component(s) with internal serrations that grip and hold prestressing strands during and after tensioning. Two or more wedges are placed around a strand and compress onto it as they are drawn into conical recesses in the anchorage during jack retraction.

wedge draw-in: wedge set: The movement of the anchorage wedges within the conical seating recesses of the anchor block or barrel during release of the jacking ram at the completion of tensioning. Such movement occurs as the strand load(s) is progressively transferred from the jack to the anchor, and results in a reduction in the prestressing force finally applied to the member.

wire: steel prestressing wire made from hot-rolled rods that is cold-drawn through dies to increase its strength.

wobble: Unintended angular deviations in a tendon's profile, resulting in additional friction losses during tensioning.

Y
yield strength: The stress at which a material exhibits a specific limiting deviation from the proportionality of stress to strain.

Young's Modulus: A mechanical property of linear-elastic solid materials that defines the relationship between stress and strain in the material.