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Post-Tensioning Manual
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Definitions in this manual pertaining to post-tensioned bridges are generally in accordance with the AASHTO Standard Specifications for Highway Bridges, the AASHTO Guide Specifications for Design and Construction of Segmental Concrete Bridges, and the Post -Tensioning Institute Specification for Grouting of Post-Tensioned Structures or similar (State Departments of Transportation) specifications.
Actual Ultimate Tensile Strength: The actual breaking strength obtained in tests of a single representative strand or bar, breaking outside the anchorage. For multi-strand or bar tendons, AUTS equals the AUTS of a single tendon element (strand, bar) times the number of such elements in the tendon. Representative samples must be from the same coil of strands or the same bar from which strands or bars are cut and used in connection efficiency tests. (Reference PTI "Acceptance Standards for Post Tensioning Systems". See also, "GUTS" and MUTS".)
Anchor nut: The threaded device that screws onto a threaded bar and transfers the force in the bar to the bearing plate.
Anchor plate: That part of the anchorage hardware that bears directly on the concrete and by which the tendon force is transmitted to the structure.
Anchorage: An assembly of various hardware components that secure a tendon at its ends after it has been stressed and imparts the tendon force into the concrete.
Anchorage zone: The general expression for combined general and local zones; see General zone, Local zone.
Anticipated Set: This is that set which was assumed to occur in the design calculation of the post-tensioning forces immediately after load transfer; see Set.
Bar: Post-tensioning bars are high strength steel bars, normally available from 16mm to 44mm (5/8 to 1-3/4in) diameter and usually threaded with very coarse thread.
Basic bearing plate: Flat plate bearing directly against concrete meeting the analytical design requirements. Covered by this definition are square, rectangular, or round plates, sheared or torch cut from readily available steel plate, normally ASTM A 36.
Bearing plate: This is the steel hardware that transfers the tendon force into a structure.
Confinement reinforcement: Non-prestressed reinforcement in the local zone. Confinement reinforcement in the concrete ahead of tendon anchorages is limited to the local zone. Confinement reinforcement consists of spirals, orthogonal reinforcing bars, or a combination of both. For basic bearing plates confinement reinforcement is required in that volume of concrete in which compressive stresses exceed acceptable limits for unreinforced concrete as determined by rational analysis. For special bearing plates, confinement reinforcement is system dependent as determined by tests on individual anchorages. Test block reinforcement, in the portion surrounding the special bearing plate and immediately ahead of it, must represent the confinement reinforcement required in the local zone for that particular system.
Coupler: The means by which the prestressing force may be transmitted from one partial-length prestressing tendon to another.
Duct: Material forming a conduit to accommodate post-tensioned tendon installation and provide an annular space for grout. Post-tensioning ducts consists of spiral-wound corrugated sheet metal, corrugated plastic tubing, metal pipe, or plastic pipe. Post-tensioning ducts are used for external and internal tendons.
Family of Systems: Group of post-tensioning systems for various tendon sizes and unique tendon type with similar tendon components produced by a single supplier.
General zone: The region in which the concentrated prestressing force spreads out to a more linear stress distribution over the cross section of the structural member (Saint Venant Region). It includes the local zone. The general zone extends from the anchorage along the axis of the member for a distance equal to the overall depth of the member. The height of the general zone is equal to the overall depth of the member.
Guaranteed Ultimate Tensile Strength: This is the tensile strength of the material that can be assured by the Manufacturer. GUTS is should not be confused with "f PU" the specified ultimate tensile strength (AASHTO LRFD). (The term "GUTS" has been replaced by two definitions, "MUTS" and "AUTS" by the Post-Tensioning Institute.)
Local zone: The local anchorage zone is the volume of concrete surrounding and immediately ahead of the anchorage device where concrete compressive stresses exceed acceptable values for unconfined concrete (concrete without confinement reinforcement). The local zone is defined as a rectangular prism of concrete surrounding the bearing plate and any integral confinement reinforcement. The transverse dimensions of the prism are equal to those of the bearing plate, including any integral confinement reinforcement, plus the supplier's specified minimum edge covers. The length of the local zone extends over the confinement reinforcement. For anchorage devices with multiple bearing surfaces, the local zone extends over the distance from the loaded concrete surface to the bottom of each bearing surface of the anchorage device plus the maximum dimension of that bearing surface.
Minimum Ultimate Tensile Strength: When measured as a force, for a single strand or bar breaking outside of the anchorage or the multiple of those single strand or bar forces for multi-strand or bar tendons; MUTS is the force equal to the nominal cross-sectional area of strand, or bar, times their nominal ultimate tensile stress. (Reference PTI "Acceptance Standards for Post Tensioning Systems". See Also, AUTS and GUTS.)
Post-Tensioning: The application of a compressive force to the concrete by stressing tendons or bars after the concrete has been cast and cured. The force in the stressed tendons or bars is transferred to the concrete by means of anchorages.
Post-Tensioning Scheme or Layout: The pattern, size and locations of post-tensioning tendons shown by the Engineer of Record on the Contract Plans.
Post-Tensioning System: This is the proprietary system where the necessary hardware (anchorages, wedges, strands, bars, couplers, etc.) is supplied by a particular manufacturer or manufacturers of post-tensioning components and may also include ducts and local zone reinforcement. This may also refer to the stressing equipment.
Prestressing steel: The steel element of a post-tensioning tendon, which is elongated and anchored to provide the necessary permanent prestressing force.
Set: The total movement of a point on the strand just behind the anchoring wedges during load transfer from the jack to the permanent anchorages. Set movement is the sum of slippage of the wedges with respect to the anchorage head and the elastic deformation of the anchor components. For bars, set is the total movement of a point on the bar just behind the anchor nut at transfer and is the sum of slippage of the bar and the elastic deformation of the anchorage components.
Sheathing: General term for the duct material surrounding the prestressing element to provide corrosion protection or conduit for installation.
Special bearing plate: Any hardware that transfers tendon anchor forces into the concrete but does not meet the analytical design requirements. Covered by this definition are devices having single or multiple plane bearing surfaces, and devices combining bearing and wedge plate in once piece. They normally require confinement reinforcement.
Strand: An assembly of several high strength steel wires wound together. Strands usually have six outer wires wound in long-pitch helix around a single straight wire of a similar diameter.
Tendon: A single or group of prestressing elements and their anchorage assemblies, which impart a compressive force to a structural member. Also included are ducts, grouting attachments and grout. The main prestressing element is usually a high strength steel member made up of a number of strands, wires or bars.
Tendon size: The number of individual strands of a certain strand diameter or the diameter of a bar.
Tendon type: The relative location of the tendon to the concrete shape, internal or external and structural function, i.e., draped, cantilever or continuity.
Wedge: Small conically shaped steel components placed around a strand to grip and secure it by wedge action in a tapered hole through a wedge plate.
Wedge Plate: A circular steel component of the anchorage containing a number of tapered holes through which the strands pass and are secured by conical wedges.
Wire: A single, small diameter, high strength steel wire, typically the basic component of strand.
Admixture: A material, usually a liquid or powder, that is used as an ingredient of the cementitious grout and is added immediately before or during mixing.
Bleed: The autogenous flow of mixing water within or its emergence from, newly placed grout, caused by the settlement of the solid materials within the mass.
Contamination: Any foreign material found in a tendon at any point in time.
Cavitation: Air trapped during the grouting process through an irregular flow of grout through the duct. Cavitation can occur when grouts are injected from high points in the tendon profile or by a poor combination of grouting rate and viscosity, in which the grout traps air as it moves to the low point and does not completely fill the duct.
Final Set: A degree of stiffening of the grout mixture greater than the initial set, indicating the time required for the grout to stiffen sufficiently to resist, to an established degree, the penetration of a weighted test needle.
Fluidity: A measure of time, expressed in seconds necessary for a stated quantity of grout to pass through the orifice of a flow cone.
Grout: A mixture of cementitious materials and water with or without mineral additives or admixtures, proportioned to produce a consistency that may be pumped without segregation of the constituents when injected into the duct to fill the space around the prestressing steel.
Grout Cap: A device which contains the grout and forms a protective cover sealing the post-tensioning steel at the anchorage.
Initial Set: A degree of stiffening of the grout mixture less than the final set, indicating the time required for the grout to stiffen sufficiently to resist, to an established degree, the penetration of a weighted test needle.
Inlet: Tubing or duct used for injection of the grout into the duct.
Outlet: Tubing or duct to allow the escape of air, water, grout and bleed water from the duct.
Permeability to Chloride: A measure of the grout's ability to resist chloride ion penetration.
Potable Water: Water as defined by EPA (Environmental Protection Agency) drinking water standards.
Pressure Rating: The maximum pressure that water in a duct or in a duct component can exert continuously with a high degree of certainty that failure of the duct or duct component will not occur (sometimes referred to as working pressure).
Recharge: The ability of water, outside of the post-tensioning tendon, to migrate through some path and enter the tendon, usually, through the anchorage or at a breach in the duct.
Set Time: The lapsed time for the addition of mixing water to a cementitious mixture until the mixture reaches a specified degree of rigidity as measured by a specific procedure.
Setting: The process, due to the chemical reactions, occurring after the addition of mixing water, which results in a gradual development of rigidity of a cementitious mixture.
Thixotropic: The property of a material that enables it to stiffen in a short time while at rest, but to acquire a lower viscosity when mechanically agitated.
Volume Change: The change in volume produced by continued hydration of cement, exclusive of effects of the applied load and change in thermal or moisture content.
Water-Reducing Admixture: An admixture that either increases the slump of freshly mixed grout without increasing the water content or that maintains the slump with reduced amount of water due to factors other than air entrainment.
Construction Engineering and Inspection (CEI): The person, firm, or organization engaged by the Owner to act as the Owner's representative and be responsible for the overall technical oversight and contract administration to ensure that the project is constructed in accordance with the contract plans, specifications and other contract documents.
Contractor: The person, firm, or organization who enters into a contractual agreement with the Owner to construct the project and who has the prime responsibility for the overall construction of the project in accordance with the contract plans, specifications and other contract documents.
Design-Bid-Build: A process where an Owner engages a designer (Engineer of Record) to produce a complete and final set of Plans, Specifications, Estimates and other Contract Documents to let for open bid by Contractors. The Owner then enters into a contract with the winning or qualified bidder for the construction of the project. The Engineer of Record is independent of the Contractor and may be retained by the Owner to provide reviews or other engineer services during construction.
Design-Build: A process where an Owner invites technical, priced and time scheduled proposals for the complete design and construction of a project to meet an established set of specific, Owner defined, requirements. The Owner then enters into a contractual agreement with the qualifying bidder to design, construct and deliver the completed project in accordance with those requirements. The Engineer of Record (designer) is a member of the Design-Build team.
Engineer of Record: The person, firm, or organization engaged by the Owner to prepare the design, contract plans, specifications or other contract documents for the construction of the project.
Owner: The person, firm, or organization that initiated the design and construction of the project, provides or arranges for funding, is responsible for partial and final payments and who will take possession and ownership of the project upon completion.
Quality Assurance: Actions taken by an Owner or his representative to provide assurance that what is being done and what is being provided are in accordance with the specifications and applicable standards of good practice for the work.
Quality Control: Actions taken by the Contractor to provide control over what is being done and what is being provided to ensure that the specifications and applicable standards of good practice for the work are being followed.
Sub-Contractor: A person, firm, or organization engaged by the Contractor to provide selected construction activities, materials or other specialized construction or engineering services.
AASHTO: American Association of State Highway and Transportation Officials (For publications: 444 North Capitol Street, N.W., Suite 249, Washington, DC 20001; www.transportation.org)
API: American Petroleum Institute - (For documents, contact API Publications, Global Engineering Documents, 15 Inverness Way East, M/S C303B, Englewood, Co, 80112-5776, U.S.A., Phone: 303-397-7956, Fax: 303-379-2740, Internet: www.global.ihs.com)
ASBI: American Segmental Bridge Institute - (For documents, contact: American Segmental Bridge Institute, 9201 N. 25th Avenue, Suite 150B, Phoenix, Az., 85021-2721, Phone: 602-997-0064, Fax: 602.997.9965, Internet: www.asbi-assoc.org)
ASTM: American Society for Testing and Materials - (For documents, contact ASTM, 100 Bar Harbor Drive., West Conshohocken, Pa., 19428-2959, U.S.A., Phone: 601-832-9585, Fax: 610-832-9555, Internet http://www.astm.org)
AUTS: Actual Ultimate Tensile
BC: Balanced Cantilever
CIP: Cast-in-Place
CIPBC: Cast-in-Place Balanced Cantilever
EPDM: Ethylene Propylene Deine Monomer (see "External Duct Connections" Chapter 4)
GUTS: Guaranteed Ultimate Tensile Strength.
HDPE: High Density Polyethylene (see "Ducts for Tendons", Chapter 4).
HDPP: High Density Polypropylene (see "Ducts for Tendons", Chapter 4).
I-Girder: A girder (beam), usually precast, typically of a cross-section in the form of an "I" albeit a standard AASHTO I-girder or other section. In the general sense, the term "I-girder" also includes "bulb-T" beams, single and double "T beams", "U-beams" (tubs) and other similar precast or cast-in-place sections. Cast-in-place sections include boxes, slabs and voided slabs that contain post-tensioning tendons.
MUTS: Minimum Ultimate Tensile Strength
PC: Precast
PCBC: Precast Balanced Cantilever
PCSS: Precast Span-by-Span
PT: Post-Tensioning
PTI: Post-Tensioning Institute - (For documents, contact, Post-Tensioning Institute, 8601 North Black Canyon Highway, Suite 103, Phoenix, Arizona 85021, Phone: 602-870-7540, Fax: 602-870-7541, Internet: www.post-tensioning.org)
SS: Span-by-Span
