Post-Tensioning Terminology

Mohammed Zaid
Posted on : 22 Feb 2016

Adopted From TAB.3-13 Post-Tensioning Terminology (PTT)

Anchor - For unbonded single strand tendons, a device that houses the wedges and transfers the prestressing force to the concrete.

Anchorage assembly - A mechanical device consisting of all components required to transfer the posttensioning force from the prestressing steel to the structure, including all accessories for encapsulation or grouting.

Anchorage stressing- The anchorage at one or both ends of a tendon that is used for stressing.

Back-up bars- For unbonded single strand tendons, minimum nonprestressed reinforcement parallel to slab edge used to resist tensile forces in the concrete caused by the applied prestressing force.

Bursting steel-For unbonded single strand tendons, nonprestressed reinforcement used to resist the tensile forces in the concrete caused by the applied prestressing force from multiple anchorages.

Confinement reinforcement-Nonprestressed reinforcement, typically a spiral, in the local anchorage zone.

Duct-A conduit to accommodate prestressing steel installation and provide an annular space for grouting.

Inlet-Tubing with connection to duct used for injection of the grout into the duct.

Local zone reinforcement-For multistrand tendons, nonprestressed reinforcement used as confinement reinforcement of the local anchorage zone.

Monostrand (Single Strand) - Tendon with one strand.

Multistrand-Tendon with more than one strand.

Outlet-Tubing with connection to duct used to allow the escape of air, grout, and bleed water from the duct.

Pocket former-A device that forms a temporary recess in the concrete to allow access for stressing.

Sheathing-For unbonded single strand tendons, an enclosure in which prestressing steel is encased to prevent bond with surrounding concrete that provides corrosion protection and contains PT coating.

Strand-High strength steel wires wound around a center wire, typically seven-wire strand, conforming to ASTM A416/A416M.

Strand tail-The protruding length of the strand outside of the wedges that remains in place after the tendon tail has been cut off.

Stress bar-High strength steel bar used in post-tensioning conforming to ASTM A722 / A722 M.

Stressing pocket-The recess created by the pocket former between the stressing or intermediate anchorage and the edge of the concrete to allow the nosepiece access for stressing.

Tendon-A complete assembly of a prestressing element consisting of anchorages and couplers, prestressing steel, and sheathing or duct with PT coating for unbonded applications or grouted ducts, grout caps, and grout vents for bonded applications.

Bonded tendon-Tendon in which prestressing steel is bonded to the concrete and is permanently prevented from moving relatively to the concrete.

Unbonded tendon-Tendon in which the prestressing steel is prevented from bonding to the concrete, and is permanently free to move relatively to the concrete. The prestressing force is transferred to the concrete only by the anchorages or deviators.

Encapsulated tendon-A tendon that is completely enclosed in a watertight covering from end to end, including anchorages, sheathing with PT coating and an encapsulation cap over the strand tail at each end.

Temperature tendon-Tendon used to resist shrinkage and temperature stresses.

Added tendon-Tendon, usually short in length, added to continuous tendons and placed in specific locations, such as end bays, to increase the local prestressing force.

Banded tendons-Closely spaced groups of tendons in a narrow strip in one direction in two-way floor systems, typically centered on column or support lines.

Distributed tendons-Single tendon or groups of tendons, uniformly spaced in one direction, typically perpendicular to banded tendons or to beams.

Tendon tail-The protruding length of the tendon outside of the stressing anchorage needed temporarily for stressing of the tendon.

Trumpet-Connection piece between bearing plate and duct, in which the strands transition from the wedge plate pattern into a tight bundle inside the duct.

Wedges-Pieces of tapered high-strength heat-treated steel with serrations (teeth) that penetrate the prestressing steel during transfer of prestressing force. Some anchorage systems use two-part wedges and some use three-part wedges.

Wedge cavity-The tapered opening in the anchor or wedge plate designed to allow the strand passing through and to accommodate the seating of the wedges.

Wedge plate-For multistrand tendons, a device that houses the wedges and transfers the prestressing force to a bearing plate.

Stressing equipment-Equipment used for stressing tendons, consisting of a hydraulic jack and gauge(s) calibrated as a unit, and a hydraulic pump.

Jack, monostrand-A mechanical device (normally hydraulic) used to apply force to a single strand.

Nosepiece-The front part of the monostrand jack that bears against the anchor in order to align

Jacking force-The specified temporary force exerted by the stressing jack on the tendon during stressing.

Partial stressing-Stressing of tendons to a force less than the full jacking force before the concrete reaches the concrete strength required for full stressing. Normally used to mitigate cracking due to plastic shrinkage and restraint to shortening.

Stage stressing-Stressing of tendons at different times instead of stressing at one time.

Anchorage zone-The portion of the member through which the concentrated prestressing force is transferred to the concrete and distributed across the section. It includes the local and general anchorage zones.For anchorage devices located away from the end of the member, the anchorage zone includes the disturbed regions behind and ahead of the anchorage.

Local anchorage zone-The prismatic region in which the concentrated prestressing force is introduced into the concrete, surrounding the bearing plate including confinement reinforcement and the minimum concrete cover. The length of the local anchorage zone extends over the confinement reinforcement.

General anchorage zone-The region in which the concentrated prestressing force spreads out over the cross section of the structural member (Saint Venant Region). It includes the local anchorage zone. The general anchorage 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 anchorage zone is equal to the overall depth of the member.

Balanced moments-Moments caused by balanced loads.

Balanced loads-Loads applied to the member by the prestressing tendon.

Barrier cable-A vehicular barrier and/or pedestrian guard consisting of a group of parallel high-strength steel strands.

Eccentricity-Distance between the center of gravity of the concrete cross-section and center of gravity of the prestressing steel (CGS) at any point along the length of a member.

Elongation-Increase in length of prestressing steel due to the stressing force.

Friction loss-The loss of force in prestressing steel resulting from friction between the prestressing steel and its enclosure, affected by the angular deviation of the tendon.

Effective Prestress-Stress in a member due to final effective force.

Final effective force-Force in prestressing steel after all prestress losses.

Initial losses-The loss of force in a prestressing tendon that occurs during stressing resulting from friction losses, elastic shortening of concrete, and seating loss.

Initial stress-Stress in the prestressing steel immediately after anchor set.

Post-tensioning-Method of prestressing in which prestressing steel is tensioned after concrete has

PT Installation Drawings-Drawings furnished by the PT supplier showing information about the specifics of the PT system and tendon placement including, but not limited to the number, size, length, marking, location, elongation and profiles.

PT supplier-Contracting entity responsible for furnishing and delivering to the job site all components of the PT system including PT installation drawings and stressing equipment.

Post-tensioning system (PTS)-A tendon of a particular size, including prestressing steel, anchorages, local anchorage zone reinforcement, duct, trumpets, couplers, grout caps, inlets, outlets, etc. all supplied by a single PT supplier.

Prestressed concrete-Structural concrete in which internal compressive stresses are induced by means of prestressed reinforcement to reduce tensile stresses in the concrete due to applied loads.

Prestressing steel-High-strength steel used to prestress concrete, consisting of seven-wire strands, bars, wires, or groups of such elements.

Pretensioning-Method of prestressing in which prestressing steel is tensioned before the concrete is placed.

Primary moments-Prestressing force multiplied by eccentricity at any point along the tendon profile.

Seating loss-The loss of force in prestressing steel resulting from anchor set.

Secondary effects-Moments, shears and axial loads generated in an indeterminate member as a result of restraint of the member's supports to free movement of the member due to prestressing.

Secondary moments-Moments caused by reactions to balanced loads only.

Tendon support system-The support bars, chairs, slab bolsters and other accessories required to maintain the tendon profile.

Tendon profile-The specified path of a tendon from end to end in a member.

Detensioning-A method for releasing the force in a stressed tendon.

Time dependent losses-The loss of force in a prestressing tendon that occurs over time resulting from concrete shrinkage and creep, and relaxation in the prestressing steel.

Wobble friction-Friction due to unintended angular deviations in the tendon profile.





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