ICC Prestressed Concrete SI key terms

A group of high-strength steel wires twisted helically into a single tension member, commonly seven wires with one straight core and six wrapped around it, used to apply compressive force to concrete.

Strand manufactured and stabilized so that its loss of tension from creep under sustained load is greatly reduced, typically to about one-quarter of the loss in stress-relieved strand.

The standard prestressing strand configuration of six outer wires helically wrapped around a central king wire, giving a nominal area and diameter used in design tables.

A single drawn high-strength steel element, smaller in diameter than strand, used individually or grouped in anchorage systems for post-tensioning and for some pretensioned products.

A straight, hot-rolled, quenched and tempered steel bar with threads or upset ends, used for post-tensioning where a stiff, high-capacity tendon and threaded anchorage are wanted.

A tapered, hardened steel piece with serrated inner bore that grips the strand and seats in a conical hole in the anchor head, transferring tendon force into the concrete.

A block, usually steel, with conical holes that receive wedges and bear against a bearing plate, distributing post-tensioning tendon force into the concrete member.

An enlarged, formed end on a prestressing wire that bears against an anchor plate, used in wire tendon systems instead of wedges for gripping.

A threaded connector joining two lengths of high-strength prestressing bar end to end so that force can be transmitted continuously through the splice.

A complete assembly of prestressing steel, anchorage, and sheathing or duct that is stressed after the concrete has hardened and then usually grouted or left unbonded.

A method in which prestressing steel is tensioned against the casting bed before concrete is placed, and the force is transferred to the concrete by bond when the strands are released.

A post-tensioning tendon whose duct is filled with cementitious grout after stressing, so that prestressing steel and concrete act together through bond.

A post-tensioning tendon coated with corrosion-protective grease or wax and encased in a plastic sheath, so it can move relative to the concrete and is not bonded to it.

A metal or plastic tube cast into concrete to form a void that houses a post-tensioning tendon and, in bonded systems, later receives cementitious grout.

The plastic or coated covering around an unbonded tendon that contains corrosion-protective grease and prevents bond between steel and surrounding concrete.

A cementitious mixture placed into a duct after stressing to protect the steel from corrosion and to bond tendon and concrete together in a bonded system.

The gradual loss of stress in a prestressing steel held at constant length over time, caused by creep of the steel itself and influenced by initial stress and temperature.

The stress in the prestressing steel immediately after transfer or after stressing and seating, before time-dependent losses such as shrinkage, creep, and relaxation occur.

The stress remaining in the prestressing steel after all losses have occurred, used in service-load design checks for stresses, camber, and deflection.

The reduction of prestressing force over time from elastic shortening, concrete shrinkage, concrete creep, steel relaxation, anchorage seating, and friction in post-tensioning.

Immediate loss of prestress caused by the concrete compressing elastically when the prestressing force is applied, reducing the steel strain and therefore its stress.

Immediate loss of tendon force in post-tensioning as the wedges or anchorage settle into place when the jack is released, allowing a small inward movement of the strand.

The act of releasing pretensioned strands from the bed so their force is delivered to the hardened concrete through bond, usually done when concrete strength is sufficient.

The distance from the end of a pretensioned member over which the prestressing force is gradually transferred from steel to concrete by bond.

The length over which prestressing steel must be bonded to concrete to develop its design stress, including transfer length plus the flexural bond length beyond it.

The controlled operation of cutting or detensioning pretensioned strands, performed in a sequence that avoids shock, imbalance, or cracking of the concrete member.

Time-dependent deformation of concrete under sustained compressive stress, which shortens the member and reduces the stretch and stress in the prestressing steel.

Volume reduction of concrete as it dries and cures, which shortens a prestressed member and causes a loss of prestress in bonded systems.

The upward deflection built into or resulting from a prestressed member, produced by eccentric prestressing force and partly offset over time by creep and applied loads.

The distance between the centroid of the prestressing steel and the centroid of the concrete section, which controls the bending moment and camber produced by the prestress.

The temporary force applied by a hydraulic jack to a tendon during stressing, measured by calibrated gauge or load cell and corrected for friction and seating.

Field measurement of tendon stretch during stressing, compared with calculated elongation to verify that the intended force has been developed and friction assumptions are correct.

Friction loss in a post-tensioning tendon caused by unintended small angular deviations along its length, growing with distance from the jacking end.

Friction loss in a post-tensioning tendon caused by its intended curvature, proportional to the total angle change between jacking end and the point considered.

The least distance from the surface of prestressing steel or duct to the concrete surface, specified to protect steel from corrosion and to provide fire resistance.

The amount of chloride ion in concrete, limited by code because high levels promote corrosion of embedded steel, particularly in prestressed members where it is restricted severely.

Accelerated curing in which cast members are held in a moist steam environment under a controlled temperature cycle to speed strength gain before strand release.

The rigid casting surfaces and long stressing bed that hold pretensioned strand at tension and shape the concrete until it hardens sufficiently for release.

A factory-produced, prestressed concrete foundation element that must be lifted, stored, transported, and driven without overstressing it at any handling stage.

A designated location on a prestressed member where it may be picked up, chosen so that handling stresses and camber remain within design limits.