ICC Prestressed Concrete SI flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Nominal strand area

Tabulated cross-sectional area of seven-wire strand based on nominal wire diameter; used for all design and elongation calculations instead of measured area.

Characteristic breaking load

Fpk equals nominal strand area times characteristic tensile strength fpk; the basis for anchorage efficiency and tensioning force calculations.

Low-relaxation strand

Strand with relaxation loss of about 2.5 percent or less after 1000 hours at 0.7 fpk and 20 degrees C, achieved by stabilising treatment during manufacture.

Anchorage efficiency requirement

A prestressing anchorage assembly must develop at least 95 percent of the actual breaking load of the strand in a static tensile test.

Wedge-type anchorage

Anchor head with tapered bore and split wedges that grip the strand by wedge action; load transfer depends on wedge seating, not on bond.

Button-head anchorage

Wire anchorage using an enlarged upset head bearing on a plate; heading temperature must be controlled to avoid embrittlement of the wire.

Relaxation test basis

Steel relaxation is measured at constant strain and initial load of 0.6, 0.7, or 0.8 fpk at 20 degrees C for 1000 hours, with permitted extrapolation.

Fatigue test of anchorage

Cyclic loading, commonly two million cycles between specified stress limits, followed by a static tensile test that must still meet the efficiency requirement.

Threaded bar tendon

High-strength alloy bar with threaded ends and nuts, coupled by threaded couplers; can be restressed and is used where bonded strand is unsuitable.

Duct internal diameter

Corrugated or plastic sheath bore must exceed the strand bundle envelope by a code-specified margin to allow threading and grout flow.

Transfer strength

Concrete strength at the time of prestress transfer, typically at least 0.6 to 0.7 of the specified transfer strength; verified by cylinders cured with the member.

Elastic shortening loss

Loss equal to modular ratio Ep/Eci times the average concrete stress at tendon level, using the modulus at transfer rather than at 28 days.

Creep and shrinkage drivers

Losses increase with low relative humidity, high volume-to-surface ratio, early age at loading, and high sustained stress in the concrete.

Steam curing temperature cap

Concrete temperature during steam curing is typically limited to about 60 to 65 degrees C to avoid later-age strength loss and thermal cracking.

Water-cement ratio for release

Prestressed mixes commonly use 0.35 to 0.40 water-cement ratio with rapid-hardening cement to achieve release strength at early age.

Chloride limit for prestressed

Acid-soluble chloride limits for prestressed concrete are stricter than for reinforced concrete because strand is prone to pitting and stress corrosion.

Elongation tolerance

Measured tendon elongation must fall within roughly plus or minus 5 to 7 percent of the calculated value; outside that band requires investigation.

Jacking force verification

Jacking force is confirmed by calibrated pressure gauge reading and by measured elongation; both records are required for each tendon.

Gradual release requirement

Pretensioning release must be gradual and symmetrical to prevent shock loading, strand slip, and end-zone cracking.

Grouting time limit

Post-tensioning ducts are grouted within a specified period after stressing, often 7 to 14 days, using approved grout and venting high points.

Tensioning record contents

Record tendon identification, jacking force, gauge pressure, measured elongation, anchorage slip, and ambient temperature at stressing.

Strand sampling frequency

Strand is sampled per lot mass, commonly one sample per 20 to 50 tonnes, for tensile, yield, elongation, and relaxation tests.

End-zone crack inspection

Horizontal cracks along the tendon path, anchorage spalling, and splitting cracks indicate inadequate confinement and require engineering review.

Camber as inspection tool

Camber measured after detensioning is compared with predicted values; unexpected low camber can indicate strand slip or loss of prestress.

Calibration interval

Jacks and pressure gauges are calibrated at defined intervals, commonly every six months or after repair, with records available at the plant.

Lifting point rule

Lift pretensioned members only at designer-specified points, usually near the ends; lifting elsewhere can overstress or crack the member.

Storage bearing support

Store members on dunnage at the designated bearing points, off the ground, avoiding stacking on strand or thin edges.

Dynamic lift allowance

Lifting inserts and loops are rated for member weight times a dynamic factor, commonly 1.25 to 1.5 times the static weight.

Inspector hold points

Concrete strength at transfer, tensioning, grouting, and final dimensional checks are hold points requiring inspector sign-off before proceeding.

Referenced steel standards

EN 10138 and ASTM A416 cover prestressing strand and wire; ASTM A722 covers high-strength bars; EN 13391 covers prestressing systems.

Nonconformance disposition

The inspector rejects non-conforming work, reports to the engineer of record, and does not allow the next step until disposition is approved in writing.

Traceability requirement

Each tendon and member must be traceable to heat numbers, mill certificates, test reports, and tensioning records; missing records are a compliance failure.