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ICC Prestressed Concrete SI study materials
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ICC Prestressed Concrete SI practice questions

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Question 1Prestressing Materials and Components

In a post-tensioning system, what is the primary function of the anchorage assembly?

  1. To provide the ductile link between precast segments
  2. To reduce friction losses between the tendon and the duct
  3. To transfer the prestressing force from the tendon to the concrete Correct answer.
  4. To protect the tendon from corrosion along its free length

Explanation

The anchorage is the mechanical device that grips the tendon and bears against the concrete, transferring the jacking force into the member. Corrosion protection and friction reduction are handled by sheathing, ducts, and grout, not by the anchorage itself.

Question 2Prestressing Materials and Components

Which tendon type bonds directly to the surrounding concrete along its full length once the concrete has hardened?

  1. External tendon in a free-length duct
  2. Grouted stay cable
  3. Unbonded post-tensioned strand
  4. Pre-tensioned strand Correct answer.

Explanation

In pre-tensioning, strands are stressed before the concrete is cast and bond directly to the concrete after release. Unbonded and external tendons rely on anchorages and deviators for force transfer rather than direct bond along their length.

Question 3Prestressing Materials and Components

A 7-wire prestressing strand is designated by which two properties in common SI product standards?

  1. Ultimate tensile strength and relaxation class
  2. Nominal diameter and nominal cross-sectional area Correct answer.
  3. Coating thickness and lay length
  4. Yield stress and elongation at fracture

Explanation

Strand is normally specified and ordered by nominal diameter together with the corresponding nominal steel area, from which the guaranteed breaking load follows for a given grade. Coating, lay length, and relaxation class are supplementary attributes rather than the primary designation.

Question 4Prestressing Materials and Components

What does the relaxation of a prestressing tendon describe?

  1. The loss of stress in a tendon held at constant length over time Correct answer.
  2. The creep of the anchorage head into the concrete
  3. The slip of the wedge during load transfer
  4. The elastic shortening of the concrete under sustained compression

Explanation

Relaxation is the time-dependent loss of stress in steel held at essentially constant strain, and it is measured in a relaxation test at a stated initial load. Elastic shortening, anchorage set, and creep of concrete are separate loss mechanisms.

Question 5Prestressing Materials and Components

Which material is commonly used for the ducts of internal post-tensioned tendons in bridge and building work?

  1. Uncoated high-strength strand wound into a helix
  2. Plain mild steel plate welded into rectangular boxes
  3. Cast iron pipe sections joined with threaded couplings
  4. Corrugated galvanized steel or plastic sheathing Correct answer.

Explanation

Internal post-tensioning ducts are typically thin corrugated steel or plastic sheathing, which provides a void for the tendon and allows grout to be pumped after stressing. The corrugations improve bond and stiffness, and plastic ducts also serve as a corrosion barrier.

Question 6Prestressing Materials and Components

What is the purpose of a grout vent in a post-tensioning duct?

  1. To hold the tendon in its design profile during concreting
  2. To allow air and excess grout to escape so the duct can be fully filled Correct answer.
  3. To measure the stress in the tendon after transfer
  4. To inject additional prestressing force after seating

Explanation

Vents are located at high points and at the ends of the duct so that air can be expelled ahead of the grout and complete filling can be verified. Without adequate venting, voids can remain and compromise corrosion protection and bond.

Question 7Prestressing Materials and Components

In pre-tensioned members, what is the function of the end anchor plates used in some systems at the ends of the strands?

  1. To distribute the concentrated release force into the concrete over a larger area Correct answer.
  2. To allow the strand to be coupled to a subsequent strand
  3. To provide a bearing surface for the lifting hook
  4. To seal the member against water ingress

Explanation

At release, the transfer of force from strand to concrete is highly concentrated near the member ends, and anchor plates or similar end fittings spread that force to control splitting. They are not coupling devices, seals, or lifting points.

Question 8Prestressing Materials and Components

Which property of prestressing strand distinguishes it from ordinary reinforcing bar of similar diameter?

  1. Much higher tensile strength with no distinct yield plateau Correct answer.
  2. Lower modulus of elasticity
  3. Much higher ductility under cyclic loading
  4. A well-defined yield point followed by strain hardening

Explanation

Prestressing strand is cold-drawn to very high tensile strength and shows a smooth stress-strain curve without a defined yield plateau, which is why a proof stress is used. Its modulus is similar to reinforcing steel, and its ductility is lower rather than higher.

Question 9Prestressing Materials and Components

A designer specifies low-relaxation strand for a post-tensioned floor. What does this specification primarily control?

  1. The creep coefficient of the concrete
  2. The anchorage seating loss at transfer
  3. The time-dependent stress loss in the tendon under sustained load Correct answer.
  4. The friction coefficient along the duct

Explanation

Low-relaxation strand is manufactured and tested to limit stress loss under sustained load, typically to a much lower value than standard strand. Anchorage set, duct friction, and concrete creep are governed by other design parameters.

Question 10Prestressing Materials and Components

Why is the wedge set of an anchorage important in the design of a post-tensioned tendon?

  1. It governs the corrosion protection class of the anchorage
  2. It increases the breaking load of the tendon
  3. It causes a short-term loss of prestress that must be added to the jacking force Correct answer.
  4. It reduces the friction between strand and duct

Explanation

When the jack is released, the wedges seat into the anchor head and the tendon retracts slightly, producing an anchorage set loss. Designers account for this by over-jacking or by deducting the loss in the stress calculation.

Question 11Prestressing Materials and Components

In a bonded post-tensioned member, what is the main structural benefit of grouting the ducts after stressing?

  1. It bonds the tendon to the concrete and provides corrosion protection Correct answer.
  2. It increases the initial jacking force available
  3. It allows the tendon to be restressed in future
  4. It eliminates all long-term relaxation of the strand

Explanation

Grout fills the duct, bonds the tendon to the surrounding concrete so that strain compatibility governs behavior, and passivates the steel against corrosion. It does not raise jacking force, remove relaxation, or facilitate future restressing.

Question 12Prestressing Materials and Components

A post-tensioned beam uses a duct with a high wobble coefficient. What effect does this have on the tendon stress along its length?

  1. Prestress remains constant along the tendon
  2. Prestress decreases more rapidly with distance from the jack Correct answer.
  3. Prestress is unaffected but anchorage set doubles
  4. Prestress increases toward the far end

Explanation

The wobble coefficient accounts for unintended curvature of the duct, and a higher value increases the friction loss per unit length, so stress falls more steeply away from the jack. The effect is cumulative and is separate from anchorage set.

Question 13Prestressing Materials and Components

Which component is used to change the direction of an external tendon at an intermediate point along a span?

  1. A grout cap
  2. A deviator Correct answer.
  3. A coupler
  4. A spiral reinforcement cage

Explanation

Deviators are saddle or pipe assemblies that impose the required geometry on external tendons at intermediate points and transfer the transverse force into the structure. Couplers join tendon lengths, and grout caps and spirals serve other purposes.

Question 14Prestressing Materials and Components

What is the role of confining reinforcement, such as spirals or closed stirrups, behind a post-tensioning anchorage?

  1. To prevent grout from leaking out of the duct
  2. To resist the bursting and splitting forces generated by the concentrated anchorage load Correct answer.
  3. To reduce the relaxation of the strand
  4. To carry the tendon force directly into the far support

Explanation

The anchorage force enters the concrete over a small bearing area and spreads out, creating transverse tensile stresses that can crack the concrete. Confining reinforcement is detailed to resist these bursting and splitting forces in the anchorage zone.

Question 15Prestressing Materials and Components

Which factor most directly determines the friction coefficient used in tendon stress calculations?

  1. The relaxation class of the strand
  2. The diameter of the confining spiral
  3. The concrete strength at transfer
  4. The combination of duct material, tendon type, and lubrication condition Correct answer.

Explanation

The friction coefficient reflects the interaction between the tendon and the duct surface, so duct material, tendon type, and whether the system is lubricated or sheathed all matter. Concrete strength, relaxation class, and spiral diameter do not govern this coefficient.

Question 16Prestressing Materials and Components

What is the purpose of the trumpet or transition piece at a post-tensioning anchorage?

  1. To guide the splayed strands from the anchor head into the duct with a smooth transition Correct answer.
  2. To measure the extension of the tendon
  3. To lock the wedges into the anchor head
  4. To provide a grout injection port only

Explanation

The trumpet forms a tapered transition between the compact anchor head and the larger duct, allowing strands to fan out gradually and reducing stress concentrations. Wedge locking is done by the anchor head and wedges, and extension is measured at the jack.

Question 17Prestressing Materials and Components

A precast pretensioned element shows horizontal cracks along the strand line near the ends shortly after release. Which material or component issue is most likely implicated?

  1. Undersized grout cap diameter
  2. Wrong relaxation class of the strand
  3. Insufficient end-zone confinement or too-rapid release of the strands Correct answer.
  4. Excessive grout vent spacing

Explanation

Splitting along the strand line at the ends is a classic transfer-zone failure caused by inadequate confining reinforcement or by releasing strands before the concrete has sufficient strength. Grout vents, relaxation class, and grout caps are unrelated to this cracking pattern.

Question 18Prestressing Materials and Components

Why must the duct in a post-tensioned member be continuous and well sealed before concreting?

  1. To reduce the amount of confining reinforcement required
  2. To increase the friction coefficient for better bond
  3. To allow the tendon to be electrically grounded
  4. To prevent cement paste from entering and blocking the duct Correct answer.

Explanation

If paste leaks into the duct during casting, it can block the passage and prevent strand installation or grouting, and it can also impair corrosion protection. Sealing and continuity of the duct are therefore checked before concrete is placed.

Question 19Prestressing Materials and Components

Which statement best describes the behavior of a strand coupler in a post-tensioned tendon?

  1. It measures the load in the tendon
  2. It seals the duct after grouting
  3. It joins two tendon lengths and must transmit the full tendon force Correct answer.
  4. It redirects the tendon at a deviator point

Explanation

Couplers are mechanical fittings that connect successive tendon lengths so that force can be transmitted continuously along the tendon. They are typically located where both ends can be stressed or where the force is low.

Question 20Prestressing Materials and Components

In a bonded post-tensioned slab, why are ducts usually given a parabolic or draped profile rather than a straight line?

  1. To increase the relaxation class of the strand
  2. To simplify the anchorage detailing at the ends
  3. To reduce the amount of grout required
  4. To place the prestressing force where it counteracts the bending moments from applied loads Correct answer.

Explanation

Draping the tendon allows the prestress to develop a transverse component that balances applied loads, so the eccentricity follows the bending moment diagram. Grout quantity, anchorage detailing, and relaxation are not the reason for the profile.

Question 21Prestressing Materials and Components

A post-tensioned tendon is specified with a guaranteed breaking load based on nominal area and tensile strength. What does this value represent?

  1. The load at which the strand first yields
  2. The load at which relaxation begins
  3. The load the jack applies during normal stressing
  4. The minimum load the strand must sustain without failure in a tensile test Correct answer.

Explanation

The guaranteed breaking load is the minimum tensile capacity the strand must achieve, derived from nominal area and specified tensile strength. Design stresses are kept well below it, and it is not a jacking load or a yield value.

Question 22Prestressing Materials and Components

An engineer compares two anchorage systems for the same tendon: one with a short wedge set and one with a long wedge set. How does the larger wedge set affect the prestress distribution near the anchorage?

  1. It has no effect on the stress distribution
  2. It produces a longer zone over which stress is reduced, and may require a higher jacking force Correct answer.
  3. It increases the stress at the anchorage above the jacking stress
  4. It removes the friction loss entirely

Explanation

A larger wedge set causes more retraction at the anchorage, so the affected length over which stress is reduced becomes longer. To maintain the required stress further along the tendon, the jacking force must be increased accordingly.

Question 23Prestressing Materials and Components

Which combination of tendon and anchorage features is most appropriate for a structure that must allow future restressing of an external tendon?

  1. A pretensioned strand cast directly into the concrete
  2. A fully grouted bonded tendon with sealed grout caps
  3. A re-stressable anchorage with accessible wedges and an unbonded or greased tendon in a duct Correct answer.
  4. A strand coupler buried in a concrete joint

Explanation

Restressing requires access to the anchorage and freedom of the tendon to move, so a re-stressable anchorage with an unbonded or greased tendon is used. Bonded, pretensioned, or buried coupler arrangements prevent later adjustment of the force.

Question 24Prestressing Materials and Components

Why is plastic duct used in some aggressive environments instead of galvanized steel duct for internal post-tensioning?

  1. It eliminates the need for grouting
  2. It increases the friction coefficient to improve bond
  3. It provides a continuous electrically isolating barrier that resists chloride attack Correct answer.
  4. It has a higher melting point than steel

Explanation

Plastic ducts are chosen where chloride or moisture exposure makes steel ducts vulnerable, because the polymer provides a durable barrier and can support impedance-based corrosion monitoring. Grouting is still required, and a higher friction coefficient would be undesirable.

Question 25Prestressing Materials and Components

A pretensioned member is released at a concrete strength lower than specified. Which consequence is most consistent with prestressing technology principles?

  1. Increased risk of end-zone splitting and excessive elastic shortening losses Correct answer.
  2. Increased breaking load of the strand
  3. Lower friction losses along the tendon
  4. Higher relaxation losses in the strand

Explanation

Releasing at low concrete strength reduces the capacity to resist transfer forces, raising the risk of splitting, and increases the elastic shortening loss because the concrete modulus is lower. Relaxation, friction, and strand breaking load are not improved by early release.

Question 26Prestressing Materials and Components

Which material property of a seven-wire prestressing strand is the main reason it is used instead of mild steel bar in pretensioned members?

  1. Its ability to be welded on site
  2. Its high ductility under repeated loading
  3. Its high tensile strength achieved through cold drawing Correct answer.
  4. Its low modulus of elasticity

Explanation

Prestressing strand is cold drawn to develop tensile strengths far above ordinary mild steel, which allows a small tendon area to impose a large prestress force. Welding is not permitted on strand, and its modulus is similar to or slightly lower than that of bar, so strength is the governing advantage.

Question 27Prestressing Materials and Components

A post-tensioning anchorage is described as having a 'dead end'. What does this term indicate about the anchorage?

  1. It accommodates the largest wedge set in the system
  2. It is the end where the jack applies force
  3. It is embedded in concrete and cannot be stressed again from that end Correct answer.
  4. It contains a grout inlet for the duct

Explanation

A dead end is a fixed anchorage cast into the concrete, typically used at one extremity of a tendon, and stressing is carried out only from the live end. It is not designed for repeated jacking, so access for a stressing jack is not provided there.

Question 28Prestressing Materials and Components

A designer needs a duct for an internal post-tensioned beam in a dry, non-aggressive environment and wants to minimize cost while maintaining adequate stiffness during concreting. Which duct is the conventional choice?

  1. Rigid PVC pipe with solvent-welded joints
  2. Fabricated rectangular steel duct
  3. Flexible plastic duct with a smooth bore
  4. Corrugated galvanized steel duct Correct answer.

Explanation

Corrugated galvanized steel duct is the conventional, economical choice for internal tendons in non-aggressive conditions, providing stiffness and reliable grout confinement. Plastic ducts are usually reserved for aggressive environments or where corrosion protection demands it, and rigid PVC is not standard for tendon ducts.

Question 29Prestressing Materials and Components

A strand is specified as having a nominal diameter of 15.2 mm and a nominal area of 140 mm². Why does the nominal area differ from the area calculated from the nominal diameter?

  1. Because galvanizing adds a coating that increases the measured diameter
  2. Because the nominal diameter includes the duct wall thickness
  3. Because the strand is oval rather than round
  4. Because the strand's helical geometry means its circumscribed diameter exceeds the area-equivalent diameter Correct answer.

Explanation

Seven-wire strand is helical, so the circle enclosing the outer wires is larger than the circle with the same steel area. The nominal area is therefore established from the actual wire areas and mass, not from the nominal diameter.

Question 30Prestressing Materials and Components

A post-tensioned tendon is to be stressed from one end only, and the designer wants to limit the loss of prestress caused by friction along a long, curved profile. Which measure is most directly effective?

  1. Reducing the concrete strength at transfer
  2. Increasing the tendon's nominal area
  3. Using a larger duct diameter
  4. Stressing from both ends so that each half of the tendon has a shorter friction path Correct answer.

Explanation

Friction loss accumulates exponentially with the length of the stressed path, so stressing from both ends halves the path for each jack and reduces the maximum friction loss. The other options do not shorten the friction path and may even worsen behavior.

Question 31Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

A 7-wire prestressing strand is designated by its nominal diameter and by which additional property in the standard SI designation used in ICC practice?

  1. The characteristic breaking load of the strand
  2. The relaxation class of the strand
  3. The cross-sectional area of the strand
  4. The guaranteed ultimate tensile strength of the strand Correct answer.

Explanation

Strand is designated by nominal diameter plus its guaranteed ultimate tensile strength, for example 12.7 mm, 1860 MPa. Area and breaking load follow from those two values, and relaxation class is a separate supplementary designation.

Question 32Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Which statement correctly describes the difference between prestressing wire and prestressing strand as supplied to site?

  1. Wire is always stress-relieved after stranding, whereas strand is always quenched and tempered.
  2. Wire has a lower carbon content than strand and is therefore not suitable for prestressing.
  3. Wire is produced only in the quenched-and-tempered condition, whereas strand is cold drawn.
  4. Wire is a single cold-drawn high-strength steel element, whereas strand is a group of wires helically wound together. Correct answer.

Explanation

Prestressing wire is an individual cold-drawn high-strength steel element, while strand is formed from several wires twisted helically around a central wire. Both are made from high-carbon steel and both are normally stress-relieved after drawing or stranding.

Question 33Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

In a bonded post-tensioning system, what is the primary function of the anchorage at the live end?

  1. To provide the duct alignment needed for grouting
  2. To allow the tendon to slip freely during stressing
  3. To act as the sole corrosion protection for the tendon end
  4. To transfer the prestressing force from the tendon to the concrete through the bearing plate and wedge grip Correct answer.

Explanation

The live-end anchorage grips the strand with wedges in a tapered anchor head and bears on a plate cast into the concrete, transferring force into the member. Grouting and ducting serve other functions, and slip during stressing is controlled rather than freely permitted.

Question 34Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Which anchorage type relies on the strand being looped or splayed and cast into a concrete block to develop the prestressing force?

  1. Cast anchorage or dead-end block Correct answer.
  2. Button-head anchorage
  3. Threaded bar coupler
  4. Wedge-type anchor head

Explanation

A cast anchorage develops force by looping or splaying the strands inside a concrete block so that bond and bearing transfer the load. Wedge and button-head anchorages are mechanical devices, and couplers join threaded bars.

Question 35Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

What does the term 'low-relaxation' mean when applied to prestressing strand?

  1. The strand has been stabilised so that its stress loss under sustained strain is substantially reduced compared with normal-relaxation strand. Correct answer.
  2. The strand elongates less than standard strand at the same stress during initial stressing.
  3. The strand is supplied with a lower initial prestress applied by the manufacturer.
  4. The strand has a lower guaranteed ultimate tensile strength than standard strand.

Explanation

Low-relaxation strand is produced by a stabilising treatment so that, at constant length, it loses much less stress with time than normal-relaxation strand. Strength and elastic modulus are essentially unchanged, and the manufacturer does not pre-stress the strand.

Question 36Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Which steel grade range is typical for high-strength prestressing wire and strand used in ICC-type design?

  1. Around 1600 to 1900 MPa tensile strength Correct answer.
  2. Around 250 to 350 MPa tensile strength
  3. Around 400 to 500 MPa yield strength
  4. Around 800 to 900 MPa tensile strength

Explanation

Cold-drawn prestressing wire and strand typically have guaranteed ultimate tensile strengths in the region of 1600 to 1900 MPa. Structural mild steel reinforcement is far lower, in the few-hundred MPa range.

Question 37Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

What is the purpose of the helical twist in a 7-wire prestressing strand?

  1. To reduce the relaxation loss of the strand to zero
  2. To allow the strand to be spliced by simple twisting on site
  3. To increase the guaranteed ultimate tensile strength above that of the individual wires
  4. To hold the wires together as a single unit and improve bond and handling characteristics Correct answer.

Explanation

The helical lay holds the seven wires together so the strand behaves as one tension element and bonds well in grouted or embedded conditions. It does not raise the aggregate strength above the wire strength, eliminate relaxation, or permit field splicing by twisting.

Question 38Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Which statement best describes a prestressing bar anchorage using a threaded nut and bearing plate?

  1. The bar is anchored solely by bond over its embedded length.
  2. The bar is anchored by heading its end into a button that bears on a plate.
  3. The bar carries a thread at its end, and force is transferred through a nut bearing on a plate. Correct answer.
  4. The bar is anchored by wedges driven into a tapered sleeve.

Explanation

Threaded prestressing bars develop force through a nut threaded onto the bar end and bearing on a plate. Wedges and button heads are used for strand or wire, and pure bond anchorage is a different system.

Question 39Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

A post-tensioning anchorage is described as 'dead end'. What typically distinguishes it from a live end in a bonded system?

  1. It contains no anchorage component and relies entirely on friction in the duct.
  2. It is stressed after the concrete has hardened, whereas the live end is stressed before casting.
  3. It is fixed before stressing and does not require a stressing operation at that location. Correct answer.
  4. It is the only end that is grouted after stressing.

Explanation

The dead end is the fixed anchorage where no jacking is performed; the live end is where the jack applies force. Both ends are anchored components, and the whole tendon is grouted in a bonded system.

Question 40Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

A strand has a nominal area of 140 mm² and a guaranteed ultimate tensile strength of 1860 MPa. What is its characteristic breaking load?

  1. About 260 kN Correct answer.
  2. About 372 kN
  3. About 186 kN
  4. About 130 kN

Explanation

Breaking load equals area times strength: 140 mm² × 1860 N/mm² ≈ 260 000 N, or about 260 kN. Multiplying or dividing by the wrong factor gives the other distractors.

Question 41Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

During stressing, the measured elongation of a tendon is significantly less than the calculated value. Which condition is most consistent with this observation?

  1. The jack calibration is reading low.
  2. The strand has a lower guaranteed ultimate tensile strength than specified.
  3. There is an obstruction or excessive friction in the duct restricting movement. Correct answer.
  4. The strand has a higher elastic modulus than assumed.

Explanation

Short elongation at the expected jacking force indicates the tendon is not moving freely, commonly from duct obstruction, kinks, or excess friction. A higher modulus would give less elongation but is not the usual field cause, and strength does not govern elastic elongation.

Question 42Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Which factor most directly governs the anchorage set (slip) loss at a wedge anchorage?

  1. The grout compressive strength at the time of stressing
  2. The duct diameter relative to the tendon
  3. The relaxation class of the strand
  4. The draw-in of the strand as the wedges seat into the anchor head Correct answer.

Explanation

Anchorage set loss arises from the strand drawing into the anchor head as the wedges seat when the jack force is released. Grout strength, duct clearance, and relaxation class affect other losses or behaviours.

Question 43Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Why are button-head anchorages less common than wedge anchorages in modern multi-strand post-tensioning?

  1. Button heads cannot be used in bonded systems.
  2. Button heads are only permitted with low-relaxation strand.
  3. Button heads cannot develop the full strength of high-strength wire.
  4. Button heads require the wire end to be formed by heading and need more space, which complicates multi-strand anchor heads. Correct answer.

Explanation

Button-head systems require each wire to be headed and bear on a plate, which is bulky and labour-intensive for multi-strand tendons; wedge anchor heads grip strands directly and are more compact. Button heads can develop wire strength and are not restricted by relaxation class or bonding.

Question 44Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

What is the role of the spiral or confining reinforcement placed behind a post-tensioning anchorage?

  1. To prevent grout from escaping the duct
  2. To bond the duct to the surrounding concrete
  3. To align the strand bundle inside the duct
  4. To resist bursting and spalling forces in the concrete local to the anchorage and distribute the concentrated force Correct answer.

Explanation

The high concentrated anchorage force creates transverse tensile stresses behind the bearing plate, so confining reinforcement is provided to control bursting and spalling. It does not serve duct bonding, grout retention, or alignment functions.

Question 45Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Which statement correctly describes the elastic modulus assumed for prestressing strand in typical design?

  1. Around 100 GPa, about half that of structural steel
  2. Around 300 GPa, well above structural steel
  3. Around 195 to 200 GPa, essentially the same as structural steel Correct answer.
  4. Around 200 GPa, similar to ordinary structural steel

Explanation

Prestressing strand has an elastic modulus of roughly 195 to 200 GPa, close to that of structural steel. The high strength of prestressing steel comes from drawing, not from a higher stiffness.

Question 46Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

In a strand tendon, which wires carry the largest share of the tensile force when the strand is tensioned?

  1. The central straight core wire carries a larger share than each outer wire because of the shorter lay path. Correct answer.
  2. The six outer helical wires carry all the force because the core is slack.
  3. All seven wires carry equal force regardless of lay geometry.
  4. The outer wires carry no force until the core yields.

Explanation

Because the outer wires follow a helical path, they are slightly longer for the same axial extension, so the straighter core wire attracts a somewhat larger share of the force. The difference is modest, but the core is not slack and the outer wires are not unloaded.

Question 47Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

Which anchorage component is designed to grip the strand by wedging action and is normally supplied as a matched set with the anchor head?

  1. The grout cap
  2. The trumpet or transition piece
  3. The wedge and wedge barrel assembly Correct answer.
  4. The duct coupler

Explanation

Wedges seat in the tapered holes of the anchor head and grip the strand by wedging action; they are matched to the anchor head and strand size. Trumpets, grout caps, and duct couplers perform transition, sealing, and duct-joining functions.

Question 48Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

A designer specifies stress-relieved prestressing wire rather than as-drawn wire. What is the main benefit?

  1. Complete elimination of anchorage set
  2. Reduced relaxation and improved ductility with straighter, more uniform wire Correct answer.
  3. Higher guaranteed ultimate tensile strength
  4. Elimination of the need for corrosion protection

Explanation

Stress relief after cold drawing reduces residual stresses, lowering relaxation and improving ductility while producing straighter wire. It does not raise strength above the drawn grade, remove anchorage set, or provide corrosion protection.

Question 49Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

A tendon is stressed to 75 percent of the guaranteed ultimate tensile strength of the strand. Which statement about the anchorage design implication is correct?

  1. The anchorage only needs to resist the jacking force divided by the strand count.
  2. The anchorage must be capable of developing at least the full guaranteed breaking load of the tendon without failure. Correct answer.
  3. The anchorage capacity is governed solely by the bearing plate area.
  4. The anchorage need not be tested because the stress is below the yield point.

Explanation

Anchorages are required to develop the full guaranteed breaking load of the tendon so that the tendon, not the anchorage, governs the strength of the system. The jacking force level does not reduce this requirement, and bearing plate area is only one aspect of capacity.

Question 50Prestressing Steel: Strand, Wire, Bar, and Anchorage Systems

In a bar-tendon system, what is the function of a coupler?

  1. To join two threaded bar lengths so that force is transferred through the threaded connection Correct answer.
  2. To anchor the bar by bond in concrete
  3. To reduce relaxation of the bar
  4. To provide the duct for grouting

Explanation

Couplers are threaded sleeves that join bar lengths end to end and transmit force through the threads. They are not bond anchorages, do not change relaxation, and are not the grouting duct.