This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Need and Terminology”.
1. The significant observations which resulted from the pioneering research on prestressed concrete were ___________
a) High strength steel and losses of prestress
b) High strength tendon and losses of creep
c) High strength bars and losses of strain
d) High strength rings and losses of shrinkage
Explanation: The necessity of using high strength steel, concrete and recognisation of losses of prestress due to various causes were the observations which resulted in research on prestressed concrete while high strength tendons, bars, rings are used for transmitting prestress and losses of creep, strain and shrinkage are types of loss considered in post and pretensioned members.
2. The necessity of high strength concrete in prestressed concrete is due to ___________
a) Shear and Bonding
b) Loading and Unloading
Explanation: High strength concrete is necessary in prestressed concrete, as the material offers high resistance in tension, shear, bond and bearing while loading and unloading, cracking, bending actions are actions occurring at the time of transfer of concrete.
3. In the zone of anchorages the material preferred to minimize costs is ___________
a) High strength steel
b) High strength bars
c) High strength tendons
d) High strength concrete
Explanation: In the zone of anchorages, the bearing stresses being higher, high strength concrete is invariably preferred to minimize costs and it is less liable to shrinkage cracks, and has a higher modulus of elasticity.
4. The length of the prestressing tendon between the end of the member and the point where the steel attains its stress is called ___________
b) De bonding
c) Cracking load
d) Transmission length
Explanation: The length of the prestressing tendon between the end of the member and the point where the steel attains its full stress and adequate transmission length is necessary to reduce the radial forces acting on the concrete.
5. In cab cable, the curved portion of the tendon and anchors lie in ___________
a) Compression and Tension zone
b) Cracking zone
c) Tension and Compression zone
d) Loading zone
Explanation: A short curved tendon arranged at the interior support of a continuous beam where the anchors are in compression zone and the curved portion is in the tensile zone is called as a cab cable and it is small in size and consists of anchorages and its sides.
6. The load at which the prestressed member develops its first crack is called as ___________
a) Transfer load
b) Creep load
c) Bending load
d) Cracking load
Explanation: The load on the structural element corresponding to the first visible crack is called as cracking load and transfer refers to the phase in which the prestress is transferred to the concrete, transfer load occurs at pretensioned members when prestress is released from bulk heads while in post tensioned members, transfer occurs after the tensioning of tendons.
7. In circular prestressing members, the tendons are supplied in form of ___________
Explanation: The term circular prestressing refers to prestressing in round members, such as tanks and pipes and the members are prestressed in a circular way while the use of bar tendons with threaded anchorages reduces the possibility of pull and are used in post tensioning system, wire tendons are mainly used in post tensioning system, cables are formed by arrangement of wires or strands.
8. In case of continuous prestressed concrete members to gain continuity, splicing is done by ___________
Explanation: A stretched element used in a prestressed concrete member which serves the purpose of transmitting the prestress to concrete and it may be in the form of high tensile steel wires, cables or strands.
9. The phenomena of drying process of contraction concrete refer to ___________
a) Moisture loss
b) Shrinkage of concrete
c) Drying process
d) Weight loss
Explanation: Shrinkage of concrete is due to moisture loss resulting in difference in volume results in contraction of concrete on drying and it is based on relative humidity, exposure time, quantity and type of aggregate, water cement ratio in the mix.
10. The ratio between the creep strain and elastic strain of concrete is defined as ___________
a) Creep ratio
b) Creep elasticity
c) Creep coefficient
d) Creep factor
Explanation: Creep coefficient is progressive increase in the inelastic deformation of concrete under sustained stress components and the estimation of loss of prestress due to creep of concrete is carried out by creep coefficient method.
11. The phenomena of reduction of stress in steel at a constant strain are known as ___________
a) Reduction of stress
b) Relaxation of stress
c) De bonding
d) Proof stress
Explanation: Relaxation of stress refers to decrease of stress in steel at constant strain, at a certain level reduction of stress in steel occurs at a constant strain in concrete member and this phenomena occurs as a result of creep in steel while the relaxation of stress in steel changes according to the variation of percentage of creep.
12. A device which helps the tendons to transmit prestress to the member and maintain it for the design period is?
a) Cab cable
Explanation: Anchorage is the term used to denote a device which helps the tendons to transmit prestress to the member and maintain it for the design period, generally used to enable the tendon to impart and maintain prestress in concrete and the commonly used anchorages are Freyssinet, Magnel, Balton, Gifford-udall, Leon hardt etc.
13. Which of the following type of prestress applied to concrete in which tensile stresses to a limited degree are permitted is known as ___________
a) Moderate prestressing
b) Partial prestressing
c) Full prestressing
d) Axial prestressing
Explanation: Partial prestressing refers to the prestressing of concrete members in which some flexural cracking is allowed at full service load and an additional tensile reinforcement is also provided to achieve adequate bending strength.
14. Prevention of bond between the steel and concrete is known as ___________
a) Bond prestressed concrete
b) Axial prestressing
c) De bonding
d) Proof stress
Explanation: Prevention of bond between the steel wire and the surrounding concrete is known as de bonding, the concrete in which prestress is imparted to concrete through bond between tendons and surrounding concrete, members in which the entire cross section of concrete has a uniform compressive prestressing is termed as axial prestressing, the tensile stress in steel which produces a strain of 0.2 percent of the original gauge length on unloading is proof stress.
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