This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Basic Concepts”.
1. The phenomena of development of internal tensile stresses in a concrete member by means of tensioning devices are called as ____________
c) Prestressing of concrete
d) Thermoelectric prestressing
Explanation: Prestressed concrete is basic concrete, in which internal stresses of a suitable magnitude and distribution are introduced so that the stresses resulting from external loads are counteracted to a desired degree.
2. In reinforced concrete members the prestress is commonly introduced by ___________
a) Tensioning the steel reinforcement
c) Shortening of concrete
Explanation: In reinforced concrete members, the prestress commonly introduced is by tensioning the steel reinforcement while rings i.e stirrups are used while placing columns or foundation in structures, tendon is a stretched member of a prestressed concrete element which serves the purpose of transmitting the prestress to concrete and shortening of concrete phenomena occurs while placing of concrete.
3. Which of the following basic concept is involved in the analysis of prestressed concrete members?
a) Combined and bending stresses
b) Principle stresses
c) Shear stresses
d) Overhead stresses
Explanation: The basic concept involved in the analysis of prestressed concrete members is concept of combined direct and bending stresses used for columns whereas principle and shear stresses are formed in case of tensioning the prestressed and reinforced structures, overhead stresses are formed while the stresses in structures goes beyond safe limit provided by different codes.
4. The prestressing of concrete member is carried out to reduce ___________
a) Compressive stresses
b) Tensile stresses
c) Bending stresses
d) Shear force
Explanation: The prestressing of concrete members is done to reduce the compressive stresses developed in the concrete members to the required extent while tensile stresses is the stress state where the length of member tends to expand in tension side while the volume remains constant, shear forces and bending stresses occurs at the cross section of the beam as the unbalanced vertical force and algebraic sum of moment of forces to right or left of section.
5. The earliest examples of wooden barrel construction by force-fitting of metal bands and shrink-fitting of metal tiers of wooden wheels indicate the art of ___________
Explanation: Wooden barrel construction by force-fitting of metal bands and shrink-fitting of metal tyres on wooden wheels indicate the art of prestressing and it has been practiced from ancient times while the example of tensioning is bracing for building and bridges whereas stress occurs in a member at a force per unit area and strain phenomena occurs by change in length of a unstressed element.
6. The concept is used in many branches of civil engineering and building construction?
a) Reinforced concrete
b) Prestressed concrete
c) Steel concrete
d) Lump sum concrete
Explanation: Prestressed concrete is widely used in many branches of civil engineering and building construction and in recent days it is experiencing greatest growth in the field of commercial building because of its acoustic properties and its ability to provide long open space.
7. The attempt to introduce permanently acting forces in concrete to resist the elastic forces is ___________
Explanation: Freyssinet attempted to introduce permanently acting forces in concrete to resist the elastic forces developed under loads and this idea was later developed under the name of prestressing while the loading and bending phenomena occurs in a member while placing and during excessive loads and pre-straining occurs in prestressed concrete structures.
8. In reinforced concrete members, the prestress commonly introduced is ___________
a) Tensioning steel reinforcement
b) Tensioning wood reinforcement
c) Tensioning rings
d) Tensioning plates
Explanation: In reinforced concrete members steel is commonly used by tensioning steel reinforcement and Steel was commonly used in reinforcement in earlier days and had several disadvantages in case of residential buildings.
9. Development of early cracks in reinforced concrete is due to ___________
a) Strains of steel
b) Stresses of steel
c) Ultimate load
d) Bending of steel
Explanation: Development of early cracks in reinforced concrete is due to incompatibility in the strains of steel and concrete and it was perhaps the starting point in the development of a new material like prestressed concrete.
10. Concrete is weak in?
Explanation: Concrete is not able to resist direct tension in comparison of its ability to resist direct compression because of its low tensile strength and brittle nature, it behaves non linearly at all times because it has essentially zero strength in tension it is always used as reinforced concrete, as a composite material and it is a mixture of sand, aggregate, cement and water whereas structures are highly vulnerable to tensile cracking due to very low thermal coefficient of expansion.
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