The phenomena of development of internal tensile stresses in a concrete member by means of tensioning devices are called as ____________
a) Pre-tensioning
b) Post-tensioning
c) Prestressing of concrete
d) Thermoelectric prestressing
Answer: c
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.
In reinforced concrete members the prestress is commonly introduced by ___________
a) Tensioning the steel reinforcement
b) Tendons
c) Shortening of concrete
d) Rings
Answer: a
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.
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
Answer: a
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.
The prestressing of concrete member is carried out to reduce ___________
a) Compressive stresses
b) Tensile stresses
c) Bending stresses
d) Shear force
Answer: a
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.
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 ___________
a) Prestressing
b) Tensioning
c) Stress
d) Straining
Answer: a
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.
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
Answer: b
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.
The attempt to introduce permanently acting forces in concrete to resist the elastic forces is ___________
a) Prestressing
b) Loading
c) Pre-straining
d) Bending
Answer: a
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.
In reinforced concrete members, the prestress commonly introduced is ___________
a) Tensioning steel reinforcement
b) Tensioning wood reinforcement
c) Tensioning rings
d) Tensioning plates
Answer: a
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.
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
Answer: a
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.
Concrete is weak in?
a) Compression
b) Tension
c) Loading
d) Bending
Answer: b
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.
The structures of prestressed concrete are less liable to ___________
a) Bending
b) Loading
c) Placing
d) Cracks
Answer: d
Explanation: In case of fully prestressed members which are free from tensile stresses under working loads cross-section is more efficiently utilized when compared with a reinforced concrete section that is cracked under working loads.
Which of the following concrete offers pleasant appearance and durability?
a) Reinforced concrete
b) Prestressed concrete
c) Shrinkage concrete
d) Hardened concrete
Answer: b
Explanation: Prestressed concrete offers pleasant appearance and durability when compared to reinforced concrete and the two structural features of prestressed concrete, namely high strength concrete and freedom from cracks, contributes to the improved durability of structure under aggressive environmental conditions.
The prestressing members have better ability of absorbing energy when the structures are subjected to ___________
a) Tensile loads
b) Axial loads
c) Bending loads
d) Impact loads
Answer: d
Explanation: Prestressing of concrete improves the ability of the material for energy absorption under impact loads and working loads proved to be good in prestressing than in reinforcing and it is done in concrete members to reduce the compressive stresses developed in the members to the required extent.
The loads of same intensities when subjected to structures, it increases ___________
a) Life of material
b) Durability of material
c) Stiffness of material
d) Bending of material
Answer: a
Explanation: When loads of same intensities are subjected to structures, then the prestressing increases the mean stresses in steel and the effects caused due to fluctuations in stresses are minimized which increase the life of the material.
The prestressed concrete flexural member under working load conditions offers superior amount of ___________
a) Flexibility
b) Rigidity
c) Transfer
d) Stability
Answer: b
Explanation: A superior amount of rigidity is offered by the prestressed concrete flexural members under the working load conditions when compared with that offered by reinforced concrete members of equal dimensions.
The application of prestressed concrete is done for depth ratio’s having ___________
a) Small span
b) Larger span
c) Same span
d) Equal span
Answer: b
Explanation: Prestressed concrete is used for the construction of buildings and other structures which are having the value of span to depth ratio in large or for larger span members and other criteria such as equal, small, same span criteria are considered in various other structural members.
The prestressed concrete structures are considered as ___________
a) Economical structures
b) Uneconomical structures
c) Tensile structures
d) Loading structures
Answer: b
Explanation: Prestressed concrete structures are considered as uneconomical structures and it is well established fact that the basic economy of prestressed concrete lies in its high strength to weight and strength to cost ratios, its resistance to fire and cracking, and its versatility and adaptability.
The prestressed concrete involves problems like ___________
a) Architectural and construction
b) Financial and land
c) Placing of material
d) Tensioning devices
Answer: a
Explanation: The prestressed concrete involves many architectural or construction related problems formulated due to curved surfaces and involve sophisticated erection problems, a high quality control is required for production of materials and while placing the tendons and when the members are subjected to a system of loads then the existing problems due to long term creep moments are increased.
The utilization of concrete in tension zone of prestressed concrete member saves concrete ranging between ___________
a) 15 to 30 percent
b) 20 to 50 percent
c) 35 to 60 percent
d) 10 to 20 percent
Answer: a
Explanation: Due to the utilization of concrete in the tension zone, an extra saving of 15 to 30 percent in concrete is possible in comparison with reinforced concrete high tensile steels are used in prestressed members and its ultimate strength is equal to 2100n/mm2 and the saving in steel are even higher, 60 – 80 percent mainly due to high permissible stresses allowed in the high tension wires.
The overall economy in using prestressed concrete reduces?
a) Design loads and costs
b) Tendons
c) Anchorages
d) Bars
Answer: a
Explanation: An overall economy in using prestressed concrete decreases the dead weight due to which the design loads and cost of foundation reduces although there is considerable saving on the quantity of materials used in prestressed concrete members in compression with reinforced concrete members, it is not much significant due to additional costs incurred for high strength concrete, tensile steel, anchorages and other hard wires required for the production of prestressed member.
The compression in concrete and tension in steel are developed by?
a) Joint cements
b) Expansion cements
c) Water cement ratio
d) Hardened cements
Answer: b
Explanation: Compression in concrete and tension in steel is developed by use of expanding cements due to its elastic property or expanding property, joint cement is an adhesive used primarily for attaching the joint tape that is placed over the beams whereas water cement ratio is the ratio of the weight of water to weight of cement used in a concrete mix.
The prestressing used for arches and pavements involves the application of ___________
a) Direct forces
b) Compressive forces
c) Tensile forces
d) Axial forces
Answer: a
Explanation: The prestressing used for arches and pavements is the application of direct forces between abutments, whereas to impart the desired forces, flat jacks are used and axial force is the compression or tension force acting in a member if the axial force acts through the centroid of the member it is called concentric loading.
The classification of prestressed concrete is based on the method of ___________
a) Designing
b) Bending moments
c) Loading
d) Stresses acting
Answer: a
Explanation: Classification of prestressed concrete is based on the method of design like externally, internally, partial, moderate, axial, eccentric, concordant, uni-axial, biaxial, tri-axial, non distortional, linear, circular, post and pre tensioning, prestressed concrete has considerable increase resilience due to its capacity for completely recovering from substantial effects of overloading without undergoing any serious damage.
The linear prestressing is mostly applicable for ___________
a) Bent members
b) Straight members
c) Cracked members
d) Overloaded members
Answer: b
Explanation: Linear prestressing is mostly applicable for straight members such as slabs, beams etc and the members are prestressed in a linear manner, tendons are spliced in case of continuous prestressed concrete members to gain continuity and the various types of splices used as tendons are screw connector, torpedo splices, clamp splice and wrapped splice.
In pre-tensioning system, after curing and hardening of concrete the reinforcement is set ___________
a) Free
b) Fixed
c) Locked
d) Jacked
Answer: b
Explanation: In pre-tensioning system, the tendons are tensioned first and then the casting of concrete is carried out and the edge of the tendon at its either side is fixed to an abutment and its other edge is pulled with the application of jack and then the reinforcements are set free after curing and hardening.