Prestress Concrete MCQ Quiz - Objective Question with Answer for Prestress Concrete - Download Free PDF
Last updated on Mar 28, 2025
Latest Prestress Concrete MCQ Objective Questions
Prestress Concrete Question 1:
Calculate the anchorage value of 45° and 90° bend for a 25 mm diameter bar.
Answer (Detailed Solution Below)
Prestress Concrete Question 1 Detailed Solution
Explanation:
As per IS 456: 2000,
- A standard hook has an anchorage value equivalent to a straight length of 16ϕ.
- The anchorage value of the standard U-type hook shall be 16 times the diameter of the bar.
- The anchorage value of the standard bend shall be considered as 4 times the diameter of the bar for each 45o bend subject to a maximum value of 16 times the diameter of the bar.
Calculation:
Given:
Diameter = ϕ = 25 mm
Anchorage value for 45° = 25 × 4 = 100 mm
Anchorage value for 90° = 25 × 8 = 200 mm
Prestress Concrete Question 2:
According to IS 1343: 2012, for the end zone in post-tensioned members, on the areas immediately behind external anchorages, the permissible unit bearing stress on the concrete, after accounting for loses due to the relaxation of steel, elastic shortening and seating of anchorages, shall NOT exceed:
(Where fci is the cube strength at transfer, Abr is the bearing area and Apun is the punching area.)
Answer (Detailed Solution Below)
Prestress Concrete Question 2 Detailed Solution
Concept:
As per IS 1343:2012, Clause 19.6.2.1 (a), the permissible unit bearing stress on concrete in the end zone of post-tensioned members (areas immediately behind external anchorages), after accounting for losses due to relaxation of steel, elastic shortening, and seating of anchorages, shall NOT exceed:
\( 0.48f_{ci} \sqrt{\frac{A_{br}}{A_{pun}}} \) or \( 0.8f_{ck} \), whichever is smaller.
Where:
• \( f_{ci} \) = Cube strength at transfer
• \( f_{ck} \) = Characteristic compressive strength of concrete
• \( A_{br} \) = Bearing area
• \( A_{pun} \) = Punching area
Prestress Concrete Question 3:
High Strength Concrete (Grade M70 and above) has several distinguishing properties that separate it from normal strength concrete. Which of the following is NOT a characteristic of High Strength Concrete?
Answer (Detailed Solution Below)
Prestress Concrete Question 3 Detailed Solution
Explanation:
Characteristics of High Strength Concrete
High Strength Concrete (Grade M70 and above) possesses certain notable properties which distinguish it from normal strength concrete. These properties include:
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High durability: This type of concrete has enhanced durability due to its dense microstructure and lower water-cement ratio.
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Reduced permeability: The dense microstructure also results in lower permeability, making the concrete less susceptible to water ingress and chemical attacks.
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Increased shrinkage: Despite its advantages, high strength concrete can experience increased shrinkage due to its lower water content and higher cementitious material content.
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Lower cement content: This is not a characteristic of high strength concrete. In fact, higher grade concrete generally requires more cementitious materials to achieve the desired strength and durability.
Analyzing the Given Options
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"High durability" (Characteristic)
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High strength concrete is known for its enhanced durability due to its dense microstructure and low porosity.
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"Reduced permeability" (Characteristic)
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The dense microstructure of high strength concrete results in lower permeability, reducing the risk of water and chemical ingress.
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"Increased shrinkage" (Characteristic)
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High strength concrete can experience increased shrinkage due to its lower water content and higher cementitious material content.
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"Lower cement content" (NOT a characteristic)
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High strength concrete typically requires more cementitious materials to achieve the desired strength, making this statement incorrect.
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Prestress Concrete Question 4:
As per IS 1343: 1980, the recommended value of transmission length for pre-stressed concrete with plain and intended wires is? (ϕ is the diameter of wire)
Answer (Detailed Solution Below)
Prestress Concrete Question 4 Detailed Solution
Explanation:
Transmission length:
- Prestress is transferred over a certain length from each end of a member which is called transmission length or transfer length. (Lt).
- The stress in the tendon is Zero at the ends of the members and increases over the transmission length to the effective prestress under the service loads.
- Then, remains constant, after the transmission length.
As per IS: 1343 - 1980, Clause 19.6
Type of tendon/Wire | Transmission length |
Plain and intended wires | 100 ϕ |
Crimped wire | 65 ϕ |
Strands | 30 ϕ |
- These values are recommended by codes in absence of test data.
- These values are applicable when the concrete is well compacted
- Also, its strength is not less than 35 N/mm2 at the transfer, and tendons are released gradually.
Prestress Concrete Question 5:
In a prestressed beam with bonded tendons, tensile stress in steel at failure stage is influenced by
Answer (Detailed Solution Below)
Prestress Concrete Question 5 Detailed Solution
Top Prestress Concrete MCQ Objective Questions
As per IS code, the minimum grade of concrete for the design of a Pre-tensioned concrete structure is:-
Answer (Detailed Solution Below)
Prestress Concrete Question 6 Detailed Solution
Download Solution PDFExplanation
Minimum grade of concrete to be used in the design of prestressed concrete structure as per IS 1343 is as below:
1. For Post tensioning minimum grade of concrete used is M-30.
2. For Pre-tensioning minimum grade of concrete used is M-40.
Cover to be used in the design of prestressed concrete structure as per IS 1343 is as below:
1. For Posttensioning minimum cover to be used is 30 mm.
2. For Pre-tensioning minimum cover to be used is 20 mm.
The suitability of post tensioning is good for:
Answer (Detailed Solution Below)
Prestress Concrete Question 7 Detailed Solution
Download Solution PDFThe correct answer is longs spans.Key Points
- Post tensioning is a construction technique that involves the use of high-strength steel strands or cables to reinforce concrete structures.
- The suitability of post tensioning depends on various factors such as span length, design requirements, and construction constraints.
- Post tensioning allows for longer spans to be achieved without the need for intermediate supports.
- This is because the high-strength steel cables can provide the necessary tensile strength to counteract the weight of the structure and any applied loads.
- Longer spans can result in more open and flexible interior spaces, which can be beneficial for certain building types such as sports arenas, exhibition halls, and airports.
- Post tensioning can also help reduce the overall weight of the structure, which can lead to cost savings in materials and construction.
- The use of post tensioning can improve the durability and resilience of concrete structures, as the cables can help prevent cracking and deformation due to temperature changes, shrinkage, and other factors.
Additional Information
- End spans refer to the sections of a structure that are adjacent to a support, such as a column or a wall.
- Post tensioning can be used for end spans, but it may not be as necessary as for long spans.
- Break spans are sections of a structure that are interrupted by an expansion joint or a construction joint.
- Post tensioning can be used for break spans, but it may require additional design considerations and construction techniques.
- Edge spans are sections of a structure that are located at the perimeter, such as a balcony or a cantilevered slab.
- Post tensioning can be used for edge spans, but it may require additional reinforcement to account for wind loads and other lateral forces.
Drying shrinkage strain develops slowly, as it_______.
Answer (Detailed Solution Below)
Prestress Concrete Question 8 Detailed Solution
Download Solution PDFExplanation:
As per IS 1343 Clauses 6.2.4:
Shrinkage
- The total shrinkage of concrete depends upon the constituents of concrete, size of the member and environmental conditions.
- For a given humidity and temperature, the total shrinkage of concrete is most influenced by the total amount of water present in the concrete at the time of mixing.
- The total shrinkage strain is composed of two components, (i) the autogenous shrinkage strain and (ii) the drying shrinkage strain
Autogenous shrinkage strain:
- Develops during hardening of concrete
- The major part develops in the early days after casting.
- It is a linear function of concrete strength
Drying shrinkage strain:
- The drying shrinkage strain develops slowly as it a function of migration of the water through the hardened concrete.
The purpose of reinforcement in prestressed concrete is
Answer (Detailed Solution Below)
Prestress Concrete Question 9 Detailed Solution
Download Solution PDFExplanation:
Prestressing is the process by which a concrete element is compressed, generally by steel wires or strands.
The purpose of reinforcement in prestressed concrete is to impart initial compressive stress in concrete
Precast elements may be prestressed during the construction process (pre-tensioning) or structures may be stressed once completed (post-tensioning).
Prestressing compensates for the tensile stresses introduced when the element is loaded. Hence the concrete generally remains in compression.
Prestressing serves two main purposes:
1. To improve the resistance of the member to the dead and live loads.
2. To modify the behavior of the member or structure in such a way so as to make it more suitable for its intended purpose.
The primary purpose of prestressing steel is to apply a force to a concrete, either by bond or by means of special anchoring devices.
At the time of initial tensioning, the maximum tensile stress, fpi immediately behind the anchorage shall not exceed____ of the ultimate tensile strength, fpu of the wire of bar or strand.
Answer (Detailed Solution Below)
Prestress Concrete Question 10 Detailed Solution
Download Solution PDFExplanation:
As per CI. 19.5.1 of IS 1343 At the time of initial tensioning, the maximum tensile stress, fpi immediately behind the anchorages shall not exceed 76 percent of the ultimate tensile strength, fpu of the wire or bar or strand.Important Points
Grade of concrete:
- M 40 for pre-tensioned members
- M 30 for post-tensioned members
The grade of concrete used for prestressed member lies in the range of:
Answer (Detailed Solution Below)
Prestress Concrete Question 11 Detailed Solution
Download Solution PDFMinimum grade of concrete to be used in the design of prestressed concrete structure as per IS 1343 is as below:
1. For Post tensioning minimum grade of concrete used is M-30.
2. For Pre-tensioning minimum grade of concrete used is M-40.
Hence it can be seen that grade of concrete used for prestressed member lies in the range of M30 to M60
Important Points
Cover to be used in the design of prestressed concrete structure as per IS 1343 is as below:
1. For Posttensioning minimum cover to be used is 30 mm.
2. For Pre-tensioning minimum cover to be used is 20 mm.
The minimum grade of concrete that can be used for pre-tensioned beam system is
Answer (Detailed Solution Below)
Prestress Concrete Question 12 Detailed Solution
Download Solution PDFA minimum grade of concrete to be used in the design of the prestressed concrete structure as per IS 1343 is as below:
1. For Post-tensioning minimum grade of concrete used is M-30.
2. For Pre-tensioning minimum grade of concrete used is M-40.
Cover to be used in the design of the prestressed concrete structure as per IS 1343 is as below:
1. For Posttensioning minimum cover to be used is 30 mm.
2. For Pre-tensioning minimum cover to be used is 20 mm.A simply supported concrete beam pre-stressed with a force of 2500 kN is designed by load balancing concept for an effective span of 10 m and to carry a total load of 40 kN/m, the central dip of the cable profile should be
Answer (Detailed Solution Below)
Prestress Concrete Question 13 Detailed Solution
Download Solution PDFConcept:
Prestress concrete is the concrete in which internal stresses are produced due to compression or tension applied before applying external load and these stresses are counter balanced by the applied load to the desired degree.
Calculation:
Given,
Prestressing force = 2500 KN
Effective span length = 10 m
Total external load = 40 kN/m
We know that,
\(M = P.e = {WL^2 \over 8}\)
\(e = {WL^2 \over 8P} = {40\times10^2 \over 8\times2500} = 0.2 m = 200 mm\)
A concrete beam is pre-stressed by a cable carrying an initial pre-stressing force of 300 kN, the area is 300 mm2. What is the percentage of loss of stress due to shrinkage in pre-tensioned members?
Answer (Detailed Solution Below)
Prestress Concrete Question 14 Detailed Solution
Download Solution PDFConcept:
Shrinkage loss
Time-dependent strain measured in an unloaded and unrestrained specimen at a constant temperature.
Loss of pre-stress (Δfp) due to shrinkage = EP × ϵsh
Where Ep is the modulus of pre-stressing steel and
ϵsh is shrinkage strain
The approximate value of shrinkage strain for design shall be assumed as follows (IS 1383):
For pre-tensioning = 0.0003
Calculation:
Given,
initial Prestressing force, Po = 300 kN, Area = 300 mm2
Assume, Ep of steel = 2 × 105 N/mm2
Initial stress, f = Po/A = 300000/300 = 1000 N/mm2
Loss of pre-stress due to shrinkage, (Δfp) = EP × ϵsh
(Δfp) = 2 × 105 × 0.0003 = 60 N/mm2
Loss of stress (%) = \(\frac{{{\Delta f_p}}}{f} \times 100 = \frac{{60}}{{1000}} \times 100 = 6\%\)
So, the percentage of loss of stress due to shrinkage in pre-tensioned members is 6 %. Hence the most appropriate option is 1 i.e 6.3 %.
Which of the following losses occurs only in post-tensioning pre-stressed concrete structures
Answer (Detailed Solution Below)
Prestress Concrete Question 15 Detailed Solution
Download Solution PDFConcept:
Loss due to friction and anchorage slip occurs only in the post-tensioned beam.
- In prestressed concrete, the most important parameter is the prestressing force.
- If the prestressing force reduces with time, prestresses also get reduced.
- Various reductions of the prestressing force are termed as the losses in prestressing.
- Total loss of prestress consists of those losses which are instantaneous at the transfer stage as well as those which are time-dependent.
Important Points
Losses of prestress:
Pre-tensioning |
Post-Tensioning |
||
1. |
Elastic shortening loss |
1. |
No elastic shortening loss in cables if pulled simultaneously, however, losses will be there if cables are pulled are by one. |
2. |
Creep loss |
2. |
Friction loss |
3. |
Shrinkage loss |
3. |
Anchor slip loss |
4. |
Relaxation loss |
4. |
Creep loss |
5. |
Shrinkage & Relaxation |