This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “End Zone Reinforcement”.
1. What are necessary to prevent failure at the end zones, in the transfer zone of pretensioned beams?
Explanation: In the transfer zone of pretensioned beams, transverse reinforcements are necessary to prevent the failure of the end zones due to cracking of concrete as a consequence of large transverse tensile stresses, which often exceed the tensile strength of concrete.
2. The designed anchorage zone in the main reinforcement using transverse stress distribution should withstand the ____________
a) Compression tension
b) Bursting tension
c) Anchorage tension
d) Principal tension
Explanation: By using the transverse stress distribution the designed anchorage zone in the main reinforcement should withstand the bursting tension and coincides with the line of action of the largest individual force on the critical axis.
3. The arrangement of reinforcement in end blocks like links, loops, helices, mats are placed in ____________
a) Linear directions
b) Parallel directions
c) Perpendicular directions
d) Angular directions
Explanation: The arrangement of reinforcement for Freyssinet type of anchorages in end blocks the links or loops, helices, mats are placed in the perpendicular directions of the reinforcements, the reinforcement is provided in the form of closed stirrups enclosing all the tendons, wherever single leg stirrups are used care should be taken to anchor the stirrups to bottom and top tendons with cross section.
4. Which is more efficient than mat reinforcement?
a) Helical reinforcements
b) Loops reinforcements
d) Hair pin bars
Explanation: When compared to mat reinforcements, the helical reinforcement is more efficient and it is tested by Zielinski and Rowe, the first stirrup should be placed at close to the end face as possible with due regard to the minimum cover reinforcements.
5. Which are necessary in case of short bond length, along with the deformed bars, loops?
a) Parallel bends
b) Right angle bends
c) Transverse bends
d) Tensile bends
Explanation: Along with the deformed bars, loops, hooks or right angle bends are necessary in the case of short bond lengths; about half of the total reinforcement is preferably located within a length equal to one third of transmission length from the end, the rest being distributed in the remaining distance.
6. What should be provided in case of end zone reinforcements to prevent failure of corner zones?
c) Hair pin bars
d) Transverse bars
Explanation: To prevent failure in case of end zone reinforcement of corner zones, where spalling or secondary tension develops at the corners, the hair pin bars of suitable steel should be provided, while designing the formwork, the use of cap cables must be considered and the space provided for fixing and handling the hydraulic jack must be sufficient especially at the soffits of beam when cap cables are used.
7. The secondary reinforcements can be bent if the suitable packets are provided behind the ____________
Explanation: The secondary reinforcements can be bent if the suitable packets are provided behind the anchorages and after the operations of prestressing are done, the pocket is filled with mortar, In case of uncracked members bond stresses are computed by considering the complete section, which is effective.
8. In case of end blocks, the steel case should be provided with bearing plates to overcome ____________
Explanation: In case of end blocks, the steel cage should be provided to overcome the overlapping of it with bearing plates when they are placed close to the edge of the block, in case of cracked flexural members, bond stresses change suddenly at the cracks due to the abrupt transfer of tension from concrete to steel in the vicinity of the cracks.
9. The cost of end anchorage steel compared to entire structural element is ____________
Explanation: The cost of end anchorage steel is low when compared to the entire structural members so, Morice, advices that it is better to provide extra reinforcement in doubtful situations in case of anchorage zone reinforcements and proper compaction of concrete in the end zones by vibration is essential to achieve dense concrete associated with high strengths.
10. In case of designing the formwork, the use of cab cables is ____________
b) Not considered
c) Made equal
d) Made Zero
Explanation: While designing the formwork, the use of cap cables must be considered and the space provided for fixing and handling of the hydraulic jack must be sufficient especially at the soffits of the beam when the cap cables are used.
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