This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Circular Prestressing”.
1. A reinforced concrete pressure pipe requires a large amount of __________
a) Span
b) Reinforcement
c) Area
d) Deflection
View Answer
Explanation: Liquid retaining structures, such as circular pipes, tanks and pressure vessels are admirably suited for circular prestressing and the circumferential hoop tension developed due to the internal fluid pressure and a reinforced concrete pressure pipes requires a large amount of reinforcement to ensure low tensile stresses resulting in a crack free structure, however, circular prestressing eliminates cracks and provides for an economical use of materials and in addition, prestressing safeguards against shrinkage cracks in liquid retaining structures.
2. In circular prestressing, the member may be prestressed by overlapping __________
a) Anchorages
b) Ridges
c) Tendons
d) Bars
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Explanation: In circular prestressing, the member may be prestressed by overlapping tendons within the ducts so as to minimize frictional losses an alternative method is to wrap the high tensile wires under tension around precast cylindrical members and this method was developed much earlier than linear prestressing and has been in use for a considerable period of time for the production of pressure pipes.
3. In circular prestressing the tension in the wire is produced by pulling it through __________
a) Tendons
b) Anchorages
c) Bars
d) Die
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Explanation: The tension in the wire is produced by pulling it through a die which reduces its section, consequently developing the required amount of tensile stress in the steel and the wrapped wires are generally protected against corrosion by a coating of cement mortar recent developments reported by dandies include the use of picovex mortar which consists of a proprietary epoxy resin formulation containing coal tar used as the binder of a sand filled mortar.
4. A preformed spiral of high strength steel is placed in the form, the concrete made by using __________
a) Expanding cements
b) High strength cements
c) Colored cement
d) Aggregates
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Explanation: Expanding cement is places and consolidated and the completed until is cured carefully controlled conditions to achieve the correct degree of expansion after the set and it is important to note that calcium chloride must never be used as an accelerating admixture in prestressed concrete since a number of failures of prestresssed concrete pipes and tanks have been recorded due to phenomenon of chloride corrosion.
5. The pretressed concrete pipes are ideally suited for a pressure range of __________
a) 0.6 to 4n/mm2
b) 0.5 to 4n/mm2
c) 0.8 to 4n/mm2
d) 0.10 to 4n/mm2
View Answer
Explanation: The pretressed concrete pipes are ideally suited for a pressure range of 0.5 to 4n/mm2 for this pressure range, while cast iron and steel pipes are not economical, reinforced concrete pipes are not practicable due to their limited cracking strength and the technique of prestressing pipes was first introduced in 1930 and ever since, numerous pipelines have been installed throughout the world.
6. The classification of prestressed concrete pipes may be done depending upon the method of __________
a) Curing
b) Placement
c) Manufacture
d) Tension
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Explanation: According to Ooykaas prestressed concrete pipes may be classified depending upon the method of manufacture under the following groups:
Monolyte construction based on the principle that a mix of fresh concrete subjected to triaxial pressure behaves in some respects like a solid body, two stage construction the method of manufacturing a non cylinder pipe (without steel cylinder) was developed by Lewiston pipe corporation around 1930.
7. In monolyte construction the manufacturing process consists of pouring concrete under high frequency of __________
a) Vibration
b) Pressure
c) Tension
d) Bending
View Answer
Explanation: The manufacturing process consists of pouring concrete under high frequency vibration in a vertically placed steel mould consisting of an inner and outer shell and the outer shell consisting of longitudinal sections held together by spring assembles, permits the mould to expand while the inner steel mould is covered with an expansible rubber membrane.
8. In stage construction, the main function of the longitudinal prestress is to prevent __________
a) Blocking
b) Cracking
c) Linking
d) Wedging
View Answer
Explanation: The main function of the longitudinal prestress is to prevent cracking in concrete during circumferential winding and cracking due to the bending stresses develop during the handling and installation of pipes and the prestressed pipes, which were produced by the vacuum concrete (overseas) co.Inc in collaboration with an Indian firm are to be used for the veernam scheme to convey water to madras.
9. The diagram of prestressed concrete pipes of circumferential prestressing may be with or without __________
a) Transversal prestress
b) Longitudinal prestress
c) Elliptical prestress
d) Rounded prestress
View Answer
Explanation: Circumferential prestressing winding with or without longitudinal prestressing, landing stresses with or without longitudinal prestressing condition in which a pipe is supported by saddles at extreme points with full water load but zero hydrostatic pressure.
10. In design of concrete pipes the full working pressure conforming to the limit state of __________
a) Design
b) Collapse
c) Serviceability
d) Tension
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Explanation: According to the Indian standard code IS:784, the design of prestressed concrete pipes should cover the following five stages:
Dull working pressure conforming to the limit state of serviceability and the first crack stage corresponding to the limit state of local damage, in addition, it is also necessary to examine the stage of bursting or failure of pipes correspond to the limit state of collapse, mainly to ensure a desirable load factor against collapse.
11. The percentage of reinforcement for prestressed concrete pipes varies between __________
a) 0.5 and 1
b) 0.10 and 2
c) 0.8 and 4
d) 0.7 and 3
View Answer
Explanation: For prestressed concrete pipes, the percentage of reinforcement varies between 0.5 and 1 percent and the modular ratio between 5 and 6 hence the loss to elastic deformation is about 3 to 6 percent of initial stress and in addition to the elastic deformation loss, various other losses of stress due to steel relaxation, creep and shrinkage of concrete should also be considered to arrive at an overall estimate of the losses of prestress.
12. An ingenious method of casting spherical shells at the centre with conical shape was adopted by __________
a) Finsterwalder
b) Darles
c) Hinge
d) Larcan
View Answer
Explanation: An ingenious method of casting spherical shells at the centre with conical shape was adopted towards the top and bottom was first adopted by Finsterwalder for the large sludge digestion tanks at the sewage treatment works in Berlin and Frankfrust using a form work consisting of sectional units which can be rotated about the central axis and the tank prestressed, sector wise with coupled tendons and splices and the most impressive examples of a prestressed conical sheel, is te 58m high tower at Orebro in Sweden which comprises a concical shell with an external diameter of 46m, supported on atail tower and the tank with a water storage capacity of 900m is prestressed by 206 freyssinet cables each made up of 12 wires of 7mm diameter.
13. The square or rectangular tanks are required for __________
a) Structural use
b) Industrial use
c) Aggregate use
d) Commercial use
View Answer
Explanation: Cylindrical tanks are by far the most commonly used types from structural and constructional consideration and the some of the largest prestressed concrete tanks constructed are circular in shape and a cylindrical shape is well suited for circumferential wire wrapping, which constitutes the major prestressing operation in tanks and square or rectangular tanks spanning either vertically or horizontally, are required for industrial use and square tanks are advantageous for storage in congested urban and industrial sites where land space is a major constraint.
14. The base slab forming the floor or tank is generally made of __________
a) Prestressed concrete
b) Reinforced concrete
c) Aluminium concrete
d) Coloured concrete
View Answer
Explanation: The base slab forming the floor or tank is generally made of reinforced concrete constructed on a flat bituminous surfacing or a tin concrete binding with the inter position of a sliding layer such as oil paper so that the slab can move over the compacted soil bed and the slab should be sufficiently flexible so that it can adapt itself to the local deformations of the pre compacted sub soil and the reinforcement in the slab should be well distributed to control the cracking of the slab due to shrinkage and temperature changes.
15. The joint between the walls of the tank and floor slab may be any of the following of?
a) 3
b) 4
c) 5
d) 6
View Answer
Explanation: The joint between the walls of the tank and floor slab may be any one of the following three types: fixed base, hinged base, sliding base and the ring tension and bending moment developed in the walls of the tank are mainly influenced by the type of connection between walls and the base slab and in hinged base is not generally adopted for prestressed concrete and in this type, the wall is supported over an annular bearing resting on the footing from which the base slab is isolated by a joint from which the base slab is isolated by a joint contains a compressible filling and in the case of large tanks and especially for those which have to store hot liquids a movable or sliding joint is the ideal solution to minimize or completely eliminate the moments at the base of wall.
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