This set of Prestressed Concrete Structures Multiple Choice Questions & Answers focuses on “Prestressing of Poles and Sleepers”.
1. The prestressed concrete poles are currently used in __________
a) Mass
b) Heat
c) Current
d) Wave
View Answer
Explanation: Prestressed concrete poles are currently mass produced and are widely used in most countries for railway power and signal lines, lightening poles, antenna masts, telephone transmission, low and high voltage electric power transmission and substation towers main advantage resistance to corrosion in humid and temperature climate and to erosion in desert areas, freeze throw resistance in cold regions.
2. The appearance of prestressed concrete poles is __________
a) Rusty
b) Greesy
c) Clean
d) Black
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Explanation: Clean and neat in appearance and requiring negligible maintenance for a number of years, thus ideally suited for urban installation and have increased crack resistance, rigidity and can resist dynamic loads better than reinforced concrete poles, lighter because of reduced cross section when compared with reinforced concrete poles and fire resistant, particularly to grass and brush fires near the ground line.
3. The maximum moment of resistance in a pole is generally required at __________
a) Base
b) Corner
c) Edge
d) Middle
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Explanation: The maximum moment of resistance in a pole is generally required at Base and consequently, the maximum cross-sectional area is required at the base section and poles are generally tapered with a hollow core to reduce the weren’t, which also helps in providing a race way for electric wires and typical cross sections of transmission line poles widely employed in different countries and for small lengths of up to 12m, the square or rectangular sections are preferable as they are easily manufactured and occupy less space in transportation.
4. The prestressed concrete poles for power transmission lines are generally designed as members with __________
a) Partial pressure
b) Chemical prestress
c) Uniform prestress
d) Total prestress
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Explanation: The prestressed concrete poles for power transmission lines are generally designed as members with Uniform prestress since they are subjected to bending moments of equal magnitude in opposite directions and they are generally designed for following critical load conditions and bending due to wind load on the cable and on the exposed face, combined bending and torsion due to eccentric snapping of wires, maximum torsion due to failure of all the wires on one side of the pole and handling and erection stresses.
5. In the case of tapered poles with a reduced cross section the effective prestressing force should be __________
a) Increased
b) Decreased
c) Bended
d) Equal
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Explanation: In the case of tapered poles with a reduced cross section towards the top, the effective prestressing force should be reduced in proportion to the cross section by the techniques of de bonding or by dead ending or looping some of the tendons at mid height and according to Gerwick a constant cross section proves to be better solution in many cases since the top must be as strong as the base for resisting torsion with the added advantage of the effective use of prestressing and easier connections.
6. The main advantage of prestressed concrete piles over traditional reinforced and concrete steel piles is __________
a) Moment carrying capacity
b) Beam carrying capacity
c) Column carrying capacity
d) Foundation carrying capacity
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Explanation: The main advantages according to Gerwick of prestressed concrete piles over traditional reinforced concrete and steel piles are high load and moment carrying capacity, standardization in design for mass production, excellent durability under adverse environmental conditions, crack free characteristics under handling and driving, resistance to tensile loads due to uplift combined load moment capacity, particularly advantages for deep foundations to carry heavy loads in weak soils.
7. Prestressed concrete piles have been used as which type of piles in sands?
a) Rotation
b) Friction
c) Twisting
d) Torsion
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Explanation: Prestressed concrete piles have been used as which type of piles in sands friction piles in sands, silts and clays and a bearing piles on rocky strata and in size as small as 250mm diameter with length up to 36m and layer diameters of up to 4m is used in Oester schedule bridge in Netherlands pile of considerable lengths of up to 80m cast and driven in one piece were used for the off-shore platform in the gulf of Maracaibo, Venezuela.
8. The rebound tensile stresses in pile reinforcements are resisted by the __________
a) Effective prestress
b) Non effective prestress
c) Absolute prestress
d) Normal prestressing force
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Explanation: The rebound tensile stresses are resisted by the effective prestress together with the tensile strength of concrete and hence the steel tendons area at yield should have an equal or greater force than the prestress plus concrete tensile strength to prevent failure due to low cycle fatigue based on theory and experience Gerwide recommends a minimum tendon area of not less than 0.5 percent of the concrete section.
9. Pile shoes are required for driving through __________
a) Hard materials
b) Plastic materials
c) Soft materials
d) Tensile materials
View Answer
Explanation: Pile shoes are required for driving through extremely soft materials like buried timbers and rocky strata however for driving prestressed concrete piles into sands, silts, clays and soft shales, pile shoes are un necessary and pile shoes are formed by thick steel plates or stubs welded to the reinforcing bar anchors and firmly embedded into the pile tip bar anchors and firmly embedded into the pile tip.
10. Prestressed concrete sheet piles are ideally suited for the construction of __________
a) Air frond bulkheads
b) Water frond bulkheads
c) Half brick walls
d) Full brick walls
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Explanation: Prestressed concrete sheet piles are ideally suited for the construction of Water frond bulkheads construction of waterfront bulkheads, cut off walls, grains wave baffles and retaining walls to supports soil and hydrostatic pressure in embankment or in excavations since prestressed concrete piles resist tensile stresses under driving and bending stresses under service loads, they are preferred to timber and steel for marine structure, such as soldier beams, back stays and transverse struts and the high strength concrete used in sheet piles with proper compaction, provides excellent resistance to corrosion and other destructive effects of the aggressive marine environment.
11. The prominent prestressed sleepers which have been adopted by railways of various countries is?
a) Single block sleepers
b) Gauge sleepers
c) Two block sleepers
d) Friction sleepers
View Answer
Explanation: The developments in sleeper design extending over the last three decades has resulted in the adoption of different types and the prominent types which have been adopted by the railways of the various countries are: two block sleepers connected by a pipe filled with concrete and containing high tensile bars for compressing the concrete in the blocks, longitudinal sleepers located continuously under the rails and connected by flexible tie bars for gauge retention, beam type single piece prestressed concrete sleepers, which are quite similar to the convential wooden type sleepers in shape, length and supporting area and in contrast to the two block type, the beam type sleepers are flexurally stiff over their entire length and have the additional advantage of providing greater measure of rigidity to the track if the rails and tightly fastened to the sleepers, preventing rotation at the seatings and bulking of the rails and solid heavy prestressed sleepers have thus made possible the adoption of long colded rails, resulting in smooth running and increased safety of the vehicles and permanent way.
12. The prestressed concrete biological shields are used for __________
a) Containment vessels
b) Pressure vessels
c) Rolled vessels
d) Tension vessels
View Answer
Explanation: The use of prestressed concrete biological shields for reactor and containment vessels offers many advantages and the world wide annual demand for all forms of energy will increase tremendously and numerous electrical power plants will be required to fulfill this stupendous energy requirement and reduced possibility of sudden-bursting failures triggered by local cracking due to the high redundancy of the tendon concrete system and progressive mode of college is endured so that ample time is available for taking precautionary measures against core melting.
13. Which type of prestressing is used in prestressed concrete pavements?
a) Expansion
b) Longitudinal
c) Transverse
d) Contraction
View Answer
Explanation: Longitudinal prestressing can effectively eliminate the formation of cracks in slabs and in addition expansion joints and weak edge zones are entirely eliminated by the introduction of moderate pre compression in the concrete slabs and the introduction of the jet aircrafts has necessitated the use of jointless runways as the sealing compounds used as joint filers cannot withstand the high temperatures of the exhaust gases of the jet engine.
14. The longitudinal prestressing of the slabs is achieved by __________
a) Internal prestressing
b) External prestressing
c) Tensile stress
d) Principle stresses
View Answer
Explanation: Longitudinal prestressing of the slabs is achieved either by external prestressing against rigid abutments or by internal prestressing by means of tensioned bars or cables and the method of external prestressing by using flat jacks against fixed abutments at the ends of the slab has the following disadvantages and difficulty of providing unyielding abutments yielding of abutments reduces the prestress in the slab, the compressive stress in the slab gradually decreases with time due to the shrinkage and creep of concrete.
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