Category: Prestressed Concrete Structures Objective Questions

Prestressed Concrete Structures Multiple Choice Questions on “Transmission by Bond”.

1. In a pretensioned system, when a wire is released from its temporary anchorage the end of the wire swells as a result of __________
a) Contraction
b) Expansion
c) Release
d) Joining
Answer: a
Clarification: In a pretensioned system, when a wire is released from its temporary anchorage on the prestressing bed, the end of the wire swells as a result of the recovery of the lateral contraction and develops a wedge effect and this is generally referred to as the Hoyer effect and this is to enable the prestressing force to become at the end of the wire.

2. The swelling of the wire produces which action on concrete?
a) Linear pressure
b) Axial pressure
c) Radial pressure
d) Upcoming pressure
Answer: c
Clarification: The swelling of the wire is only a few thousandth of a millimeter, but it nevertheless produces considerable radial pressures on the concrete, giving rise to large frictional forces, the general provisions in the Indian code for the transmission length are expressed in terms of the diameter of the wire, bar or strand, taking into considerations the surface characteristics of the tendons.

3. How many factors are considered while prestressing force in steel is transferred to concrete through bond?
a) 4
b) 6b
c) 3
d) 10
Answer: c
Clarification: The prestressing force in steel is transferred to concrete considering three factors through the bond having adhesion, friction, shearing resistance; the limits were made for wire tendons of 100 to 140 diameter and for 7 wires strands 45 to 90 diameter of tendons.

4. The bond stress in the prestress members is mainly due to __________
a) Friction and shrinkage
b) Compression and bondage
c) Tension and torsion
d) Anchorages and tendons
Answer: a
Clarification: The bond stress in the prestress members is mainly due to friction, shearing resistance and for perfect bond; friction is considered generally, the FIP recommendations regarding the anchorage lengths to ensure the transmission of the prestress to the concrete.

5. The bond stress at intermediate points is resisted by __________
a) Friction
b) Shrinkage
c) Adhesion
d) Anchorage
Answer: c
Clarification: Bond stress at intermediate points is resisted by adhesion and in transfer zone the adhesion is destroyed by invariable slip and sink of tendons into concrete, transversely ribbed steel type of wire has a diameter of 20 to 40 mm2 area of bond length 500mm.

6. Which zone attains maximum bond stress?
a) Transverse tension
b) Transverse anchorage
c) Transverse tendon
d) Transverse compression
Answer: d
Clarification: The zone of transverse compression attains maximum bond stress and when the bond stress becomes zero various changes occur, 2 or 3 strand wire of diameter 2 to 3 has a bond length of 700mm, 7 wire strand of diameter 2 to 4 has a bond length of 1000mm.

7. The steel and concrete reach their maximum values of stress when bond stress is?
a) Zero
b) Constant
c) 4
d) 6
Answer: a
Clarification: When the bond stress in zero, the steel and concrete reach their maximum values of stresses with uniform stress distribution in this section, the bond lengths recommended in German specifications are compiled in drawn steel of diameter 3 to 8 and bond length 600mm.

8. The term transmission refers to attainment of uniform __________
a) Strain distribution
b) Stress distribution
c) Level distribution
d) Cross section distribution
Answer: b
Clarification: The length needed for achieving uniform stress distribution in a member is termed as transmission length, the transmission length for plain smooth wires is considerably greater than that for deformed bars or strands due to absence of a mechanical interlock.

9. At intermediate points along the length of a beam, the bond stress is resisted by __________
a) Friction
b) Adhesion
c) Shear
d) Torsion
Answer: b
Clarification: At intermediate points along the length of a beam, the bond stress is resisted by adhesion, while in the transfer zone the tendons invariably slip and sink into the concrete destroying most of the adhesion.

10. The shearing resistance is also termed as __________
a) Trumpet
b) Dilatancy
c) Capacity
d) Adhesion
Answer: b
Clarification: Shearing resistance is also known as dilatancy, it is considered in case of transmission of prestressing force from steel to concrete through bond, the ACI code recommendations are based on the investigations of Kaar and Hatson it includes both length required to develop the effective prestress as also the additional length over which the strand must be bonded to the concrete so that the tensile stresses develop in the strand at the limit state of collapse of the member.

Prestressed Concrete Structures Multiple Choice Questions on “Design for Compression and Bending”.

1. Most compression members, such as long columns and piles are subjected to ____________
a) Bending moment and cracking forces
b) Bending moment and tension forces
c) Bending moment and axial forces
d) Bending moment and compression forces
Answer: c
Clarification: Due to handling in some members like portal frames and masts the sections are subjected to compression and bending and most compression members such as long columns and piles are subjected to bending moment and axial forces.

2. The load moment interaction diagrams are more or less similar to ____________
a) Prestressed columns
b) Reinforced concrete columns
c) Aluminium columns
d) Steel columns
Answer: b
Clarification: The load moment interaction diagrams are more or less similar to prestressed columns those of reinforced columns expect that precompression exists in prestressed concrete columns and the prestressed columns are much advantageous than any other elements which are replicable.

3. The compression failure mode develops under?
a) Static loading
b) Moment loading
c) Concentric loading
d) Tensile loading
Answer: c
Clarification: The compression failure mode develops under concentric loading and this type of failure mode develops under concentric loads and the section is considered to have failed when the concrete strain ε0 reaches a value of 0.02.

4. The balanced failure develops when there is simultaneous ____________
a) Tension yielding
b) Compression yielding
c) Flexure yielding
d) Prestress yielding
Answer: a
Clarification: Balanced failure develops when there is simultaneously tension yielding of prestressing steel and crushing of concrete, the eccentricity of the axial load is defined as balanced eccentricity E_b. and this eccentricity factor is used for various failures considering top and bottom fibers.

5. The charts proposed by Bennett are useful in dimensioning columns of ____________
a) L section
b) I section
c) T section
d) Edge section
Answer: b
Clarification: Bennett has proposed design charts with dimensionless parameters expressed in terms of the service loads and moments, and section properties and permissible stresses in concrete expressed as a fraction of the characteristic strength these charts are useful in dimensioning columns of I section with non uniform prestress and allowing desirable tensile stresses in concrete as in class 3 type members.

6. The steps involved in design of biaxially loaded column are ____________
a) 15
b) 4
c) 8
d) 6
Answer: c
Clarification: The load contour method of analysis, detailed by Nawy and generally termed Bresler-Parme counter method is ideally suited for the design of biaxially loaded columns and the design procedure is outlined the following steps: give the ultimate moments, determine the larger of the equivalent required, assumed cross section, verify the ultimate load carrying capacity, calculate the actual nominal moment capacity, the moment value.

7. The Prestressed concrete compression members should have a minimum average effective prestress of not less than?
a) 1.55n/mm²
b) 1.0n/mm²
c) 1.15n/mm²
d) 1.25n/mm²
Answer: a
Clarification: According to ACI 318-1989, a minimum non prestressed reinforcement ratio of one percent should be provided in compression members with an effective prestress of lower than 1.55n/mm² and the American code specifies the various effective prestress in prestressed concrete members considering all the factors and makes them economical.

8. The Spirals are particularly useful in increasing the ____________
a) Tensile strength
b) Ductility
c) Strain
d) Stress
Answer: b
Clarification: Closely spaced spirals reinforcement increases the ultimate load capacity of the column due to confinement of concrete in the core and spirals are particularly useful in increasing the ductility of the member and hence are preferred in high earthquake zones.

9. The pitch of spiral is computed as v
a) S = 4a_s(D_c – d_s)/D_c² ρ_s
b) S = 2a_s(D_c – d_s)/D_c² ρ_s
c) S = 6a_s(D_c – d_s)/D_c² ρ_s
d) S = 10a_s(D_c – d_s)/D_c² ρ_s
Answer: a
Clarification: S = 4a_s(D_c – d_s)/D_c² ρ_s, a_s = cross sectional area of spiral, D_c = core of the column measured to the outside diameter of the helix, d_s = diameter of spiral wire, ρs = ratio of the volume of helical reinforcement.

10. The pitch of spirals is limited to a range of ____________
a) 40 to 45mm
b) 25 to75mm
c) 15 to 30mm
d) 10 to 30mm
Answer: b
Clarification: The pitch of spirals is limited to a range of 25 to 75mm and the spiral should be well anchored by providing at least 11/2 extra turns when splicing rather than welding of spirals is used and the pitches of the spirals are limited to certain ranges.

Prestressed Concrete Structures Multiple Choice Questions on “Circular Prestressing”.

1. A reinforced concrete pressure pipe requires a large amount of __________
a) Span
b) Reinforcement
c) Area
d) Deflection
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: d
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: a
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: b
Clarification: 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
Answer: a
Clarification: 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.

Prestressed Concrete Structures MCQs on “Structural Forms and High Rise Structures”.

1. In the case of large floor and roof coverings using prestressed concrete as material, one of the structural forms for adoption is?
a) Concrete panels
b) Reinforced disc
c) Spherical domes
d) Trapezoidal domes
Answer: c
Clarification: In the case of large floor and roof coverings using prestressed concrete as material, there are several types of structural forms for adoption and some of them are as follows: Tee beam and slab floors, continuous beam and slab floors, coffered or grid floors, flat slab floors, folded plate roofs, shell roofs, spherical domes, trusses and framed roofs, composite construction using prestressed and reinforced concrete.

2. If cement, fine aggregate and coarse aggregate are simultaneously charged then it improves ____________
a) Tension in concrete
b) Uniformity in concrete
c) Compression in concrete
d) Strain in concrete
Answer: b
Clarification: Uniformity in concrete improves if cement, fine aggregate and coarse aggregate are simultaneously charged into mixer and chemical admixtures should be charged into the mix as solutions and the liquids should be considered as part of the mixing water.

3. Under usual conditions up to which percentage the water should be placed in the mixer drums.
a) 15%
b) 20%
c) 10%
d) 12%
Answer: c
Clarification: Concrete may be mixed using stationary mixes on job site or central mixes as used in ready mix plants and under usual conditions up to about 10% of the mixing water should be placed in the mixer drum before the solid materials are added and there after water should be added uniformly with the solid materials leaving about 10% to be added after all other materials are in drum.

4. When the mixture is mixed in the plant the time should not be less than?
a) 50s
b) 100s
c) 20s
d) 10s
Answer: a
Clarification: When mixed in a central mixing plant, the mixing time should be not less than 50s nor more than 90s and when truck mixer is used as in the case of ready mixed concrete, a minimum of seventy to a maximum of 100 revolutions of the drum or blades at mixing speed are required for complete mixing.

5. For heavily reinforced concrete members the nominal maximum size of aggregates shall be ____________
a) 10mm
b) 1mm
c) 2mm
d) 5mm
Answer: d
Clarification: For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of aggregate shall be 5mm less than the spacing between the cables, strands or sheathings and aggregates containing particular varieties of silica, which are suspectable to attack by alkalis present in cement resulting in expansive reaction should be avoided.

6. The strength of concrete primarily depends upon the ____________
a) Workability
b) w/c ratio
c) Aggregates ratio
d) Cement content
Answer: b
Clarification: The strength of concrete primarily depends upon the w/c ratio and hence the first step in proportioning a concrete mix should be the selection of approximate w/c ratio depending upon the types of cement used to achieve the desired durability and strength intended for the works.

7. What are the advantages of reducing the w/c ratio?
a) Superior dimensional stability
b) Cost
c) Area
d) Workability
Answer: a
Clarification: The various advantage of reducing the w/c ratio is as follows:
Increased compressive, flexural and tensile strength, increased density of concrete with lesser voids, increased water tightness, lower absorption of moisture due to less porosity, increased resistance to weathering, better bond between concrete and reinforcement, superior dimensional stability, lesser shrinkage cracks.

8. In massive structures, concrete should be placed in ____________
a) Trapezoidal layers
b) Horizontal layers
c) Longitudinal layers
d) Edge layers
Answer: b
Clarification: In massive structures, concrete should be placed in horizontal layers not more than 300mm thick expect in thinner slabs and when less than a complete layer is placed in one operation, it should be terminated in a vertical bulk head.

9. Each layer should be placed before the preceding batch undergoes the initial set of ____________
a) Torsion
b) Tension
c) Consolidation
d) Strain
Answer: c
Clarification: Each layer should be placed and consolidated before the preceding batch undergoes the initial set to prevent injury to the green setting concrete and to avoid surfaces of separation between the batches if taller lifts are encountered in structures like column and retaining walls, suitable regarding agents should be used.

10. In the case of horizontal shallow beams, concrete should preferably deposited starting from ____________
a) Centre of span
b) Edge of span
c) Outer portion of span
d) Inner portion of span
Answer: a
Clarification: In the case of horizontal shallow beams, concrete should preferably be deposited starting from centre of span and working towards the ends and for deeper girders, concrete should be deposited preferably for the length and brought up evenly in horizontal layers and concrete in slab panels should be placed in one continuous operation for each span.

To practice MCQs on all areas of Prestressed Concrete Structures,