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Prestressed Concrete Structures MCQ Set 1

1. The phenomena of development of internal tensile stresses in a concrete member by means of tensioning devices are called as:
a) Pre-tensioning
b) Post-tensioning
c) Prestressing of concrete
d) Thermoelectric prestressing

View Answer

Answer: c [Reason:] Prestressed concrete is basic concrete, in which internal stresses of a suitable magnitude and distribution are introduced so that the stresses resulting from external loads are counteracted to a desired degree.

2. In reinforced concrete members the prestress is commonly introduced by:
a) Tensioning the steel reinforcement
b) Tendons
c) Shortening of concrete
d) Rings

View Answer

Answer: a [Reason:] In reinforced concrete members, the prestress commonly introduced is by tensioning the steel reinforcement while rings i.e stirrups are used while placing columns or foundation in structures, tendon is a stretched member of a prestressed concrete element which serves the purpose of transmitting the prestress to concrete and shortening of concrete phenomena occurs while placing of concrete.

3. Which of the following basic concept is involved in the analysis of prestressed concrete members?
a) Combined and bending stresses
b) Principle stresses
c) Shear stresses
d) Overhead stresses

View Answer

Answer: a [Reason:] The basic concept involved in the analysis of prestressed concrete members is concept of combined direct and bending stresses used for columns whereas principle and shear stresses are formed in case of tensioning the prestressed and reinforced structures, overhead stresses are formed while the stresses in structures goes beyond safe limit provided by different codes.

4. The prestressing of concrete member is carried out to reduce:
a) Compressive stresses
b) Tensile stresses
c) Bending stresses
d) Shear force

View Answer

Answer: a [Reason:] The prestressing of concrete members is done to reduce the compressive stresses developed in the concrete members to the required extent while tensile stresses is the stress state where the length of member tends to expand in tension side while the volume remains constant, shear forces and bending stresses occurs at the cross section of the beam as the unbalanced vertical force and algebraic sum of moment of forces to right or left of section.

5. The earliest examples of wooden barrel construction by force-fitting of metal bands and shrink-fitting of metal tiers of wooden wheels indicate the art of:
a) Prestressing
b) Tensioning
c) Stress
d) Straining

View Answer

Answer: a [Reason:] Wooden barrel construction by force-fitting of metal bands and shrink-fitting of metal tyres on wooden wheels indicate the art of prestressing and it has been practiced from ancient times while the example of tensioning is bracing for building and bridges whereas stress occurs in a member at a force per unit area and strain phenomena occurs by change in length of a unstressed element.

6. The concept which is used in many branches of civil engineering and building construction?
a) Reinforced concrete
b) Prestressed concrete
c) Steel concrete
d) Lump sum concrete

View Answer

Answer: b [Reason:] Prestressed concrete is widely used in many branches of civil engineering and building construction and in recent days it is experiencing greatest growth in the field of commercial building because of its acoustic properties and its ability to provide long open space.

7. The attempt to introduce permanently acting forces in concrete to resist the elastic forces is:
a) Prestressing
b) Loading
c) Pre-straining
d) Bending

View Answer

Answer: a [Reason:] Freyssinet attempted to introduce permanently acting forces in concrete to resist the elastic forces developed under loads and this idea was later developed under the name of prestressing while the loading and bending phenomena occurs in a member while placing and during excessive loads and pre-straining occurs in prestressed concrete structures.

8. In reinforced concrete members, the prestress commonly introduced is:
a) Tensioning steel reinforcement
b) Tensioning wood reinforcement
c) Tensioning rings
d) Tensioning plates

View Answer

Answer: a [Reason:] In reinforced concrete members steel is commonly used by tensioning steel reinforcement and Steel was commonly used in reinforcement in earlier days and had several disadvantages in case of residential buildings.

9. Development of early cracks in reinforced concrete is due to:
a) Strains of steel
b) Stresses of steel
c) Ultimate load
d) Bending of steel

View Answer

Answer: a [Reason:] Development of early cracks in reinforced concrete is due to incompatibility in the strains of steel and concrete and it was perhaps the starting point in the development of a new material like prestressed concrete.

10. Concrete is weak in?
a) Compression
b) Tension
c) Loading
d) Bending

View Answer

Answer: b [Reason:] Concrete is not able to resist direct tension in comparison of its ability to resist direct compression because of its low tensile strength and brittle nature, it behaves non linearly at all times because it has essentially zero strength in tension it is always used as reinforced concrete, as a composite material and it is a mixture of sand, aggregate, cement and water whereas structures are highly vulnerable to tensile cracking due to very low thermal coefficient of expansion.

Prestressed Concrete Structures MCQ Set 2

1. The magnitude of bond stresses is developed between:
a) Concrete and steel
b) Aggregates and steel
c) Water and steel
d) Bricks and steel

View Answer

Answer: a [Reason:] The magnitude of bond stresses developed between concrete and steel and its variation in the transfer zone of pretensioned beam, the deformation of concrete shrinkage depends on environmental conditions, age of concrete, size of concrete, concrete composition etc.

2. The bond stress is zero at the distance equal to the:
a) Tensile length
b) Span length
c) Transmission length
d) Anchorage length

View Answer

Answer: c [Reason:] The bond stress is zero at the end but builds up rapidly to a maximum over a very short length and this value decreases as the stress in the wire builds up at a distance equal to the transmission length, the bond stress is almost zero while the stress in steel and concrete reach their maximum values.

3. The relations proposed by Marshall for bond stress are given as:
a) (τ bp)x = (τ bp)maxe-4ψx/ϕ
b) (τ bp)x = (τ bp)maxe-4ψx
c) (τ bp)x = (τ bp)maxe-4ψ
d) (τ bp)x = (τ bp)maxe-4

View Answer

Answer: a [Reason:] Based on tests conducted at the university of leeds, the following relations have been proposed by marshall (τ bp)x = (τ bp)maxe-4ψx/ϕ, fx = fsc(1-e-4ψx/ϕ), (τ bp)x = maximum value of bond stress, (τbp)max = bond stress of a distance x from the free end, ϕ = diameter of wire, fx = stress in steel a distance x from the free end, fse = effective stress in steel at the ends of transfer zone, ψ = constant, x = distance measured from the free end in mm.

4. According to Marshall the wires of 2 and 5mm diameter are stressed to:
a) 1500 and 1700n/mm2
b) 1575 and 1100n/mm2
c) 1400 and 1800n/mm2
d) 1250 and 1600n/mm2

View Answer

Answer: b [Reason:] Based on tests conducted according to Marshall using wires of 2 and 5mm diameter stressed to 1575 and 1100n/mm2 respectively in conjunction with a concrete having cube strength of 80n/mm2, the values of maximum bond stress and constant ψ found to be 7.42n/mm2 and 0.00725 respectively.

5. The magnitude of the average bond stress compared to the maximum local bond stress is considerably:
a) Less
b) More
c) Zero
d) Constant

View Answer

Answer: a [Reason:] The magnitude of the average bond stress is considerably less than the maximum local bond stress but according to the investigations of Ros, the average bond stress varied from 3.25 to 1n/mm2 for round wires of 1.5 to 5mm diameter in the case of wires initially tensioned to a stress of 1200n/mm2 and tensile stress shall not be allowed at any loading stage up to cracking in case of members assembled out of precast blocks.

6. The stress in a steel wire gradually increases from zero to the:
a) Middle
b) Bottom
c) End
d) Top

View Answer

Answer: c [Reason:] The stress in a steel wire gradually increases from zero at the end of the beam to 100 percent of the effective stresses at the end of the transmission length, after the beam is placed the slab is casted and different rates of shrinkage imposed forces are developed because a moment is induced if the slab is not at the neutral axis of section.

7. The prestressing force of 90 to 95 percent is obtained at about:
a) Half of transmission length
b) Three fourth of transmission length
c) Four third of transmission length
d) 1.5 of transmission length

View Answer

Answer: b [Reason:] The effective prestressing force of 75 to 80 percent develops to about half of the transmission length, 90 to 95 percent of the prestressing force is attained at about three fourths of the transmission length from the end face of the beam.

8. A pre tensioned beam is prestressed with the cube strength of concrete at transfer is 30n/mm2 (β = 0.0235) calculate the transmission length?
a) 645mm
b) 1100mm
c) 485mm
d) 1600mm

View Answer

Answer: c [Reason:] β = 0.0235, cube strength of concrete is 30n/mm2, Transmission length (Lt) = ((fcu)1/2 x 103/β)1/2 = ((30)1/2 x 103/0.0235) = 485mm.

9. A pretensioned beam is prestressed using 5mm diameter wires, τ bp = 7.42, ϕ = 0.00725, Lt = 485mm. Calculate the bond stress at l/4 and l/2 the transmission length from the end?
a) 3.7n/mm2 and 1.82n/mm2
b) 2.2n/mm2 and 5.8n/mm2
c) 4.8n/mm2 and 10.5n/mm2
d) 1.5n/mm2 and 7.4n/mm2

View Answer

Answer: a [Reason:] Bond stress given by (τ bp)x = (τ bp)maxe-4ψx/ϕ = 7.42 e-(4×0.00725xX)/5 τ bp = 7.42e-0.0058X Bond stress at L/4 is given by: τ bp = 7.42e-0.0058×121.25 = 8.7n/mm2, τ bp = 7.42e-0.0058×242.5 = 1.82n/mm2.

10. A pre tensioned beam is prestressed using 5mm diameter wires with an initial stress of 80 percent of the ultimate strength of steel fpu = 1600n/mm2. Calculate average bond stress?
a) 4.20n/mm2
b) 3.30n/mm2
c) 2.0n/mm2
d) 4.9n/mm2

View Answer

Answer: b [Reason:] fpu = 1600n/mm2, d = 5mm, initial stress = 80% = 0.08, Average bond stress = (τ bp)average = (19.6×0.8×1600/πx5x485) = 3.30n/mm2.

Prestressed Concrete Structures MCQ Set 3

1. The concept of load balancing is useful in selecting:
a) Anchorage profile
b) Shaft profile
c) Tendon profile
d) Span profile

View Answer

Answer: c [Reason:] The concept of load balancing is useful in selecting a tendon profile and they provide suitable force system in concrete member, consider a prestressed concrete beam which is provided with a tendon at an eccentricity and is subjected to a hogging moment such that the beam deflects, the slope gets modified as the beam is subjected to a downward external load, if the beam is subjected to a UDL of W per unit run for the complete span, then the net slope at each end can be calculated as: Δ = Wl3/24EcI – Pel/2EcI.

2. In a prestressed concrete member, cable profile is suitable for balancing loads of:
a) External type
b) Internal type
c) Bent type
d) Curved type

View Answer

Answer: a [Reason:] In a prestressed concrete member, external type of loads is balanced by transverse component of suitable cable profile, on effect of loading the net deformation increases the stress, strain and length of the tendon, extension of tendon = 2eδ, increase in strain 2eδ/l, increase in stress = 2eδ/l Ec.

3. The reactions of cable are obtained by replacing the forces acting on:
a) Reinforcement
b) Concrete
c) Edges
d) Steel

View Answer

Answer: b [Reason:] The shape of profile depends on the reaction of cable and these are obtained by replacing the forces acting on concrete with tendons, a prestressed concrete beam with bent tendons has extreme fiber stress, f = P/A+M/z and P/A-M/Z, prestressed concrete beam with parabolic tendon has a net downward force acting on the beam as F = W-We.

4. In a concrete member, trapezoidal cable profile is adopted when the beam is subjected to:
a) UDL
b) SSB
c) Point loads
d) Concentrated loads

View Answer

Answer: d [Reason:] In a concrete member, trapezoidal profile is adopted when the beam is subjected to two concentrated loads and parabolic profile is used when it is subjected to UDL, the curve and sharp angles of cable develop uniformly distributed and concentrated loads respectively and the straight portion of cable does not produce any reactions at the end.

5. The net downward force of prestressed concrete beam with bent tendon is given as:
a) W-2psinθ
b) W+2psinθ
c) Zero
d) 2

View Answer

Answer: a [Reason:] Bent tendons are used in prestressed concrete beams as they tends to provide an upward pressure in the beam and hence reduces the effect of external loading to a great extent, consider a prestressed concrete beam AB of length l it is subjected to a point load W at centre and a prestressing force of P at the ends, the tendon is bent at an angle of θ at the ends, neglecting the frictional losses, the tendon will develop an upward force of magnitude 2Psinθ at the bent at the centre of span, the upward force reduces the effect of the externally applied force in the beam considering equilibrium in vertical direction, the net downward force F = W-2psinθ.

6. The pressure line is also known as:
a) C line
b) E line
c) G line
d) I line

View Answer

Answer: a [Reason:] Consider a beam which is lying over the ground provided with a tendon and is free from all external loads such that the beam remains unaffected by any external bending moments, the tension force and compression force act at the same level when no external bending moments are acting over the beam and the tendon line (p line) or the line in which compressive force is acting is known as pressure line and it is also known as P line or C line.

7. In the concept of pressure line the C line moves over a P line due to the effect of:
a) Stress
b) Strain
c) Moment
d) Prestress

View Answer

Answer: c [Reason:] If the beam is effected by a moment M, in pressure line then the C line moves over the P line at a distance x and the distance is known as lever arm, x = M/P = external moment/p, x = shift of C line from P line.

8. If the section of a rectangular beam is subjected to the prestressing force and dead load then the stress distribution is given by:
a) Pressure line
b) Kern distance
c) Permissible pressure
d) Fracture of steel

View Answer

Answer: b [Reason:] Consider a rectangular beam section subjected to a prestressing force of magnitude p and if the section is subjected to the prestressing force and live and dead load only then the stress distribution across the section is given by kern distance in the form of upper and lower kern distance.

9. If the force acts at the lower kern point then the bottom fibers of the beam are subjected to:
a) Maximum permissible stress
b) Minimum permissible stress
c) Tensile stress
d) Principle stress

View Answer

Answer: a [Reason:] The points a, b, represents the points of application of forces P and C respectively, now if the beam is subjected to live load in addition to dead load and prestress then the point of application of force c reach point a from point a, the point of application of force p and the magnitude of force C remain unchanged, if 0 represents the centroid of the beam section, then the distance ob is kb and oa’ is kt, if the force C acts at the lower kern point the bottom fibers of the beam are subjected to maximum permissible stresses and the top fibers are subjected to minimum permissible stress.

10. The strength concept can also be used to determine the position of:
a) Kern line
b) C line
c) S line
d) E line

View Answer

Answer: b [Reason:] The strength concept can also be used to determine the position of c line, eccentricity and distribution of stress in concrete and it is expressed as: Extreme stress in concrete = C/A+ or – Eccentricity of c/Z.

Prestressed Concrete Structures MCQ Set 4

1. The computation of total ultimate moment required for the design of prestressed beams, knowledge of is necessary:
a) Spans
b) Self weights
c) Loads
d) Deflection

View Answer

Answer: b [Reason:] Generally, the self weight may be assumed on the basis of previous experience and the use of design chart containing dimensions of beams for various spans and applied loads as recommended by magnel is very useful in the regard.

2. The estimation of self weight is expressed as:
a) wmin/wud = KDcgβ(L/h)L/fcu(d/h)2
b) wmin/wud = KDcgβ(L/h)L/fcu
c) wmin/wud = KDcgβ(L/h)
d) wmin/wud = KDc

View Answer

Answer: a [Reason:] Bennelt has recently proposed a simple formula for estimating the self weight of the girder by considering several influencing parameters wmin/wud = KDcgβ(L/h)L/fcu(d/h)2 wmin = Self weight or minimum load, L = effective span, K = numerical constant, Dc = density of the concrete member, g = acceleration, β = moment coefficient, h = overall depth of girder, wud = Ultimate design load.

3. In the case of unsymmetrical I girders the range of values of hf/d for economical designs is generally?
a) 0.15 to 0.10
b) 0.15 to 0.25
c) 0.8 to 1.0
d) 3.4 to 6.0

View Answer

Answer: b [Reason:] In the case of unsymmetrical I girders the range of values of ht/d and bw/b for economical designs is generally 0.15 to 0.25 and 0.2 to 0.3 respectively, however the thickness of web, bw is designed based on the dual criteria shear and housing the cables with adequate cover.

4. The breadth of the compression face may be assumed by considering the number of:
a) Anchorages
b) Splices
c) Girders
d) Ridges

View Answer

Answer: c [Reason:] In dimensioning prestressed concrete flexural members the effective depth and breadth of the section at the compression face are determined solely on basis of the ultimate flexural strength requirements and The breadth of the compression face may be assumed by considering the number of covering a given width of bridge deck of a suitable ratio of b’d being in the range of 0.4 to 0.6.

5. The thickness of the web is generally determined on the basis:
a) Shear stress
b) Shear strength
c) Principle shear
d) Tensile shear

View Answer

Answer: b [Reason:] The thickness of the web is generally determined on the basis of shear strength considerations discussed according to british code recommendations shear reinforcements are not required where V is less than 0.5vc and in members of minor imporatance when the shear for V exceeds (Vc to 0.4bwd), shear reinforcement are designed at spacing Sv = Asv0.8fy/0.4bw.

6. The small span girders with straight tendons, bw is:
a) 0.85vu/fth
b) 0.60vu/fth
c) 0.70vu/fth
d) 0.69vu/fth

View Answer

Answer: a [Reason:] In the case of small span prestressed members, thinner webs of about 40 to 60mm may be used however in the case of long span, heavily loaded girders when large, curved cables have to pass through the webs a minimum thickness of 120 to 150mm is mandatory to accommodate the cables with adequate cover.

7. The condition that the principal tensile stress is not to exceed the tensile strength of concrete yields a criterion of the type:
a) bw > (vu/ (I/s) ft(1-fcp/ft)1/2
b) bw > (vu/ (I/s) ft(1+fcp/ft)1/2
c) bw > (vu/ (I/s)
d) bw > (vu/ (I/s) ft

View Answer

Answer: b [Reason:] The value of the shear moment arm I/S varies between 0.67 and 0.85h for I sections, the ratio fcp/ft generally varies between 2 and 3 for small span girders with straight tendons for long span girders with curved tendons, the ratio, fcp/ft can be taken between 3 and 4 and the effective shear as 0.8vu since the curved cables contribute to the ultimate shear resistance of the section.

8. The ultimate design load includes?
a) Partial factor of safety and live load
b) Ultimate load
c) Tensile load
d) Overloaded load

View Answer

Answer: a [Reason:] The ultimate load includes the self weight enhanced by partial factor of safety γf1q+γf2wmin, Wud = γf1q/1-γf2(Wmin/Wud).

9. The value of numerical constant K is between:
a) 4 to 5
b) 6 to 7.5
c) 4 to 8
d) 5 to 9

View Answer

Answer: b [Reason:] The value of numerical constant K is between 6 to 7.5 for rectangular sections and I section girders of short spans, while it takes a value between 4 and 5 for the flanged T or I section girders of long spans for self weight equation.

10. The load combination of dead and imposed has a beneficial dead load of:
a) 1.0
b) 1.5
c) 1.8
d) 2.0

View Answer

Answer: a [Reason:] Load combinations: Dead and imposed (and earth and water pressure) – Dead beneficial is 1.0, Dead and wind( and earth and water pressure) – Dead beneficial is 1.0, Dead and wind and imposed(and earth and water pressure) – Dead beneficial is 1.2.

Prestressed Concrete Structures MCQ Set 5

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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

Answer: d [Reason:] 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

View Answer

Answer: a [Reason:] 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

Answer: b [Reason:] 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

View Answer

Answer: c [Reason:] 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

Answer: a [Reason:] 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

Answer: b [Reason:] 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

Answer: b [Reason:] 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

View Answer

Answer: c [Reason:] 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

Answer: a [Reason:] 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

Answer: a [Reason:] 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 hig 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

Answer: b [Reason:] 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

Answer: b [Reason:] 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

Answer: a [Reason:] 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.