Category: Prestressed Concrete Structures Objective Questions

Prestressed Concrete Structures Multiple Choice Questions on “Tensioning Devices”.

1. In pre tensioning system, type of prestressing tendon used is ___________
a) Bars
b) Wires
c) Strands
d) Cables
Answer: c
Clarification: The strand tendons are used in both pre tensioning and post tensioning, they are made by winding seven cold drawn wires together on a stranding machine, the addition of strands in subsequent layers of wire forms strands of 19 or 37 wires, large post tensioning applications can cope with stressing requirements by use of these tendons.

2. The yield stress relieved in wires is about ___________
a) 620mpa
b) 1300mpa
c) 1250mpa
d) 600mpa
Answer: b
Clarification: The wire tendons are mainly used in post tensioning system for prestressed concrete, they are cold drawn and stress is relieved with a yield stress of about 1300mpa and the diameter generally ranges from between 5mm-8mm.

3. The use of bar tendons with threaded anchorages reduces the possibility of ___________
a) Push
b) Pull
c) Break
d) Bend
Answer: b
Clarification: The bar type tendons are used in certain post tensioning systems, the bars are of high strength alloy steel of yield strength about 620mpa and diameter up to 40mm and the use of bar tendons with threaded anchorages reduces the possibility of pull in at the anchorages and also anchorage cost.

4. The cables are formed by arrangement of wires or strands in ___________
a) Bundles
b) Rings
c) Ducts
d) Steel
Answer: a
Clarification: The cables are formed by arrangement of wires or strands in bundles and the performed duct in concrete member can be stressed and tensioned by appropriate post tensioning method by using cables, post tensioning is invariably used for strengthening concrete dams, circular prestressing of large concrete tanks and biological shields of nuclear reactors.

5. How many types of splicing arrangement are widely used in post tensioning systems?
a) 4
b) 5
c) 3
d) 2
Answer: a
Clarification: Screw connectors are normally employed to splice large diameter high tensile bars which can be threaded at ends, the torpedo splice consists of triple wedges for securing the wires and the entire unit is covered and protected by a sleeve, clamp splices are equipped with bolts and nuts with a series of clamp plates to house the tendons between them for splicing of small diameter wires of 3-6mm.

6. The commonly used mechanical devices used in the following statement.
a) Weight with lever transmission
b) Geared transmission without pulley blocks
c) Hydraulic jacks
d) Tendons
Answer: a
Clarification: The commonly used mechanical devices are weights with the level transmission, weight without lever transmission, geared transmission with pulley blocks; screw jacks without gear drives, wire winding machinery and the mechanical devices are generally used for imparting prestress in the concrete members which are prepared in large amounts in big factories.

7. The hydraulic jacks are the simplest and most widely used devices for providing prestress of ___________
a) High magnitudes
b) High discharges
c) High Bending moment
d) High tension
Answer: a
Clarification: Hydraulic jacks are the simplest and most widely used devices for providing prestress of high magnitudes and various hydraulic devices are prepared by different scientists from which the commonly used devices Freyssinet, Magnel Balton, Gifford Udall system, Baur Leonhardt, lee mc call system, Prescon system etc.

8. The applied force should be measured accurately in hydraulic devices while?
a) Tensioning the tendons
b) Tensioning the wires
c) Tensioning the cables
d) Tensioning the anchorages
Answer: a
Clarification: The prestressing members with hydraulic devices, the applied force should be measured accurately while tensioning the tendons and this can be achieved by providing pressure gauges with the jacks.

9. The electrical devices are commonly used for tensioning of ___________
a) Bend wires and steel wires
b) Deformed bars and steel wires
c) Torsion and steel wires
d) Compression wires and steel wires
Answer: a
Clarification: Electrical devices are used commonly for the tensioning of deformed bars and steel wires and the method of pre stressing involves the heating up of steel wires and anchoring them before filling the moulds with concrete.

10. The basic chemical substance used for pre stressing forces in concrete member is ___________
a) Aluminium
b) Sulphur
c) Shrinkage cement
d) Expanding cement
Answer: d
Clarification: Chemical substances are also used for developing pre stressing force in concrete members and the basic chemical substance used is expansive cement, when expansive cement is used in construction, the tendons are subjected to tension (while setting).

Prestressed Concrete Structures Multiple Choice Questions on “Short Term Deflections”.

1. The short term deflections are also known as __________
a) Cracked
b) Un cracked
c) Instantaneous
d) Non instantaneous
Answer: c
Clarification: Short term deflections of prestressed members are also known as instantaneous deflections governed by distribution of bending moment throughout the span and flexural rigidity of member, these theorems are applied for determining the deflections due to prestressing force, imposed loads and self weight.

2. Which of the following is the equation given Mohr’s first theorem?
a) Area of bending moment deflection/flexural rigidity
b) Moment/flexural rigidity
c) Deflection/flexural rigidity
d) Loads/flexural rigidity
Answer: a
Clarification: When the beam AB is subjected to a bending moment distribution due to prestressing force or self weight or imposed loads, ACB is the centre line of the deformed structure under the system of given loads, According to Mohr’s first theorem
Slope = area of bending moment deflection/flexural rigidity, θ = A/EI.

3. Which of the following is the equation given by Mohr’s second theorem?
a) Mid span/flexural rigidity
b) Moment of area of bending moment diagram/flexural rigidity
c) End span/flexural rigidity
d) Thickness/flexural rigidity
Answer: b
Clarification: Mohr’s second theorem states that
Intercept, a = (moment of the area of bending moment deflections/flexural rigidity), a = AX/EI,
a = deflection at the centre for symmetrically loaded, simply supported beam (since the tangent is horizontal for such cases), A = area of bending moment deflection between A and C, x = distance of the centroid of the bending moment deflection between A and C from the left support, EI = flexural rigidity of beam.

4. Which of the following deflections are directly obtained by Mohr’s second area theorem?
a) Simply supported beam
b) Uniformly distributed load
c) Point beams
d) Fixed beams
Answer: a
Clarification: The deflections of symmetrically loaded and simply supported beam at the mid span point are directly obtained from the second moment area theorem since the tangent is horizontal at this span, In most of cases of prestressed beams tendons are located with eccentricities towards the soffit of the beam to counteract the sagging bending moments due to transverse loads.

5. The problems involving unsymmetrical loading can be solved by __________
a) Mohr’s theorem
b) Kennedy’s theorem
c) Row’s theorem
d) Casagrande’s theorem
Answer: a
Clarification: More complicated problems involving unsymmetrical loading may be solved by combining both the moment area theorems Mohr’s first theorem and second theorem, since the bending moment at every section is the product of prestressing force and eccentricity the tendon profile itself will represent the shape of the bending moment diagram.

6. A straight tendon at a uniform eccentricity below the centroidal axis is given as __________
a) –PeL²/4EI
b) –PeL²/8EI
c) –PeL²/14EI
d) –PeL²/16EI
Answer: b
Clarification: A straight tendon at a uniform eccentricity below the centroidal axis is given as:
If the camber of beam with straight tendons upward deflections are considered as negative and
a = -(PeL) (L/4)/EI = -PeL²/8EI, P = effective prestressing force, e = eccentricity, L = length of beam.

7. A tendon with a trapezoidal profile considering the bending moment and deflection at the centre of the beam is obtained by __________
a) –Pe/6EI(2l₁²+6l₁l²+3l₂²)
b) –Pe/6EI(2l₁²+6l₁l²+3l₂²)
c) –Pe/6EI(2l₁²+6l₁l²+3l₂²)
d) –Pe/6EI(2l₁²+6l₁l²+3l₂²)
Answer: b
Clarification: A draped tendon with a trapezoidal profile considering the bending moment diagram the deflection at the centre of the beam is obtained by taking the moment of the area of the bending moment diagram over one half of the span A = –Pe/6EI(2l₁²+6l₁l²+3l₂²).

8. The deflection of a beam with parabolic tendon is given as __________
a) –5PeL²/48EI
b) –10PeL²/48EI
c) –15PeL²/48EI
d) –3PeL²/48EI
Answer: a
Clarification: The deflection of the beam with parabolic tendons having an eccentricity e at the center and zero at the supports is given by a = –5PeL²/48EI, a beam with a parabolic tendon having an eccentricity e₁ at the centre of span and e₂ at the support sections and the resultant deflection at the centre is obtained as the sum of the upward deflection of a beam with a parabolic tendon of eccentricity e₁+e₂ at the centre and zero at the supports and the downward deflection of a beam subjected to a uniform sagging bending moment of intensity pe₂ throughout the length, the resultant stress becomes a = PL²/48EI(-5e₁+e₂).

9. The deflection is computed in a way similar to sloping tendon is given as __________
a) 2PL²/24EI
b) 4PL²/24EI
c) PL³/24EI (-2e₁+e₂)
d) PL²/24EI (e₁+e₂)
Answer: c
Clarification: The deflection in sloping tendon is computed in a way similar to:
A = (-PL²/12EI (e₁+e₂)) + (Pe2L²/8EI)
A = (PL³/24EI (-2e₁+e₂)).

10. The deflection due to self weight and imposed loads are __________
a) 5(g+q)L⁴/384EI
b) 5(g+q)L⁴/384EI
c) 5(g+q)L⁴/384EI
d) 5(g+q)L⁴/384EI
Answer: a
Clarification: At the time of transfer of prestress, the beam hogs up due to the effect of prestressing, at this stage the self weight of the beam includes downward deflections, which further increases due to the effect of imposed loads on the beam a = 5(g+q)L⁴/384EI and deflections due to concentrated live loads can be directly computed by using Mohr’s theorem.

Prestressed Concrete Structures Multiple Choice Questions on “End Zone Reinforcement”.

1. What are necessary to prevent failure at the end zones, in the transfer zone of pretensioned beams?
a) Reinforcements
b) Blocks
c) Anchorages
d) Tendons
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: c
Clarification: 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
c) Links
d) Hair pin bars
Answer: a
Clarification: 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
Answer: b
Clarification: 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?
a) Ducts
b) Anchorages
c) Hair pin bars
d) Transverse bars
Answer: c
Clarification: 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 ____________
a) Tendons
b) Jacks
c) Springs
d) Anchorages
Answer: d
Clarification: 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 ____________
a) Overlapping
b) Compression
c) Tensioning
d) Torsion
Answer: a
Clarification: 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 ____________
a) High
b) Low
c) Equal
d) Zero
Answer: b
Clarification: 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 ____________
a) Considered
b) Not considered
c) Made equal
d) Made Zero
Answer: a
Clarification: 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.

Prestressed Concrete Structures Multiple Choice Questions on “Design of Post Tensioned Beams”.

1. Calculate ultimate moment and shear of effective span is 30m, live load is 9kn/m, dead load excluding self weight is 2kn/m, load factors for dead load is 1.4 for live load is 1.6 cube strength of concrete f_cu is 50n/mm² cube strength at transfer is f_ci is 35n/mm², tensile strength of concrete E_c is 34kn/mm² loss ratio ɳ is 0.85 and 8mm diameter high tensile strength f_pu is 1500n/mm² are available for use and the modulus of elasticity of high tensile wires is 200kn/mm²?
a) 340 and 450kn
b) 240 and 340kn
c) 140 and 240kn
d) 100 and 200kn
Answer: a
Clarification: W_min/W_ud = (50x2400x9.81×0.125x25x30/50×10⁶x0.85²) = 0.31
Ultimate load excluding the factored selfweight = (1.4×2)+(1.6×9) = 17.2kn/m, W_ud = 17.2/1-1.4×0.31 = 30KN/M, W_min = (0.31×30) = 9.3kn/m, Ultimate moment, M_u = (0.125x30x30²) = 3400knm, Ultimate shear, V_u = (0.5x30x30) = 450kn.

2. Find cross-sectional dimensions thickness of web if h_f/d ratio is 0.23 and b_w/b ratio is 0.25 and b is 0.5d?
a) 100mm
b) 110mm
c) 120mm
d) 30mm
Answer: c
Clarification: h_f/d =0.23 and b_w/b = 0.25 and b = 0.5d,
M_u = 0.10f_cubd² d = (3400×10⁶/0.10x50x0.5)^1/3 = 1130mm, h = (1130/0.85) = 1300, b = 600mm, h_f = (0.2×1130) = 250mm, adopt an effective depth, d = 1150mm, thickness of web, b_w = (0.6vu/fth) = (0.6x450x10³/1.7×1300) = 120mm.

3. Calculate working moment if design working load is 19.8kn/m covered over a span of 30m (actual self weight of girder is 8.8kn/m)?
a) 3000
b) 2000
c) 4340
d) 2230
Answer: d
Clarification: Actual self weight of the beam and the girder = 8.8kn/m, span = 30m
Minimum moment M_min = 990knm, Design working load = 19.8kn/m,
Working moment M_d = (0.125×19.8×30²) = 2230knm.

4. Find the Permissible stresses and range of stresses for class 1 structure f_cu = 50n/mm², f_ck = 35n/mm² according to BS: 8110 recommendations for f_cu = 50n/mm² and f_ci = 35n/mm²,f_ct = 0.5f_ci = 17.5n/mm²?
a) 16.5n/mm²
b) 12.56n/mm²
c) 13.56n/mm²
d) 12.00n/mm²
Answer: a
Clarification: f_cu = 50n/mm²,f_ck = 35n/mm² according to BS: 8110 recommendations for f_cu = 50n/mm² and f_ci = 35n/mm², f_ct = 0.5f_ci = 17.5n/mm²For class 1 structure f_u = h_tw = 0, f_br = (ɳf_ct-ftw) = (0.85×17.5) = 15n/mm², f_cw = 0.33f_cu = (0.33×50) = 16.5n/mm², f_cu = (fcw-ɳfu) = 16.5n/mm².

5. Find prestressing force if area is 36.75mm² of eccentricity 580 given f_inf is 26.5kn/m and z_b is 99×10⁶?
a) 405
b) 308
c) 453
d) 206
Answer: b
Clarification: Area = 36.75mm², e = 580, f_inf = 26.5kn/m, z_b = 99×10⁶
p = (Af_infZ_b/Z_b+A_e) =(367500×26.5x99x10⁶/(99×10⁶)+(367500×580)) = 308x104kn/m².

6. Find force in cable using Freyssinet cables 12-8mm diameter and stressed to 1100n/mm² of eccentricity 50 and the prestressing force is given as 1000n/mm²?
a) 660kn
b) 234kn
c) 300kn
d) 230kn
Answer: a
Clarification: 12 diameter, stress = 1100n/mm², e = 50, prestressing force = 1000n/mm²
Force in each cable = ((12x50x1100)/1000)) = 660kn.

7. Find ratio for ultimate flexural strength at the centre – span section given that A_ps = 3000mm², d = 1150mm, f_cu = 50n/mm², b_w = 150mm, f_pu = 1500n/mm², b = 600mm, h_t = 250mm, design ultimate moment m_ud = 3400knm?
a) 9.5
b) 0.23
c) 6.7
d) 3.4
Answer: b
Clarification: A_ps = 3000mm², d = 1150mm, f_cu = 50n/mm², b_w = 150mm, f_pu = 1500n/mm², b = 600mm, h_t = 250mm, design ultimate moment m_ud = 3400knm, according to BS: 8110-1985, _Aps = (A_pw+A_pf) = A_pf = 0.45×50(600-150)(250/1500) = 0.45xf_cu(b-b_w)(h_f/f_pu) = 1680mm², A_pw = (1300-1680) = 1320mm², ratio(f_puA_pw/f_cub_wd) = (1500×1320/50x150x1150) = 0.23.

8. Calculate the slope of cable section at support uncracked in flexure given that eccentricity is 410, length is 30m and stress induced is 1000?
a) 0.0547
b) 2.456
c) 0.0234
d) 0.0123
Answer: a
Clarification: e = 410, length = 30m, stress induced = 1000
Slope of cable θ = (4e/l) = ((4×410)/(30×1000)) = 0.0547.

9. Calculate the span section cracked in flexure (M=M0) F_cp = 23.4n/mm², z_b is 99×106 and stress induced is 1000?
a) 1200kn
b) 1850kn
c) 2300kn
d) 4300kn
Answer: b
Clarification: F_cp = 23.4n/mm², zb is 99×10⁶, stress is 1000
m₀ = (0.8f_cpZ_b) = (0.8 x 23.4 x (99×10⁶/1000)) = 1850knm.

10. Find resultant maximum long term deflection if ϕ is 2.6, α_y is 38.5mm, α_g is 46mm, α_p is 74.7mm?
a) 95mm
b) 35mm
c) 55mm
d) 20mm
Answer: a
Clarification: E_ce = (E_c/1+ϕ) = (E_c/2.6), ϕ = 2.6, α_y = 38.5mm, α_g = 46mm, α_p = 74.7mm, resultant maximum long term deflection = (2.6×46)+38.5-(0.85×74.7) = 95mm which is less than the code limit (span/250) = 120mm, ɳ = 0.85.

Prestressed Concrete Structures Multiple Choice Questions & Answers on “Prestressing of Poles and Sleepers”.

1. The prestressed concrete poles are currently used in __________
a) Mass
b) Heat
c) Current
d) Wave
Answer: a
Clarification: 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
Answer: c
Clarification: 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
Answer: a
Clarification: 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
Answer: c
Clarification: 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
Answer: b
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: a
Clarification: 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
Answer: c
Clarification: 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
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: a
Clarification: 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.

To practice all areas of Prestressed Concrete Structures,