Category: Prestressed Concrete Structures Objective Questions

250+ TOP MCQs on Resultant Stresses and Answers

Prestressed Concrete Structures Multiple Choice Questions on “Resultant Stresses”.

1. The resultant stresses in concrete at any section are obtained by the effect of ___________
a) Prestress and flexural stresses
b) Prestress and bending stresses
c) Prestress and shear stresses
d) Prestress and torsion stresses
Answer: a
Clarification: Resultant stresses in concrete at any section are obtained by superimposing the effect of prestress and flexural stresses developed due to the loads, other common types of corrosion frequently encountered in prestressed concrete construction are pitting corrosion and chloride corrosion, a critical review of the different types of corrosion of high tensile steel in structural concrete is reported.

2. The resultant stress distribution due to eccentric prestressing, dead and live loads at any given section are obtained as ___________
a) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
b) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
c) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
d) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
Answer: a
Clarification: If Mq and Mg are live loads and dead load moments at the central span section;
Mq=ql2/8
Mg=gl2/8
prestressed-concrete-structures-questions-answers-resultant-stresses-q2

3. A concrete beam of rectangular section, 250mm wide and 600mm deep. Calculate the bending moment that can be applied without applying tension at the soffit of the beam with given m/z value as 5.74?
a) 26.4
b) 54.8
c) 34.5
d) 86.1
Answer: d
Clarification: m/z = 5.74, b = 250mm, d = 600mm
Z = (250×6002/6) = 15×106mm3,
M = (5.74×15×106) = 86.1×106nmm = 86.1knm.

4. A prestressed concrete beam of section 200mm wide by 300mm deep of imposed load 4kn/m at a span of 6m, density of concrete is 24kn/m3. Find the concentric prestressing force necessary for zero fiber stress at the soffit?
a) 490
b) 560
c) 230
d) 310
Answer: a
Clarification: b = 200mm, d = 300mm, A = (200×300) = 6×104mm2, g = (0.2×0.3×24),
Mg = (0.125×1.44×62) = 6.48knm, Mq = (0.125×4×62) = 18knm, Zb=Zt = (200×3002/6) = 3×106mm3
P/A = 8.16, P = (8.16×6×104) = 489.6kn.

5. The locus of the points of application of resultant force in any structure is termed as ___________
a) Pressure line
b) Hollow line
c) Beam line
d) Tendon line
Answer: a
Clarification: The combined effect of prestressing force and the externally applied load will result in a distribution of concrete stresses that can be resolved into a single force and the locus of the points of application of this resultant force in any structure is termed as “pressure or thrust line”.

6. The concept of pressure line is very useful in understanding the concept of ___________
a) Load carrying mechanism
b) Bending mechanism
c) Shear mechanism
d) Torsion mechanism
Answer: a
Clarification: The concept of pressure line is very useful in understanding the load carrying mechanism of a prestressed concrete section, if a prestressed concrete member is cracked, it behaves similar to that of a reinforced concrete section, in contrast to the direct method of analysis of resultant stresses at a section of a prestressed concrete beam outlined the pressure or thrust line concept can also be used to evaluate stresses.

7. The location of the pressure line depends upon ___________
a) Breakage and Bondage
b) Magnitude and direction
c) Shear and Torsion
d) Pressure and equilibrium
Answer: b
Clarification: In the case of prestressed concrete members, the location of the pressure line depends upon the magnitude and direction of the moments applied at the cross section and the magnitude and distribution of stresses due to the prestressing force, the increase in resultant forces are due to a more or less constant lever arm between the forces, characterized by the properties of the composite section.

8. The eccentricity e in the pressure line diagram is?
a) h/16
b) h/12
c) h/15
d) h/8
Answer: a
Clarification: At the support section, since there are no flexural stresses resulting from the external loads, the pressure line coincides with that of the centroid of steel, located at an eccentricity of h/6, at the centre of the span section the external loading is such that the resultant stress developed in maximum at the top fiber and zero at the bottom fibers and it can be easily be seen that for this section the pressure line has shifted towards the top fiber by an amount equal to h/3 from its initial position.

9. The change in the external moments in the elastic range of prestressed concrete beam results in ___________
a) Bending moment in pressure line
b) Torsion in pressure line
c) Flexure in pressure line
d) Shift of the pressure line
Answer: d
Clarification: “A change in the external moments in the elastic range of a prestress concrete beam results in a shift of the pressure line rather than in an increase in the resultant force in the beam, this is in contrast to a reinforced concrete beam section where an increase in the external moment results in a corresponding increase in the tensile force and the compressive force.

10. The shift of pressure line measured from centroidal axis is obtained as ___________
a) (m/p)-e
b) (m/q)-e
c) (m/r)-e
d) (m/i)-e
Answer: a
Clarification: The shift of pressure line is measured from the centroidal axis is obtained as
E’= (a-e) = (m/p)-e, basically the load carrying mechanism is comprised of a constant force with a changing lever arm as in the case of prestressed concrete sections, and a changing force with a constant lever arm prevailing in reinforced concrete sections.

250+ TOP MCQs on Types of Flexural Failure and Answers Quiz

Prestressed Concrete Structures Multiple Choice Questions on “Types of Flexural Failure”.

1. The failure due to fracture of steel in tension in the beam is because of __________
a) Excess amount of steel reinforcement
b) Excess amount of prestressed concrete
c) Least amount of reinforcement
d) Least amount of prestressed concrete

Answer: c
Clarification: The percentage of steel provided, both tensioned and un tensioned taken together should be sufficient so that when the concrete in the pre compressed tensile zone cracks, the steel is in a position to bear the additional tensile stresses transferred to it by the cracking of the adjacent fibers of the concrete, thereby preventing a sudden failure of the beam due to fracture of steel in tension.

2. If the concrete in tension zone get cracks will lead to development of __________
a) Principal stresses
b) Compression
c) Tensile stresses
d) Strain

Answer: c
Clarification: The sudden failure of a prestressed member without any warning is generally due to fracture of steel in the tension zone, this type of failure is imminent when the percentage of steel provided in the section is low that when the concrete in the concrete in the tension zone cracks, the steel is not in a position to bear up the additional tensile stress transferred to it by the cracked concrete.

3. The failure due to fracture steel in tension can be prevented by providing a steel reinforcement is?
a) 0.15 – 0.2%
b) 0.20% – 0.35%
c) 0.2% – 0.6%
d) 0.6% – 0.10%

Answer: a
Clarification: In order to prevent this failure a minimum steel reinforcement is provided in the cross section of beam IS: 1343 recommended a minimum reinforcement of 0.15% – 0.2% of the cross sectional area in pretensioned units of small sections when a high yield strength deformed reinforcement is used, the minimum steel percentage is reduced to 0.15 percent.

4. In under reinforced section failure the beam observes __________
a) Excess elongation
b) Less elongation
c) Edge elongation
d) Mid span elongation

Answer: a
Clarification: In this mode of failure, the beam observes excess elongation of steel along with the crushing of concrete this is because large amount of steel is provided in the compression zone (greater than minimum steel reinforcement in the tension zone).

5. Due to excess elongation of steel, the neutral axis near the compression face gets __________
a) Increased
b) Decreased
c) Elongates
d) Crushes

Answer: a
Clarification: If the cross section is provided with an amount of steel greater than the minimum, the failure is characterized by an excessive elongation of steel followed by the crushing of concrete and as the bending loads are increased excessive elongation of steel raises the neutral axis near the compression face at the critical section of beam.

6. Which type of deflections is observed in compression face during under reinforced section failure?
a) Small deflections
b) Large deflections
c) Bondage deflections
d) Shrinkage deflections

Answer: b
Clarification: Large deflections and wide cracks are observed in compression face and this is because the area of concrete provided is unable to resist the resultant internal compression forces and the member also fails in flexure due to crushing of concrete considerable warnings are observed before impending failure.

7. The over reinforced section fails due to sudden crushing of __________
a) Beam
b) Column
c) Concrete
d) Steel

Answer: c
Clarification: Over reinforced section fails due to sudden crushing of concrete and this section observes small deflections and narrow cracks the effective reinforcement due to which the compressive strength of concrete and tensile strength of steel are increased up to a certain range of values then the section is said to be over reinforced.

8. The amount of steel provided in this section should not be greater than __________
a) Steel required
b) Concrete required
c) Water required
d) Tension required

Answer: a
Clarification: In this section large amount of steel is provided which resists the stresses developed at the failure to reach the tensile strength of steel and the amount of steel provided in this section should not be greater than the steel required for balancing the section.

9. Which one of the following are other modes of failure?
a) Failure due to tension
b) Torsion failure
c) Reinforcement failure
d) Transverse shear failure

Answer: d
Clarification: Other modes of failure like transverse shear failure and web crippling are caused due to improper design of member in shear and by providing thin webs in the section, in case of pretensioned members, the failure of bond between the steel and the surrounding concrete is likely due to the inadequate transmission lengths at the ends of members, in post tensioned members anchorage failures may take place if the end block is not properly designed to resist the transverse tensile forces.

10. The failure due to other modes like transverse shear failure is mainly caused due to __________
a) Principal stresses
b) Tensile stresses
c) Compressive stresses
d) Strain

Answer: a
Clarification: These failures are mainly caused due to excessive principle stresses developed in the members when they are subjected to transverse loading, prestressed concrete members subjected to transverse loads may fail in shear before their full flexural strength is attained, if they are not adequately designed for shear, web shear cracks may develop if the principal stresses are excessive and if thin webs are used, the failure may occur due to web crushing.

250+ TOP MCQs on Analysis by Zielinski and Rowe and Answers

Prestressed Concrete Structures Multiple Choice Questions on “Analysis by Zielinski and Rowe”.

1. The Zielinski and Rowe conducted experiments on concrete prismatic specimens using the technique?
a) Surface stress
b) Surface strain
c) Surface tension
d) Surface edge
Answer: b
Clarification: Experimental investigation on concrete prismatic specimen was conducted by Zielinski and Rowe using the technique of surface strain measurements if groups of anchorages are encountered the end block is divided into a series of symmetrically loaded prisms and each prism is analyzed for bursting tensile forces using the recommended Indian code provision expressions.

2. The parameters considered for concrete prisms are ____________
a) Midspans
b) Blocks
c) Cross sectional area
d) End block
Answer: c
Clarification: The concrete prisms act as end blocks and the investigations were carried out on parameters like cable duct or hole, the ratio of loaded to cross sectional area, the cracking, type of anchorages and ultimate loads.

3. The distribution of transverse stress and ultimate load of the end block is not effected by ____________
a) Anchorage material
b) Curing concrete
c) Tendons applied
d) Jacking provided
Answer: a
Clarification: The studies revealed that the distribution of transverse stress and ultimate load of the end block is not affected by: the anchorage being either embedded or external, the material of the anchorage, the method of anchoring the wires.

4. The Zielinski and Rowe developed empirical relations for computation of ____________
a) Maximum transverse tensile stress
b) Minimum transverse tensile stress
c) Zero
d) Constant
Answer: a
Clarification: Zienlinski and Rowe developed empirical relations to compute the maximum transverse tensile stress and the bursting tension and when an end block is subjected to a concentrated load at the end face and at equal distances to 0.5ẙ the distribution of transverse stress is found to be maximum.

5. The equation for maximum tensile stress, fmax is given as?
a) fc(0.98-0.825(ypo/yo))
b) fc(0.98-0.825(ypo/yo))
c) fc(0.98-0.825(ypo/yo))
d) fc(0.98-0.825(ypo/yo))
Answer: a
Clarification: The maximum tensile stress, fvmax = fc(0.98-0.825(ypo/yo)) which is valid for ypo/yo = 0.3 to 0.7 bursting tension, Fbst = pk(0.48-0.4(ypo/yo)), (ypo/yo) = ratio of sides of loaded area to bearing area of the prism, fv = transverse tensile stress, fc = average compressive stress in the prism, pk = applied compressive force on the end block.

6. The creating bursting tension is given by?
a) Fbst(3-(fv/fv,max)2)
b) Fbst(3-(fv/fv,max)2)
c) Fbst(3-(fv/fv,max)2)
d) Fbst(3-(fv/fv,max)2)
Answer: c
Clarification: When allowance is provided for tension taken by concrete, the creating bursting tension is given by Fbst, corred = Fbst(3-(fv/fv,max)2), ft = permissible tensile strength of concrete.
To resist bursting tension, the reinforcement should be arranged between 0.2y0 and 2y0 providing the maximum intensity of stress.

7. Estimate the position and magnitude of the maximum transverse tensile stress and bursting tension for the end block with a concentric anchor force of 100kn using Rowe’s method?
a) 26.5n/mm2
b) 26.5n/mm2
c) 26.5n/mm2
d) 26.5n/mm2
Answer: d
Clarification: pk = 100kn, 2ypo = 50mm, 2ypo = 100mm, ypo/yo =0.5, fc = (100×103/100×100) = 10n/mm2, fv(max) = fc(0.98-0.825(ypo/y0)) = 10(0.98-0.825(0.5)) = 5.68n/mm2.

8. The end block and a prestressed beam, 200mm wide and 300mm deep, has two Freyssinet anchorages (100mm diameter) with their centre at 75mm from the top and bottom of the beam. The force transmitted by each anchorage being 200kn, estimate the maximum tensile and bursting tension?
a) 100kn
b) 50kn
c) 150kn
d) 200kn
Answer: b
Clarification: Anchorage diameter = 100mm, equivalent side of square 2ypo = (π/4×1002) = 89mm, side of the surrounding prism 2yo = 150mm, ypo /yo = 0.593, average compressive stress fc = (200×103/150×150) = 8.9n/mm2, Tensile stress fv(max) = 8.9(0.98-0.825(0.593)) = 4.45n/mm2, Transverse tension Fbst = 200×103(0.48-0.4(0.593)) = 50000n = 50kn.

9. In case of large bridge girders with massive end block, for computation of bursting tension end block is divided into ____________
a) Axially
b) Rectangular
c) Symmetrically
d) Rounded
Answer: c
Clarification: In the case of large bridge girders with massive end block supporting multiple anchorages, the end block is divided into a series of symmetrically loaded prisms for the computation of the bursting tension.

10. The design strength assumed to act to sustain bursting tension is ____________
a) 0.56fy
b) 0.49fy
c) 0.87fy
d) 0.12fy
Answer: c
Clarification: The reinforcement is designed to sustain this bursting tension and it is assumed to act at its design strength of 0.87fy and the stress however is limited to value corresponding to a strain of 0.1% when the concrete cover is less than 50mm.

250+ TOP MCQs on Analysis of Stresses and Answers

Prestressed Concrete Structures Multiple Choice Questions on “Analysis of Stresses”.

1. The stresses developed in the prestressed structures are computed using __________
a) Simple bending equations
b) Stress strain theory
c) Strain analysis
d) Stress curves
Answer: a
Clarification: The stresses developed in prestressed and cast insitu concrete are computed using the simple bending equations until the stage of cracking and if the precast prestressed unit is unpropped during the placing of insitu concrete, the stresses that develop in the precast unit are sum of stresses due to self weight of members.

2. Once the insitu concrete hardens, we assume the section to be ___________
a) Dilithic
b) Monolithic
c) Transverse
d) Longitudinal
Answer: b
Clarification: After the insitu concrete has hardened the whole section is assumed to be monolithic and the stresses that develop due to subsequent live loads are computed using the properties of the composite sections.

3. If the precast unit is propped during the placing of insitu concrete, the stresses due to self weight are computed using ___________
a) Section modulus
b) Eccentricity
c) Tension
d) Principle stress
Answer: a
Clarification: The stresses developed due to self weight of the insitu concrete are computed using the section modulus of the composite section and in all cases the live loads stresses are based on the composite section.

4. In most composite constructions which involve prestressed units and insitu cast concrete the latter is of ___________
a) High strength concrete
b) Medium strength concrete
c) Colored concrete
d) Reinforced concrete
Answer: b
Clarification: In most composite constructions which involve precast prestressed units and insitu cast concrete the latter is invariably of low or medium strength concrete while the former are generally made of high strength concrete of grade exceeding M35.

5. For computing the live load stresses, the effect of different moduli between the cast in situ and precast unit is considerable by ___________
a) Eccentricity
b) Modular ratio
c) Tensile stresses
d) Deflections
Answer: b
Clarification: For computing the live load stresses, the effect of different moduli between the cast in situ and precast unit is considerable by using the modular ratio of precast insitu concrete for calculating the area, centroid, second moment of area and second modulus of the equivalent composite sections.

6. In modulus of elasticity of insitu concrete of grade M20 will be about ___________
a) 25kn/mm2
b) 30kn/mm2
c) 35kn/mm2
d) 40kn/mm2
Answer: a
Clarification: In most practical instances, the modulus of elasticity of insitu concrete of grade M 20 will be about 25kn/mm2, while the modulus of concrete in precast prestressed units could vary from 28 to 36kn/mm2 for concrete grades of M30 toM60.

7. The modular ratio of precast prestressed unit is ___________
a) 2.0 to 1.6
b) 1.1 to 1.5
c) 2.4 to 1.4
d) 2.2 to 1.7
Answer: b
Clarification: The modular ratio of precast prestressed unit varies in the range of 1.1 to 1.5 however this value could be larger if light weight concrete with a modulus in the range of 5 to 12kn/mm2 is used in conjunction with precast units made of normal weight aggregates.

8. A precast pretensioned beam of rectangular section has a breadth of 100mm and depth of 200mm and the beam with an effective span of 5mm is prestressed by tendon with their centroidal coinciding with the bottom kern and the initial force in the tendons is 150kn. Find prestressing force?
a) 20n/mm2
b) 34n/mm2
c) 15n/mm2
d) 12n/mm2
Answer: c
Clarification: A = (100×200) = 20000mm2, p = 150kn = 150×103
Stresses due to prestressing force = (2P/A) = (2x150x103/20000) = 15n/mm2.

9. Calculate stresses due to slab weight in precast sections given moment due to slab weight is 1200nm of section modulus 667×103?
a) 1.8n/mm2
b) 1.5n/mm2
c) 2.5n/mm2
d) 2.3n/mm2
Answer: a
Clarification: Section modulus Z = 667×103, moment due to slab weight is 1200nm
Stresses due to slab weight in the precast sections = (1200000/667×103) = 1.8n/mm2.

10. Calculate the stress of pretensioned beams assuming as propped during the casting of the slab if Zt is 225×10, Zb is 128x104mm3 and moment due to self weight is 1200nmm?
a) 12.3 and 4.5
b) 0.53 and 0.94
c) 0.23 and 0.45
d) 1.23 and 0.67
Answer: b
Clarification: Zt = 225×10, Zb = 128×104mm3, moment due to self weight = 1200nmm
Stresses due to this moment in the composite section:
At top = (1200000/225×104) = 0.53n/mm2 (compression), At bottom = (1200000/128×104) = 0.94n/mm2 (tension).

250+ TOP MCQs on Application to Prestressed Structures and Answers

Prestressed Concrete Structures online test on “Application to Prestressed Structures”.

1. In the design of prestressed concrete structural elements the objective is?
a) Total cost of member
b) Design of the member
c) Economy of the member
d) Foundation of the member
Answer: a
Clarification: The objective or merit function is generally the total cost of the member per unit length comprising the individual costs of concrete, high tensile steel and supplementary reinforcement and in a typical flexural member, the objective function can be expressed as: F(x) = CcA+CsAs+CpAp, F(x) = cost of the member unit length, CcCsCp = unit costs of concrete supplementary and high tensile steel respectively, ApAsAp = areas of concrete supplementary of high tensile steel and respectively.

2. The stresses developed at the top and bottom fibres of the critical section developed at ____________
a) Stages of stresses
b) Stages of deflection
c) Stages of transfer
d) Limits of transfer
Answer: c
Clarification: Stresses are developed at the top and bottom fibres of the critical section at the stages of transfer of prestress and under service loads these conditions yield four inequalities expressed as:
(p/a –pe/zt + Mg/zl) > fu, (p/a+pe/zb-Mg/zb) < fct
(p/a-pe/zt+mg+mq/zt) < fcw, (p/a+pe/zb-mg+mq/zb) > ftw.

3. The deflection constraint at the limit state of serviceability is taken as ____________
a) a < ap
b) a > ap
c) a > ae
d) a < ae
Answer: a
Clarification: Where a and ap are the actual and permissible deflection, which is usually a small fraction of the span code requirements for the limit state of collapse to ensure desirable load factors against flexural failure which can be written as Mu > (δf1Mg+δf2Mq).

4. The limitation on the minimum and maximum ratios of reinforcements is expressed as ____________
a) ρmin < ρ < ρmax
b) ρmin < ρ
c) ρ < ρmax
d) ρmin > ρ > ρmax
Answer: a
Clarification: ρmin < ρ < ρmax where ρ is the ratio of reinforcement provided ρmin is the minimum ratio required to prevent to prevent failure by fracture of steel in tension, ρmax is the maximum permissible ratio to ensure failure of the section by yielding of steel.

5. In case of partially prestressed members cracks of limited width are permissible under?
a) Deflection loads
b) Working loads
c) Tensile loads
d) Compressive
Answer: b
Clarification: In the design of fully prestressed (class 2) members, all the constraints as given in a < ap, ρmin < ρ < ρmax are not valid, however in this case of partially prestressed members where cracks of limited width of permissible under working loads an additional constraint to impose limitations on the width of crack is required and this can be expressed as: w < wp, w = actual widt, wp = permissible crack width.

6. The additional constraints are imposed on the geometrical dimensions of ____________
a) Cross section
b) Edges
c) Corners
d) Ranges
Answer: a
Clarification: The additional constraints are imposed on the geometrical dimensions of the cross section such as the minimum thickness of the web and bottom flange, based on practical requirements of housing the cables with due regard to cover requirements and the constraints being non linear the optimal solution is obtained by the non linear programming techniques.

7. The complete definition of the optimum design of prestressed beams for class 1 is?
a) 24 constraints
b) 27 constraints
c) 23 constraints
d) 20 constraints
Answer: b
Clarification: The complete definition of the optimum design of prestressed beams for class 1 is 24 and the complete definition of the optimum design of prestressed beams involves 27 constraints for class 2, 26 constraints for class 2 and 40 constraints for class 3 structure and further, they have reported a saving of 60 percent in high tensile steel in class 3 structure design when compared with a fully prestressed class1 structure design and however their studies on a 40m long higway bridge has also revealed that the cost wise savings in class 2 and 3 structure designs are nearly 14.3 and 9.4 percent in comparison with class 1 structure design.

8. Which elements were standardized and tabulated for design office use?
a) Bridge girders
b) Span Girders
c) Foundation girders
d) Transverse girders
Answer: a
Clarification: Optimization studies as applied to prestressed concrete structures have been pursued during the last decade and some organizations have developed practical programmes for the analysis and design of simple structures like highway bridge girders comparative cost studies have been standardized and tabulated for design office use by using computer programmes developed at the structural engineering research centre.

9. Optimization studies were conducted for slabs of type ____________
a) Pretensioning
b) Post tensioning
c) Partially prestressed slabs
d) Limited slabs
Answer: c
Clarification: Bond has reported optimization studies on partially prestressed in which several parameters, such as span, volume of the prestressing wire and steel bar reinforcements, cube strength, thickness of the slab and permissible tensile stress are examined in relation to the total cost of the slab per unit area.

10. The structural shapes, unit costs are assumed without considering ____________
a) Machines used
b) Site conditions
c) Constructions
d) Funds
Answer: b
Clarification: Many of the studies have included only a few variables and invariably the structure and shapes, unit costs of labour and materials are assumed without considering the specific site conditions and constructional techniques which can have a greater influence on the overall costs of the structural scheme and further studies in this field should include cost estimates of alternative schemes, formwork design, probabilistic design considering the variability of load applications and materials properties.

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250+ TOP MCQs on Strengthening Structures of Externally Bonded Plates and Answers

Prestressed Concrete Structures Questions and Answers for Experienced people on “Strengthening Structures of Externally Bonded Plates”.

1. The restoration of structures by rectifying constructional deficiencies are as a result of ____________
a) Cross section
b) Span
c) Dimensioning
d) Slab
Answer: c
Clarification: The range of application of this strengthening technique is ideally suited for the following situations: restoration of structures by rectifying constructional deficiencies that impair the safety of the structure as a result of faulty dimensioning, corrosion of reinforcement, insufficient reinforcement, overloading etc.

2. The first attempt to strengthen concrete flexural elements by externally bonded steel plates was attempted in?
a) Germany
b) France
c) America
d) Russia
Answer: b
Clarification: The first reported attempts to strengthen concrete flexural elements by externally bonded steel plates were attempted in France around 1964-65 and practical applications date back to 1966-67 in France and South Africa followed by Japan and Russia.

3. The load bearing capacity of a structural element can be increased by changing ____________
a) Foundation
b) Design
c) Span
d) Loads
Answer: c
Clarification: The strengthening of an existing structural element by increasing its load bearing capacity and altering the load supporting system by changing spans by shifting or removing of supports, conversion of continuous beam to single span beam and vice versa etc.

4. In Switzerland the externally bonded steel plates were used for ____________
a) Bridges
b) Crops
c) Dams
d) Tanks
Answer: a
Clarification: In Switzerland this method has been extensively used in both buildings and bridges and experiments conducted have shown that reinforced concrete beams, when epoxy bonded with steel plates on the tension face it exhibits significant increase up to 3% in the ultimate flexural strength in comparison with non plated beams.

5. Which grade of structural steel is suitable for bonded reinforcing plates?
a) M25
b) M35
c) Any grade
d) M10
Answer: c
Clarification: Generally any grade of structural steel is suitable for bonded reinforcing plates and plate gauges below 3mm are not suitable because sand blasting can deform them and steel plates between 6-16mm thick were used in some strengthening works.

6. The pretreatment of concrete surface is generally carried out by ____________
a) Sand blasting
b) Forrowing
c) Bleeding
d) Blasting
Answer: a
Clarification: Pretreatment of the concrete surface is generally carried out by sand blasting, shotcrete blasting, grinding or roughening with pneumatic needle gun or granulating hammer and the grain structure of the concrete must be exposed before the steel plates are fixed.

7. The tensile shear strength of the adhesive is initially proportional to the square root of ____________
a) Span
b) Thickness
c) Area
d) Eccentricity
Answer: b
Clarification: The adhesive joint is generally between 1-3mm thick and tests have shown that the tensile shear strength of the adhesive is initially proportional to the square root of the thickness however the tensile shear strength reaches a maximum and then starts decreasing as the adhesive thickness is further increased and hence the thinner layers prove stronger and have greater resistance than thick ones.

8. The repair procedure in severe damage includes ____________
a) Grouting
b) Collapse
c) Shortcrete
d) Mud
Answer: c
Clarification: The detailed examination of the damage and review of calculations will help in selecting a cost effective and appropriate restoration technique for the damaged structure and the loss of prestress is excessive resulting in tensile cracks, preloading method should be seriously considered in making concrete repairs in order to restore the equivalent full or partial prestresss effect, as per original designs and the repair procedure may also include epoxy resin pressure injection, Shortcrete and additional welded fabric with drilled anchors and guniting.

9. Before patching the exposure strands should be coated with ____________
a) Thick cement grout
b) Slurry cement grout
c) Hardened cement grout
d) Watery cement grout
Answer: b
Clarification: In moderate damage it is recommended that welded wire fabrics be attached to drilled dowels placed at about 500mm spacing or to the existing reinforcement in the damaged area and if the prestressing strands are exposed, sufficient care must be taken so as not to damage the steel during the cleaning operation and the exposed strands should be coated with epoxy resin bonding compound or slurry cement grout before patching.

10. Elastomers have excellent adhesion to concrete and are not susceptible to ____________
a) Hardening
b) Shaving
c) Collapsing
d) Softening
Answer: d
Clarification: Elastomers have excellent adhesion to concrete and are not suspectable to softening within the normal range of ambient temperatures and normally Elastomers exhibit a higher degree of elongation of as much as 10 percent extension but in practice, this should be limited to 50 percent and the groove depth to width ratio should be 1.2, the material should be prevented from adhering to the bottom so that the crack remains free as a live crack.

Prestressed Concrete Structures for Experienced people,