Category: Prestressed Concrete Structures Objective Questions

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

1. The chemical pre stressing is also called as ___________
a) Self stressing
b) Whole stressing
c) Half stressing
d) Model stressing
Answer: a
Clarification: Self stressing or chemical pre stressing of concrete was made possible by the development of expanding cements by Lossier of France in 1944 and generally expanding cement consist of 75% Portland cement, 15% alumina cement and 10 % gypsum which result in formation of calcium Sulpho aluminate.

2. The linear expansion of the cement in chemical pre stressing is about ___________
a) 5-10%
b) 2-3%
c) 3-4%
d) 6-7%
Answer: c
Clarification: The linear expansion of the cement in chemical prestressing is about 3 to 4% Mikhailov has reported that expansive cements have been used for pre stressing purposes in erstwhile in USSR since 1949 and splices are adopted for circular prestressing of tanks and the advantage is that there is no reduction in the strength of wire.

3. The degree of expansion can be controlled by varying the conditions of ___________
a) Bending
b) Bonding
c) Heating
d) Curing
Answer: d
Clarification: The degree of expansion can be controlled by varying the curing conditions in expanding cements and when the concrete is subjected to compression the amount and rate of expansion is controlled by controlling the curing conditions of the member.

4. The expansion of the concrete is restrained by ___________
a) High-tensile steel
b) High-strength concrete
c) Precast members
d) Concrete members
Answer: a
Clarification: concrete is composite material consisting of an aggregate and a binder phase and the binder phase is hardened cement and the expansion of concrete is restrained by high tensile steel wires, the compressive stresses that develop in concrete and steel wires are subjected to tensile stresses.

5. The tensile stresses developed in steel by the expansion of concrete are about ___________
a) 850n/mm²
b) 250n/mm²
c) 600n/mm²
d) 500n/mm²
Answer: a
Clarification: Tensile stresses of up to 850n/mm² were developed in steel by the expansion concrete results of laboratory investigations of several types of chemically pre stressed elements, such as beams, slabs, frames, columns, pipes and hyperbolic parabolic sheets have demonstrated the feasibility of chemical pre stressing.

6. The chemical pre stressing is generally suited for elements like ___________
a) Pre cast beams and columns
b) Bonding elements
c) Breakage elements
d) Tensioning elements
Answer: a
Clarification: It has been found that structural elements ideally suited for chemical pre stressing include pipes, thin walls and slabs, shells; folded plates and composite columns as well as pre cast beams and columns.

7. The method of chemical pre stressing is not suited for ___________
a) High degrees of prestress
b) High degrees of compression
c) High degrees of anchoring
d) High degrees of jacking
Answer: a
Clarification: In the present state of art, chemical pre stressing can be applied to structural elements and systems in which the optimum amount of pre stress is relatively low and this method is most not suited for high degrees of prestress and high percentages of steel where mechanical pre stressing can be conveniently used.

8. The suitability of post tensioning is good for ___________
a) Long spans
b) Break spans
c) Edge spans
d) End spans
Answer: a
Clarification: The suitability of post tensioning is good for medium to long span in situ work, where the cost of tensioning is very less and the major advantage of is the stopped off and curved cables are allowed by which designer can easily differ the prestresss distribution.

9. The long span decks are fabricated by ___________
a) Post tensioning
b) Pre tensioning
c) Thermo electric prestress
d) Chemical prestress
Answer: a
Clarification: Post tensioning is ideally suited in concrete construction work involving stage prestressing most of the long span bridge structures are constructed using post tensioning system and long span bridge decks are also fabricated by the use of post tensioning.

10. The concrete dams are constructed using which?
a) Post tensioning
b) Thermo electric pre tensioning
c) Biological pre tensioning
d) Elongation pre tensioning
Answer: a
Clarification: Concrete dams, biological shields of nuclear reactors and circular pre stressing of large concrete tanks are strengthened by using post tensioning and high tensile wire is wrapped under high tension using a wire serving machine developed by the inventors.

Prestressed Concrete Structures Multiple Choice Questions on “Deflections of Cracked Members”.

1. Which knowledge is essential to comply with the limit state of deflection?
a) Bending moment
b) Shear stress
c) Shear torsion
d) Load deformation
Answer: d
Clarification: Cracks of limited width are acceptable under occasional overloads or even under working loads according to CED-FIP recommendations and knowledge of the load deformation characteristics of cracked members is essential to comply with the limit state of deflection.

2. The tensile stress of about which limit are invisible to naked eye?
a) 5n/mm²
b) 6n/mm²
c) 3n/mm²
d) 10n/mm²
Answer: c
Clarification: Experimental investigations have shown that micro cracks develop at a tensile stress of about 3n/mm² which is invisible to the naked eye, on further loading cracks are first visible at flexural tensile stresses between 3.5 and 7n/mm² the higher values generally correspond to beams with well bonded steel distributed close to the tensile face as in the case of pretensioned members.

3. The load deflection curve is approximately linear up to stage of __________
a) Invisible cracking
b) Visible cracking
c) Invisible deflection
d) Visible deflection
Answer: b
Clarification: The load deflection curve is approximately linear up to the stage of visible cracking, but beyond this stage the deflections increase at a faster rate due to the reduced stiffness of the beam, if the beam is sufficiently loads, tensile stresses develop in the soffit and when this exceeds the tensile strength of concrete, cracks are likely to develop in the member.

4. In post cracking stage, the behavior of the beam is similar to __________
a) Prestressed concrete members
b) Reinforced concrete members
c) Chemical concrete members
d) Biological concrete members
Answer: c
Clarification: In the post cracking stage, the behavior of the beam is similar to that of reinforced concrete members, the instantaneous deflections in post cracking stage is obtained as the sum of the deflections up to the cracking load based on gross section and beyond the cracking load considering the cracking section.

5. The deflections of cracked structural concrete members may be estimated by __________
a) Unilinear method
b) Matrix method
c) Step method
d) Elongation method
Answer: a
Clarification: The deflection of cracked structural concrete members may be estimated by the Unilinear or bilinear method recommended by the European concrete committee, the slope of first line corresponding to the stiffness of the uncracked section and slope of the second line to that of the cracked section.

6. Which of the following equation is used to compute deflections of unilinear method?
a) βL²e/E_cI_t
b) βL²M/E_cI_t
c) βL³/E_cR
d) βL⁴/E_cR_t
Answer: b
Clarification: The revised American code considers the bilinear character of the load deflection characteristics by incorporating a suitable effective value of the flexural rigidity in the unilinear formula, In the Unilinear method, the deflections are computed by a simple equation of the form
A = βL²M/E_cI_t, a = maximum deflection, L = effective span, M = maximum moment in the beam, E_c = modulus of elasticity of concrete, I_c = second moment of area equivalent cracked moment, β = constant.

7. The actual load deflection behavior is possible by assuming __________
a) Bilinear moment curvature
b) Multilinear moment
c) Trilinear moment curvature
d) Bin linear moment curvature
Answer: a
Clarification: In the bilinear method recommended by the 1963 European concrete Committee the moment curvature is approximated by two straight lines, Experimental investigations have shown that a closer approximation to the actual load deflection behavior is possible by assuming bilinear moment curvature relationships.

8. The British code recommended for long time deflection of cracked members is __________
a) BS: 2150-1970
b) BS: 2150-1970
c) BS: 2150-1970
d) BS: 2150-1970
Answer: b
Clarification: The British code BS: 8110-1935 recommendations are comprehensive in this regard, as they incorporate the use of curvature of cracked sections, including the effect of shrinkage and creep in computing long term deflections.

9. The additional long term deflection resulting from creep and shrinkage of flexural members is determined by multiplying the deflection caused by __________
a) Effective load
b) Compressive load
c) Tensile load
d) Sustained load
Answer: d
Clarification: According to ACI: 318-1989 uses a similar approach whereby an additional long term deflection resulting from creep and shrinkage of flexural members is determined by multiplying the immediate deflection caused by the sustained load.

10. The equation for long term deflection of cracked members is __________
a) ξ/1+50ρ’
b) π/1+50ρ’
c) σ/1+50ρ’
d) e/1+50ρ’
Answer: a
Clarification: The prediction of time dependant deflections is complicated in the case of cracked members due to the redistribution of flexural stresses, according to Neville an exact solution results in nonlinear integral equations for which no closed solution is available is λ = ξ/1+50ρ’
ρ’ = (A’_s/bd) at midspan, A’_s = area of compression reinforcement, b = width of the section, d = effective depth, ξ = time dependent factor.

Prestressed Concrete Structures Multiple Choice Questions on “Stress Distribution in End Block”.

1. During stress distribution in end blocks the prestressing force is applied as ______________
a) Concentrated force
b) Deviated force
c) Tension force
d) Torsion force
Answer: a
Clarification: The prestressing force is applied as a concentrated force in a tendon along the anchorages during stress distribution in end blocks, the compressive stresses of concrete ahead of the anchorage devices, location and magnitude of the bursting force and the edge tension forces can be estimated with approximate method of design of end blocks when the accurate analysis are not available.

2. The stress distribution in concrete member which is away from the anchorage and in the region of the anchorage will be ____________
a) Non uniform
b) Zero
c) Constant
d) Uniform
Answer: d
Clarification: The stress distribution in concrete member which is away from the anchorage and in the region of the anchorage will be uniform reasonably and complex respectively this is stated by st.venant’s principle, a product of the correction factor in each direction is used if a group of anchorage are closely spaced in two directions in case of computation of compressive stresses.

3. The tensile stresses which tend to split the concrete are placed in the transverse direction to the ____________
a) Edge of member
b) Span of member
c) Axis of member
d) End of member
Answer: c
Clarification: The tensile stresses which tend to split the concrete are placed in the transverse direction to the axis of the member which is the more important effect for the design, the spalling and longitudinal edge tension forces are induced when the location of centroid of all the tendons is considered to be outside the keen of the section.

4. The bursting tensile forces in end bocks with proportion P_i is given as ____________
a) F_bst = Pi(0.32-0.3(y_po/y_o))
b) F_bst = fi(0.32-0.3(y_po/y_o))
c) F_bst = Ti(0.32-0.3(y_po/y_o))
d) F_bst = πi(0.32-0.3(y_po/y_o))
Answer: a
Clarification: The bursting tensile force in end blocks with proportion pi is given as:
F_bst = P_i(0.32-0.3(y_po/y_o)), y_po/y_o < or equal 0.3, F_bsr/P_i = 0.23,
y_po/y_o > or equal 0.3, F_bst/P_i = 0.11.

5. The longitudinal extent of the concrete member which is rectangular in cross section is ____________
a) Zero
b) Equal
c) Constant
d) Unity
Answer: b
Clarification: The longitudinal extent of the concrete member which is rectangular in cross section is at least equal to the largest transverse dimension of the cross section; the axial flexural beam analysis at one half the depth of section away from the loaded area enables to determine the longitudinal edge tension force.

6. The member within or ahead of the anchorage zone will not have any ____________
a) Strain
b) Stress
c) Discontinous
d) Torsion
Answer: c
Clarification: The member within or ahead of the anchorage zone will not have any discontinuities but they are subjected to stress during prestressing, the more detailed analysis is required such as strut-and-ties models or another analytical procedures to find out the spalling forces for larger spacing.

7. The main plate of the member in the anchorage zone has minimum edge distance of at least ____________
a) 2.0
b) 1.5
c) 1.8
d) 3.0
Answer: b
Clarification: The main plate of the member in the anchorage zone has minimum edge of at least 1.5 times the corresponding lateral dimension compressive stresses of the anchorage devices, the basic anchorage devices which satisfies below condition will have no additional check of compressive stresses of concrete f_b< 0.7ϕf”c_i(A/A_g).

8. The anchorage zone consists of how many devices?
a) 5
b) 3
c) 2
d) 1
Answer: d
Clarification: The anchorage zone consists of only one anchorage device or group of anchorages devices which are closely spaced, at the interface between the local zone and the general zone of the special anchorage devices ahead, the concrete compressive stresses.

9. If the centre to centre spacing of the anchorage devices will not exceed 1.5 times width then they are considered as ____________
a) Closely spaced
b) Gapely spaced
c) Farley spaced
d) Rectangular spaced
Answer: a
Clarification: If the center spacing of the anchorage devices will not exceed 1.5 times the width of these devices in the direction in which it is considered is treated as closely spaced devices and if the centre to centre spacing for multiple anchorages is less than 0.4 times the depth of section, the spalling forces will not be less than 2% of the total factored tendon force in any case.

10. If the anchor force points are towards the centroid, the center line of the member will not be greater than ____________
a) 15_o
b) 10_o
c) 20_o
d) 25_o
Answer: b
Clarification: If the anchorage force points are towards and away from the centroid of the section, the center line of the sectional member will not be greater than 20_o and 5_o respectively will be the angle of inclination of a tendon.

Prestressed Concrete Structures Multiple Choice Questions on “Composite Structural Members”.

1. The composite sections provide one monolithic action between ______________
a) Prefabricated units
b) Post fabricated units
c) Pasteurized units
d) Tensioned units
Answer: a
Clarification: In a composite construction precast prestressed members are used in conjunction with the concrete cast in situ so that the members behave as monolithic unit under service loads and stirrups produced from the prestressed unit into the added concrete or by castellation on the surface of the prestressed unit adjoining the concrete which in cast in situ.

2. The high strength prestressed units are used in which zone?
a) Compression zone
b) Tension zone
c) Span zone
d) Beam zone
Answer: b
Clarification: The high strength prestressed units are used in the tension zone while the concrete which is the cast in situ of relatively lower compressive strength is used in the compression zone of the composite members and the composite action between the two components is achieved by roughening the surface of the prestressed unit on to which the concrete is cast insitu thus giving a better frictional resistance.

3. The Composite construction was first tries for a motorway bridge?
a) 1940
b) 1945
c) 1960
d) 1980
Answer: a
Clarification: The phenomenon of differential shrinkage between the concrete cast insitu and the prestressed units also contributes to the monolithic action of the composite members and composite construction was first tried for a way bridge in 1940 and detailed calculations were prestressed by morch in 1943.

4. Due to the effect of composite action sizes of precast prestressed units can be ______________
a) Increased
b) Reduced
c) Deducted
d) Serviced
Answer: b
Clarification: The sizes of precast prestressed units can be reduced due to the effect of composite action and low ratio of size of the precast unit to that of the whole component member and appreciable saving in the cost of steel in a composite member compared with a reinforced or prestressed concrete member.

5. In many cases precast prestressed unit serve as ____________
a) Supports and dispences
b) Girders and dispences
c) Area and dispences
d) Beams and dispences
Answer: a
Clarification: In many cases precast prestressed units serve as supports and dispense with the form work for placement of insitu concrete and composite members are ideally suited for constructing bridge decks without the disruption of normal traffic.

6. The efficient utilization of material in a composite section in which the low and medium strength concrete resists?
a) Tensile forces
b) Principal forces
c) Compressive forces
d) Axial forces
Answer: c
Clarification: The efficient utilization of material in a composite member in a composite section in which the low and medium strength concentration of insitu construction resists compressive forces while the high strength prestressed units resist tensile forces.

7. The combination of light weight concrete for the cast insitu slab results in reduced ____________
a) Live loads
b) Dead loads
c) Constant loads
d) Limited loads
Answer: b
Clarification: Combination of light weight concrete for the cast in situ slab results in reduced dead loads leading to economy in the overall costs and the precast prestressed units which require skilled labour and workmanship can be cast in a factory or casting yard and conveyed to the site of construction.

8. In case of conventional method there will be a steel beam and slab construction in which the components carries their?
a) Entire load
b) Half load
c) Span load
d) Deflection
Answer: a
Clarification: In case of conventional method, there will be a steel beam and slab construction in which the components carries their entire load transmitted by the slab and there will be no composite action between the members when compared than conventional method of construction the precast unit’s method facilitates a greater structural efficiency.

9. The main components of the composite beam are prestressed precast stem and ____________
a) A cast insitu flange
b) A cast insitu beam
c) A cast insitu slab
d) A cast insitu column
Answer: a
Clarification: The main components of the composite beam are prestressed precast stem and a cast insitu flange and the prestressed precast stem of higher grade concrete is prepared in a factory while the flange having a concrete of lower grade is used for casting is done at the site.

10. To attain the composite action the precast stem and the flange is ____________
a) Laced together
b) Tied together
c) Keyed together
d) Cutted together
Answer: c
Clarification: To attain the composite action the precast stem and the flange is keyed together and facilitates in carrying the heavier loads effectively between the prefabricated beam and cast in situ slab shear connection should be provided in which they act as one unit and resist the loads by composite action as in reinforced concrete T beams.

Prestressed Concrete Structures Multiple Choice Questions on “Maintenance of Structures”.

1. In prestressed concrete structures the primary problem is damaged caused to ____________
a) Bridge decks
b) Spans
c) Anchorages
d) Ridges
Answer: c
Clarification: In prestressed concrete structures the primary problem is damage caused to anchorages and unbounded tendons due to rusting under exposure to humid weather conditions and good maintenance practice requires periodical surveillance identification of local damage, deterioration and loss of durability of the structure due to environmental and other load effects and in such cases local repairs are needed.

2. Rehabilitation of structures may be required due to several reasons. Choose the correct reason.
a) Environmental effects
b) Tensile effects
c) Compressive effects
d) Range effects
Answer: a
Clarification: Rehabilitation of structures may be required due to several reasons one reason is:
Environmental effects some common causes are constructional deficiency, environmental effects, deficiency in design, overloading of structures either due to un anticipated loading or due to accidents and user made changes in the structures during the service life of the structure.

3. What is the problem of rehabilitation?
a) Unique
b) Submerged
c) Lined
d) Layered
Answer: a
Clarification: The problem of rehabilitation is Unique, For the particular structure and hence the use of common techniques for rehabilitation of various structures is limited and as far as maintenance is concerned, several new cementations materials and epoxy resigns and compounds have been developed which are highly effective in protecting the basic structure from the destructive effects of severe exposure conditions in the environment.

4. Maintaining prestressed concrete structures of various types in a fit and serviceable condition is primary function of ____________
a) Maintenance engineer
b) Design engineer
c) Surface engineer
d) Structural engineer
Answer: a
Clarification: Maintaining prestressed concrete structures of various types in a fit and serviceable condition is primary function of Maintenance engineer investment towards effective periodical maintenance forms only a fraction of the cost to be incurred due to major repairs to rehabilitate the structures and hence it is always advisable to establish a programmed preventive maintenance system to detect any signs of distress in the initial stages itself through inspection procedures and appropriate repairs.

5. The structural concrete slab panels can be repaired by ____________
a) Internal bonding
b) External bonding
c) Stress bonding
d) Layered bonding
Answer: b
Clarification: The structural concrete slab panels and beams exhibiting distress can be repaired by external bonding of steel plates to the soffit by using epoxy adhesives and hollows, honey combs and cavities in concrete can be repaired by the process of guniting and shortcreting applied pneumatically with impact force.

6. The impression of structure is?
a) 3
b) 4
c) 2
d) 6
Answer: c
Clarification: Routine inspection under this category, general inspections are carried out quickly and frequently by highway maintenance engineers having reasonably practical knowledge of highway structures through not necessarily experts in design.
Detailed inspection: This type of inspection can be further divided as general and major depending upon the frequency and extent of inspection.
Special inspection: Special inspection is resorted to under extraordinary situations such as earthquakes, high intensity/ abnormal loading, floods etc.

7. Which type of inspection is more intensive involving examination of structural elements?
a) Minor inspection
b) General inspection
c) Major inspection
d) Reverse inspection
Answer: c
Clarification: Major inspection is generally more intensive involving detail examination of all structural elements and even requiring setting up of special access facilitates (like soffits of long span beams and articulation locations, bearing etc) where required depending upon the importance of the structure, this type of inspection is spaced between 2 and 3 years or may be at smaller intervals for sensitive structures which are exposed to aggressive environments.

8. Prestressed concrete structures showing visible signs of distress in the form of ____________
a) Surface cracks
b) Patterns
c) Patches
d) None of the mentioned
Answer: a
Clarification: Prestressed concrete structures showing visible signs of distress in the form of surface cracks, spalling of concrete should be special inspection using instruments to users the extent of damage to the structure.

9. One of the testing equipments used for inspection is?
a) Strain gauges
b) Measuring jar
c) Test tubes
d) None of the mentioned
Answer: a
Clarification: Modern testing equipments which could be of use to the specialized inspection team are listed below:
Rebound hammer compressive strength (Schmidt hammer), ultrasonic pulse velocity detection of cracks, snooper-crawler and adjustable ladders, magnetic decor for measuring thickness of concrete cover and for locating reinforcement bars, mechanical extensometer, transparent templates and microscope for reading of crack widths on the surface of the concrete hydraulic jacks, pressure transducers or load cells for measurement of forces etc, electronic strain gauges for measurement of strain in concrete and steel, vibration measuring equipment, electrical resistance meter(for rust pockets).

10. The pachometer is used to locate the ____________
a) Steel reinforcement
b) Aluminium reinforcement
c) Tensile reinforcement
d) Surface reinforcement
Answer: a
Clarification: A wide variety of electronic equipment is presently available in the market in many countries for monitoring and inspection of distress in different types of structures and ultrasonic meters are used to determine the degree of deterioration and distress and / or material imperfections that are relevant to the structural integrity of the structure to be inspected and pachometer is used to locate the steel reinforcements and measures the sizes of the bars embedded in concrete to an accuracy of 3m.

11. In case of bridge greater than 10.7m in height and which cannot be inspected from beneath due to watery situation the instrument suited for inspection work is?
a) Electrical resistance meter
b) Strain gauges
c) Barins snooper vehicle
d) Rain guages
Answer: c
Clarification: In the case of bridges greater than 10.7m in height and in those bridges which cannot be inspected from beneath due to rugged terrain or watery situations, a mechanical contraction widely known as Barins snooper vehicle is ideally suited for inspection work and the snooper is mounted on a heavy duty truck with a swiveling platform and the underside of the bridge deck can be inspected by using the hydraulically operated platform.

12. In the case of dormant cracks wider than about 1m, it is more economical to use ____________
a) Epoxy resin
b) Grouting
c) Tensioning
d) Ranging
Answer: b
Clarification: In the case of dormant cracks wider than about 1mm, it is more economical to use the grouting and sealing technique and this method involves enlarging the crack along its exposed face and then the crack is cleaned and grouted and the surface is then sealed with a suitable joint sealant and various other techniques widely used for repair of dormant or dead cracks include dry packing, polymer impregnation over lays and surface treatments and autogenous handling.

13. How many sealants are there used depending upon their suitability in a given situation?
a) 3
b) 2
c) 4
d) 1
Answer: a
Clarification: The following three types of sealants are generally used depending upon their suitability in given situation: Mastics are asphalts with a low melting point with added fillers or fibers and they are recommended where the total movements will not exceed 15 percent of the width of groove, Thermoplastics comprising of asphalts, pitches and coal tar become liquid or semi viscous when heated and the groove depth to width ratio should 1:1 and the total design movement is of order of 25 percent of groove width and Elastomers include a wide range of materials such as poly sulphides, epoxy poly sulphides, poly urethane, silicones and acrylics and these materials advantages since they can be used without heating.

14. How many types of damages are present in classification of damage?
a) 1
b) 2
c) 3
d) 4
Answer: c
Clarification: Minor damage requires superficial patching by using epoxy grout or guniting using Shortcrete and the damages and delaminated concrete is removed by hand tools and the surface is cleaned before the application of epoxy grout, moderate damage involves extensive spalling and cracking of concrete is generally applicable as in minor repairs and in Several damage Prestressed concrete girders requires a detailed structural analysis of a design check based on the conditions of the damage and the best engineering assumptions and judgments.

15. If the loss of prestress is excessive resulting in tensile cracks, which method should be used?
a) Preloading method
b) Hollow method
c) Transparent method
d) Layered method
Answer: a
Clarification: If the loss of prestress is excessive resulting in tensile cracks, preloading methods should be seriously considered in making concrete repairs in order to restore the equivalent full or partial prestress effect, as per original designs.