Prestressed Concrete Structures MCQ Set 1
1. The length of beam within which the dispersion of prestressing force takes place is known as:
a) Zone of action
b) Zone of transmission
c) Zone of anchorage
d) Zone of tendons
Answer: b [Reason:] The length of beam within which the dispersion of the prestressing force takes place is called as zone of transmission; Guyon has developed design tables for the computation of bursting tension in the end blocks which are based on his earlier mathematical investigations concerning the distribution of stress in end blocks subjected to concentrated loads.
2. The tensile forces developed in the transverse direction to the axis are known as:
a) Bursting forces
b) Concentrated forces
c) Reduced forces
d) Tensioned forces
Answer: a [Reason:] The tensile forces developed in the transverse direction to the axis of concentrated force are called as bursting forces; the concept of symmetrical or equivalent prism for eccentric cables and the method of partitioning for the analysis of stresses developed due to multiple cables have been introduced by Guyon.
3. The adjacent surface to the anchor plate is also subjected to:
a) Compressive forces
b) Tensile forces
c) Transverse forces
Answer: b [Reason:] The adjacent surface to the anchor plate is also subjected to tensile force at the end section and these are called as spalling forces, the eccentric forces and multiple cables, the symmetric prism method may be used, this consists of a prism of concrete of side equal to twice the distance of the prestressing force from the nearest free edge.
4. During zone of transmission prestressing force is applied through the anchor plate at:
Answer: c [Reason:] The prestressing force p is applied through the anchor plate which is placed at the centre of the end beam during zone of transmission, When the forces are arranged such that the resultant of the stress distribution at a distance equal to the depth of the end block coincides with the line of action of the force then the forces are considered to be evenly distributed.
5. Which are formed due to the horizontal, vertical and shear stresses induced at zone of transmission:
Answer: d [Reason:] Due to the horizontal, vertical and shear stresses induced at zone of transmission, trajectories of principle stresses are formed, the line of action of the resultant force is taken as the axis of an equivalent prism of length and depth equal to twice the distance of axis from the free edge or the adjoining equivalent prism.
6. The transmission length is influenced by:
Answer: b [Reason:] The transmission length is influenced by depth of the anchor plate and is taken equal to the depth of beam in general, the transverse stress distribution is computed by using the coefficients under the category of concentrated eccentric force and eccentric shear forces since the coefficients are applicable for forces at interval of one eighth of the prism depth, the end forces have to be replaced by a statically equivalent system of normal and shear forces acting at these regular intervals.
7. The transmission length and bursting forces can be obtained depending on the ratio of:
a) Depth of anchorages
b) Depth of tendons
c) Depth of bond
d) Depth of curve
Answer: a [Reason:] Depending on the ratio of depth of anchor plate to the depth of beam, the transmission length and bursting force can be obtained, the position of zero stresses, maximum transverse stress and its magnitude for the forces which are evenly distributed are computed by using the coefficiants under the category of distributed axial forces. According to guyon, the bursting tenson is expressed as, Fbst = 0.3P(1-(ypo/yo)0.58, p = anchorage force, ypo/yo = distribution ratio.
8. In general the transmission length and depth of beam are taken as:
c) Less than 1
d) More than 1
Answer: b [Reason:] Generally, the transmission length is taken as equal to the depth of beam and bursting forces are considered in case of transmission length, when it is not possible to arrange the end forces evenly, Guyon recommended that transverse tensile stresses be investigated along successive resultants, such as resultant of all forces, resultant of smaller groups of forces, lines of action of individual forces.
9. The bursting force with depth of beam d’ and the depth of anchor plate d is given by:
Answer: a [Reason:] The bursting force with depth of beam d’ and the depth of anchor plate d is given by:
Pb = 0.3P (1-d’/d), the distribution of bursting stress for d’/d = 0.8 and d’/d = 0.5 are given as distance along the transmission line.
10. The d’/d value for 0.42d is:
Answer: b [Reason:] The distribution of bursting stresses d’/d = 0.8 and for d’/d = 0.5 are shown below:
Prestressed Concrete Structures MCQ Set 2
1. The philosophy of design is termed as:
a) Limit state approach
b) Limit area method
c) Limit design approach
d) Limit elasticity approach
Answer: a [Reason:] The philosophy of design termed as “Limit state approach” adopted by the Russian code in 1954 and the American and British codes in 1971, it requires a proper knowledge of the behavior of structural concrete members at the multiple limit states, of which deflection forms an important criterion for the safety of the structure.
2. The structural concrete members if not designed to have adequate stiffness, it affects:
b) Local conditions
Answer: a [Reason:] In general, according to various national codes, the structural concrete members should be designed to have adequate stiffness to limit deflections, which may adversely affect the strength or serviceability of the structure at working loads.
3. The large deflections under dynamic effects may cause:
a) Likely appearance to users
b) Discomfort to users
c) High bending
d) Requires more construction materials
Answer: B [Reason:] Large deflections under dynamic effects and under the influence of variable loads may cause discomfort to users, the members of structural concrete are designed in such a way that it possess adequate stiffness to control the deflections or it may leads to a very great impact on serviceability conditions and strength of a structure at working loads.
4. The excessive deflections are likely to cause damage to:
Answer: a [Reason:] Excessive deflections are likely to cause damage to finishes, partitions and associated structures, the principal structural members which resulted in excessive sagging condition makes the floor area not suitable for further use.
5. Which of the following influence the deflections of prestressed concrete members?
a) Cable profile
b) Wall profile
c) Type of aggregates
d) Type of cement
Answer: a [Reason:] The deflections of prestressed concrete members are influenced by the following salient features: imposed load and self weight, magnitude of the prestressing force, cable profile, and second moment of area of cross section, modulus of elasticity of concrete, shrinkage, creep, relaxation, span, and fixity conditions.
6. Which type of deflections is solved by Mohr’s theorem?
c) Middle span
d) End span
Answer: a [Reason:] The computations of short term or instantaneous deflections, which occur immediately after the transfer of prestress and on application of loads is conveniently done by Mohr’s theorem from certain surveys it is concluded that the maximum deflection should be noted including with limiting deflection span ratio.
7. In the pre cracking stage, the deflections are computed by:
a) Prestressing force
b) Sectional area
d) Second moment of area
Answer: d [Reason:] In the pre cracking stage the whole cross section is effective and the deflections in this stage are computed by using the second moment of area of the gross concrete section, as the length of the structural member increases the deflections can be controlled to a maximum extent possible.
8. In a post cracking stage, a prestressed concrete beam behaves in a manner similar to:
a) Reinforced concrete beam
b) Flexural beam
c) High strength of concrete
d) Soffit beam
Answer: a [Reason:] In the post cracking stage, a prestressed concrete beam behaves in a manner similar to that of a reinforced concrete beam, these beams undergo cracking under working loads, they undergo large deflections and reinforced concrete beam require shear reinforcement in this testing of steel and concrete cannot be done.
9. The computations in post cracking stage are by considering:
a) Moment of inertia
b) Moment curvature
c) Moment design
d) Moment area
Answer: b [Reason:] The computations of deflections in this stage are made by considering moment curvature relationships which involve the section, properties of the cracked beam, based on prestressing forces and live loads the deflections of prestressed concrete members can be calculated if the longitudinal distribution of curvatures and magnitude of beam can be known at that particular time.
10. In both pre and post cracking stages the effect of creep and shrinkage of concrete is to increase the:
a) Short term deflections
b) Middle span deflections
c) Long span deflections
d) Edge span deflections
Answer: c [Reason:] In both pre and post cracking stages the effect of creep and shrinkage of concrete is to increase the long term deflections under sustained loads, which is estimated by using empirical methods that involve the use of effective (long term) ,modulus of elasticity or by multiplying short term deflections by suitable factors.
Prestressed Concrete Structures MCQ Set 3
1. The super structure in Swanley bridges in U.K is made up of a continuous slab supported on:
a) Longitudinal piers
b) Transverse piers
c) Inclined piers
d) Curved piers
Answer: c [Reason:] These highway bridges from part of M25 and M20 mortar way intersection and the super structure is made up of continuous slab supported on the inclined piers and shortly after the bridge was opened for traffic, cracks were observed on the soffit of deck slab at the end sections.
2. A design review indicated that the reinforcements at the cracked locations were:
Answer: b [Reason:] A design review indicated that the reinforcements at the cracked locations were inadequate hence the missing reinforcement was introduced in the form of bonded steel plates 6mm thick, 250mm wide and 3 to 6m long plates bonded in three layers in each strip and each strip of reinforcement was 12m long and 15 strips were distributed over the entire width of the bridge.
3. The concrete deck slab and girders of Gizener bridge, Switzerland was built in the year:
Answer: a [Reason:] The concrete deck slab and girders of this bridge built in the year 1911 and located in Switzerland has to be strengthened to withstand planned future loading and the damaged parts of the bridge deck slab was repaired using epoxy resin mortar.
4. The super structure of Obra singrauli bridge, located on eastern railway in Indian is of span:
Answer: b [Reason:] The super structure of Obra singrauli bridge located on eastern railway in India comprises of 4 numbers of 18.3m spans and one number of 24.4m span and decking is made up of two prestressed concrete girders stressed with Freyssinet system of post tensioning and after 15 years of service the prestressed girders developed large number of cracks at the junction of girder and deck slab on both internal and external faces.
5. The deck in Quinton bridge in U.K is made of:
a) Voided slabs
b) Concrete slabs
c) Prestressed slabs
d) Elongated slabs
Answer: a [Reason:] The deck is made up of voided slabs 90-105cm thick and routine inspection indicated cracks in the soffit of end and central sections and review of design calculations indicated deficient tensile reinforcements at certain locations of the deck slabs, the following two rehabilitation methods were examined: installation of prestressing elements and external reinforcement with bonded on steel plates.
6. The super structure of Katepura bridge in Maharashtra state comprises of:
a) Cantilever beam
d) Simple beam
Answer: b [Reason:] The super structure of Katepura bridge in Maharashtra state comprises of simply supported concrete girders with reinforced concrete structures deck slab and the bridge has 4 spans of 37.8m and the girders were cast in place over temporary staging and side shifted to position after necessary post tensioning of the girders.
7. The restoration of the end block of the girder can be done completely dismantling the:
Answer: a [Reason:] The restoration of the end block of the girder was done by completely dismantling the concrete in the end block after distressing of the cables and new reinforcement was welded with the existing reinforcement of the girder and new concrete with vertical joint was provided with extra care.
8. The Chambal bridge is on a state highway connecting:
a) Karnataka and Kerala
b) Delhi and Hyderabad
c) Uttar Pradesh and Madhya Pradesh
d) West Bengal and Assam
Answer: c [Reason:] The Chambal bridge is on a state highway connecting Uttarpradesh and Madhya Pradesh, built across river Chambal near etawah in Uttarpradesh and the bridge is 592m long with a bridge deck comprising of single cell reinforced concrete box girders of 11.1m length projecting on either side of the pier and the suspended span comprises of two prestressed concrete girders with reinforced concrete deck slab of span 40.6m.
9. The suspended span comprises of how many prestressed concrete girders?
Answer: b [Reason:] The suspended span comprises of two prestressed concrete girders with reinforced concrete deck slab of span 40.6m and cast steel rocker and roller bearings have been provided at articulations for supporting the suspended span and soon after the bridge was constructed and opened to traffic in1975, it developed distress due to improper placing of roller bearings.
10. The investigations revealed that the bearings were not at:
a) 60 degrees
b) 30 degrees
c) 90 degrees
d) 20 degrees
Answer: a [Reason:] The investigations revealed that the bearings were not at right angles to the axis of the bridge and the level of downstream side bearing was lower by 35mm as compared to the elevation of upstream bearing and hence due to transfer inclination of the bearings towards downstream, the span had a tendency to move in the transverse direction.
Prestressed Concrete Structures MCQ Set 4
1. The concrete shell roof has been widely used to cover:
a) Small floor spaces
b) Large floor spaces
c) Middle span spaces
d) Edge floor spaces
Answer: b [Reason:] The concrete shell roofs have been widely used to cover large floor spaces of industrial structures and they are generally preferred to other structural forms as they use a minimum amount of materials yielding maximum structural advantage, the cross section being optimally used to resist the forces.
2. Reinforced concrete shells are ideally suited to cover floor spaces of up to:
Answer: c [Reason:] Reinforced concrete shells are ideally suited to cover floor spaces over medium to long range spans of up to 30m and in the case of longer spans, the tension develops in the edge beams of cylindrical shells is very high and results in congestion of reinforcement and improper compaction of concrete in these zones.
3. Long spans exceeding 30m necessitate:
Answer: a [Reason:] Longer spans exceeding 30m necessitate the lapping or wielding of reinforcement in addition, the structure may be rendered unfit for its intended use at the serviceability limit states due to excessive deflections and objectionable cracking and most of these problems are eliminated by prestressing the edge beams of long span shell structures.
4. The parabolic profile of the cables in the edge beam counteracts the:
Answer: c [Reason:] The parabolic profile of the cables in the edge beam counteracts the deflections due to the dead and live loads, so that the resulting deflection is well within the safe permissible limits and prestressing the shell considerably reduced the quantity of reinforcement in the structure as demonstrated by Goldstein.
5. The investigations by Marshall have shown that prestressing considerably reduces:
a) Sagging moment
b) Transverse moment
c) Hogging moment
d) Longitudinal moment
Answer: b [Reason:] The investigations by Marshall have shown that prestressing considerably reduces transverse moments and the development of cracking due to high tensile stresses at the soffits of edge beams can be completely eliminated by eccentric prestressing and in addition precompression in concrete inhibits the formation of temperature and shrinkage cracks.
6. The compressive state of stress in the shell membrane results in which construction:
a) Airtight construction
b) Water tight construction
c) Lever construction
d) Soffit construction
Answer: b [Reason:] The compressive state of stress in the shell membrane results in which construction water tight construction and according to Haas prestressing has a favorable influence in providing adequate safety against the limit state of collapse by inelastic bulking India in 1941 over spans of 36m, with a chord width of 10.5m, the thickness of the shell being 63mm and the prestressed shell roof of the aircraft hangar at Karachi was built in 1942 over spans of 40m and as these shells gave satisfactory performance and were also economical in France, U.K, Germany and other countries.
7. In general, concrete shells have thin cross sections, which prectude the use of large diameter:
Answer: a [Reason:] In general, concrete shells have thin cross sections, which prectude the use of large diameter Cables and the tendons consisting of 5 to 8mm diameter wires accommodated in narrow sheaths are conveniently used in post tensioning the lower parts of the shell membrane to overcome the problem of correctly positioning the curved cables along the space curves at the junction of the shell and edge beam, it is general practice to impart prestress by post tensioning the curved cables that housed entirely in the deep edge beams and the edge beams being invariably deep, it is convenient to arrange the cables one over the other so that maximum eccentricity is available at the centre of span.
8. The analysis of circular cylindrical shells with prestressed edge beam is more or less similar to:
a) Prestressed concrete beam
b) Reinforced concrete beam
c) Chemically prestressed beam
d) Partially prestressed beam
Answer: b [Reason:] The analysis of circular cylindrical shells with prestressed edge beam is more or less similar to Reinforced concrete beam however, the effect of prestressing is to be considered in formulating the boundary conditions at the junction of the shell and the edge beam and in addition to the normal boundary conditions such as zero horizontal displacement and rotation of the shell edge, which are also applicable for reinforced concrete shells.
9. The rigorous methods generally involve computations to estimate the:
a) Transverse reactions
b) Longitudinal reactions
c) Redundant reactions
d) Span reactions
Answer: c [Reason:] The rigorous methods generally involve lengthy computations to estimate the redundant reactions between the shell and the edge beam and in the case of long shells with span/radius ratio exceeding 3, the beam theory developed can be conveniently used for the preliminary analysis of prestressed shells without the loss of much accuracy and in this method the shell is considered or a beam of curved cross section and the flexural and shear stresses are computed using the well known beam formulas.
10. The general bending theory of thin curved shells is governed by a:
a) Differential equation
b) Parabola equation
c) Ellipse equation
d) Moment equations
Answer: a [Reason:] The general bending theory by thin curved shells is governed by a differential equation of eighth order involving the main shell parameters and deformations and solution based on simplifying approximations have been developed by several investigators and a comparative analysis of various analytical approximations.
11. The hyperbolic parabolic shells, grouped under the category of:
a) Singly curved shells
b) Doubly curved shells
c) Three curved shells
d) Four curved shells
Answer: b [Reason:] Hyperbolic paraboloid shells, grouped under the category of doubly curved antielastic sells were first successfully used as roofing units by silberkuhl in germany and parts of one shear hyperboloid units, with a geometric from closely following a circular curve in the length(span) direction and hyperbolic curve in the direction of width are well suited for mass production since they are ruled surfaces.
12. Fold plates are widely used for:
Answer: a [Reason:] Folded or hipped plates are widely used for roofs of industrial structures, coal bunkers and cooling towers and the simplicity of the form used for casting folded plates makes them competitive shell construction for covering large floor space and the plates have a triangular or trapezoidal zig-zag cross sectional shape and prestressing is generally done by curved cables or straight tendons lying within the plate in the longitudinal direction to counteract the beam action.
13. The folded plate is also analyzed for:
Answer: b [Reason:] The folded plate is also analyzed for transverse moment by considering the plate as a continuous slab with imaginary supports at the junctions and the transverse reinforcement are designed to resist these moments and according to IS:224 nominal reinforcements consisting of 10mm bars are to be provided in the compression zones at 200mm centers and the maximum spacing of reinforcements in any direction is limited to five times the thickness of the member and minimum reinforcement in the section should conform to the provisions in various national codes.
14. The spherical domes are supported by a ring beam at the:
Answer: a [Reason:] Concrete domes are generally preferred for covering circular tanks and for roofs of large span circular structures, such as sports arenas and churchus where an uninterrupted floor space is desirable and a prestressed concrete hemispherical dome of 40m diameter has been used for the roof of the atomic reactor at Kota, Rajasthan, India and the spherical domes are supported by a ring beam at the base, which can be conveniently prestressed by winding tensioned wires or by cables to counteract the hoop tension developed in the ring beam and the main disadvantage of the reinforcement becoming congested in large diameter reinforced concrete ring beams is overcome by prestressing the ring beams in addition there are significant savings in cost, when compared with other equivalent roofs of conventional design.
15. The peripheral ring beam is prestressed by which type of wire winding:
Answer: b [Reason:] The peripheral ring beam is prestressed by which type of wire winding Trapezoidal similar to that of tank walls, or by cables housed in the ring beams with anchorage points at 90 degrees spacing, opposed and phased at 45 degrees and in the case of cables, due provisions should be made be about 10 to 15percent due to the large curvature of the cables.
Prestressed Concrete Structures MCQ Set 5
1. The prestressed concrete poles are currently used in:
Answer: a [Reason:] 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:
Answer: c [Reason:] 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:
Answer: a [Reason:] 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 [Reason:] 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:
Answer: b [Reason:] 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 [Reason:] 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:
Answer: b [Reason:] 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 [Reason:] 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 [Reason:] 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 [Reason:] 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 [Reason:] 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 [Reason:] 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?
Answer: b [Reason:] 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 [Reason:] 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.
Prestressed Concrete Structures MCQ Set 6
1. The structures of prestressed concrete are less liable to:
Answer: d [Reason:] In case of fully prestressed members which are free from tensile stresses under working loads cross-section is more efficiently utilized when compared with a reinforced concrete section which is cracked under working loads.
2. Which of the following concrete offers pleasant appearance and durability?
a) Reinforced concrete
b) Prestressed concrete
c) Shrinkage concrete
d) Hardened concrete
Answer: b [Reason:] Prestressed concrete offers pleasant appearance and durability when compared to reinforced concrete and the two structural features of prestressed concrete, namely high strength concrete and freedom from cracks, contributes to the improved durability of structure under aggressive environmental conditions.
3. The prestressing members have better ability of absorbing energy when the structures are subjected to:
a) Tensile loads
b) Axial loads
c) Bending loads
d) Impact loads
Answer: d [Reason:] Prestressing of concrete improves the ability of the material for energy absorption under impact loads and working loads proved to be good in prestressing than in reinforcing and it is done in concrete members to reduce the compressive stresses developed in the members to the required extent.
4. The loads of same intensities when subjected to structures, it increases:
a) Life of material
b) Durability of material
c) Stiffness of material
d) Bending of material
Answer: a [Reason:] When the loads of same intensities are subjected to structures, then the prestressing increases the mean stresses in steel and the effects caused due to fluctuations in stresses are minimized which increase the life of the material.
5. The prestressed concrete flexural member under working load conditions offers superior amount of:
Answer: b [Reason:] A superior amount of rigidity is offered by the prestressed concrete flexural members under the working load conditions, when compared with that offered by reinforced concrete members of equal dimensions.
6. The application of prestressed concrete is done for depth ratio’s having:
a) Small span
b) Larger span
c) Same span
d) Equal span
Answer: b [Reason:] Prestressed concrete is used for the construction of buildings and other structures which are having the value of span to depth ratio in large or for larger span members and other criteria such as equal, small, same span criteria are considered in various other structural members.
7. The prestressed concrete structures are considered as:
a) Economical structures
b) Uneconomical structures
c) Tensile structures
d) Loading structures
Answer: b [Reason:] Prestressed concrete structures are considered as uneconomical structures and it is well established fact that the basic economy of prestressed concrete lies in its high strength to weight and strength to cost ratios, its resistance to fire and cracking, and its versatility and adaptability.
8. The prestressed concrete involves problems like:
a) Architectural and construction
b) Financial and land
c) Placing of material
d) Tensioning devices
Answer: a [Reason:] The prestressed concrete involves many architectural or construction related problems formulated due to curved surfaces and involve sophisticated erection problems, a high quality control is required for production of materials and while placing the tendons and when the members are subjected to a system of loads then the existing problems due to long term creep moments are increased.
9. The utilization of concrete in tension zone of prestressed concrete member saves concrete ranging between:
a) 15 to 30 percent
b) 20 to 50 percent
c) 35 to 60 percent
d) 10 to 20 percent
Answer: a [Reason:] Due to the utilization of concrete in the tension zone, an extra saving of 15 to 30 percent in concrete is possible in comparison with reinforced concrete high tensile steels are used in prestressed members and its ultimate strength is equal to 2100n/mm2 and the saving in steel are even higher, 60 – 80 percent mainly due to high permissible stresses allowed in the high tension wires.
10. The overall economy in using prestressed concrete reduces?
a) Design loads and costs
Answer: a [Reason:] An overall economy in using prestressed concrete decreases the dead weight due to which the design loads and cost of foundation reduces although there is considerable saving on the quantity of materials used in prestressed concrete members in compression with reinforced concrete members, it is not much significant due to additional costs incurred for high strength concrete, tensile steel, anchorages and other hard wires required for the production of prestressed member.
Prestressed Concrete Structures MCQ Set 7
1. To develop continuity the short and straight tendons may be used over the:
Answer: c [Reason:] Continuity in prestressed concrete construction is achieved by using curved or straight cables which are continuous over several spans and it is also possible to develop continuity between two precast beams by using cap cables alternatively short straight tendon may be used over the supports to develop continuity between two precast prestressed beams.
2. Based on method of construction, continuous beams may be classified into:
a) 3 types
b) 2 types
c) 5 types
d) 4 types
Answer: b [Reason:] Based on the method of construction continuous beams may be classified as fully continuous beams in which tendons are generally continuous from one end to the other and particularly continuous where each span is first precast as a simple bend and the elements are assembled to form a continuous member by using cap cables or short tendons over the supports.
3. The primary moment is the apparent bending moment at a:
c) Cross section
d) Equal distance
Answer: a [Reason:] The primary moment is the apparent bending moment at a section in a statically indeterminate structure due to the actual eccentricity of the tendons from the centroid axis and primary moment at every cross section of the two span continuous beams is Pe as it is a hogging moment.
4. The secondary moment is also known as:
a) Parallel bending moment
b) Eccentric bending moment
c) Parasitic bending moment
d) Elliptical bending moment
Answer: c [Reason:] The secondary moment also known as parasitic bending moment are additional moments induced at a section of a statically indeterminate structure due to the redundant reactions developed as a consequence of prestressing the structure and the variation of secondary moment is a two span continuous beam prestressed by a straight eccentric tendon.
5. The resultant moment is a section of:
a) Determinate prestressed structure
b) Indeterminate structure
c) Hollow structure
d) Transverse prestressed structure
Answer: b [Reason:] The resultant moment at a section of an indeterminate prestressed structure is the sum of primarily and secondary moments:
Resultant moment = (Determinate moment +Secondary moment).
6. The resultant thrust line in a two span continuous beam is prestressed by a:
a) Trapezoidal cable
b) Straight cable
c) Bent cable
d) Parabolic cable
Answer: d [Reason:] The resultant thrust line in a two span continuous beam prestressed by a parabolic cable with zero eccentricity at all the supports and if tendon profile is made to coincide with the resultant thrust line, the redundant reactions are completely eliminated and the cable may be considered as concordant.
7. A Transformation profile is any tendon profile consisting of:
a) Parallel lines
b) Straight lines
c) Bent lines
d) Transverse lines
Answer: b [Reason:] A transformation profile is any tendon profile consisting of straight lines between the rigid supports and having zero eccentricity at simple end supports and a tendon following such profile will produce support reactions and uniform longitudinal compression but bending moments.
8. How many common methods are there for analyzing statically indeterminate prestressed structures?
Answer: c [Reason:] There are several methods for analyzing statically indeterminate prestressed structures to compute the secondary moments that develop from prestressing the structure and the commonly used methods are based on the principles of three moment theorem, consistent deformation and tendon reaction and the methods in b and c are also generally referred to as the flexibility influence coefficient method and the method of equivalent loads respectively and the merits and demerits of these methods and their suitability for given cases are outlined with the help of examples.
9. Which diagram is considered in three moment method analysis of secondary moments?
a) Stress strain diagram
b) Bending moment diagram
c) Pressure line diagram
d) Tee beam diagram
Answer: b [Reason:] The classical method of linear structural analysis such as the three or four moment theorem can be conveniently used to analyze the second moments developed in a continuous prestressed concrete structure and in this method the free bending moment diagram to be considered is that due to the primary moment represented by the tendon profile with the longitudinal axis of the member as the horizontal axis.
10. The simplified form of moment equation is given by:
a) Mab+2Mba+2KMbc+KMcb = Kba+KKbc
b) Mab+2Mba+2KMbc = Kba+KKbc
c) Mab+2Mba = Kba+KKbc
d) Mab = Kba+KKbc
Answer: a [Reason:] The simplified form of moment equation is given by: Mab+2Mba+2KMbc+KMcb = Kba+KKbc depending upon the degree of indeterminacy of the structure a suitable number of equations are formulated and then solved to evaluate the secondary moments and the resultant moment at any section is computed as the sum of primary and secondary moments and this method can also handle members of variable cross section along the length of the structure.
11. The tendon reaction method is based on the principle of:
a) Equivalent tendon placing
b) Replacing the tendons
d) None of the mentioned
Answer: b [Reason:] The tendon reaction method, suggested by Guyon, for analyzing statically indeterminate prestressed structure is based on the principle of replacing the tendon by an equivalent system of loads acting on the concrete member which correspond to the reactions exerted by the tendon concrete.
12. The analysis of indeterminate structure supporting the equivalent loading directly yields the:
a) Span moments
b) End moments
c) Resultant moments
d) Strain moments
Answer: c [Reason:] It is important to note that the analysis of the indeterminate structures supporting the equivalent loads directly yields the resultant moments consequently, the secondary moments, if required are obtained as the difference of the resultant and primary moments at every cross section of the structure.
13. In statistically indeterminate prestressed concrete structures it is possible to make simple modification to:
a) Predetermined tendon profile
b) Elongated tendon profile
c) Collapse tendon profile
d) Ridge tendon profile
Answer: a [Reason:] In statistically indeterminate prestressed concrete structures it is possible to make simple modification to Predetermined tendon profile without altering the pressure line I the members this is an important property of continuous prestressed beams first enunciated by Guyon as follows: In a continuous prestressed beam, if the tendon profile is displaced vertically any of the intermediate supports by any amount but without altering its intrinsic shape between the supports, the resultant line of thrust is unchanged.
14. The axial contraction in case prestressed structures does not influence:
a) Force and Moment
b) Reactions and moment
c) Deflection and moments
d) Area and moments
Answer: b [Reason:] In case of prestresssed structures comparing unidirectional members, such as continuous beams, the axial contraction due to the effect of prestressing does not significantly influence the force and moment in the continuous structure.
15. In structure like portal frames prestressing of transform results in:
a) Tensile contraction
b) Axial contraction
d) Principle contraction
Answer: a [Reason:] In structures like portal frames with members in different directions, prestressing of transform results in an axial contraction, which in turn introduced tertiary moments in the frames due to the lateral displacement of the junction of the transform and column members.
Prestressed Concrete Structures MCQ Set 6
1. The dimensioning of composite sections involves determining the required size of:
a) Precast sections
b) Precast beams
c) Composite sections
d) Prestressed beams
Answer: c [Reason:] The dimensioning of composite sections involves determining the required size of the composite section using a standard precast prestressed beam of known section properties in order to support the required design service loads.
2. What is necessary to design a precast prestressed section?
b) Section modulus
c) Factor safety
d) Reinforcement details
Answer: b [Reason:] It may become necessary to determine the section modulus of the precast prestressed section for a composite slab of given depth and either case, formulae relating the section moduli of the precast prestressed and composite section loading on the member, permissible stresses in the concrete and loss ratio may be developed by considering various stages of loading.
3. The critical stress condition generally occurs at:
Answer: a [Reason:] The critical stress condition generally occurs at the soffit of the precast prestresssed beam is calculated in order to support the required design service load calculate the overall depth of composite slab by assuming the trial depth and add the trial depth to the depth of standard prestressed beam.
4. The first two factors considered in design considerations of composite sections are:
a) Sectional properties and overall depth
b) Elevation properties and overall depth
c) Design properties and overall depth
d) Construction properties and overall depth
Answer: a [Reason:] The known sectional properties of the precast prestressed beam is calculated in order to support the required design service load, calculated the overall depth of composite slab by assuming the trial depth and add the trial depth to the depth of standard prestressed beam.
5. The design considerations of composite section in step 3 and step 4 are:
a) Alignment and forces
b) Self weight and moments
c) Area and moments
d) Deflection and moments
Answer: b [Reason:] Calculate the self weight of the precast beam and insitu concrete self weight of precast beam W = overall depth x width x unit weight of concrete, w = d x b x 24 and Calculate the moment due to self weight and live load moment due to self weight M = 0,125xwxl2. Moment due to live load Ml = 0.125xBxPxL2 according to the specification the permissible compressive stress in concrete = 0.5fct, fci = compressive strength of precast pretensioned member.
6. Under minimum and maximum moments the critical stresses occur at:
Answer: b [Reason:] In Step 5 under minimum and maximum moments we calculate the critical stresses that occur at the soffit of the precast prestressed element. The stress conditions are (Pinf – Mmin/b) < Pct (ɳPinf-M/Zb-Mb/Zb) > or equal to pth.
7. In typical detail of expansion joint the open cell compression seal is dependant upon its ability to maintain:
Answer: c [Reason:] In typical detail of expansion joint the open cell compression seal is dependent upon its ability to maintain Pressure on the joint side walls with varying degree of stress and generally elastometric (Neoprene) compression seals for expansion joints in bridge decks and they are made of polychloroprene otherwise known as Neoprene.
8. The coupling units are used in prestressing steel for:
Answer: a [Reason:] The coupling units are used in prestressing steel for coupling units used for joining of high tensile wires should have an ultimate strength of not less than the individual strengths of the wires or bars being joined and welding is not permitted for joining of high tensile wires or bars.
9. The prestressing steel, sheathing and anchorages should be stored at:
Answer: a [Reason:] The prestressing steel, sheathing and anchorages should be stored at site in such in such a way as to provide them with adequate corrosion protection and after stressing the steel in the sheath, it should be provided with permanent protection as soon as possible preferably within one week and while providing protection by pressure grouting of cement, care should be taken that the neighboring cables are penetrated by grout.
10. The prestressing tendons are not grouted in the case of:
a) Nuclear pressure vessels
b) Earth vessels
Answer: a [Reason:] the prestressing tendons are not grouted in the case of nuclear pressure vessels and protection against corrosion is ensured by filling the ducts with petroleum based jelly and the unbounded tendons facilitate re tensioning operations whenever required and the force in the tendons can be checked at periodical intervals.
11. The bottom fiber of the prestressed beams is expressed as:
a) Ptw – Mmin/Zt
b) Ptw + Mmin/Zt
c) Ptw – Zt/Mmin
d) Ptw + Zt/Mmin
Answer: a [Reason:] The required top and bottom fibers of the precast prestressed beams are calculated in 7 step they are expressed as:
Pt > or less than (Ptw/ɳ + M/ɳZb + Ml/ɳZb‘)
Pb > or less than (Ptw – Mmin/Zt) where Pt = characteristic tensile strength of concrete (n/mm2), Pb = stress at bottom fiber (n/mm2).
12. The maximum eccentricity in the design of composite sections is given as:
a) e = ZtZb(Pt) / A(PbZt+PtZb)
b) e = ZtZb(Pt-Pb) / A(PbZt+PtZb)
c) e = ZtZb(Pt+Pb) / A(PbZt+PtZb)
d) e = ZtZb / A(PbZt-PtZb)
Answer: b [Reason:] The maximum eccentricity for composite sections is given in step 8 is
e = ZtZb(Pt-Pb) / A(PbZt+PtZb) where Zt = section modulus of the top fiber, Zb section modulus of bottom fiber, the minimum prestressing force is given as W = A(PtZb+PbZt) / Zt+Zb.