Prestressed Concrete Structures MCQ Set 1
1. In general, a satisfactory design must ensure the achievement of an acceptable:
a) Life of structure
Answer: a [Reason:] In general, a satisfactory design must ensure the achievement of an acceptable probability that the specified life of a structure is not curtailed prematurely due to the attainment of unsatisfactory conditions or limit state, which covers the various forms of failure.
2. The limit states at which the structure ceases to function the most important among them is:
Answer: b [Reason:] There are several limit states at which the structure ceases to function the most important among them being the limit state of collapse, excessive deflection and cracking, each of these limit states may be attained due to different types of loading configurations however in practice only one or two of these are of primary significance in design.
3. The failure of one or more critical sections in:
Answer: a [Reason:] Failure of one or more critical sections in flexure, shear, and torsion or due to their combinations is one of the criteria concerning prestressed concrete for ultimate limit state, the ultimate load analysis of slabs by the yield line theory also suffers from similar deficiencies in that the deformation characteristics of the slab at service loads cannot be predicted by ultimate loads.
4. One of the criteria considered for ultimate limit state is:
a) Bursting of midspan
b) Bursting of endblock
c) Bursting of edge block
d) Bursting of middle block
Answer: b [Reason:] Bursting of prestressed concrete end block is one of the criteria considered for ultimate limit state is bursting of end block, In erstwhile U.S.S.R as far back of 1930, problems were considered concerning the formulation of a design concept to take into account the variabilities inherent in the materials of construction and design process and building construction.
5. The bearing failure at which point is considered as criteria for ultimate limit state?
a) Bearing failure at edges
b) Bearing failure at midspan
c) Bearing failure at supports
d) Bending failure at edge
Answer: c [Reason:] The bearing at support, anchorages or under concentrated imposed load, bond and various types of failure are also considered as bearing failure at supports, basically limit state design is a method of designing structures based on a statistical concept of safety and the associated statistical probability of failure.
6. The failure due to which member is considered as criteria for ultimate limit state:
a) Elastic instability of members
b) Elastic stability of members
c) Deformation of members
d) Relaxation of members
Answer: a [Reason:] Bond and anchorage failure of reinforcement, failure of connections between precast and cast insitu elements and failure due to elastic instability of members are the factors which are considered in limit states due to their characteristics of sustain.
7. The limit state of collapse may be attained due to:
Answer: d [Reason:] The limit state of collapse may also be attained due to fatigue, vibrations, and corrosive environment impact as a consequence of explosions or earthquakes and disintegration due to fire or frost, a comprehensive and critical review of the limit states design concepts embodied in various codes was presented in his reports reinforced concrete and prestressed concrete.
8. The structure may be rendered unfit due to:
a) Collapse limit states
b) Nature limit states
c) Serviceability limit states
d) Loaded limit states
Answer: c [Reason:] The structure may be rendered unfit for its intended purpose due to various serviceability limit states being reached, there are six factors which effect the limit states and the different failures of the members are also considered in this factors in case of limit states.
9. The excessive deflection or displacement, adversely affects the:
d) Beam detailing
Answer: a [Reason:] Excessive deflections or displacement, adversely affecting the finishes and causing discomfort to the users of the structure is serviceability limit states, the method of design foe a structure must ensure an acceptable probability that the structure during its life will not become unfit for the intended purpose.
10. The excessive local damage resulting in cracking impairs the:
d) Dead loads
Answer: a [Reason:] Excessive local damage resulting in cracking or spalling of concrete, which impairs the efficiency or appearance of the structure, the acceptable probability should give a satisfactory balance between the initial and maintenance costs during the life of the structure together with the cost of those insurance premiums that are based on the probability of the structure becoming unfit for the design purpose.
Prestressed Concrete Structures MCQ Set 2
1. In the case of composite members, deflections are computed by taking into account the different stages of:
Answer: b [Reason:] In the case of composite members, deflections are computed by taking into account the different stages of loading as well as the differences in the modulus of elasticity of concrete in the precast prestressed unit and then insitu cast element.
2. The initial deflection is due to:
a) Self weight
b) Cross section
c) Beam weight
Answer: a [Reason:] The initial deflection due to prestress of self weight of the beam and the weight of the insitu cast concrete if the beam is not propped is computed on the basis of the section and the modulus of elasticity of the precast unit.
3. The live load deflection is always estimated using:
a) Beam sections
b) Composite sections
c) Bent sections
d) Rolled sections
Answer: b [Reason:] The live load deflection is always estimated using composite properties if the precast beam is propped during construction and the deflections due to dead weight of in situ concrete is also computed on the basis of composite sections.
4. When the modulus of elasticity of the precast and insitu cast concrete are different the flexural rigidity is worked out by:
a) First moment of area
b) Second moment of area
c) Limit states
d) Composite beam
Answer: b [Reason:] When the modulus of elasticity of the precast and insitu cast concrete are different the flexural rigidity is worked out by computing the equivalent second moment of area of the composite sections using the modular ratio and the deflections computed under service loads should not exceed the limiting values prescribed in the codes.
5. One of the knowledge required for planning of any structural component is:
a) Seismic nature of terrain
b) Regional nature of terrain
c) Wind nature of terrain
Answer: a [Reason:] Planning of any structure like a building, bridge, marine structures or storage structures requires comprehensive knowledge of the various parameters like site conditions availability of skilled labour and materials, transportation facilities, seismic nature of the terrain, sub soil water conditions, choice of material like steel, reinforced or prestressed concrete, weather and durability considerations, clients requirements and the funds earmarked for the structures.
6. In general appropriate technology must necessarily involve the prevailing:
Answer: b [Reason:] In general, appropriate technology must necessarily involve the prevailing local infrastructure like raw materials, man power, plant and machinery, power and financial resources and an excellent example of appropriate technology can be found in the low cost suspension bridges built by Girish bharadwaj in south India.
7. The factors which influence the cost of a bridge are:
a) Method of erection
b) Length of beam
c) Cost of water
d) Testing of materials
Answer: a [Reason:] In general the quantities of concrete and steel expressed per unit area of deck can be considered as indicative of economy although these figures are not the only ones which governs the overall cost of the bridge and the various factors which influence the cost of a bridge are: the length of individual spans, the type of cross section of deck, the number of longitudinal girders, the width of bridge deck, depth and type of foundation, excavations etc, the cost of form work, the cost of materials and labour, the type of construction, such as cast in situ or precast, the method of erection of precast elements.
8. For spans less than 35m, SSB beams are?
Answer: b [Reason:] For spans less than 35m, SSB are the cheapest type of construction and as the span increases, the cost of simply supported beams increases rapidly and it is prohibitively costly for spans exceeding 60m.
9. Which are more expensive than continuous beams of unequal spans?
Answer: a [Reason:] Portals are slightly more expensive than continuous beams of unequal spans and however for very long spans especially in deep ravines, reinforced concrete arched bridges are more economical and concrete arches are seldom prestressed because prestressing adds very little to the natural advantage of thrust in arch design.
10. In the early 1960, based on which analysis have reported the variation of the cost of bridge decks:
a) Rigorous computations analysis
b) Tension analysis
c) Strain analysis
d) Stress analysis
Answer: a [Reason:] As early as in 1960, Sarkar based on a rigorous computational analysis have reported the variations of the cost of bridge deck in relation to span and the number of longitudinal girders in a tee girder bridge and although the cost was more or less the spans up to 15m the cost increased with the increasing number of girders for spans in the range of 15 to 35m.
Prestressed Concrete Structures MCQ Set 3
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 [Reason:] 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?
Answer: c [Reason:] 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 [Reason:] 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 [Reason:] 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 [Reason:] 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?
Answer: b [Reason:] 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/EcIt , a = maximum deflection, L = effective span, M = maximum moment in the beam, Ec = modulus of elasticity of concrete, Ic = 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 [Reason:] 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 [Reason:] 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 [Reason:] 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:
Answer: a [Reason:] 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 dependant factor.
Prestressed Concrete Structures MCQ Set 4
1. Most compression members, such as long columns and piles are subjected to:
a) Bending moment and cracking forces
b) Bending moment and tension forces
c) Bending moment and axial forces
d) Bending moment and compression forces
Answer: c [Reason:] Due to handling in some members like portal frames and masts the sections are subjected to compression and bending and most compression members such as long columns and piles are subjected to bending moment and axial forces.
2. The load moment interaction diagrams are more or less similar to:
a) Prestressed columns
b) Reinforced concrete columns
c) Aluminium columns
d) Steel columns
Answer: b [Reason:] The load moment interaction diagrams are more or less similar to prestressed columns those of reinforced columns expect that precompression exists in prestressed concrete columns and the prestressed columns are much advantageous than any other elements which are replicable.
3. The compression failure mode develops under:
a) Static loading
b) Moment loading
c) Concentric loading
d) Tensile loading
Answer: c [Reason:] The compression failure mode develops under concentric loading and this type of failure mode develops under concentric loads and the section is considered to have failed when the concrete strain ε0 reaches a value of 0.02.
4. The balanced failure develops when there is simultaneous:
a) Tension yielding
b) Compression yielding
c) Flexure yielding
d) Prestress yielding
Answer: a [Reason:] Balanced failure develops when there is simultaneously tension yielding of prestressing steel and crushing of concrete, the eccentricity of the axial load is defined as balanced eccentricity Eb. and this eccentricity factor is used for various failures considering top and bottom fibers.
5. The charts proposed by Bennett are useful in dimensioning columns of:
a) L section
b) I section
c) T section
d) Edge section
Answer: b [Reason:] Bennett has proposed design charts with dimensionless parameters expressed in terms of the service loads and moments, and section properties and permissible stresses in concrete expressed as a fraction of the characteristic strength these charts are useful in dimensioning columns of I section with non uniform prestress and allowing desirable tensile stresses in concrete as in class 3 type members.
6. The steps involved in design of biaxially loaded column are:
Answer: c [Reason:] The load contour method of analysis, detailed by Nawy and generally termed Bresler-Parme counter method is ideally suited for the design of biaxially loaded columns and the design procedure is outlined the following steps: give the ultimate moments, determine the larger of the equivalent required, assumed cross section, verify the ultimate load carrying capacity, calculate the actual nominal moment capacity, the moment value.
7. The Prestressed concrete compression members should have a minimum average effective prestress of not less than:
Answer: a [Reason:] According to ACI 318-1989, a minimum non prestressed reinforcement ratio of one percent should be provided in compression members with an effective prestress of lower than 1.55n/mm2 and the American code specifies the various effective prestress in prestressed concrete members considering all the factors and makes them economical.
8. The Spirals are particularly useful in increasing the:
a) Tensile strength
Answer: b [Reason:] Closely spaced spirals reinforcement increases the ultimate load capacity of the column due to confinement of concrete in the core and spirals are particularly useful in increasing the ductility of the member and hence are preferred in high earthquake zones.
9. The pitch of spiral is computed as:
a) S = 4as(Dc – ds)/Dc2 ρs
b) S = 2as(Dc – ds)/Dc2 ρs
c) S = 6as(Dc – ds)/Dc2 ρs
d) S = 10as(Dc – ds)/Dc2 ρs
Answer: a [Reason:] S = 4as(Dc – ds)/Dc2 ρs, as = cross sectional area of spiral, Dc = core of the column measured to the outside diameter of the helix, ds = diameter of spiral wire, ρs = ratio of the volume of helical reinforcement.
10. The pitch of spirals is limited to a range of:
a) 40 to 45mm
b) 25 to75mm
c) 15 to 30mm
d) 10 to 30mm
Answer: b [Reason:] The pitch of spirals is limited to a range of 25 to 75mm and the spiral should be well anchored by providing at least 11/2 extra turns when splicing rather than welding of spirals is used and the pitches of the spirals are limited to certain ranges.
Prestressed Concrete Structures MCQ Set 5
1. The design loads for various limit states are obtained as product of the:
a) Characteristic loads
b) Seismic loads
c) Ultimate loads
d) Wind loads
Answer: a [Reason:] The design loads for various limit states are obtained as products of the characteristic loads and partial safety factor and are expressed as:
Fd = γf Fk, where Fd = appropriate design load, γf = partial safety factor for loads, Fk = characteristic load.
2. The characteristic load is expressed as:
a) Mean load – K x standard deviation
b) Mean load + K x standard deviation
c) Load – standard deviation
d) Load + standard deviation
Answer: b [Reason:] The characteristic load Fk which is independent of the limit state considered and is seldom exceeded in service is defined as: Characteristic load = Mean load + K x standard deviation, K is a factor so chosen as to ensure that the probability of the characteristic load being exceeded is small and a value of 1.64 for K ensures the probability that the characteristic load is exceeded by only 5 percent during the intended life of the structure.
3. The statistical data required to define the characteristic loads, need recording of data and:
Answer: a [Reason:] The statistical data required to define the characteristic loads for different types of occupancy is not readily available, since loading statistics are invariably difficult to compile as they need a systematic observations and recording of data on loading and the nominal imposed loads provided in various national codes, such as IS: 875-1987, BS: 6399 may be treated as characteristic loads.
4. The characteristic values of the loads take account of expected variations but do not allow for:
a) Variations in stress
b) Variations in dimensional accuracy
c) Variation in strain
d) Variation in loads
Answer: b [Reason:] The characteristic values of the loads take account of expected variations but do not allow possible unusual increases in load beyond those considered in deriving the characteristic load, in accurate assessment of effects of loading and unforeseen stress distribution within the structure and variations in dimensional accuracy achieved in construction.
5. The values of partial safety factors are recommended for:
Answer: a [Reason:] Partial safety factor γf are therefore used for each limit state being reached and the values of partial safety factors for loads recommended in the British, Indian and American codes and FIP recommendations.
6. The design strength of materials is expressed as:
a) Fd = Fe / γk
b) Fd = Fc / γk
c) Fd = Fk / γm
d) Fd = Fd / γm
Answer: c [Reason:] FIP recommendations regarding partial safety factors are comprehensive, as they provide for a combination coefficients for basic variable actions as well as for other variable factors depending upon different types of structures, such as dwellings, offices, parking area and highway bridges and the design strength of materials are expressed as: Fd = Fk / γm.
7. The term WL is termed as:
a) Wind load
c) Live load
d) Wall load
Answer: a [Reason:] DL is the dead load, LL is the live load and WL is the wind load while considering earthquake effects substitute EL for WL and these loads are considered while calculation of loads and deflections of the beam.
8. In characteristic strength of the material, the tensile strength of tendons below which the failure are not more than:
Answer: c [Reason:] Fk is the characteristic strength of the material which corresponds to the 28 days cube strength compressive strength of concrete or the tensile strength of tendons below which the failures are not more than 5 percent.
9. The characteristic strengths of concrete and steel may be taken as the works cube strength and:
a) Yield strength
d) Principle strength
Answer: a [Reason:] In the absence of statistical data, the characteristic strengths of concrete and steel may be taken as the works cube strength and the specified proof or yield strength respectively as provided for in the codes.
10. The partial safety factor (γm) for materials has a value which depends upon the importance of the:
a) Principal sates
b) Limit states
c) Strain states
d) Stress states
Answer: b [Reason:] The partial safety factor (γm) for materials has a value depends upon the importance of limit states being considered, materials when tested and when incorporated in construction during service life of the structure.