Prestressed Concrete Structures MCQ Set 1
1. The shrinkage of concrete in prestressed members results in:
Answer: a [Reason:] The shrinkage of concrete in prestressed members is due to the gradual loss of moisture which results in changes in volume, rich mixes exhibit relatively greater shrinkage than lean mixes since the contraction of the cement gel increases with the cement content, the shrinkage also depends upon the degree of hardening of the concrete at the commencement of drying and the shrinkage of concrete in prestressed members results in a shortening of tensioned wires and hence contributes to the loss of stress.
2. The shrinkage of concrete is influenced by:
a) Type of cement
b) Type of chemical
c) Type of admixtures
d) Type of retarders
Answer: a [Reason:] The shrinkage of concrete is influenced by the type of cement and aggregates and the method of curing used, the rate and amount of shrinkage of the structural member under ambient conditions will depend very much upon the ratio of surface area to volume of the member, as the exchange of moisture between the concrete and the atmosphere must take place through the surface.
3. Which of the following is used to reduce shrinkage of concrete?
a) High strength concrete
d) Low water cement ratio
Answer: a [Reason:] The use of high strength concrete with low water cement ratios results in a reduction in shrinkage and consequent loss of prestress, aggregates of rock type having high modular of elasticity and low values of deferred strain are more effective in restraining the contraction of the cement paste and their use reduces the shrinkage of concrete.
4. The rate of shrinkage is higher at:
Answer: b [Reason:] The rate of shrinkage is higher at the surface of the member and the primary cause of drying shrinkage is the progressive loss of water from concrete, the phenomena of shrinkage being time dependant only the total anticipated or residual shrinkage strain is considered in the computation of loss of prestress to be used in design.
5. The differential shrinkage between the interior and surface of large members result in:
a) Surface gradient
b) Strain gradient
c) Compatibility gradient
d) Stress gradient
Answer: b [Reason:] The differential shrinkage between the interior and surface of large members may result in strain gradients leading to surface grading; it is the effect due to relative deformation caused by the shrinkage of cast in situ concrete and combined action of shrinkage plus creep in the prestressed concrete.
6. Which curing is adopted in case of pretensioned members to prevent shrinkage?
a) Surface curing
b) Edge curing
c) Moist curing
d) Total curing
Answer: c [Reason:] In the case of pretensioned members, generally moist curing is resolved to in order to prevent shrinkage until the time of transfer, the magnitude of relative strain and the stresses induced depend on the concrete composition and surrounding environment to which the composite member is exposed.
7. After the transfer of prestress, the total residual shrinkage will be larger in case of:
a) Pretensioned members
b) Post tensioned members
c) Chemical tensioned members
d) Biological tensioned members
Answer: a [Reason:] The total residual shrinkage strain will be larger in pretensioned members after transfer of prestress in comparison with post tensioned members, where a position of shrinkage will have already taken place by the time of transfer of stress.
8. Which of the following Indian standard code is recommended for the loss of prestress due to shrinkage?
a) IS: 1445
b) IS: 1343
c) IS: 1210
d) IS: 1550
Answer: b [Reason:] The Indian standard code IS:1343 is recommended for the loss of prestress due to the shrinkage of concrete, individual shrinkage strains are evaluated from British code BS 8110 the shrinkage stresses are calculated.
9. The loss of prestress due to shrinkage is obtained by multiplying:
a) Shrinkage strain and modulus of elasticity
b) Principal stress and durability of concrete
c) Curing and grade of concrete
d) Compression and tension
Answer: a [Reason:] The loss of prestress due to shrinkage is obtained by multiplying the shrinkage strain with modulus of elasticity of steel, Δfs = Esh×Es , Es = Residual shrinkage, Es = modulus of elasticity of steel and light weight aggregates with low modulus of elasticity may lead to higher than normal concrete shrinkage where light weight aggregates are used, the value of shrinkage should be increased by 50%.
10. The post tensioned members in dry atmospheric conditions, the shrinkage may be increased by:
Answer: a [Reason:] For post tensioned members in dry atmospheric conditions, the shrinkage strain may be increased by 50% however, it should not exceed the value of 300×10-4units for pretensioned members and 2.0 x 10-4/ log(t+2) for post tensioned members, where t is the age in days of the concrete at transfer.
11. A concrete beam is prestressed by a cable carrying an initial prestressing force of 300kn, area is 300mm2. Calculate the percentage of loss of stress due to shrinkage in pretensioned members?
Answer: a [Reason:] Initial stress in wires = (300×103/300) = 1000n/mm2,
If the beam is pretensioned the total residual shrinkage strain = 300×10-6,
Loss of stress = (300×10-6)(210×103) = 63n/mm2, % loss 0f stress = (63×1000/100) = 6.3%.
Prestressed Concrete Structures MCQ Set 2
1. In prestressed concrete structures the primary problem is damaged caused to:
a) Bridge decks
Answer: c [Reason:] 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 one reason is:
a) Environmental effects
b) Tensile effects
c) Compressive effects
d) Range effects
Answer: a [Reason:] 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. The problem of rehabilitation is:
Answer: a [Reason:] 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 [Reason:] 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 [Reason:] 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 of:
Answer: c [Reason:] 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 [Reason:] 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
d) None of the mentioned
Answer: a [Reason:] 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 [Reason:] 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 [Reason:] 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 [Reason:] 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
Answer: b [Reason:] 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:
Answer: a [Reason:] 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?
Answer: c [Reason:] 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 [Reason:] 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.
Prestressed Concrete Structures MCQ Set 3
1. The concrete used in trusses is normally of grade ranging from:
Answer: a [Reason:] Concrete used in trusses is normally of grade ranging from M35 to M60 which can be considered as high strength concrete and this high strength are design mixes which are used for heavy structures.
2. The requirement in consists of:
a) Aluminium bars
b) HYSD bars
c) Torsion bars
d) Wooden bars
Answer: b [Reason:] The reinforcements consists of mild steel or HYSD bars together with high tensile steel wires or cables use in the tie members and the material requirements per truss varies with the span and spans of trusses.
3. The trusses spacing for 6m prestressed bow string truss with cable reinforcement span for 18m material requirement per truss?
Answer: a [Reason:] The trusses spacing for 6m prestressed bow string truss with cable reinforcement span for 18m material requirement per truss prestressed bow string truss with cable reinforcement span 24m-steel 621-689, 30m-steel 1041-1219.
4. The polygonal built up from blocks with prestressed bottom chord having wire cable for 18m – concrete requirement per truss (m3) is?
Answer: b [Reason:] The polygonal built up from blocks with prestressed bottom chord having wire cable: for 18m – concrete requirement per truss (m3) 24m-3.85m3, 30m-5.28m3 and the difference in truss is observed for different diameters of wire cables.
5. The truss spacing 12m prestressed bow string of linear element with wire reinforcement (18m) grade of concrete (n/mm2)
a) 30- 40n/mm2
b) 10- 50n/mm2
c) 20- 70n/mm2
d) 40- 90n/mm2
Answer: a [Reason:] 24m = 30-50, 30m = 30-50, weight of truss (Kn) 18m = 7.7-9.1, 24m = 14.9-17.4, 30m = 25.5-29.8 are the different truss spacing for spans prestressed bow string of linear element with wire reinforcement for grade of concrete.
6. Calculate effective length of warehouse shed such that length is given as 2.11m and area is given as 650mm2?
Answer: d [Reason:] L = 2.11m, A = 650mm2 = 0.65m2 Effective length = Lc = (0.65×2.11) = 1.37m.
7. Calculate total diameter ratio (d’/D) of reinforced concrete truss member such that the internal diameter is 40mm and external diameter is given as 200mm?
Answer: c [Reason:] d’ = 40mm, D = 200mm
d’/D ratio = (40/200) = 0.2mm.
8. Calculate moment of reinforced concrete truss such that bending moment is given as 4.3 and breadth is given as 250mm and depth is 200mm, characteristic strength of concrete is 35n/mm2?
Answer: a [Reason:] Mu = (1.5×4.3) = 6.45knm, b = 250mm, D = 200mm, fck = Mu = (1.5×4.3) = 6.45knm, b = 250mm, D = 200mm, fck = 35n/mm2,
M = Mu /fck b D = (6.45×106/35x250x2002) = 0.48.
9. Calculate the compression moments of reinforced concrete trusses such that compression in the member is 395, characteristic strength is 35n/mm2, breadth is 250mm and depth is given as 200?
Answer: b [Reason:] Pu = (1.5×395) = 592.5kn, b = 250mm, D = 200mm, fck = 35n/mm2 Pu/fckbD = (592.5×103/35x200x200) = 0.338.
10. Calculate minimum reinforcement of 0.8% in the section such that given breadth is 250mm, Diameter is 200m?
Answer: a [Reason:] b = 250mm, D = 200mm
Minimum reinforcement of 0.8% in the section As = (0.8x200x250/100) = 400mm2.
Prestressed Concrete Structures MCQ Set 4
1. In the case of large floor and roof coverings using prestressed concrete as material, one of the structural forms for adoption is:
a) Concrete panels
b) Reinforced disc
c) Spherical domes
d) Trapezoidal domes
Answer: c [Reason:] In the case of large floor and roof coverings using prestressed concrete as material, there are several types of structural forms for adoption and some of them are as follows: Tee beam and slab floors, continuous beam and slab floors, coffered or grid floors, flat slab floors, folded plate roofs, shell roofs, spherical domes, trusses and framed roofs, composite construction using prestressed and reinforced concrete.
2. If cement, fine aggregate and coarse aggregate are simultaneously charged then it improves:
a) Tension in concrete
b) Uniformity in concrete
c) Compression in concrete
d) Strain in concrete
Answer: b [Reason:] Uniformity in concrete improves if cement, fine aggregate and coarse aggregate are simultaneously charged into mixer and chemical admixtures should be charged into the mix as solutions and the liquids should be considered as part of the mixing water.
3. Under usual conditions up to which percentage the water should be placed in the mixer drums:
Answer: c [Reason:] Concrete may be mixed using stationary mixes on job site or central mixes as used in ready mix plants and under usual conditions up to about 10% of the mixing water should be placed in the mixer drum before the solid materials are added and there after water should be added uniformly with the solid materials leaving about 10% to be added after all other materials are in drum.
4. When the mixture is mixed in the plant the time should not be less than:
Answer: a [Reason:] When mixed in a central mixing plant, the mixing time should be not less than 50s nor more than 90s and when truck mixer is used as in the case of ready mixed concrete, a minimum of seventy to a maximum of 100 revolutions of the drum or blades at mixing speed are required for complete mixing.
5. For heavily reinforced concrete members the nominal maximum size of aggregates shall be:
Answer: d [Reason:] For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of aggregate shall be 5mm less than the spacing between the cables, strands or sheathings and aggregates containing particular varieties of silica, which are suspectable to attack by alkalis present in cement resulting in expansive reaction should be avoided.
6. The strength of concrete primarily depends upon the:
b) w/c ratio
c) Aggregates ratio
d) Cement content
Answer: b [Reason:] The strength of concrete primarily depends upon the w/c ratio and hence the first step in proportioning a concrete mix should be the selection of approximate w/c ratio depending upon the types of cement used to achieve the desired durability and strength intended for the works.
7. One of the advantages of reducing the w/c ratio is:
a) Superior dimensional stability
Answer: a [Reason:] The various advantage of reducing the w/c ratio is as follows:
Increased compressive, flexural and tensile strength, increased density of concrete with lesser voids, increased water tightness, lower absorption of moisture due to less porosity, increased resistance to weathering, better bond between concrete and reinforcement, superior dimensional stability, lesser shrinkage cracks.
8. In massive structures, concrete should be placed in:
a) Trapezoidal layers
b) Horizontal layers
c) Longitudinal layers
d) Edge layers
Answer: b [Reason:] In massive structures, concrete should be placed in horizontal layers not more than 300mm thick expect in thinner slabs and when less than a complete layer is placed in one operation, it should be terminated in a vertical bulk head.
9. Each layer should be placed before the preceding batch undergoes the initial set of:
Answer: c [Reason:] Each layer should be placed and consolidated before the preceding batch undergoes the initial set to prevent injury to the green setting concrete and to avoid surfaces of separation between the batches if taller lifts are encountered in structures like column and retaining walls, suitable regarding agents should be used.
10. In the case of horizontal shallow beams, concrete should preferably deposited starting from:
a) Centre of span
b) Edge of span
c) Outer portion of span
d) Inner portion of span
Answer: a [Reason:] In the case of horizontal shallow beams, concrete should preferably be deposited starting from centre of span and working towards the ends and for deeper girders, concrete should be deposited preferably for the length and brought up evenly in horizontal layers and concrete in slab panels should be placed in one continuous operations for each span.
Prestressed Concrete Structures MCQ Set 5
1. The first approach in optimization methods is:
a) Theory of bending
b) Theory of layout
c) Theory of elongation
d) Theory of stress
Answer: b [Reason:] The first approach is the theory of layout in which the uniaxial structural members are arranged to yield a minimum volume structure for specified loads and materials based on the theorems established by Maxwell in 1854 and later developed and used by michell, cox and hemp.
2. During which period the simultaneous mode of failure approach was persued:
a) 1940 to 1950
b) 1930 to 1940
c) 1920 to 1930
d) 1910 to 1920
Answer: a [Reason:] During the period from 1940 to 1950, the simultaneous mode of failure approach was persued in which each component of the complete structure is at its limit of strength as the complete structure reaches the limit state of collapse and based on the classical ideas of function minimization, this approach was used to solve simple structural forms having a limited applicability to practical design.
3. The third major approach of structural optimization is based on the concept:
a) Criterion of design
b) Criterion of optimality
c) Criterion of texture
d) Criterion of span
Answer: b [Reason:] The third major approach of structural optimization is based on the concept developed by Prager and Taylor and this approach derived from the extremum principles of structural mechanics and after the advent of the finite element techniques, large scale computer programmes have been developed to demonstrate the practical utility of the optimality criterion approach to the design of minimum weight structures.
4. The structural optimization problem is generally expressed as:
a) Maximize Z = F(x)
b) Minimize Z = F(x)
c) Z = F(x)
d) Z = F(t)
Answer: b [Reason:] The structural optimization problem is generally expressed in the mathematical form, involving the design variables, objective function and constraints accordingly the problem is expressed as:
Minimize Z = F(x), subject to Gj(x) < 0, j = 1,2….m
Where x is the design variable, represented by the column vector of dimensions n and each design represented by x is a point in hyper-space defined by the design variables, F(x) = the objective or merit function, Gj(x) = constraints, m = number of constraints.
5. The fourth major area of development is the:
a) Mathematical programming
d) Machine design
Answer: a [Reason:] The fourth major area of developed is the mathematical programming formulations, first applied to structural optimization problems by livesley and pearson an excellent survey of optimum structural design using mathematical programming procedure has been reported by schmit and the excellent example which users tis method is the twenty five bar transmission tower reported by marcel and venkayya.
6. What is a constraint?
Answer: c [Reason:] A constraint is a limitation or restriction imposed directly on a variable or group of variables in order that the design is acceptable and they are expressed in the equality or inequality from and are divided into two groups and they are side constraints and behavior constraints.
7. The behavior constraints are those imposed on the:
a) Cross sectional response
b) Structural response
c) Sequential response
d) Durability response
Answer: b [Reason:] Behavior constraints are those imposed on the structural response typical explicit behavior constraints are given by formulae presented in design specifications are generally non linear function of design variables are implicitly related to design variables.
8. In structural designs, behavior constraints are imposed on:
Answer: a [Reason:] In structural designs, behavior constraints are usually imposed on stresses and displacements constraints prescribe the global rigidity of the structure side constraints are specified limitations (minimum or maximum) imposed on a design variable are usually explicit in form.
9. The objective function in a structural design problem is:
Answer: d [Reason:] In a structural design problem, there should be a well defined criterion by which the performance or cost of the structure can be judged under different combinations of the design variables and the index is generally referred to as the objective cost or merit function.
10. In the design of prestressed concrete structural elements, the objective function comprises cost of:
a) Steel and concrete
Answer: a [Reason:] In the design of prestressed concrete structural element the objective function may comprise the cost of steel and concrete in the member and a general guide for selecting an objective function is that the design should be optimized with respect to the most important design property that can be meaningfully quantified and which is not constrained in advance.