This set of Prestressed Concrete Structures MCQs focuses on “Structural Forms and High Rise Structures”.
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
Explanation: 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
Explanation: 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.
Explanation: 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?
Explanation: 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 ____________
Explanation: 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
Explanation: 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. What are the advantages of reducing the w/c ratio?
a) Superior dimensional stability
Explanation: 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
Explanation: 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 ____________
Explanation: 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
Explanation: 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 operation for each span.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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