Prestressed Concrete Structures Multiple Choice Questions on “Prestressing of Slabs and Floors”.
1. The prestressed concrete slab systems are ideally suited for __________
a) Roofs
b) Slabs
c) Beam
d) Column
Answer: b
Clarification: Prestressed concrete slabs systems are ideally suited for floor and roof construction of industrial buildings where the live loads to base supported are of a higher order and the uninterrupted floor space is desirable for which reason longer span between the supporting elements are required.
2. The precast prestressed hollow core slabs, with or without topping is an important structural element in __________
a) Structures
b) Industries
c) Aquariums
d) Nurseries
Answer: b
Clarification: Precast prestressed hollow core slabs, with or without topping are important structural elements in industrialized and large panel building construction and the slabs, produced on long casting beds using the pretensioning systems and cut to shorter specified span lengths, are mainly used in one way floors which are freely supported by transverse walls or base.
3. Prestressed pretensioned cored slabs with differ types of cavities are widely used as __________
a) Floor panels
b) Tendons
c) Wall coatings
d) Reinforcements
Answer: a
Clarification: Prestressed pretensioned cored slabs with differ types of cavities are widely used as Floor panels of civil and industrial buildings in erstwhile U.S.S.R Graduck reports that these panels are produced in multiples of 200mm nominal width and lengths from 3.6 to 6.4m and hollow panels of oval cavity type are most economical for larger spans since they contain the least volume of concrete as compared to round cavity panels and prestressed concrete ribbons have been used as reinforcement for hollow-cored slabs and these consist of tensioned wires or strands embedded in high grade concrete of star of rectangular cross section.
4. One way slabs may be supported across the entire width of the slab by means of __________
a) Columns
b) Piers
c) Ridges
d) Footings
Answer: b
Clarification: One way slabs may be supported across the entire width of the slab by beams, piers or abutments or bearing walls, which are positioned perpendicular to the longitudinal axis of the span or the supports may be at an angle of the span directions and one way slabs may be continuous over one or several support.
5. The simple or continuous slabs are analyzed for __________
a) Design foundation
b) Design reinforcement
c) Design moments
d) Design slab
Answer: c
Clarification: The simple or continuous slabs are analyzed for design moments by considering a unit width of the slab and the prestressing force and the eccentricity of the cable required at prominent sections to resist the dead and live load moments are determined and the spacing of the cables or wires fixed based on the availability of type of tendon.
6. The design of a two-way-slab supported on all four sides involves the computation of __________
a) Moments
b) Cross sections
c) Bending moment
d) Deformations
Answer: c
Clarification: The design of a two way slab supported on all four sides involves the computation of bending moment in the principal directions of the slab and the slab may be supported on masonry walls or beams and mayor may not be continuous over the supports and transverse loads are resisted by the development of two way slab action, resulting in moments in longer and shorter span directions.
7. The moment coefficients derived from the ultimate load method are generally lower in __________
a) Span
b) Eccentricity
c) Strength
d) Magnitude
Answer: d
Clarification: The moment coefficients derived from the ultimate load method are generally lower in magnitude than those evaluated from elastic theories thus naturally resulting in savings in reinforcement and however slabs designed by the ultimate load method should be checked service loads according to the principle of limit state design.
8. A simple prestressed flat slab is generally supported by a network of __________
a) Beams
b) Columns
c) Spans
d) Deflections
Answer: b
Clarification: A simple prestressed flat slab is generally supported by a network of columns without beams and prestressed in two perpendicular directions and the design of typical simple flat slab involves the analysis of moments in the two principal directions so that cables may be arranged to resist these moments and the slab is analyzed as one way slab and the total number of cables required to resist the moments in each of two principal directions are determined.
9. The proportioning of tendons in design of prestressed concrete simple flat slab between the column and middle strips may be based on __________
a) Moments
b) Codes
c) Deflections
d) Loads
Answer: b
Clarification: The column strips being stiffer than the middle strips, a greater percentage of the tendons are housed in the column strips and the proportioning of the tendons between the column and middle strips may be based on the provisions of codes such as IS:456 and BS:8110, where column strips share a higher proportion of total moment.
10. The design principles of continuous flat slab floors are similar to __________
a) One way slab
b) Two way slab
c) Continuous
d) Deformed
Answer: b
Clarification: The design of continuous flat slab floors are similar to those of two way reinforced concrete slabs and a strip of slab of unit width continuous over supports is analyzed as continuous beam and its prestressing results in secondary moments.