# Prestressed Concrete Structures Questions and Answers – Deflections of Composite Members

This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Deflections of Composite Members”.

1. In the case of composite members, deflections are computed by taking into account the different stages of ___________
a) Tension
c) Ranging
d) Hogging

Explanation: 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
d) Foundation

Explanation: 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

Explanation: 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

Explanation: 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

Explanation: 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.
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6. In general appropriate technology must necessarily involve the prevailing?
a) Structures
b) Infastructure
c) Codes
d) Books

Explanation: 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

Explanation: 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?
a) Costly
b) Cheapest
c) Zero
d) Constant

Explanation: 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?
a) Portals
b) Hinges
c) Layers
d) Arches

Explanation: 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 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

Explanation: 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.

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