This set of Prestressed Concrete Structures Interview Questions and Answers focuses on “Importance and Factors Influencing Deflections”.
1. The philosophy of design is termed as:
a) Limit state approach
b) Limit area method
c) Limit design approach
d) Limit elasticity approach
Explanation: The philosophy of design termed as “Limit state approach” adopted by the Russian code in 1954 and the American and British codes in 1971, it requires a proper knowledge of the behavior of structural concrete members at the multiple limit states, of which deflection forms an important criterion for the safety of the structure.
2. The structural concrete members if not designed to have adequate stiffness, it affects:
b) Local conditions
Explanation: In general, according to various national codes, the structural concrete members should be designed to have adequate stiffness to limit deflections, which may adversely affect the strength or serviceability of the structure at working loads.
3. The large deflections under dynamic effects may cause:
a) Likely appearance to users
b) Discomfort to users
c) High bending
d) Requires more construction materials
Explanation: Large deflections under dynamic effects and under the influence of variable loads may cause discomfort to users, the members of structural concrete are designed in such a way that it possess adequate stiffness to control the deflections or it may leads to a very great impact on serviceability conditions and strength of a structure at working loads.
4. The excessive deflections are likely to cause damage to:
Explanation: Excessive deflections are likely to cause damage to finishes, partitions and associated structures, the principal structural members which resulted in excessive sagging condition makes the floor area not suitable for further use.
5. Which of the following influence the deflections of prestressed concrete members?
a) Cable profile
b) Wall profile
c) Type of aggregates
d) Type of cement
Explanation: The deflections of prestressed concrete members are influenced by the following salient features: imposed load and self weight, magnitude of the prestressing force, cable profile, and second moment of area of cross section, modulus of elasticity of concrete, shrinkage, creep, relaxation, span, and fixity conditions.
6. Which type of deflections is solved by Mohr’s theorem?
c) Middle span
d) End span
Explanation: The computations of short term or instantaneous deflections, which occur immediately after the transfer of prestress and on application of loads is conveniently done by Mohr’s theorem from certain surveys it is concluded that the maximum deflection should be noted including with limiting deflection span ratio.
7. In the pre cracking stage, the deflections are computed by:
a) Prestressing force
b) Sectional area
d) Second moment of area
Explanation: In the pre cracking stage the whole cross section is effective and the deflections in this stage are computed by using the second moment of area of the gross concrete section, as the length of the structural member increases the deflections can be controlled to a maximum extent possible.
8. In a post cracking stage, a prestressed concrete beam behaves in a manner similar to:
a) Reinforced concrete beam
b) Flexural beam
c) High strength of concrete
d) Soffit beam
Explanation: In the post cracking stage, a prestressed concrete beam behaves in a manner similar to that of a reinforced concrete beam, these beams undergo cracking under working loads, they undergo large deflections and reinforced concrete beam require shear reinforcement in this testing of steel and concrete cannot be done.
9. The computations in post cracking stage are by considering:
a) Moment of inertia
b) Moment curvature
c) Moment design
d) Moment area
Explanation: The computations of deflections in this stage are made by considering moment curvature relationships which involve the section, properties of the cracked beam, based on prestressing forces and live loads the deflections of prestressed concrete members can be calculated if the longitudinal distribution of curvatures and magnitude of beam can be known at that particular time.
10. In both pre and post cracking stages the effect of creep and shrinkage of concrete is to increase the:
a) Short term deflections
b) Middle span deflections
c) Long span deflections
d) Edge span deflections
Explanation: In both pre and post cracking stages the effect of creep and shrinkage of concrete is to increase the long term deflections under sustained loads, which is estimated by using empirical methods that involve the use of effective (long term) ,modulus of elasticity or by multiplying short term deflections by suitable factors.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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