Prestressed concrete per IS 1343: The total shrinkage strain to be considered for a pretensioned member is approximately equal to which value?
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A3.0 × 10^-2
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B3.0 × 10^-3
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C3.0 × 10^-4
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D3.0 × 10^-5
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E3.5 × 10^-5
Answer
Correct Answer: 3.0 × 10^-4
Explanation
Introduction / Context:Shrinkage of concrete shortens prestressed members and reduces effective prestress via time-dependent losses. IS 1343 recommends typical values of total shrinkage strain for design purposes in the absence of detailed testing.
Given Data / Assumptions:
- Pretensioned prestressed concrete member.
- Use standard code-recommended total shrinkage strain.
Concept / Approach:
Total shrinkage strain is an order of 10^-4 for normal concretes; adopting 3.0 × 10^-4 is a common design value for pretensioned members as per IS practice.
Step-by-Step Solution:
Select from given magnitudes: 10^-2 and 10^-3 are too large; 10^-5 too small.Adopt 3.0 × 10^-4 as the representative value.Verification / Alternative check:
Comparisons with code tables and standard textbooks confirm this order of magnitude for total shrinkage strain.
Why Other Options Are Wrong:
10^-2 or 10^-3 would imply unrealistically huge shortening; 10^-5 values underestimate shrinkage and associated prestress loss.
Common Pitfalls:
Confusing shrinkage with creep; mixing units of strain and stress.
Final Answer:
3.0 × 10^-4