Indian Standards Code recommends a minimum cube strength of _______for pre-tensioned system.
- A20 N/mm²
- B25 N/mm²
- C30 N/mm²
- D40 N/mm²Correct
Solution
Concept
Minimum concrete strength for pre-tensioned concrete
Formula
NONE
Step-by-step solution
1. Pre-tensioned concrete requires immediate transfer of high prestressing forces via bond between steel and concrete. 2. Indian Standards IS 1343 specifies minimum concrete cube strength to prevent local bond failure at transfer. 3. The specified minimum concrete strength for a pre-tensioned system is 40 N/mm² (M40). Answer: D
Explanation
Indian Standard code IS 1343 requires a minimum concrete compressive strength of 40 N/mm² for pre-tensioned prestressed concrete members. High concrete strength is necessary to safely resist high initial prestress forces transferred directly through bond stress without crushing or excessive creep losses. Post-tensioned systems generally require a lower minimum strength of 30 N/mm².
Why the other options are wrong
A) 20 N/mm² is inadequate for pre-tensioned prestressed concrete applications. B) 25 N/mm² does not meet the minimum strength requirements for pre-tensioned members. C) 30 N/mm² is the minimum cube strength required for post-tensioned systems.
Shortcut
Minimum concrete strength: Pre-tensioned = 40 N/mm² (M40), Post-tensioned = 30 N/mm² (M30).
Common mistake
Confusing the minimum strength requirement for pre-tensioned systems (40 N/mm²) with post-tensioned systems (30 N/mm²).
Correct answer: D) 40 N/mm²