In case of unavailability of space for providing development length in an RCC beam which option shall NOT be used to satisfy the criteria of development length?
- ABends
- BChairsCorrect
- CMechanical anchorages
- DHooks
Solution
Concept
When straight development length is not available, IS 456 allows bends, hooks or mechanical anchorages.
Formula
Ld = φ σs / (4 τbd)
Step-by-step solution
1. Development length Ld is needed to transfer bar force to concrete by bond. 2. If space is not enough, the bar can be anchored by hooks, bends or mechanical anchorages. 3. Chairs only support top bars at the correct level during concreting. 4. So chairs cannot satisfy development length. Answer is B.
Explanation
Hooks, bends and mechanical anchorages give extra anchorage when the straight length is short. Chairs are small bar supports that keep top steel in position. They do not anchor the bar, so they cannot replace development length.
Why the other options are wrong
A, C, D: Bends, mechanical anchorages and hooks are all accepted ways to provide anchorage when space is limited.
Shortcut
Chairs hold bars up; they do not anchor bars.
Common mistake
Thinking any extra bar detail (like a chair) adds to bond length.
Correct answer: B) Chairs