The equivalent length of a column of length L having both ends fixed is:
Try it first: pick an option, then read the explanation.
Correct answer: C. L/2
Asked in SSC JE 23/01/2018 (Evening)
Detailed Explanation
A fixed–fixed column buckles with zero slope at both ends. Its inflection points are at quarter points, so the middle half behaves like a pin-ended column.
Why “L/2” Is Correct
The equivalent length is L/2, giving P = 4π²EI/L².
Why the Other Options Are Wrong
- A. 2L: 2L is fixed–free.
- B. L: L is hinged–hinged.
- D. L/√2: L/√2 is fixed–hinged.
Key Point
Fixed–fixed: le = L/2 (shortest), P = 4π²EI/L² (largest).
Key Concepts for Students
- The middle L/2 between inflection points acts as a pinned column.
- IS 800 recommends 0.65L because full fixity is not achieved.
- Four times the hinged–hinged load.
Practice more: this is question 15 in Columns and Struts MCQs – Part 1. Try the whole set and check every answer instantly.