If a column's ends are effectively held in position and restrained against rotation at both ends, the effective length is:
Try it first: pick an option, then read the explanation.
Correct answer: B. L/2
Asked in SSC JE 2011
Detailed Explanation
Held in position (no sway) and restrained against rotation at both ends means the column is fixed at both ends.
Why “L/2” Is Correct
The theoretical effective length is L/2 (IS 800 recommends 0.65L for design).
| Restraint at the two ends (IS 800 Table 11 / IS 456 Table 28) | Theoretical le | Recommended le |
|---|---|---|
| Held in position and restrained in direction at both ends (fixed–fixed) | 0.5L | 0.65L |
| Fixed at one end, held in position but free to rotate at the other (fixed–hinged) | 0.7L | 0.80L |
| Held in position at both ends, free to rotate (hinged–hinged) | 1.0L | 1.0L |
| Fixed at one end; other end restrained in rotation but free to translate (sway) | 1.0L | 1.2L |
| Fixed at one end; other end free (not held in position nor restrained in direction) | 2.0L | 2.0L |
| Hinged at one end; other end restrained in rotation but free to translate | 2.0L | 2.0L |
Code values are larger than the theoretical ones for restrained ends because perfect fixity is never achieved in practice.
Why the Other Options Are Wrong
- A. 2L: 2L is fixed–free.
- C. 0.707L: 0.707L is fixed–hinged.
- D. L: L is hinged–hinged (held in position but free to rotate).
Key Point
Both ends fixed (no sway, no rotation): le = L/2 in theory, 0.65L in design.
Key Concepts for Students
- Read code phrases as restraints.
- "Restrained against rotation" = fixed end.
- Code values are conservative.
Practice more: this is question 30 in Columns and Struts MCQs – Part 2. Try the whole set and check every answer instantly.