In a section undergoing pure bending, the neutral surface is subjected to:
Try it first: pick an option, then read the explanation.
Correct answer: C. zero strain
Asked in SSC JE 2013
Detailed Explanation
When a beam bends, fibres on the convex side stretch and those on the concave side shorten. Somewhere between lies a layer that does neither.
Why “zero strain” Is Correct
That layer is the neutral surface. Its length does not change, so it has zero strain (and zero bending stress).
Why the Other Options Are Wrong
- A. compressive strain: Compression is on the concave side, above the N.A. for sagging.
- B. tensile strain: Tension is on the convex side, below the N.A. for sagging.
- D. none of the above: Zero strain is listed.
Key Point
Neutral surface: no change in length ⇒ zero strain and zero bending stress.
Key Concepts for Students
- Neutral axis = intersection of the neutral surface with the cross-section.
- N.A. passes through the centroid in elastic bending.
- With axial load added, the zero-strain line shifts.
Practice more: this is question 62 in Bending and Shear Stress MCQs – Part 5. Try the whole set and check every answer instantly.