The net area of a round bar resisting tension is the area of cross-section at:
Try it first: pick an option, then read the explanation.
Correct answer: B. the root of the thread
Asked in SSC JE 27/01/2018 (Evening)
Detailed Explanation
Cutting a thread on a round bar removes material, so the bar is thinner at the bottom (root) of the thread grooves than in the plain shank.
Why “the root of the thread” Is Correct
The bar fails at its smallest cross-section. So the net tensile area is the area at the root of the thread (core diameter). This is why tie rods are sometimes upset (thickened) at the threaded ends.
Why the Other Options Are Wrong
- A. the mid-section: The plain mid-section is larger than the threaded root.
- C. the difference of mid-section and root of the thread: A difference of areas has no physical meaning here.
- D. None of these: Root of thread is correct.
Key Point
Threaded bar in tension: use the root (core) area.
Key Concepts for Students
- Bolt tensile stress area is between root and nominal area.
- Upset ends keep the root area ≥ shank area.
- Net area = gross area − holes, for plates.
Practice more: this is question 10 in Stress and Strain MCQs – Part 1. Try the whole set and check every answer instantly.