For a beam with a rectangular cross-section, the shear stress at the neutral axis is always:
Try it first: pick an option, then read the explanation.
Correct answer: B. maximum
Asked in SSC JE 25/09/2019 (Morning)
Detailed Explanation
In a rectangle the width is constant, so τ follows Aȳ, which is largest at the neutral axis.
Why “maximum” Is Correct
The shear stress at the neutral axis is always the maximum, 1.5 times the average.
Why the Other Options Are Wrong
- A. zero: Zero shear stress is at the top and bottom fibres; zero bending stress is at the N.A.
- C. minimum: The minimum (zero) is at the extreme fibres.
- D. infinite: Stress is finite everywhere for a finite shear force.
Key Point
Rectangle: τ maximum at the N.A., zero at the extreme fibres.
Key Concepts for Students
- Do not confuse with bending stress, which is zero at the N.A.
- τmax = 3V/(2bd).
- Same holds for a circle (4/3 τavg).
Practice more: this is question 51 in Bending and Shear Stress MCQs – Part 4. Try the whole set and check every answer instantly.