Question

Consider the following statements :
1. In a beam, the maximum shear stress occurs at the neutral axis of the beam cross-section.
2. The maximum shear stress in a beam of circular cross-section is 50% more than the average shear stress.
3. The maximum shear stress in a beam of triangular cross-section, with its vertex upwards occurs at b/6 above the neutral axis.

Which of these statements are correct?

• A. 1, 2 and 3
• B. 2 and 3 only
• C. 1 and 2 only
• D. 1 and 3 only

Answer 1

The correct option is D 1 and 3 only

The maximum shear stress in beam of circular cross section is $33\frac{1}{3}$% more than the average shear stress.
If b is the height of the triangle, then maximum shear stress will occur at $\frac{b}{2}$ from the vertex. The neutral axis lies at a distance $\frac{2b}{3}$ from vertex.
$\therefore$ Distance at which maximum shear stress occur from neutral axis $=\frac{2b}{3}-\frac{b}{2}=\frac{b}{6}$