Question

The ratio of the flexural strength of two beams of square cross-section, the first beam being placed with its top and bottom sides horizontally and the second beam being placed with one diagonal horizontally, is

• A. $\sqrt{3}$
• B. $1/\sqrt{3}$
• C. $1/\sqrt{2}$
• D. $\sqrt{2}$

Answer 1

The correct option is D $\sqrt{2}$

Flexural strength is proportional to sectional modulus of beams. For both beams moment of inertia will be same. Section modulus for first

beam $Z_1=\frac{2I}{a}$ (a = side of cross - section)

Section modulus for second beam,
$Z_2=\frac{\sqrt{2}I}{a}$

$\therefore \frac{Z_1}{Z_2}=\sqrt{2}$