Question

Out of the two beams of same material and same cross-sectional area one is of circular cross-section and other is of square cross-section. If these are subjected to bending moment of same magnitude, then

• A. both sections would be equally strong
• B. both sections would be equally economical
• C. Square section would be more economical than circular section
• D. square section would be less economical than circular section

Answer 1

The correct option is C Square section would be more economical than circular section

Section modulus for square section,

$Z_1=\frac{a^3}{6}$

Section modulus for circular section,

$Z_2=\frac{\pi d^3}{32}$

$Since,\frac{\pi d^2}{4}=a^2;So,\frac{Z_1}{Z_2}=1.18;$

Hence square section is stronger or economical.