The following three beams having the same length, same weight and $.$ ade up of the same material.

$($I$)$ I$-$section $400mm180mm$ with $20mm$ thick flanges and $12\mathrm{.}5mI$ : hick web.

$($II$)$ Rectangular section of depth twice ils width.

$($III$)$ Solid circular section

Compare the strength of the I$-$section with the rectangular and circular sectio$.$