A rectangular box section is fabricated from $5mm$ and $20mm$ thick steel plates as shown in the figure. A vertical shear for of $200kN$ acts through the centroid of the section.

Verify that the centroid is located as shown and calculate the second moment of area $I_{zZ}$

What is the maximum shear stress in the section and where does it act?

HINT: Start by considering an open section by taking a cut at the midpoint of the right$-$hand vertical web

$[$Ans$.2)53\mathrm{.}6$MPa@$y=0mm,z=400mm]$