Now to the welded box$-$section beam in Figure $2$c$,$ also in S$355.$ Determine the

section$$s moment resistance for bending about the horizontal axis. The welds are

fillet welds with size a$=6$mm$.$ You will have to check both the webs and the

compression flange of the cross$-$section for possible plate buckling. The webs have a

pure bending stress distribution, and as you certainly know, the compression flange

then gets a uniform compression.