Problem $2$

A built$-$up section of two C $10$ channels and two PL $\frac{1}{2}11$ is shown in Fig. $2$ to support a service loads, $P_D=200k$ and $P_L=320k.$ The member is assumed to be $30$ftlong and is to have four lines of $\frac{3}{4}-$in $\frac{O}{?}$ bolts. Using steel A$36$ and LRFD specifications, perform all necessery checks to select the lightest section.