strong axis and $8^{\text{'}}$ in weak axis for $1)$ back$-$to$-$back case and $2)$ face$-$to$-$face case. Assume that there is no separation between two channels. As per AISC for back$-$to$-$back case, $(2)C811\mathrm{.}5$ has $Ag={6\mathrm{.}74}^{\text{'}\text{'}},rx=3\mathrm{.}11in,ry=0\mathrm{.}846.$