$1\mathrm{.}11$ Consider the building structure introduced in Prob. $1\mathrm{.}9$ and determine the total stiffness in the north$-$south direction, which has a lateral force resisting system $($one on each side$)$ consisting of a $10-$ft$-$long, $6-$in$-$thick concrete shear wall $(E=3,500$ksi and $G=1,500$ksi.