$5\mathrm{.}63$

$5\mathrm{.}63$ Find the response of the two masses of the two$-$story building frame shown in Fig. $5\mathrm{.}32$ under the ground displacement $y(t)=0\mathrm{.}2sintm.$ Assume the equivalent stiffness of the lower and upper columns to be $800\frac{N}{m}$ and $600\frac{N}{m},$ respectively, and $m_1=m_2=50kg.$

FIGURE $5\mathrm{.}32$ Two$-$story building frame.