A rigid frame structure is shown in Figure $1.$ L$=6$m$,$ h$=3\mathrm{.}6$m$.$ All the columns

All the beams can be considered as rigid. m$=500$KNm$/$S$2$

The damping matrix is formed by measurement as:

C$=[(7$&$-3$&$0$@$-3$&$3\mathrm{.}2$&$-1\mathrm{.}4$@$0$&$-1\mathrm{.}4$&$1\mathrm{.}4)]\backslash$times $10^5$ Ns$/$m

Figure $1$

Determine the natural frequencies and corresponding mode shapes $($neglect damping$)$