Q$3)$ k $($kN$/$m$)=7645$

m $($t$)=20$

For the following structure, determine the the base moment with the mode superposition method by using the SRSS modal combination rule when subjected to an earthquake defined with the following design acceleration spectrum.

${}_1=\{0\mathrm{.}4,1{\}}^T$;$,{}_2=\{[-1,1]{\}}^T,w_1^2=\frac{3k}{5m}$;$,w_2^2=\frac{2k}{m}$