Q$3(25$pt$)$ Calculate the vertical deflection of point $C$ if a man with $1kN$ weight stands on$.,$

$I=0\mathrm{.}0031m^4,A=0\mathrm{.}0151m^2,K=1\mathrm{.}2,G=8,700$MPa, ignore the weight of the system.$)$

Virtual work formula

$1*=\frac{nN}{EA}$

$1*={\displaystyle \underset{0}{\overset{L}{}}}\frac{mM}{EI}dx$

$1*={\displaystyle \underset{0}{\overset{L}{}}}K(\frac{vV}{GA})dx$