Use either Castigliano's second theorem or the Unit Load Method to determine the vertical deflection at

point $B(v_B)$ under load $P$ applied at joint $B$ of the steel truss shown below.

Use: $,E_{\text{s}\text{t}\text{e}\text{c}}=200$GPa $($all members$)$

$A=12*{10}^{-4}{m}^2($tension members$)$

$A=32*{10}^{-4}{m}^2($compression members$)$