Problem $4$: A steel column is subjected to a concentric compressive force $\backslash ($ N $\backslash )$ as shown in the figure below. It is assumed that the column is pinned at one end and the other end is a roller $($in both $\backslash ($ x$-$x $\backslash )$ and $\backslash ($ y$-$y $\backslash )$ axes$).$ The column has a rectangular cross$-$section area with $\backslash ($ b$=20\backslash$mathrm$\{$~cm$\}\backslash )$ and $\backslash ($ h$=30\backslash$mathrm$\{$~cm$\}\backslash ).$ Based on the knowledge you have learned from the Strength of materials, you are to determine the critical compressive force $($Euler formula$),$ draw the shape of the column when the bifurcation buckling occurs, and give comments on the results $($suggestions: make comments on the relations between the critical compressive force and material parameters, dimensions of cross$-$section, and column length$)$