The theory says that been compressed a column beam buckles from trivial rectilinear shape to the arc at axial load F>F1, then the shape becomes of S-type at F>F2, then with 3 halfperiods at F>F3 and so on. However having read huge literature I didn't find real example of such behaviour.Though these higher modes of buckling had been studied in detail by Lagrange 2 centuries ago. In real the sumples are fractured after 1st form bifurcation from the trivial to arc. Nevertheless, if You plot the middle transverse shift b vs F>F1 (see fig.) You receive a curve with maximum a at F=F2 followed by decrease.