buckling of channel section

hi everyone,

 i am doing my dissertation on buckling of channel section. so i have used abaqus software to do the analysis. i did the modelling and applided unit load n given pinned-pinned end condition. and i have used constraints to both ends such that the load applied on the edge is concentrated at a point .

but the results i.e mode shapes are not coming properly even the eigen values are very less compaired to calculated buckling load.

plz help me out. 

dimensions of specimen channel section

width of web 100mm

width of flange 50mm

thickness 1.5mm

mesh details, 10x10 mm2 size elements

i have uploads few pics of specimen n the mode shapes