I want to simulate an outstand plate under axial compression;

The dimension of the plate a=49.1166mm,b=300mm,t=2.127mm;

The material properties use the R-O model E=69000Mpa;fy=205Mpa,n=22;

The boundary condition is the same as the file (outstand flange);

I use the buckle analysis first in order to introduce the geometric imperfection,

*Imperfection,file=xx,step=1

1,0.12

Then I use the riks analysis;

The mesh size is 5x5mm;

While the output ultimate strength is wrong...

My result is 6kN,while use the effective thickness method in EN 1999-1-1, the strength is 8kN.

I really do not know how to solove this. Cause I use the same analysis step in internal plates and the results are in accordance with the calculation results in specification.

Please help me, best wishes.