Post buckling of stiffened composite panel

Dear all,

I am working on postbuckling of stiffened composite panels using ANSYS. I have done few experiments and trying to simulate in ANSYS. I have performed nonlinear analysis using arc length method and the load-axial displacement curve obtained is too stiff (having 60% higher slope) compared to the experimental curve. I think BCs, material properties and loading is fine in the model. Can anyone have any suggestions to improve my results?