CBUSH Element with Nonlinear Property

Hello every one,

I have created a demo model (all dofs are constrained at bottom and upper side allowed to move in vertical direction and rotations are free as well) to understand the characteristics of CBUSH element nonlinear properties. When I load my structure with 3484 N I get 1.71 mm displacement but increasing the load increases the displacement. Here are some screenshots: 

Thank you very much for your replies. 

Regards,