I am doing nonlinear buckling analysis in an ellipsoidal dome structure. for that i did linear buckling analysis and calculated the linear buckling load through the load factor. Now I started to do nonlinear analysis. Here i used Arclength method to get solution. After getting some results from this Arclength method, I don't know how to calculate the nonlinear buckling pressure for the dome structure(Pressure vs Displacement curve). The dome structure is loaded with pressure on its outer surface.