Hi all,

I am trying to run a non-linear buckling analysis of a column that fails in local buckling using shell elements. I  have used S4R and S9R5 elements. I performed a mesh analysis with both element types until I got a mesh fine enough to get pretty much the same ultimate load with each element type. However, I realized that after the peak load is reached, S9R5 elements show a more flexible response than S4R. The deformed shape of both models is the same.

Can anyone explain to me why S9R5 elements would show a more flexible response than S4R elements after the peak load is passed?

Regards,

Fran