why there is no drilling stiffness in QUAD4?

[jsboy]

I have been using Nastran for many years and know that there is no rotational stiffness about its normal axis to it when using QUAD element(I know QUADR has drilling stiffness). Would anyone please tell me what is a theoretical reason why a rotational stiffness is not involed in traditional shell formulation? I have read some FEM books about this but none of them cleary say this reason. I am talking about linear physics only.

 

[brad]

Shell theory does not account for this. It's just not part of the theoretical formulation. This is similar to asking the question "why don't CHEXAs account for rotation"--same reason. (Note that I'm not being flip; this is the answer).

However, when this shell theory is applied to FEA, this mode becomes relevant and must be addressed (or the dof must be omitted).

Brad

 

[corus]

It is assumed that the in-plane torsional stiffness of a shell is infinite and is therefore not required. Some codes do include this 6th freedom though.