# NASTRAN 2-D Shell Elements

2D SHELL ELEMENT PROPERTIES AND HOW THEY RELATE TO MSC/NASTRAN

Brief description of the difference in DOFs supported for the 2D shell, bending panel, and 2-D solid elements types and how these property types relate to the MSC/NASTRAN property entries.

1) 2D SHELL

The 2D shell is the QUAD4/8 with stiffness in membrane and bending with transverse shear flexibility.  There are 5 degrees of freedom per node: 3 translations and 2 rotations.

The element does not have in-plane rotational stiffness unless PARAM,K6ROT is set greater than 0.0.

The amount of in-plane rotational stiffness is proportional to the value of K6ROT.  If your plate is in the XY plane and K6ROT=0.0, then there will be stiffness in DOF 12345 (1=X, 2=X, 3=Y, 4=ROTX, 5=ROTY, 6=ROTZ).
The PSHELL/QUAD bulk data for the 2D shell looks like this:

\$ Elements and Element Properties for region : 2d-shell

The Grid Point Singularity Table in the .F06 file will show that DOF 6 has no stiffness:

The asterisk at the end of each line means that DOF was internally constrained to avoid singularities.

2) 2D BENDING PANEL
The 2D bending panel is a subset of the 2D shell. It only has bending stiffness (MID2 on PSHELL). It does not have membrane stiffness or transverse shear flexibility.

The PSHELL/QUAD for the bending panel looks like this:

\$ Elements and Element Properties for region : 2d-bending-panel

If the bending panel is in the XY plane as in the above input, it will have transverse stiffness in the Z direction (DOF3), and rotational stiffness about the x and y axes (DOF 45). The grid point singularity output in the .F06 file shows that DOF 126 are constrained to avoid singularities.

3) 2D-Membrane

The 2D membrane is similar to the 2D-solid except that Plane Stress instead of plane strain assumtions are made. (This is a BIG difference.) Patran writes out a plane stress PSHELL/QUAD combinations with only membrane material properties on the PSHELL. This is suitable for thin flat surfaces with inplane loads only.

Transverse loads should only be applied to membrane elements if the element is supported on the edges by elements that can carry transverse loads (e.g. bars/beams). The PSHELL/QUAD data for the 2D-membrane looks like this:
\$ Elements and Element Properties for region : 2d-membrane

If the element is in the XY plane as shown above, it will only have stiffness in the X and Y directions.(There will be RZ stiffness if K6ROT >0.0) The grid point singularity output for this case shows that DOF 3456 are constrained to avoid singularities.