**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.