About Shell Sections

A shell section defines a structure in which one dimension (the thickness) is significantly smaller than the other two dimensions (and in which the stresses in the thickness direction are negligible).

See Also
Defining Shell Section Properties

Shell sections are applied to surfaces, which—from a geometric standpoint—have no thickness; a thickness is assigned to the surface geometry as part of the shell section definition. During the simulation the shell faces are considered to be located half the thickness distance above and below the surface geometry.