Use shell elements to model structures in which one dimension (the thickness) is significantly smaller than the other dimensions and in which the stresses in the thickness direction are negligible. A structure, such as a pressure vessel, whose thickness is less than 1/10 of a typical global structural dimension generally can be modeled with shell elements. The following are examples of typical global dimensions:
the distance between supports,
the distance between stiffeners or large changes in section thickness,
the radius of curvature, and
the wavelength of the highest vibration mode of interest.
ABAQUS shell elements assume that plane sections perpendicular to the plane of the shell remain plane. Do not be confused into thinking that the thickness must be less than 1/10 of the element dimensions. A highly refined mesh may contain shell elements whose thickness is greater than their in-plane dimensions, although this is not generally recommended—continuum elements may be more suitable in such a case.