Plates and shells are 2D structural models; in fact, the unknown, primary variables depend on two coordinates and are assumed along the third one. Plates and shells can model the structural behavior of 3D bodies in which the third dimension – the thickness, h – is much smaller than the other two. To define a plate or shell is useful to use segments of height h and the surface containing the midpoints of the segments, namely, the mid-surface. In plates, the mid-surface is flat; in shells the mid-surface is curved. Figure 1 shows the geometry of a shell, the mid-surface, or reference surface embodies the 3D features of the structure. From a mathematical standpoint, in plates and shells, expansions of the thickness coordinate (z) defines the behavior of the unknown variables along the thickness. Each term of the expansion is a...