Answer:
Since a surface is a 2D element and therefore the transition from surface to solid is a line, singularities may occur here. The moments my and mx, in particular, may cause some problems.
The best way to make the transition is to use rigid members, as shown in an example in Image 01.
In this option, the rigid members cover the height/thickness of the surface, and thus ensure clean introduction of the moment into the solid. Furthermore, the rigid members must protrude into the surface; the depth has been selected as one-half of the surface thickness.
Image 02 shows the calculation results. The model without the rigid members has a large deformation, which illustrates the effect. However, the model with the rigid members shows the same deformation as the pure surface model or solid model, in some cases.
