Instances of the objects StructuralSurfaceConnection are used to describe structural supports provided by planar elements. In most cases, it represents the interaction between the structure and the subsoil.
The properties of such model are expressed by what is called interaction parameters marked C. These parameters are assigned directly to structural elements that are in contact with the subsoil and they influence the stiffness matrix in analysis calculation.
To simplify the matter, we may imagine that C is the characteristic of elastic, more precisely pseudo-elastic, links, or surface spring constants that change according to the actual state of the analysed system. We may also use the professional slang that calls it "support on C parameters", which is the generalisation of standard Winkler idea of the supporting in the form of thick liquid g = C1 (MNm-3) or in the form of an infinitely dense system of vertical springs. The parameters of the interaction between the foundation and the subsoil depend on the distribution and loading level, or the contact stress between the structure surface and the surrounding subsoil, on the geometry of the footing surface and on mechanical properties of the soil.