A surface support can be assigned to any surface entered in RFEM graphically or using tables. Support conditions can be set either to completely 'rigid' or 'elastic' by defining a spring stiffness.
Support or Springs in Cu,x, Cu,y, Cu,z
The direction of the supports or springs refers to the local coordinate system of the relevant surface which is assigned to the surface support. The local coordinate system of the surfaces can be displayed by using the Display Navigator or the shortcut menu.
The support perpendicular to the surface is controlled by entering Cu,z. The entries for Cu,x and Cu,y describe the resistance against the displacement of the plate in the x- and y-direction.
Shear Springs Cv,xz, Cv,yz
By entering values in these boxes, the shear resistance of the soil is considered in the direction of the surface axes x or y. In most cases, the Pasternak constant Cv is between 0.1 ⋅ Cu,z (low shear resistance) and 0.5 ⋅ Cu,z (average shear resistance). Cv,xz = Cv,yz can usually be applied. If the support in uz has been set to 'rigid' (see Figure 01), no entry is possible for the shear springs Cv,xz and Cv,yz.
The theoretical background about the 'effective soil model' implemented in RFEM is documented in Chapter 4.9 of the RFEM manual.
Results for Surface Supports
Once surface supports have been used in a model, the contact stresses σz, τyz and τxz are available as a result after the calculation. In Table 4.21 'Surfaces - Contact Stresses', the columns H to J including the reaction forces Rx, Ry and Rz are additionally available for the entire surface.