Surface Support

Glossary Term

The surface support is used to support surfaces in RFEM. The support conditions ux, uy and uz as well ass the shear springs vxz and vyz can be defined here. In addition, it can be defined if a nonlinearity is applied in uz-direction. The dialog box offers also the option to activate the spring constants for the surface support determined in the RF-SOILIN add-on module.

A surface support can be assigned to any surface entered in RFEM graphically or by means of tables.  The support conditions can be set either to completely "rigid" or "elastic" by defining a spring stiffness.

Foundation 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 either with the Display Navigator or the shortcut menu.

The foundation 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 x- and y-direction.

Shear Springs Cv,xz, Cv,yz

Entries in these fields has the effect that the shear resistance of the soil is considered in direction of the surface axes x and y. The Pasternak constant Cv is in most cases 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.

Theoretical Background

The theoretical background about the "effective soil model" implemented in RFEM is documented in Section 4.9 of the RFEM manual.

Results for Surface Supports

As soon as surface supports are used in a model, the contact stresses σz, τyz and τxz are available as result after the calculation. In Table 4.21 "Surfaces - Contact Stresses" the columns H - J with the reaction forces Rx, Ry and Rz are additionally available for the whole surface.


surface support, support, foundation