FAQ 000401 EN

Calculation RFEM RSTAB

I use couplings in my system and would like to know the difference between coupling, dummy rigid, and rigid members?


A coupling member is a virtual member with definable rigid or hinged properties. You have four different options to couple the start and end node. The axial and shear forces or torsion and bending moments are directly transferred from node to node. With couplings, you can model special situations for the transfer of forces and models.

If you specify the name "Dummy Rigid" as description for the cross-section, you can use members with a high degree of stiffness, taking account of releases or other member properties.

In RFEM 5 / RSTAB 8, "Dummy Rigid" was replaced by the "Rigid" member. Because of compatibility reasons, it can still be used in the new versions.

The stiffnesses in these members are calculated depending on the member length.

The stiffnesses are determined according to the following expression, where L is the member length of the considered member.


EAx = GIx = 10^13*L
EIy = EIz = 10^13*L^3
GAy = GAz = 10^15*L


EAx =GIx = 10^13 x L
EIy =EIz = 10^13 x L^3
GAy = GAz = 0

E*Ax = Stretching stiffess
G*Ix = Torsional stiffness
E*I = Flexural stiffness
G*A = Shear stiffness

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