I would like to use couplings in a model. What is the difference between the coupling, dummy rigid and rigid members?


A Coupling member is a virtual member with definable rigid or hinged properties. There are four options available to couple the start and end node. The axial and shear forces or torsion and bending moments are directly transferred from node to node. Couplings allow you to model special situations for the force and moment transmission.

If specifying Dummy Rigid as a description of the cross-section, you can use a member with a high degree of stiffness, taking into account releases or other member properties. In RFEM 5 and RSTAB 8, Dummy Rigid was replaced by the Rigid member. However, for compatibility reasons, it is still possible to use Dummy Rigid.

The stiffnesses in these members are calculated in relation to the member length L:

  • EAx = GIx = 1013 ⋅ L
  • EIy = EIz = 1013 ⋅ L3
  • GAy = GAz = 1015 ⋅ L (RFEM) or GAy = GAz = 0 (RSTAB)


EAx is the strain stiffness 

GIx is the torsional stiffness 

EI is the flexural stiffness 

GA is the shear stiffness 


coupling coupling member rigid member dummy rigid stiffness

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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RSTAB Main Program
RSTAB 8.xx

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The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

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