During the calculation, I receive an error message in RFEM with the Error No. 1639 or in RSTAB with the Error No. 1640 'Member No. XY | Member end hinges No. YZ are freely rotating about the x-axis. Please check this in Table 1.17 (or 1.7 in RSTAB) or in a related table'. How to solve this problem?


In fact, this error message appears only if a member end hinge that allows a rotation about the local x-axis has been assigned to a member at both ends. Thus, the member can rotate freely about its own axis and is therefore unstable.

Assign a new release to one of the member ends where the degree of freedom φx is not hinged.


Error 1639 Error 1640 Freely rotating X-axis Member end hinge

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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

Price of First License
3,540.00 USD
RSTAB Main Program
RSTAB 8.xx

Main Program

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

Price of First License
2,550.00 USD