Form-Finding of Cable and Membrane Structures in RFEM 5

I have modeled a structure made of outer and inner cables as well as membranes, and get a message about instability or the error message "Jacobi matrix is not positive definite" in the RF‑FORM‑FINDING add-on module. What can I do?

Answer:

RF‑FORM‑FINDING displays this message because no stable shape of the cable and membrane structure can be found.

In the case of a structure consisting of outer (main) cables and inner cables, we recommend specifying a cable force within the cable parameters for form-finding. The force in the outer main cables should be greater than the force of the inner cables.

Example
Average force in cable:

Main cables: 20 kN
Inner cables: 5 kN

The setting can be made in the "Edit Parameters for Member of Type 'Cable'" dialog box; see the image.

Parameters for "Cable" Member Type

Author

Frank is responsible for quality assurance in the RFEM program and also assists with customer support. He oversees technical design processes and contributes to the stability and reliability of the software.

Downloads

RFEM Model File

5.35 MB

;