FAQ 000221 EN-US


Robert Vogl Calculation RSTAB RFEM

My model is stiffened by tension members. The calculation is terminated with the message about instability. How can I finish the calculation?


The calculation can be terminated due to an unstable structural system for various reasons. There can be a "real" instability due to overloading the system, but the instability effects may also be caused by failing members.

In the calulcation parameters, you can deactivate the nonlinearity "Members due to member type" (see Figure 01). If the calculation is then possible without the error message, the problem is probably caused by failing members.

The option "Failing members to be removed individually during successive iterations" in the Global Calculation Parameters dialog box (see Figure 02) allows you to prevent the complete failure of tension members. This will help in most cases. For this, the number of possible iterations should be sufficiently large.

An alternative method is to apply a prestress to the tension members in order to prevent the failure of them.


instability tension member failure abort nonlinearity error message

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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
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