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  • Answer

    Often, these problems can be solved easily and effectively.

    Especially in the edge areas of plates, the results often oscillate. In this case, the result can be improved by modeling a foundation collar with a negligible thickness around the surface. It is assigned the same foundation as the main plate. The support collar shows the edge area of the slab more accurately and the convergence behavior is often better.

    It is important that the foundation collar at least reaches sufficiently far that the settlement depression has subsided completely. Thus, it is also possible to graphically represent the influence of settlement on surrounding buildings graphically.

  • Answer

    The following causes can be responsible for this:
    • In most cases, these differences can be attributed to a lack of convergence. Increasing the iterations and increments in the calculation parameters and FE mesh settings should help.
    • High stiffness jumps result in numerical problems, which leads to errors in the result evaluation. In RSTAB, this is not a major problem with a full and analytical approach. In RFEM, on the other hand, approximation approaches are used, so higher stiffness jumps should rather be avoided.
    • Bedded bars may well be subject to deviations as well. If the bars are not or only roughly divided, there are convergence problems. A practical solution here is to select a "finer" bar pitch in the FE mesh settings.
  • Answer

    When you see this message, check the nonlinearities available in the model as well as the plausibility of the results. The sum of loads and the sum of support forces could also help with the check. If you find significant deviations there, the results should not be used for further analysis. It is often helpful to increase the number of load increments and the number of iterations in Calculation Parameters (see Figure 02).

    You can find more information about "Convergence" on our homepage under Online Manuals.

  • Answer

    In the first iteration step, all members are considered. Before the next step, the program determines which members cannot resist the determined compressive forces due to their definition, for example tension members with negative axial forces. Then, the tension member with the greatest compressive force is removed from the stiffness matrix. Thus, the next iteration step follows.

    Next, the member definitions are compared to the determined axial forces. For the next iteration step, the tension member subjected to the highest actions is removed from the stiffness matrix. This procedure is continued until no member is subject to the internal forces that it cannot resist.

    In this way, you can often achieve a better convergence behavior for the system because of redistributing effects. This calculation option requires more time because the program must run through a larger number of iterations. Furthermore, you have to make sure that a sufficient number of possible iterations is set (see the "Settings" dialog box section in Figure).

    For this method, it might also happen that the initially failed member is reinserted, because it is subjected to tension forces due to possible redistribution effects.

  • Answer

    Compressive forces in cables or tension members may arise if the number of iterations is not sufficient for this analysis so that the system did not converge. The number of iterations can be specified in the Global Calculation Parameters tab of Calculation Parameters (see figure).

    For the maximum number of iterations, the value 100 is preset. However, this does not mean that all iterations will be run. Depending on the structural system, the calculation often converges much earlier.

    Check also the settings of Reactivation of Failing Members. If the option "Assign reduced stiffness to failing members" is selected, small compressive forces may arise.

    If this is not justifiable, select the option "Failing members to be removed individually during successive iterations." However, you should pay attention to the sufficient maximum number of iterations (see above).

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