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• ### How can I increase the maximum number of iterations in RFEM/RSTAB?

The maximum number of iterations can be set within the global calculation parameters (menu "Calculation" → "Calculation Parameters", tab "Global Calculation Parameters", see the image).

• ### How can I incrementally apply the load of a load case to the model?

It is possible to imagine that the solving process collects the complete load of a load case or a load combination in a "watering can" and pours it onto the load-collecting model in portions. In this case, the number of load increments correlates with the speed of the load application. The speed is not to be understood as a real time parameter, but purely numerically.

The incremental load application has only an effect in the case of nonlinear structural systems. It usually provides a correspondingly higher result quality with increasing number of load increments. The basic aim of this method is to find a micro convergence in the respective load increments to specify new high-quality start values for the next load increment, and thus finally to achieve a macro convergence for the entire load case.

• ### How do I recognize that the flattening process in RF‑CUTTING‑PATTERN has found the convergence?

The geometrically nonlinear flattening process transfers the real mesh geometry of the planar, buckled, curved or double-curved surface components from the selected set of cutting patterns, and flattens these planar components by minimizing the distortion energy, assuming the defined material behavior.

The iterative calculation applied is controlled by the parameters in the "Calculation Parameters" menu/"Cutting Patterns" tab.

The "Maximum number of iterations" parameter limits the scope of the calculation, and stops the process when the set maximum iteration is reached. If the convergence criterion does not depend on the "Tolerance for convergence criteria" parameter in the convergence range when the maximum iteration has been reached, the program displays Error 10154.

If there is no error message displayed by the program, it is reasonable to assume the proper convergence.

You can usually resolve the error by adjusting the flattening geometry or increasing the maximum number of iterations.

• ### Is there a way how to easily prevent RF‑SOILIN from recalculating the foundation every time the load in the governing load case is changed?

No, that is not possible. The calculation of the foundation parameters in RF‑SOILIN is performed iteratively. The first iteration step requires that the start values for the foundation parameters are selected internally by the program. These start values can be used to perform a finite element analysis of the FE model in RFEM.

The result is the soil contact stress distribution. The soil contact stress of the first iteration step is included in the RF‑SOILIN calculation as the initial value. Together with the stiffness modulus of the entered soil layers, it is possible to calculate the settlement for each finite element. The settlement and the soil contact stress are then used to calculate the foundation parameters.

In the next iteration step, the new foundation parameters replace the old ones, and a new finite element analysis is started, which results in a new distribution of soil contact stress. As a convergence criterion, the new distribution of soil contact stress is compared with the old one.

As long as the deviation exceeds a certain convergence limit, the new distribution of soil contact stress in RF‑SOILIN is considered in the calculation of the new foundation parameters. In the case the the deviation of the soil contact stress distribution of two consecutive iteration steps is not reached for the first time, the iteration is ended and the foundation parameters of the last iteration step are given as a result in RF‑SOILIN.

• ### What does the calculation parameter setting 'Failing members to be removed individually during successive iterations' mean?

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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 behaviour 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.

• ### What is the effect on the internal forces if I limit the number of iterations to "1" in the calculation parameters?

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The calculation will be done faster. HOWEVER: Since only one iteration has been calculated, the results are only correct if there is also just one iteration required for the calculation. For example, this can be the case of load cases using linear static analysis. Also, object with nonlinear properties, such as tension and compression members, may not fail.

On the contrary, load combinations according to second-order analysis require an iterative calculation. Therefore, the results of one iteration only are not correct.

The number of possible iterations should always be sufficiently high. The value can also be much larger than the actually required number of iterations: Only as many iterations as necessary are run through.

Result Table 4.0 shows the number of performed iterations (see Figure).

• ### In a load case, compressive forces in a cable arise. What is the explanation for this?

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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).

If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.

First steps

We provide information and tips to help you get started with the basic program RFEM and RSTAB.

Wind Simulation & Wind Load Generation

With the stand -alone program RWIND Simulation, you can simulate wind flows around simple or complex structures by means of a digital wind tunnel.

The generated wind loads acting on these objects can be imported to RFEM or RSTAB.

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