FAQ 000425 EN

Calculation RFEM RSTAB

I want to use the second-order analysis for my structural system. I have created several load cases (LCs), including imperfection load cases. Do I have to combine the load cases in load combinations (COs) or can I also use the result combinations (RCs)?


If you want to use the second-order analysis, you must define load combinations.

In a load combination, the loads of the contained load cases are combined into "one great load case" under consideration of the corresponding partial safety factors. This load case is then calculated.

In a result combination, on the other hand, first the contained load cases are calculated. The results are superimposed under consideration of the partial safety factors. A calculation method cannot be set for the result combinations because it depends on the load cases and combination contained in it.

For the load cases and combinations, it is possible to specify the calculation method in the calculation parameters. You can calculate the load cases and combinations according to all three methods independent of each other.

To sum up:

Load case and load combinations can be calculated according to linearly static, second-order, or large deformation analysis.

In the result combinations, the results of the load cases and combinations are then superimposed.

In the result combinations, you obtain an envelope of the internal forces (max and min values).

For load cases and load combinations, you always obtain unambiguous internal forces.

For further information, see the RSTAB or RFEM manual.

If you define the member type "Cable," these elements are always calculated according to the large deformation analysis.

Because in the result combinations the results of load cases and/or load combinations are evaluated, the result combinations can contain results according to static linear or second-order analysis.

For your model, this means that you can combine the defined load combinations in a result combination, for example RC1 = CO1/permanent or CO2/permanent.

Thus, in RC1 you obtain the maximum internal forces and deformations using second-order analysis. The The 'permanent or' superposition has the effect that the one or both of the COs are used for the results. If the RC is connected with a 'Alternatively or' superposition, it is also possible that no CO is included and the internal forces and deformations become zero.

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