FAQ 002108 EN-US

Helpful Questions & Answers

  • Frequently Asked Questions (FAQs)

12/07/2019

002108

Robert Vogl

Calculation

RFEM

RSTAB

5.xx

8.xx

When trying to calculate a result combination, I get Warning No. 30014:

"Incorrect addition of load cases in the result combination!
The result combination contains load cases or load combinations with results containing second-order effects, which points towards nonlinear relationships and therefore cannot be added together."

What does this warning mean?

Answer

The warning appears if load cases or load combinations are nonlinear according to the second-order analysis or the large deformation analysis, and then superimposed in a result combination according to the following criteria:

Case 1: RC = CO1 + CO2

Since each load combination is analyzed nonlinearly according to the second-order analysis, the superposition of the respective results is problematic: Deformations and internal forces are based on different structural systems. It would not be correct to simply add up the individual CO results.

Case 2: RC = "Factor" * CO1 or "Factor" * CO2

Both load combinations are superimposed with factors. Since each CO is calculated according to the second-order analysis, the results show a nonlinear relation. The factors ensure that each internal force is multiplied by the corresponding factor. For example, the duplication of the axial force is not necessarily accompanied by the duplication of the moment. It is assumed that the results have a linear relation. This discrepancy (nonlinear calculation of the results with linear multiplication) results in the warning described above.

The solution for both cases is to calculate the load cases or load combinations linearly according to the geometrically linear analysis and then superimpose them in an RC. If there are only load cases, you can analyze them in a load combination.

Nevertheless, the results of nonlinear analyzes can be superimposed in an RC if the criterion "permanent" is used: RC = CO1/s or CO2/s. In this way, the result envelope is determined, which covers the unfavorable constellation from both COs. In this case, click [Yes] to confirm the warning. The RC internal forces then represent the extreme values from both COs and can be used for further design.

If there is a result combination with geometric nonlinearities in the model, a similar message appears. It is described in FAQ 003065.

Keywords

Load case Load combination Result combination Warning Incorrect addition Second-order analysis Superposition

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