Answer:
The warning appears if load cases or load combinations are to be calculated nonlinearly according to the second-order analysis or the large deformation analysis, 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 analyses can be superimposed in an RC if the "permanent" criterion is used: RC = CO1/s or CO2/s. This determines a result envelope that includes 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. Sie ist in der FAQ 003065 beschrieben.
