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5.6 Result Combinations
Load cases can be superimposed in a load combination (CO) and in a result combination (RC).
In a result combination, included load cases are calculated first. Then the results are superimposed while considering the partial safety factors. A load combination (see Chapter 5.5) combines the loads of the contained load cases into "one big load case" while taking the partial safety factors into account, and then calculates it.
Load cases can be combined manually (see Chapter 5.6.1) or superimposed automatically by RFEM (see Chapter 5.7), depending on settings in the Model - General Data dialog box (see Figure 12.23). These Settings also affect the appearance of the Result Combinations dialog tab in the Edit Load Cases and Combinations dialog box.
Result combinations are not suitable for nonlinear calculations because they lead to falsified results: In most cases, failure of nonlinear elements (e.g. tension members, foundations) happens differently in the individual load cases. Redistribution effects occur, so the internal forces from different models would be combined (see example in Chapter 5.5).
In a result combination, you can superimpose the results of load cases, load combinations, and results of other result combinations.
The internal forces are usually summed up. In principle, subtractions are also possible. Please note, however, that in this case, signs of the internal forces are reversed: Tensile forces become compressive forces, etc. As an alternative, it is therefore recommended to copy the load case (see Chapter 5.1) and to set the load factor to -1.00 for the load case copy in the Calculation Parameters dialog tab. Then the load case can be added in a result combination.