In all input windows of the RF-/STEEL EC3 add-on module, you can start the calculation by clicking the [Calculation] button.
RF-/STEEL EC3 searches for the results of the load cases, load combinations and result combinations to be designed. If they cannot be found, the program starts the RFEM or RSTAB calculation to determine the design-relevant internal forces.
You can also start the calculation in the RFEM or RSTAB user interface: The To Calculate dialog box (menu Calculate → To Calculate) lists the design cases of the add-on modules like load cases or load combinations.
If the RF-/STEEL EC3 design cases are missing in the Not Calculated section, select All or Add-on Modules in the drop-down list below the list.
To transfer the selected RF-/STEEL EC3 cases to the list on the right, use the 
button.
Then, click [OK] to start the calculation.
You can also calculate a design case directly by using the list in the toolbar: Set the RF-/STEEL EC3 case and click the [Show Results] button.
Subsequently, you can observe the calculation process in the solver dialog box.