Do I have to activate the favorable effect due to tension for performing a second-order analysis of a system with tension members?
In general, the check box "Consider favorable effects due to tension of members" is appropriate for every system.
In the standards, you find provisions to consider favorable effects with a smaller partial safety factor as action. The use of varying partial safety factors needs too much computing time. Therefore, RFEM and RSTAB offer you the possibility to set the tension forces to zero. The method is on the safe side. To do this, clear the check box.
On the other hand, the standards also refer to actions. Therefore, it would be possible to decide for each action, whether it has a favorable or unfavorable effect. An action that is seen as having a globally unfavorable effect can have a local favorable effect. If the axial forces are to be included in the calculation as unchanged, select the check box.