Thank you Doug and "Rapt" for the interesting discussions.
Now I understand that V_ut should be determined using unfactored loads as V_ut represents a capacity, not a load.
However, I am not sure whether to use the load combination V* and M*, or the load combination V_ser and M_serv, as V*/M* can be slighty different from V_ser/M_ser for a given load combination.
I have a floow on query relating to the loads to use to calculate M_ser and V_ser. I am considering an indeterminate structure. I can think of two ways to determine V_ut, and one is probably more appropriate:
First way: Use the primary prestressed moment in the section to produce the initial stresses and included the secondary prestressed effect as applied load to produce additional stresses. This gives me an estimate, say V_ut1, maintaining the ratio M_ser/V_ser, where M_ser and V_ser include the secondary prestressing effect.
Second way(which I have not done the calcs): Use total (primary plus secondary) prestressed moment in the section to produce the initial strsses, and not to include the secondary prestressed effect as an applied load effect. Say, this gives V_ut2, maintaining the ratio M_ser/V_ser, where M_ser and V_ser do not include the secondary prestressing effect.
Estimated V_ut1 is likely to be different from V_ut2, as the first way considers the secondary prestressing as an applied "load", which the second way doesn't.
Which of the two ways is correct/more appropriate