Answer:
Initial Prestress
You can imagine initial prestress as a temperature load: the member is cooled down and it tries to shorten. If the member is held at the ends, tensile force occurs in the member. If the member is held rigidly at the ends, the tensile force corresponds exactly to the prestressing force. If it is held elastically, the tensile force in the member is correspondingly smaller.
End Prestress (RFEM only)
In the case of end prestress, the iterative calculation method endures that the member keeps the prestressing force – without regard to the stiffness of the adjacent structure. However, the disadvantage here is that the calculation takes longer and the model might become unstable.
