Maybe the observed difference you try to explain (or reproduce) this way is a consequence of not so good guesses for other parameters, like for example
- reduction of compressive strength due to cracks (Fc reduction)
- direction of plastic flow beta
- critical compressive displacement wd
(of course, I mean without changing the values depending on prestressing).

Regards.

I am modelling slabs strengthened by prestressed CFRP laminates

Is the fracture energy Gf affected by prestressing , i mean modelling prestressing decreases or increases the fracture energy of the slabs than its normal value

Or there is no effect ?

Thank you