The Akragas II viaduct is the subject of structural reinforcement of the decks and the top structures of the piers: the pier caps. As regards the decks, the slabs and kerbs are planned to be redone for the installation of new safety barriers and especially the beams using CFRP. The most delicate intervention is also planned on the pier caps, which involves the installation of 6 external pre-stressing cables for each pier cap. This last intervention, demanding due to the need to operate inside the boxes, is aimed at securing the “Gerber” supports and the pier caps themselves which show clear signs of degradation and structural deficit. The study of the stability of the pier caps was carried out using a FEM program capable of studying the pre-stressing effect in a non-linear field considering a Strut and Tie schematization in order to verify the compressed concrete and tensioning bars by appropriately schematizing the existing reinforcement.