Parametric analysis of corrosion effects on strength of RC decks with post-tensioned tendons

This investigation originates from extensive observational surveys conducted on RC highway viaducts located in Liguria Region, Italy. Some of these viaducts were recently subjected to significant retrofitting interventions including deck seismic isolation and piers restoration. However, at the time of surveys noticeable defects and degradation mechanisms were observed in some decks, with particular reference to simply supported RC I-beams with post-tensioned tendons. The main defects were the consequence of incorrect rainwater runoff due to obsolescence of drainage systems. Damages and corrosion in ducts for post-tensioned reinforcement were also observed in some case. Finally, in one case the surveys put in evidence broken wires belonging to a post-tensioned tendon of one of the outer beams. Given the well known critical issues related with existing post-tensioned reinforcement, a parametric analysis of the I-beams is carried out by varying the ratio of ineffective to total area of prestressing steel and, correspondingly, the amount of residual prestress. Nonlinear sectional analysis up to Ultimate Limit State in bending is implemented in program Response2000 (E. Bentz, University of Toronto). The effects due to pitting corrosion are accounted for by reductions in reinforcement area and suitable changes in steel constitutive model. Preliminary results show a satisfactory beam capacity provided that the prestressing steel is totally effective. Decreases in prestressing force and beam bending capacity are computed at different levels of corrosion attack, obtaining a comparative evaluation of crack patterns.