A Study on Existing Prestressed Concrete Beams under Chloride-induced Corrosion

Corrosion of steel reinforcements is nowadays considered as one of the leading causes of the durability and performance reduction of existing reinforced (RC) and prestressed (PC) concrete structures and infrastructures. Moreover, most of the structural and infrastructural heritage has already exceeded its service life and has been characterized by evident sign of deterioration. The combination of these factors leads to the structural capacity reduction of existing RC and PC members over time, sometimes causing unexpected failures due to the lack of bending, shear or anchorage resistance. These latter failures may occur without warning signs, resulting in a great potential for life losses and causing a significant economic impact. Recent collapses, occurred worldwide, have emphasized the urgent need for reliable and stringent maintenance protocols as well as simplified analytical models capable of assessing the residual structural capacity of deteriorating RC and PC members, making the corrosion topic of great interest among the scientific community. Despite the possible corrosion forms, in the case of PC members, the chloride-induced corrosion can lead to the worst consequences, since pitting can cause stress concentration and strain localization of prestressing wires, generally subjected to initial high mechanical stresses. Although recent experimental, numerical and analytical studies have been conducted on RC members, the knowledge on PC structures subjected to corrosion is still uncertain and scarce. To partially extend the current knowledge, the present Thesis investigates several naturally corroded PC beams subjected to 10 years of sea water wet-dry cycles. The study aims to evaluate the influence of corrosion on the residual structural performance. To this end, two un-corroded PC beam specimens were manufactured with the same type of concrete and curing conditions and subsequently tested to be a reference for the quantification of corrosion effects. Second, the Thesis defines analytical constitutive laws for the prediction of the residual mechanical behaviour of corroded prestressing strands. Based on tensile tests and pitting morphology spatial variability analyses, two constitutive laws, namely CPS- and SCPS-models, were proposed to predict the tensile force-strain or stress-strain relationship of a corroded strand. The SCPS-model, is a simplified version of the CPS-model designed for the daily engineering practice and conceived on a single input parameter that is the maximum penetration depth of the most corroded wire. Finally, an analytical approach for assessing the residual flexural and shear capacity of corroded PC beams without transversal reinforcement is proposed. The accuracy and the effectiveness of the proposed models were validated through the comparison with experimental tests. Moreover, a preliminary partial safety factor for the design strength of corroded strands is determined following the probabilistic estimation of the SCPS-model uncertainties. To conclude, the main observations, the future research as well as the needed improvements are outlined.