Partial safety factor for the design strength prediction of naturally corroded prestressing strands

Existing reinforced and prestressed concrete structures are often affected by corrosion triggering high annual maintenance costs and impairing their safety, durability and serviceability. Although scientific studies have been devoted to the development of reliable methods for determining the residual resistance of such structures, the daily engineering practice is hindered by the lack of simplified models that consider all relevant uncertainties. The present contribution defines a partial factor for the calculation of the design tensile strength of corroded prestressing strands. To this aim, uncertainties related to material properties and geometry are defined according to the latest draft of the future fib Model Code 2020 prescriptions, whereas the model uncertainty is evaluated for a novel model, which derives the tensile strength based on the maximum penetration depth of the most corroded wire. First, the spatial variability of pitting corrosion of several naturally corroded prestressing strands is investigated by means of a 3D scanning technique. Second, a procedure for the estimation of the maximum penetration depth of a corroded prestressing strand is introduced. Finally, a simplified stressstrain relationship, named SCPS-model, is adopted for the prediction of the residual ultimate strength of prestressing strands. The obtained outcomes provide a useful tool for the assessment of existing prestressed concrete structures subjected to corrosion deterioration in everyday engineering practice.