Degradation modelling of external grouted post-tensioning tendons: Numerical assessment under corrosion conditions

In the last years, several brittle fractures of external bonded post-tensioning tendons in bridges have been reported due to corrosion damage, compromising the structural safety and stability of the bridges. This paper proposes a finite element non-linear modelling approach of grouted tendons to study their mechanical behaviour and risk of failure when a level and extent of corrosion of the steel strands is assumed. This approach has been first validated with the experimental tests previously presented in the literature, thus analysing the influence of the steel plasticity, large deformations and re-anchoring effect, in order to reproduce accurately the experimental tests, qualitative and quantitative. The degradation curves are derived, that is, the effective tensile force and natural frequencies versus the percentage of damage, which is defined as the percentage of broken strands, and are compared with experimental tests. Then, a parametric study is performed using the proposed modelling strategy. The objective is evaluate the critical number of strands broken for tendon failure depending on its corrosion condition, which is defined by two parameters: (i) the number of corroded strands within the tendon, and (ii) the corrosion degree of the strands. The initial stressing force of the tendon has been included within the parametric study, this is determinant in the stress redistribution and in a possible tendon failure when a strand breaks.