Corrosion effects on strands of PT bridges

In recent years, partial failures and collapses involving existing Post - Tensioned (PT) bridges highlighted the need for their structural assessment. Most of existing bridges are approaching the end of their nominal life and constitutive materials have undergone, over the decades, relevant degradation phenomena with dangerous consequences at both local and global level. A good knowledge of material properties, structural details and of the actual maintenance condition of the bridge is then required, especially if we consider that hidden defects - i.e. defects that are not visible without specific investigations - can be responsible of the activation of unexpected brittle failures. Corrosion of prestressing steel cables represents one of the most relevant aspect to investigate, being related to phenomena (such as localized pitting or hydrogen embrittlement) that cannot be detected without specific investigation techniques but that are responsible for relevant decrease of the mechanical properties of materials and modification of the failure modality. Predictive models calibrated basing on experimental results, may represent in presence of aggressive environmental conditions may represent an efficient tool for describing corrosion effects on the mechanical properties of strands and evaluating residual performance. The present work shows preliminary results of a wide experimental test campaign executed on corroded steel strands extracted from an existing prestressed concrete bridge with post-tensioned steel cables; hydrogen embrittlement effects are well visible on the mechanical properties of corroded strands. The peculiarity of the work lies in the availability of naturally corroded strands, with well-known external agents (rain, air, etc.) and exposure period. Preliminary results of FEM analyses on models calibrated basing on experimental tests' results are even presented.