Influence of axial force and corrosion on failure of prestressed concrete structures considering M-V interaction

Existing prestressed concrete structures suffer from degradation of prestressing for two main reasons: a defect of the sheath infills (cement grout) of bonded tendons, and corrosion of steel strands. These two causes, often concomitant, lead to a reduction over time of the effectiveness of initial prestressing, in addition to the ordinary tension losses due to concrete shrinkage and creep, and to steel relaxation. In many cases a consequence of bad grouting in bonded tendons is that the structure shows an intermediate behavior between that of external prestressing and that of internal bonded prestressing. This, added to damage to wires due to corrosion, makes it essential for the designer to be able to check sections of existing structures considering the interaction between the characteristics of the stress together with the changing state of tendons. In this paper a methodology for performing safety checks through M-V interaction domains with axial force N due to prestressing and external loads in the structural scheme is presented. The modification of the behavior between the intact and the degraded section due to corrosion and the consequences of bond loss are shown and discussed together with the influence of compressive axial force due to the structural scheme. Finally, an application is proposed on an emblematic case study: the deck sections of the Polcevera viaduct in Genoa.