Spatial and time-dependent reliability analysis for post-tensioned concrete decks subjected to multiple failure modes

The durability of existing infrastructures is a worldwide challenge in structural engineering. Societal demands for reducing greenhouse gas emissions, coupled with the financial constraints faced by many countries, push infrastructure management companies and owners to extend the lifespan of existing structures. However, extending the lifespan comes with a set of problems related to safety and time-dependent degradation. The latter problem is particularly acute for prestressed bridge decks with post-tensioned tendons, which are especially prone to degradation due to defects observed for bridges built using older construction techniques.

To address this problem, we propose an approach for evaluating the global time-dependent reliability of prestressed concrete bridge decks with post-tensioned tendons, which are subject to corrosion-related degradation. A model for the time-dependent corrosion process is proposed that combines physics-based formulations with empirical evidence from existing structures, accounting for the necessary thermodynamic conditions and the quality of both the concrete and the grout. Furthermore, the sections of each deck element are assessed for two failure modes, namely, bending and shear failure. The time-dependent reliability is then computed for the bridge deck as a system accounting for the spatial and failure mode dependencies. The approach is applied to evaluate the reliability and technical service life of a prestressed structure representing a typical deck configuration for Italian prestressed bridges, and the main input variables for the case study are identified through a sensitivity analysis. Finally, it is demonstrated that the comparison with consequence-related target reliabilities facilitates the determination of a structure's remaining lifespan and provides the basis for economically efficient and sustainable integrity management.