Life-cycle management of new and existing construction based on a time-dependent reliability approach: Methodology, normative developments and applications on existing bridges

This PhD thesis presents a comprehensive reliability-based framework for the life-cycle management of new and existing constructions, with a particular focus on seismic design and assessment methodologies. The study introduces probabilistic models to enhance construction safety, optimize maintenance strategies, and refine normative design criteria. It is known that the life-cycle management objective is to predict construction future, by controlling the factors that may threaten its performance. In doing so, being this prediction is affected by uncertainties, it is necessary a probabilistic description of all variables governing the construction behavior. In this study, a new reliability-based procedure is presented for the life-cycle management of existing and new constructions. It may be applied coherently either with the Level 2 method, where explicitly reliability indexes are taken into account, or with the Level 1 method, using partial factors depending on the reliability indexes. The procedure also proposes criteria for reliability checks according to Level 2 and Level 1 methods. This is validated through the application of a simply supported reinforced concrete (RC) beam, comparing Level 1 and Level 2 methods to evaluate their efficiency in reliability assessment over time. For completeness, four scenarios are considered to investigate how the assumptions made may influence year-by-year the reliability assessment. Within the reliability-based framework, a model for seismic design codes is introduced, with specific application to Italy. It demonstrates the need to move from a uniform hazard-based seismic design to a risk-targeted approach that ensures consistent levels of reliability across seismic hazard zones. The methodology provides a parameter that regulates spectral demand acceleration based on site-specific hazard characteristics, improving the design and assessment of new and existing constructions. Target seismic reliability indexes conforming to normative codes are compared with those derived from macro-seismic assessment methodologies. By analyzing empirical fragility curves derived from damage data observed after the 2009 L'Aquila earthquake, the research identifies discrepancies between theoretical and observed structural performance, highlighting challenges in defining reliability indexes from post-earthquake damage assessments. Finally, the reliability-based framework is applied to the management of existing bridges, with a focus on the life-cycle reliability assessment of reinforced concrete half-joints. The study analyzes common degradation issues and demonstrates a probabilistic assessment methodology to ensure the long-term reliability of bridge structures. This research contributes to the development of reliability-based methodologies for structural and earthquake engineering, showing the implications they lead to through practical applications in construction control and seismic risk assessment.