PSI - Issue 62

Sebastian Thöns et al. / Procedia Structural Integrity 62 (2024) 259–267 Sebastian Thöns and Ivar Björnsson/ Structural Integrity Procedia 00 (2019) 000 – 000

262

4

2.3 Service life limit quantification approach: scenario modelling and structural reliability analysis The quantification of the service of an infrastructure necessitates (1) a service life scenario modelling and (2) a probabilistic damage quantification in conjunction with a structural reliability analysis over time. The service life scenario modelling is required to identify service life limiting scenarios and causes. Technical service life scenarios encompass the assessment of (a) the preventability, (b) the detectability, and (c) the repairability of potential damages. If preventability or repairability of damages is possible, then there is in principle no technical service life end. However, repairability requires the detectability of damages to facilitate that a repair can be performed safely. On the other hand, when there is no technical service life end, repairs may cause substantial economic efforts and consequences when impairing the infrastructure functionality during the repair process. Here, an analysis would be required to quantitatively forecast these expenses and to compare these with alternatives and thresholds (this will be followed up in Section 3). The probabilistic damage quantification encompasses the physical and or empirical deterioration process modelling over time. The damage quantification should be integrated into the limit state modelling and analysis and facilitates in this way the computation of the structural reliability over time. The structural reliability can then be compared with the corresponding target reliability and the service life determined. In this way, no additional limit state modelling (as discussed for durability in Section 1) may be required. It should also be noted that the structural reliability analysis can be adapted to consider measures like repair, strengthening, component replacement and their effects on the service life can be quantified (see e.g., Thöns (2022)). Deterioration modelling and damage quantification are subjected to high uncertainties. To account for these uncertainties, deterioration modelling may be either very conservative or requires updating with additional information and measurements. The updating with information can be performed on various model levels (deterioration, damage, limit state). For the identification of structural reliability influencing variables, detectable parameters may be determined with sensitivity analyses, see e.g. Celati, Natali, Salvatore and Thöns (In Press-b). 2.4 Case study for service life quantification An example for service life quantification is documented for a 66-year-old reinforced concrete bridge located in the Province of Pisa (Celati, Natali, Salvatore and Thöns (In Press-a)). This study encompasses an integrated evaluation of both chloride-induced and carbonation-induced corrosion complying with thermodynamic conditions for corrosion processes. The service life quantification includes the gradual reduction in traffic load-bearing capacity over time due to corrosion-induced deterioration. The corrosion deterioration and damage development are explicitly modelled in conjunction (1) with the ultimate limit state models for extreme loads and (2) with a structural system reliability analysis accounting for different repair and replacement scenarios. The service life is quantified by compliance of the structural reliability over time with the target reliability according to the JCSS Probabilistic Model Code (JCSS (2001 2015)) for moderate consequences of failure and large costs of safety measures as the structure is already in service. For the structural reliability analysis, survival information is used, i.e., the probability of failure is quantified given survival up to year 66 of the service life (Fig. 1), and the failure rate function (JCSS (2001-2015)) is employed to forecast the service life.

Fig. 1: Structural system reliabilities for a series system (index SS) and a redundant system with brittle component behavior (index DS) for major repair and structural failure, respectively