PSI - Issue 78

Matteo Tatangelo et al. / Procedia Structural Integrity 78 (2026) 404–411

406

1 – ISO 2394 (1998) 2 – JCSS PMC (2001) 3 – EN 1990 (2002) 4 – fib Bulletin n. 34 (2006) 5 – ISO 13822 (2010) 6 – fib Bulletin n. 65 (2013) 7 – ISO 2394 (2015) 8 – fib Bulletin n. 80 (2016)

Fig. 1. Comparison among the target reliability indexes considered For Ultimate Limit States (ULS), target reliability indexes are differentiated by CCs (CC1, CC2, CC3) as a function of . For existing constructions, can be taken as the remaining working life. These values consider both economic optimization ( ) and human safety criteria ( ), the latter addressing both individual occupant risk and governmental group risk to prevent accidents with high casualties. The target failure probability depends on the conditional probability of individual or group casualties, with an acceptable individual risk level of 10 − 5 per year. fib Bulletin n. 80 (2016) also provides a minimum target reliability ( 0 ) below which an existing structure must be upgraded, and a target reliability for upgrading ( ). For a given , the target reliability index ( ) is determined by ( ) = max( , ) . Similarly, ( ) = min( , , , ) . In conclusion, achieving optimal reliability depends on the balance between construction costs, expected failure costs over the design life, and human safety considerations during the residual life of the construction. However, it is also important to emphasize the different meanings of service life (or remaining working life) and design life. Design life means the expected operating period of a structure without significant repairs. The reference period, on the other hand, is a specific duration chosen for statistical analysis of time-varying random variables and their impact on the probability of failure. The concept of reference period is therefore fundamentally different from the concept of design life or remaining working life (Holicky, 2018). 3. Procedure for life-cycle management This section introduces a reliability-based procedure for managing the life-cycle of both new and existing constructions (Tatangelo et al. 2024). The core of this method involves converting a time-integrated approach into a time-dependent one. This allows the estimated reliability of a structure over a specific time interval to be evaluated and compared with the target reliability for a given limit state. Specifically, it transforms a ( ) into ( , ) , where ( , ) represents the target reliability index calculated at a specific time interval, , for a given structure. ( , ) is uniquely determined if ( ) is known. For clarity, the notations ̅( ) and ̅( , ) are used for target reliability indexes. 3.1. Time-dependent approach In a time-dependent reliability assessment, the construction lifetime is divided into distinct time units or events. These units can represent defined time intervals such as a year. The reliability calculation then considers the failure probability of the construction by assuming that time units or events occur during the total useful lifetime of the construction. Once that a period is defined, the number of units remains fixed for the chosen interval.