PSI - Issue 84

Sebastian Thöns et al. / Procedia Structural Integrity 84 (2026) 1310–1317

1316

3.2. Decision analytical implications of service life extension The value of a service life extension from 100 to 200 years with and without monitoring is quantified with Equ. (4) and (5). Figure 5, left, shows the value of solely the service life extension action from 100 to 200 years. The total expected value (the summation of the individual values in regard to direct risks, indirect risk, expected emissions and expected operational costs and benefits) is positive and dominated by the value of the expected operation costs and benefits. The positive value quantification means that the service life extension is optimal, rational and coherent with the fundament decision theoretical principle, namely, the maximisation of the expected utility. However, the boundaries to the objective function (see Equ. (2)) namely the target reliabilities are not fulfilled (see Figure 1). This non-compliance with safety requirements necessitates the implementation of measures or the use of observations to reach the required target reliability.

2.00E+10

1.94E+10

1.90E+10

1.00E+00 1.00E+02 1.00E+04 1.00E+06 1.00E+08 1.00E+10

6.01E+08

4.96E+07

1.50E+10

3.27E+05

1.00E+10

Value in E[DKK]

5.00E+09

-8.30E+07 -1.00E+09 -5.50E+05

0.00E+00

Direct risks Indirect risks

Expected emissions

Exp. operat. costs and benefits

Direct risks Indirect risks

Expected emissions

Exp. operat. costs and benefits

-5.00E+09

Figure 5, left: Service life extension value disaggregated for direct risks, indirect risk, expected emissions and expected operational costs and benefits. Right: Value of service life extension to 200 years with cable fatigue monitoring (logarithmic scale) An example of using observations is shown in Figure 5, right. Here, the value of both fatigue monitoring and the service life extension from 100 to 200 years (see Section 2, Equ. (5)) is depicted. The quantified values for the risks, expected emissions and operational benefits are higher than zero and are (still) dominated by the expected operational benefits due to the service life extension. With consideration of a monitoring, the service life extension complies now also with the required target reliability (see Figure 1) and hence fulfils the boundary conditions of expected utility optimisation (see Equ. (3)). 4. Summary and conclusions This paper examines infrastructure service life extension through an integrated model basis and a basic decision analysis approach. The model basis accounts for both operational performance and structural failure and evaluates their associated direct and indirect consequences, including impacts on safety, economic performance, and carbon dioxide emissions. The decision analysis provides an approach in which observational data can be incorporated to update assessments of infrastructure performance, risks and emissions over time and with which a value of service life extension and of observed data can be quantified. The approach is demonstrated using the Øresund Fixed Link as a case study, showing how different service life extension strategies - considering scenarios with and without additional monitoring information - affect expected costs, risks, benefits, and emissions for different service durations. It has been found that the service life extension is driven by additional expected benefits in the extended service life, which are counteracted with, however, significantly lower, risks and expected emissions. The targeted implementation of monitoring leads with a high probability to a positive risk and emission reduction value and is required to fulfil the structural target reliability requirements for the service life extension. Overall, this paper represents a first step towards the establishment of a decision-theoretical basis for service life extension, which should encompass (1) the identification of optimal (or close to optimal) integrity management strategies and (2) the determination of an optimal infrastructure service life.