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

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emissions. Therefore, efforts to extend the service life of these structures hold significant potential in reducing their overall carbon footprint by delaying, or even avoiding, these emissions. Service life extension further postpones the need for resource-intensive construction processes associated with building new structures. The service life of infrastructures can be addressed and analysed with serviceability and durability approaches. The serviceability limit state refers by definition to the point beyond which a structure no longer meets its intended function without major repairs. The fib Model Code (2010) and Model Code for Service Life Design (2006) suggest that durability is the ability of a structure to maintain its serviceability against environmental influences throughout its intended lifespan. Approaches for service life design can be categorised as: fully probabilistic, partial factor design based, deemed-to-satisfy, and avoidance of deterioration. In practice, durability design is often overlooked in the construction process, leading to limited lifespans and increased environmental impacts. Approaches for service life design and durability are mostly focussed on deterioration modelling and in some instances on damage quantification. It should be noted that structural damages negatively impact the ultimate limit states, i.e., the ultimate resistance against structural component failure. For both the serviceability limit states and ultimate system failure, the compliance with corresponding target reliabilities is required, see e.g., JCSS (2001-2015) and ISO 2394 (2015). Finally, the economic efficiency of a structure throughout its service life is a critical factor. Regular maintenance and repairs can significantly extend the service life but they may compromise the economic efficiency in comparison to pre-allocated resources or an alternative provision of the infrastructure functionality. Following up on service life assessment and quantification, this paper contains a description of service life limiting structural hazards and deterioration mechanisms (Sections 2.1 and 2.2), introduces a technical service life quantification approach (Section 2.3) as well as a service life management approach (Section 3). The service life management approach encompasses the technical service life limits (including life safety requirements) in combination with the economic model and boundaries. Both, the technical service life quantification and the service life management approaches are illustrated with case studies (Section 2.3 and 3.1). The principles and main findings for service life quantification are summarised in Section 4. 2 Service life of infrastructures For the service life of infrastructures, technical and economic limitations apply. The technical end of the service life is determined by a condition, which does not comply with the safety requirements and cannot be altered, i.e., a non safe and a non-repairable condition. A non-safe condition may be caused by structural deterioration mechanisms, which cannot be prevented. An example for such a mechanism may be material fatigue. An example for an in principle preventable deterioration mechanism is steel corrosion when implementing e.g., a cathodic protection. The repairability depends on the technical design (for repairability), the detectability or the prognosis of damages. Only if detectability or a prognosis is given, a repair can be planned to ensure the safety of the infrastructure. Economic constraints may determine an infrastructure’ service life end, particularly when the monetary demands of maintaining structural integrity surpass a justifiable threshold. This phenomenon occurs when the cumulative costs associated with ongoing maintenance, encompassing activities such as systematic inspections, reparations, and necessary enhancements, reach a point where they are no longer economically viable. In these cases, alternative infrastructure solutions that offer superior efficiency and performance at a reduced operational expenditure may be sought (e.g., the construction of a new bridge). Both the technical and economic limitations depend on the environmental and societal demands placed on the infrastructure. This implies that changing demands and (environmental) hazards may also influence the service life of an infrastructure. 2.1 Hazards Changing hazards include (1) climate change related influence of the environmental conditions and (2) security hazards beside (3) interrelated projections of societal demands. From a climate changes perspective, factors such as increasing frequency of extreme weather events, sea-level rise, and temperature fluctuations may influence both, loading events and the deterioration mechanisms. According to the most recent assessment report (AR6) from the Intergovernmental Panel on Climate Change (IPCC), there is projections of increasing intensity and/or frequency environmental hazards including sea-level rise (SLR), increased temperature trend, and extreme weather events (e.g., floods, storms, see Masson-Delmotte, Zhai et al. (2021)). Nasr, Björnsson et al. (2021) identified over 30 potential impacts of climate change on bridges. Specific examples include accelerated degradation of superstructure and