Risk assessment is an essential step towards minimizing eventual consequences of infrastructure failures. Yet, numerous conceptual frameworks have been developed in various disciplines of social and natural sciences for examining the risk associated with extreme events and climate change. However, the assessment of the perceived risk of infrastructure failure, in connection with continuous deterioration mechanisms, for instance fatigue fracture due to vibration-crack-corrosion of aging waterway infrastructures, has not been extensively addressed yet. Designed for an expected service lifetime of 100 years, the bulk of navigation locks and weirs of the German Federal Waterways and Shipping Administration (WSV) were built between 1850 and 2014. More precisely, about 12% and 18% respectively of navigation locks and weirs of the network category A have already reached their desired service lifetime and these percentages are likely to reached approximately 36% and 44% over the next two decades. Also, increasingly complex structures have emerged as a result of tremendous developments in construction materials and technologies, coupled with significant advancements in designed standards. Again, with respect to the structural system, construction type and applied loads of navigation locks, gravity retaining walls, constructed with mass concrete brick- and stonework were progressively abandoned from 1960 for half-frame constructions, built with reinforced concrete.
The infrastructure portfolio of the WSV consists of over 4500 objects of various construction types and materials, distributed through 67 groups of objects, ranging from navigation locks to dykes. This immense and heterogeneous infrastructure portfolio is confronted with different deterioration mechanisms, which might seriously undermine not only the structural reliability, but also have far reaching social and economic consequences in case of failure. While some of the deterioration processes might be associated with ageing, others are rather consequences of environmental stresses, construction and structural shortcomings and deferred maintenance activities, due to budget constraints or. Indeed, as waterway infrastructure become structurally and functionally deficient, the likelihood of time –dependent structural failures, including concrete corrosion and steel reinforcement corrosion, erosion and fatigue or embrittlement increases. Nevertheless, the service lifetime of these structures could be extended through advanced inspection and monitoring technologies, innovative maintenance and repairs. However, the implementation of such strategies will require substantial funds that are not always available, as well as the closure and replacement of various infrastructures, with tremendous economic consequences.
A deteriorating infrastructure is likely to draw increased operation and maintenance costs, reduced safety and could also result in catastrophic failures with devastating environmental, social and economic consequences. Thus, based on its Maintenance management System (EMS-WSV), the Federal Waterways Engineering and Research Institute (BAW) is seeking for genuine and effective maintenance strategies to address the mounting burden of repair and renewal activities. Decision –making for the prioritization of the neediness of the aforementioned activities lies on condition ratings, which stem from damage data, recorded during visual and cyclic inspections. Beyond merely describing the degree of structural and functional deficiency of the infrastructure, including the load carrying capacity, serviceability and durability, in relation with various deterioration mechanisms, this condition assessment does not specifically address the emerging risk of infrastructure failures. Again, although the prioritization of maintenance activities is increasingly granted a great attention, neither the perceived risk of infrastructure failure, nor the vulnerability of waterway infrastructures to various deterioration mechanisms have not heretofore been incorporated into the EMS-WSV. Indeed, much of the German waterway infrastructure is rapidly ageing. This situation could unfortunately exacerbate the risk of failure of structurally deficient and functionally obsolete structures, in case of any extreme events (floods) or natural disasters. Therefore, a comprehensive condition assessment method that simultaneously addresses the age of the facility, the vulnerability to various deterioration processes, the risk of potential failure and observed damages becomes an adequate tool for effective decision making related to repair and renewal activities of our aging infrastructure. Decision support tools are needed to enable practitioners and policy makers to make rational assessments of threats to infrastructures, to evaluate the consequences of the structural degradation and failure at various facilities under different circumstances and to propose effective corrective measures.
This paper provides an insight to current research on the development of key figures for the assessment of the load-carrying capacity of existing waterway infrastructures, based on analysis of damage data, recorded during regular visual inspections. Thus, the purpose of this study is to shed more light on both the vulnerability of waterway infrastructures to various deterioration mechanisms and the perceived risk of infrastructure failures. In this paper, we propose a combined Failure Mode and Effect Analysis (FMEA)/Analytic Hierarchy Process (AHP), which is used to qualitatively assess the risk of infrastructure failure, and thereafter, to enhance decision-making with respect to prioritization of repair actions. Thus, using a Multi-Criteria Decision-Making approach, for instance integrated Analytic Hierarchy Process (AHP), various failure modes, identified in line with the conducted traditional FMEA are prioritized taking into account their potential risks of structural failure and loss of functionality. Interestingly, uncertainties, associated with damage data, collected during regular visual inspections and several aspects of the criticism to the traditional FMEA are well covered by the employed methodology. We also describe how individual score values obtained for each criterion can be used to establish guidelines for appropriate maintenance strategies for different classes of infrastructures. Equally noteworthy, much further research must be conducted to investigate the reasons and consequences of potential causes of failures with high risk-scores and to understand their effects on the functional and performance requirements of the structure as a whole. Ultimately, it is important to stress at this point that if German´s waterway infrastructure are not resilient enough, if we continue to defer maintenance activities, if we cannot meet coming societal and business transportation demands, if we cannot effectively document observed structural and material deterioration (digitalization) and if we try to run Germany on a shoddy waterway infrastructure, we are doomed to a downward spiral in our economy, standard of living and world stature.
Keywords: Risk, EMS-WSV, multi-criteria decision-making, Analytic Hierarchy Process (AHP), failure modes, uncertainties, prioritization