PSI - Issue 48

Aleksandar Šotić et al. / Procedia Structural Integrity 48 (2023) 266 – 273 Šotić et al / Structural Integrity Procedia 00 (2023) 000 – 000

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Introduction The operation of hydraulic engineering (HE) systems, which are primarily designed and built to meet certain goals of society, such as receiving flood waves, providing drinking water, generating electricity, etc., can cause undesired events, such as a dam breach, delivery of inadequate drinking water quality, discharges of insufficient downstream flow, and accompanying adverse outcomes, such as deaths, property damage, environmental degradation, etc. The very broad use of specific terms and the lack of common terminology require some clarification:  An accident is event involving an unplanned and unwanted loss (Leveson, 1995); a bit de-tailed, an accident is an undesired and unplanned event that results in a loss, including a loss of human life or human injury, property damage, environmental pollution, mission loss, financial loss, etc.  A hazard is a system state or set of conditions that, together with a particular set of worst-case environmental conditions, will lead to an accident (loss) (Leveson 2011). A system-level hazard is a system level state.  Safety is the absence of unwanted events or losses (Leveson, 1995). This definition, as an extended view of safety, includes losses such as human deaths or injuries, mission or goal losses, equipment losses or material losses, and environmental damage. Safety is considered as an emergent property associated with a set of components at one level in hierarchy, which is related to constraints upon the degree of freedom of those components (Leveson, 2002).  In engineering practice, the term 'risk' is perhaps more present than the term 'safety'. Safety is a kind of risk antipode (Sosnovskiy, 2005). Definition of risk, accepted in standardization, is effect of uncertainty on objectives, and it is assessed based on probabilities and consequences.  Resilience is adaptive capacity of a system/organization in a complex and changing environment, i.e. is the capability of a system to maintain its functions and structure in face of internal and external change (ASIS, 2009). Planners and designers of HE systems have long recognized that risk is inseparable from the work they do (USACE, 1992). Risk is involved in engineering in many ways, in determining how much effort and resources should be involved during development (planning and design) of an engineering system to prevent hazards or harms, or in ensuring an acceptable level of risk during system operation. Also, risk can be used to select events or conditions that should be considered during system operation to prevent loss, regardless of the analyses carried out during the development of the system (Leveson, 2004). A certain degree of flood protection or a certain reliability of water supply, for example, are explicit planning objectives concerned with risk reduction. Engineering infrastructure systems are almost always designed, built, and operated under unavoidable conditions of risk and uncertainty, and are usually expected to achieve multiple and conflicting goals. In order to be effective and meaningful, risk assessment and risk management must be integral and explicit part of the overall management system, that is, the decision-making process, and not some special, bureaucratic attachment or formal addition to technical analysis. This is particularly important in the management of systems traditionally defined as technical systems (Haimes, 2004). The planning, design, and operation of HE systems typically involves many components and contributing factors, each of which individually, along with the system, are subjects to uncertainties. For example, the reliability of a flood forecast depends not only on the uncertainty of the forecasting model itself, but also on the uncertainty of the input data. A storm water system design is subject to uncertainty in the runoff simulation model used, uncertainties in determining the design storm, as well as uncertainties in terms of materials used, construction and level of maintenance. Knowledge of uncertainty is useful for rational decision-making, for cost-effective design, for safe operation, and for improving awareness of the risks and reliability of water resources (Yen, 2004). However, on the other hand, it can also be observed that most engineering failures arise from a complex and often unique combination of events, and statistical data on their probability and consequences are insufficient or unavailable (Samuels and Gouldby, 2009). The uncertainty of HE subsystem interactions is rarely discussed in the literature. In recent years, there has been a discussion about the need to change the approach (paradigm) in the management of systems in the water sector, because the existing practice, which cannot go beyond the framework of reliability and probability-based risk models, does not provide acceptable results. Despite the acceptance of the fact that the HE systems are not exclusively technical, and the inclusion of human and organizational factors, probabilities remain a central concept in the risk-based approach. The new approach needs to be consistent with the nature of the problem being solved – our HE systems are complex, hierarchically organized, socio-technical, managed to accomplish their goals and be adaptive and resilient to unexpected challenges. If there is not enough information to determine the