RELIABILITY CALCULATION AND MONTE CARLO METHOD

A simple, effective and easy to implement method for the reliability calculation of the discrete systems with randomly chosen parameters is presented in this paper. Since there are many reasons for reliability decreasing, the influence of system instability to the system reliability is considered in this paper. This method is very applicable in practice, for example in safety engineering, failure analysis, etc. Random choice of parameter value for which the system has the larger probability of stability enables the maximum reliability. In this way many problems can be avoided, for example failures of components and system. The proposed method is illustrated on an example of discrete band frequency damper and its validity has been confirmed by Monte Carlo method. Key words: Reliability, Probability of stability, Monte Carlo method

ZANESLJIVOST POSAMEZNIKA PRI DELOVANJU KRITIČNE INFRASTRUKTURE SODOBNE DRŽAVE

Povzetek Vpliv posameznika na delovanje kritične infrastrukture je eden najbolj nezanesljivih in nepredvidljivih dejavnikov, zato pomeni zanjo stalno nevarnost, ki je ne smemo podcenjevati. Postavlja se vprašanje, koliko si prizadevati za še večji tehnološki napredek, da bi bile tehnološke in fizične sestavine kritične infrastrukture varnejše, po drugi strani pa, kako obravnavati posameznika pri upravljanju teh kompleksnih sistemov, saj ta postaja vse pomembnejši referent za njeno zanesljivo delovanje. Avtor predstavlja okvir modela vpliva posameznikove zanesljivosti na delovanje kritične infrastrukture sodobne države. Ugotavlja, da je zanesljivost posameznika v neobičajnih razmerah najbolj odvisna od stopnje njegove motiviranosti, usposobljenosti in pripadnosti organizaciji. Samovarovalne dejavnosti in preprečevanje možnosti za neobičajne razmere so pretežno prostovoljna dejanja, pri katerih sta najpomembnejša pojma pripravljenost in volja nekaj koristnega delati za organizacijo. Za zanesljivo delovanje posameznika moramo imeti vizijo in cilje. Ključne besede: posameznikova zanesljivost, kritična infrastruktura, tveganja, neobičajne razmere, odločanje. Abstract The influence of individuals on the operation of critical infrastructure is one of the most unreliable and unpredictable factors, and as such represents a constant threat that should not be underestimated. The question arises as to how much effort to invest in the technological progress in order to make technological and physical components of critical infrastructure safer, and, on the other hand, how to deal with individuals in the management of these complex systems, as individuals are becoming an increasingly important reference point to insure its reliable operation. The author presents the framework of the model of the influence individuals' reliability has on the operation of a modern state critical infrastructure. He notes that the reliability of an individual in unusual circumstances mostly depends on the level of their motivation, competence and affiliation to the organization. Self-protective activities and the prevention of possible abnormal circumstances are predominantly voluntary acts, where the most important concepts are willingness and the will to do something useful for the organization. A reliable performance of an individual requires a vision and goals. Key words: Reliability of individuals, critical infrastructure, risks, abnormal situation, decision making.

A TOOL FOR RISK ASSESSMENT

A lot of companies need to carry out a risk assessment, but most of them do not have the experience to determine the risk in a qualitative way. Therefore, these organizations use the tools for qualitative or qualitative - quantitative risk assessment. A useful tool for risk assessment is risk matrices (risk assessment scoring matrices/ risk ranking matrices). The aim of this paper is to present various risk matrices. Typical risk assessment matrices with different levels recommended by the American standards and other standards have also been presented in this paper. Key words: reliability, severity, risk, matrix, probability

Reliability-based inspection of post-tensioned concrete slabs

In unbonded, post-tensioned prestressed concrete slabs and beams, corrosion of prestressed tendons due to moisture ingress and their subsequent breakage has been identified as a major problem raising serious concern over the safety of aged structures. The paper presents a practical Bayesian approach to reliability assessment of such structures based on the inspection of a randomly selected sample of prestressing tendons. To minimize inspection costs, clear guidelines are presented for selecting the minimum sample size necessary to demonstrate that the annual probability of failure of an existing structure is below the target value of 10−5, implied in the Canadian Standards Association concrete design code CAN3-A23.3-M84. A systematic and cost-effective incremental strategy is developed for inspection of existing prestressed concrete structures. Key words: reliability, Bayes theorem, prestressed concrete, unbonded post-tensioned system, inspection, corrosion, probability distribution, CSA Standard CAN3-A23.3-M84, slab.

Reliability analyses of activated sludge systems in attaining effluent standards

A design-point method, or advanced first-order second-moment technique, is used for reliability-based analyses of activated sludge processes in meeting specified effluent standards. Three non-normal random variables, namely flow, influent biochemical oxygen demand (BOD), and influent suspended solids (SS) concentrations, are utilized in evaluating the performance of the activated sludge system. Two types of failure to attain specified effluent standards are considered, namely BOD failure and SS failure. The reliability of activated sludge system is studied with respect to the volume of the aeration tank using design-point method. Key words: reliability analyses, BOD, activated sludge.

Fiabilité d'une étude pédologique détaillée réalisée en terrain plat

In order to estimate the reliability of soil information presented in a detailed soil survey (1:20 000 scale) conducted in a flat terrain (Vercheres county, Quebec), 35 randomly selected delineations were inspected with 10 sites per delineation. Reliability was evaluated according to parent material (marine, estuarine and fluvial) and kind of map units (simple and compound). As a whole, mineral soils have been mapped and defined reliably for most criteria commonly used in soil interpretation systems. Reliability of soil information differed significatively with parent material. Taxonomic purity of marine, fluvial and estuarine soils delineations were 70, 58 and 28%, respectively. Although less precise, compound map units were more reliable than simple map units. Among the 13 soil variables studied, A and B horizons texture, B horizon designation and depth to carbonates were the more frequently in error. Results finally indicated that reliability is also a function of the delineation area and inspection density. In order to improve reliability of soil information and accelerate soil survey in future projects, it is suggested to adjust inspection density according to parent material, to reduce the number of classes for a few variables and to avoid excessive use of soil series'variants and delineations of small size (< 4 ha). Key words: Reliability, purity, accuracy, soil survey procedures, inspection density