Fig.1 Flow chart of risk assessment
AECEF NEWSLETTER 1-2/2000
Reliability and Risk Assessment - Trends in Education of Civil Engineers
by Assoc.Prof. Milan Holický, Ph.D., DrSc.
Faculty of Civil Engineering
Czech Technical University in Prague
1. Introduction
Building and civil engineering works (construction works) are becoming more complicated systems consisting of several subsystems (e.g. structure, fire safety, transport, health) of interrelated elements (e.g. bearing elements, fire safety elements, transportation and communications means). Further, construction works themselves (as elements) are, as a rule, very important key elements of other superior complex systems as social, political, environmental and technological systems. Moreover, inherent level of various uncertainties of the above-mentioned systems is relatively high, in some cases (e.g. in accidental situations) seems to be even increasing. Consequently, reliability analysis and risk assessment of these systems becomes an indispensable part of design and verification of many new construction works.
However, reliability and risk assessment are still working topics for specialists only. Moreover, non-specialists look upon outcomes of related studies with scepticism. This is partly caused by lack of understanding and insufficient education in the field of probabilistic methods, reliability and risk assessment. Obviously, present educational programmes in most of the Faculties of Civil Engineering do not entirely reflect current needs for education in the field of reliability theory and risk assessment. The objective of this contribution is to point out desired needs for changes in education of civil engineers taking into account characteristic features of the reliability theory and risk assessment. Foreseen future trends in education in Civil Engineering Faculties are also indicated.
2. Methods of reliability and risk assessment
Reliability is generally understood as an ability of engineering works to comply with all required functions under specified conditions during a given lifetime. As a rule probability of malfunctioning (failure) is used to describe reliability level. However, due to many uncertainties in theoretical models and methodology of available methods, results of reliability analysis have been often interpreted and applied with hesitation and certain degree of scepticism concerning their practical significance.
Recently, an extensive research has been carried out to improve existing methods and to supplement reliability analysis of construction works by risk assessment of adequate subsystems and superior systems. Developed methods of the risk assessment of a system consist of the use of all available information to estimate the risk to individuals or population, property or environment from identified hazards. Typical procedure of risk assessment includes definition of context and system, hazard identification, probability and consequences analysis, estimation of risk and risk assessment, i.e. comparison of estimated risk against specified criteria. Basic steps of risk assessment are schematically indicated in Figure 1.
Fig.1 Flow chart of risk assessment
Thus, the first step in the risk assessment involves the context (scope) definition related to the system and subsequent identification of hazards. Here the system is understood as a bounded group of interrelated, interdependent or interacting elements forming an entity that achieves in its environment a defined objective through interaction of its parts. In case of technological hazards related to construction works, a system is normally formed from physical subsystem, human subsystem, their management and environment. Note that, similarly as in most systems, risk analysis of civil engineering systems usually involves several interdependent components (e.g. human life, injuries, economic lose).
Several operational techniques have been recently developed to analyse reliability and risk of complex system (e.g. fault trees, Bayessian networks, influence diagrams). An example of simple influence diagram used to analyse construction work under permanent and accidental (fire) situation is shown in Figure 2. Obviously more complicated diagrams are needed when several inter-related hazard situations are considered.
The network in Figure 2 consists of 12 chance nodes, labelled by numbers 1 to 12, two decision nodes 13, 14, and five utility nodes 15, 16, 17, 18 and 19. An alternative distribution (yes, no) is considered for all the chance nodes. The decision node 13 is introduced in order to analyse an effect of sprinklers, the node 14 to analyse an effect of structural protection. Positive state of both decision nodes implies some costs described by the utility nodes 15 and 16. The other utility nodes 17, 18 and 19 cover effects of chance nodes 8, 10, 11 and 12. It appears that Bayesian network supplemented by decision and utility nodes (influence diagram) is an effective tool to analyse risk related to the permanent and fire design situation.
It appears, that the methods of risk analysis and assessment, which is capable to comprehend more types of uncertainties than the traditional probabilistic approaches, can significantly contribute to further improvement of current methods of reliability. A remarkable fact, that the public is better prepared to accept certain risks than to stand for specified probabilities of failure, will make application of risk assessment easier. It is therefore anticipated that in a near future the probabilistic methods of structural reliability will be supplemented by the criteria of acceptable risks.
Figure 1 and 2 clearly indicate that risk assessment is a demanding task that requires detail knowledge of the system, theoretical tools and available operational techniques to analyse the system. Up to now, as a rule, reliability and risk assessment of a selected subsystem or even elements is analysed only.
Fig. 2 A network model of construction work
3. International activities
Several international organisations and societies are at present intensively developing methods of reliability analysis and risk assessment related to construction works and appropriate systems. Most important of them are
All these organisations participate in coming conference "Safety, Risk, and Reliability - Trends in Engineering" is going to be held in Malta in March 21 - 23, 2001. The objectives of this conference are extremely closely related to the aim of this contribution. The Conference intends to provide opportunity for engineers of various kinds to exchange views and experiences on how risk and reliability based approaches and techniques are used in the decision-making process. The Conference also serves as an inter-association meeting place for members and committees of various association devoted to safety, risk, and reliability of engineering structures and other technical systems and facilities.
The scientific and technical parts of the Conference will take place on four-days, each starting with a Plenary session followed by three concurrent Working Sessions devoted to various topics including
In particular the last topic "Benchmark studies" seems to provide an extremely useful mirror of the current situation in the field of reliability analysis and risk assessment. It appears that research and development in probabilistic methods of reliability and risk assessment are far in advance of practical application and design.
Obviously, desired improvement of the present unsatisfactory situation in practical applications of theoretical tools, available methods and operational techniques is appropriate education of civil engineers and other involved specialists (including public authorities). It appears that appropriate communication among all involved partners is one of the most important conditions, which would enable more comprehensive applications of theoretical methods in the broad field of engineering.
4. Foreseen trends in education
It follows from the above discussion that education in the field of reliability and risk assessment is becoming more and more important aspect of educational programmes of Faculties of Civil Engineers in Czech Republic. In fact in some European Technical Universities courses on reliability and risk assessment are already introduced and at present are being already intensified. This remarkable trend is caused by several general aspects of current conditions in civil engineering, including:
It is foreseen that systematic education in the field of reliability and risk assessment will be in an adequate extent introduced for all undergraduate students of Faculties of Civil Engineering. However, introduction of such a course would require adequate changes in basic courses concerning the theory of probability and mathematical statistics, which seems to be insufficient.
In addition to courses for undergraduate students it is desirable to prepare specialists by introducing graduate courses in the field of reliability and risk assessment including courses with extended lectures in theory of probability and mathematical statistics.
5. Concluding remarks
Complicated civil engineering works are becoming more important elements of various complex superior systems (social, political, environmental and technological) having significant inherent uncertainties. To analyse performance of these systems traditional probabilistic methods of system reliability appears to be soon supplemented by methods of risk assessment. In order to enable effective implementation of these methods adequate changes in education of new generation of civil engineers are foreseen. Undergraduate as well as graduate programmes at Faculties of Civil Engineering should extent education in the field of theory of probability and statistics, and should introduce new courses in the field of reliability and risk assessment.
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