EkaKartikaK_Tech&Society_Bab7_Risk Assessment for Civil Engineering Facilities

8/3/2019 EkaKartikaK_Tech&Society_Bab7_Risk Assessment for Civil Engineering Facilities

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Risk Assessment for CivilEngineering Facilities : Critical

Overview and Discussion

Summarized by Eka Kartika Kd

1006735151


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Preliminary

There has been an increasing societal concern on a sustainabledevelopments focusing on conservation of the environment, thewelfare, and safety of the individual and at the same time the

optimal allocation of available natural and financial resources As a consequences, the methods of risk and reliability analysis in

civil engineering are increasingly gaining importance as decisionsupport tools in civil engineering applications

Universal Declaration of Human Rights

Both the moral and legal obligation to consider all persons asbeing equal and furthermore underlines the rights to personalsafety for all individuals fundamental aspect regard to

acceptable risk for civil engineering applications

Risk Risk is a rather commonly used notion and is used

interchangeably with words like chance, likelihood and probabilityto indicate that we are uncertain about the state of the item,issue or activity under discussion. It is necessary in decisionmaking that we are precise and consistent in our understanding ofrisk


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The Practical Implementation ofrisk analysis

Risk analyses may berepresented in a generic format,

which is largely independentfrom the application or whetherthe risk analysis is performed inorder to document that the risksassociated with a given activityare acceptable or is performed toserve as a basis for amanagement

Hazard Identification

Plays a crucial part

If relevant hazards are notidentified then the risk analysiswill result in biased decision-making, result to cost inefficientand unacceptably high risks topeople and environment

Generic Representation ofRisk Based Decision Analysis


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Logic Tree Analysis

Formulated and used for the overall risk analysis from theindividual components

Provides the tools for assessing the various branching

probabilities in the event decision trees as well as thecorresponding consequences : fault tree, even tree, cause/consequences chart

Bayesian Probability Network is promising tool for risk analysis

Uncertainly Modeling In fact the variables influencing a decision/risk analysis may be

subject to several sources of uncertainty :

Inherent or natural variability of the phenomenon itself

Modeling uncertainty: (i) uncertainty whether all factors thatinfluence the model are included, or (ii) uncertainty in how the

model describes the relationship between these factors

Statistical uncertainty

The sources of uncertainty, even for the same facility, are verydependent on the purpose of the risk analysis

The reference period of risk-decision analysis is also very

important


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Evaluation of Risk : Prior/ Posterior Analysis

In the prior-analysis, the risk (expected utility) is evaluated onthe basis of statistical information and probabilistic modelingavailable prior to any decision and/or activity (Picture : Left)

In the pre-posterior analysis, optimal decisions in regard toactivities, which may be performed in the future, e.g. theplanning of risk reducing activities and/or collection of informationmay be identified (Picture : Right)

the probabilities for the different events represented in the prioror posterior decision analyses may be assessed by logic tree

analysis, classical reliability analysis and structural reliabilityanalysis or any combination of these.


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Analysis of Consequences

A major difficulty is how to compare direct economic losses(building damage, production losses), indirect losses (user delayor inconvenience, impact on economic growth, unemployment)

and non-monetary losses resulting from loss of life or injury,damage to the environment, social disruption, etc

Considering the enormous economic impact on society originatingin political wishes related to the preservation of environment, it isof utmost importance that a consistent framework be established,based on generally non-political values allowing for the

quantification of environmental qualities

Analysis of Probabilities

The probability of failure of such components can be interpretedin terms of relative failure frequencies observed from operational

experience. The main focus is directed towards the formulation ofprobabilistic models for the estimation of the statisticalcharacteristics of the time until component failure

For reliability analysis it is thus necessary to establish probabilisticmodels for loads and resistances of components includinginformation about statistical characteristics of parameters

influencing these.


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Optimality and Risk Acceptance Criteria

The development and implementation of risk acceptance criteriainvolves:

perception of risk: ensure that level of system risk is

acceptable (or tolerable); formal decision analysis: analytical techniques to balance or

compare risks against benefits (e.g. risk cost- benefit analysis,life-cycle cost analysis); and/or

regulatory safety goals: legislative and statutory frameworkfor the development and enforcement of risk acceptance

criteria

Individual and Societal Risk :

the problem concerning risk acceptance has a fundamentaland philosophical bearing to the rights of human beings

Safety has a cost, therefore the level of safety to be

guaranteed for the individual member of society is a societaldecision with a strong bearing to what the society can afford.

Considering the acceptability of activities related to civilengineering, the main question is not the preferences of theindividual member of society but rather the preference of thesociety as expressed by the Universal Declaration of HumanRights or some other generally agreed convention


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Societal Risk and Risk Aversion:

The reason for being risk averse is that the events involvinghigh consequences often are associated with follow-on events

which themselves may contribute significantly to the risk If all such follow-on consequences are taken into account in

the risk analysis then there is indeed no need to introduce anydegree of risk averseness and the decision basis will be moretransparent

Multi-attribute and Multi-objective risk-based decision analysis :

Decision-making often leads to situations where differentattributes need to be considered simultaneously. Furthermoredifferent interest groups may have different objectives orpreferences and thus in effect value the combined effect of theattributes differently

It is also contentious converting some attributes to a commondenominator that all interested parties could agree to,particularly when the values under consideration aresubjective


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Optimization of expected utility and the Quality Index :

A decision may therefore be based on activities that maximizeexpected monetary benefits, the expected utility or anotherindex of performance such as the Life Quality Index

Time is an important factor that may influence decisions sincepsychological studies show that the preferences of a decision-maker will increase with the postponement of adverseconsequences

Regulatory safety goals and calibration of acceptable risk :

An alternative to using results from a risk analysis in a

quantitative decision analyses is to use the results moredirectly for regulatory purposes. The safety goals (riskacceptance criteria) tend to be surrogates for the risks andhazards, which are considered to be acceptable (or tolerable)to society

Other Considerations : The knowledge of the system and its performance accrued

during a risk analysis can also reveal new insights (in aqualitative sense) into system performance and how thismight be improved. As long as the purpose of risk analysis isto understand system performance, then risk analysis can be

very effective tool to improve system safety and performance


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Thank You

EkaKartikaK_Tech&Society_Bab7_Risk Assessment for Civil Engineering Facilities

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