Risk Based Maintenance Approach in the Management of Existing Civil Engineering Facilities - Research Paper Example

POTENTIALITIES OF RISK BASED MAINTENANCE APPROACH IN THE MANAGEMENT OF EXISTING CIVIL ENGINEERING FACILITIES This research paper discusses risk and risk management in existing civil engineering structures. Risk management is very important since uncertainties in infrastructures are reduced. Occurrence of a risk may cause financial losses, loss of life and even may have long term effects such as unemployment and reduced economic growth. The paper then explains the consequences of risk and their impact on environment and the society. The importance of risk management are highlighted and the various limitations that the practice faces. It also shows that a good facility should be able and ready to spend in risk management so that the survival of the facility is guaranteed. Human life should be given priority in assessing risk because no value can be attached to it and then other factors to follow. INTRODUCTION There are ways of assessing risk in the existing civil engineering facilities in an attempt to come up with decision making tools. Risk is the measure of the probability and severity of adverse effects (Lowrance, 1976) while risk assessment is the act of determining the likelihood of a risk occurring and the consequences that come with it. For sustainable development to be achieved, intense focus on risk assessment has to be put in order to maintain the existing and future infrastructure. Determining what should be done in case of occurrence of a risk, impact of current decisions on future options and the consequences due to a given activity is also part of risk management. Due to day to day changes in systems, technology and environment, risk management has to be monitored regularly. Hazard identification This is the first step of risk assessment. It is the act of identifying the sources of risk in the existing civil engineering facilities. Some of the sources of risk are human error, environmental catastrophes and system failure due to mechanical breakdown. These hazards can be identified by past experience and also in incident data banks where past records are kept. It is very important to take into account all the relevant hazards in a facility. This ensures critical decisions are made in regard to the risks. Ignoring a hazard causes negative impacts in terms of financial losses and human injuries or even lives may be at stake. Analysis of risk Risk can be analyzed using two methods, that is, logic tree analysis and uncertainty modeling. i. Logic tree analysis. Logic tree analysis provides a tool for assessing various branching probabilities divided into, fault trees, event trees and consequence charts. Fault trees explain the source of failures; event explains the occurring of possibility while consequence explains the outcomes associated with the occurrence of an event. Uncertainty modeling This is the other way of analyzing risk. It involves analysis based on information that is partially subject to uncertainty. Classified into: i. Inherent or natural variability of phenomenon ii. Modeling uncertainties iii. Statistical uncertainty Inherent or natural variability phenomenon includes those risks that are caused by natural causes like flooding and earthquakes. In modeling and statistical data, the uncertainties decrease as the understanding of the variables increases. This is to say that there are improved prediction models. This however does not apply in some cases as future events may not be directly related to past events. Evaluation of risk The simplest form of risk analysis is prior analysis. It is based on statistical information and probabilistic modeling available prior to decision making or activity. These are the data extracted from bank’s historical events that help in decision making before the improvement of an already existing facility. Another type of analysis used in evaluation of risk is the posterior analysis. Posterior analysis is used to evaluate effects of activities which have been prepared such as changes in the branching probabilities and consequences in the decision tree reflect that the considered problem has been changed as an effect of risk reduction (diamantidis, 2001). For example, the evaluation of an already existing facility would show much construction and design errors hence a more accurate and reliable information would be got from this. The final analysis used is the pre-posterior analysis. This helps in making optimal decisions in regards to identifying activities which may be performed in future, for example, planning of risk reducing activities. This is achieved by formulating rules based on future activities which will be taken as bases of the results of planned activities (Faber et al). Components needed for evaluation of risk i. Analysis of consequences These are consequences of a failure event can be classified as direct or indirect consequences. Direct consequences directly affect people and their environment. These may be attributed to loss of life, injury and economical losses. Indirect consequences are the consequences that cause indirect losses such as unemployment and negative impact on economic growth. The consequences that are most contentious are those with low probability of occurrence but their consequences are very high such as core-melt down at a nuclear power plant. Sometimes it is very difficult to estimate direct and indirect consequences. This is so because it becomes very hard to attach value to certain losses such as loss of human life. Loss of human life can be estimated by social indicators that reflect on the quality of life and ones contribution to gross national income (GNP) and life expectancy. ii. Analysis of probability Probabilistic models for the estimation of the statistical characteristics of the time until component failure. These are relative failures observed during the time of operation. Components of the same kind are put under the same load and observed to see their behavior in regards to failure. This method is not used in structures because structures fail only when under very heavy loads that exceeds their capacity or if they have been subjected to corrosion. The other reason is that every structure is unique. This is due to the difference in building materials and design geometry for every structure. This makes it difficult to compare different structures. iii. Classical reliability analysis This is a way of estimating statistical characteristics of lives of technical components in order to determine their characteristics in operation and design. These characteristics include expected failure rate, hazard function, expected life and mean time between failures (van pepper, 32) Models are constructed to evaluate various quantitative measures of performance such that component will fail in a given period of time. Components that fail during the initial stage of their life are mainly due to production errors. Components that exhibit constant rate of degradation can be monitored such that their failure does not exceed a critical point. While evaluating failure on basis of observation, care must be taken in that observation of ageing components might over estimate failure rate while observing a component for a short period of time might underestimate the failure rate. iv. Structural reliability analysis This analysis is concerned with structures and demand capacity reliability. The structure components that fall into this category are such dams, pipelines and buildings. In this category, failure events are very rare. This is due to the fact that such structures are built according to the capacity that they can handle. There failures occur due to extreme conditions such as earthquakes and flooding. Optimality and acceptance of risk In the modern world, it is impossible to do away with all the risk that faces a component. Due to this, the magnitude of various risks is examined. Decisions are made according to the magnitude of risk, acceptability and cost of the risk and also the regulatory safety goals of an organization. Much consideration is put on risk with high magnitude and severe consequences while disregarding the ones that fall under the acceptable level. Regulatory safety goals and calibration of safety goals Every civil facility should have its own safety goals. These goals should be in line with those of human rights and the regulations of the country. The facility should put long term measures to mitigate risk of optimum magnitude that may occur in an uncertain manner. The sustainability, conservation and preservation of facilities depend on whether these safety goals are attained. CONCLUSION From the research paper, it is clear that risk management is very vital in the modern world. Much focus should be put in risk management so that uncertainties in the future are reduced. Human life should be given first priority in assessing risk because no value can be attached to it. Investing in risk management pays off later for it assures continuity and survival of a facility. REFERENCES Diamantidis D. Probabilistic Assessment of Existing Structures. France: JCSS, RILEM: 2001. Faber MH, Kroon IB, Sorensen JD. Sensitivities in Structural Maintenance Planning. Reliability Engineering and System Safety 1996: 51(3):317–30. Klaassen KB, van Peppen JCL. System Reliability: Concepts and Applications. London: Edward Arnold: 1989. Villemeur A. Reliability, Availability, Maintainability and Safety Assessment. Chichester, UK: Wiley: 1991. Melchers RE, Stewart MG. Probabilistic Risk and Hazard Assessment. Netherlands: Balkema: 1993. (243–52). Melchers RE. Structural reliability: analysis and prediction. New York: Wiley; 1999. Rackwitz RA. New Approach for Setting Target Reliabilities. Proc. Safety, Risk and Reliability—Trends in Engineering, Malta. Zu¨rich: IABSE; March 21–23, 2001. (531–6) Read More