Browsing by Author "De Klerk, Altus Hugo"
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- ItemDevelopment and application of a multi-period pipe replacement model utilising risk-based prioritisation for water distribution systems(Stellenbosch : Stellenbosch University, 2016-03) De Klerk, Altus Hugo; Jacobs, H. E.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: The decision on whether to replace a pipe, with specific reference to a water distribution network, can be complicated by several aspects in the decision making process, such as available funding and required system performance. Long term budget requirements need to be assessed for the effective management of an existing water distribution network to find balance between the return on investment and customer satisfaction. Various failure prediction models are available to calculate the probability of failure of each pipe in a water network. The probability of failure is then used to determine a replacement priority for all pipes in the network accordingly. Research has shown that the choice and implementation of failure prediction models are sensitive to the availability of data and in many cases a high degree of expertise is required to sufficiently understand the results. Semi-quantitative risk assessments provide a structured way to rank pipes by accounting for likelihood and consequence of failure while providing adaptability to the availability of data. In order to utilise the advantages of the risk-based approach a multi-period replacement model was developed to determine a suitable long term investment strategy, while taking some practical considerations into account. A model was developed which utilised a risk-based approach to determine the pipe replacement priority. The model considers each pipe in a pipe inventory database based on several contributing pipe attributes and the available budget. A failure forecasting algorithm was also included in the model. The model could be used to determine the required budget based on certain fixed input parameters such as the total length of pipe to be replaced or the total allowed number of failures per year. Four hypothetical investment scenarios were analysed for a case study. The results were compared to a fifth scenario, noted as the reactive strategy, which involved no pipe replacement. For the specific case study that was analysed the reactive strategy involved the lowest total cumulative expenditure. Additional investment was required to improve the performance indicators for the number of failures, service interruption duration, estimated remaining useful life and estimated remaining asset value. This research presented a methodology across the different performance indicators noted above, wherein the relative weights of the performance indicators were used to calculate a best-fit index.