Effects of Degradation of Pipes on Seismic Rehabilitation Decision-Making for Water Distribution Networks

Seismic events disrupt the operation of water distribution networks. Proactive seismic rehabilitation decision-making methods are necessary to ensure maximum serviceability after a seismic event. Most recent proactive seismic rehabilitation decision-making models of water distribution networks are sensitive to network hydraulics and pipe fragilities. Although network hydraulics and pipe fragilities are influenced by pipe degradations, the effects of degradation on proactive seismic rehabilitation decision-making have not been studied. The probabilistic nature of the water pipe degradation makes the consideration of degradation challenging. This research aims to investigate the effects of the degradation of pipes on the seismic rehabilitation decision-making of water distribution networks. The methodology includes (1) designing simulation experiments; (2) integrating the effects of inside and outside degradation with seismic rehabilitation decision-making; and (3) conducting statistical analysis to identify the effects of integrating pipe degradation. The simulation experiments were designed to investigate the effects of degradation on the inside surface of pipes and the outside surface of pipes individually and combinedly. A simulated annealing (SA)–based optimization algorithm was used to identify the critical pipes and associated maximum serviceability for each experiment and each budget constraint. To assess the statistical significance of integrating degradation, two statistical tests were performed. The application of the proposed approach was illustrated on a benchmark network. The selected benchmark network consisted of cast iron pipe and ductile iron pipe. Degradation of cast iron pipe was considered in this study. This framework can be used for other materials. This study was based on five rehabilitation constraints with a focus on rehabilitation costs. The optimization algorithm was employed to identify critical pipes corresponding to each rehabilitation constraint. The results for each simulation experiment showed that the identified critical pipes differed. The associated maximum serviceability was reduced for the same budget constraints if outside and inside degradation were considered individually and combinedly. The associated maximum serviceability was reduced by 3%–4% because of the individual effect of outside or inside degradation, and 6%–7% because of the combined effect of inside and outside degradation. The changes in the identified critical pipes and associated maximum serviceability due to the consideration of outside and inside degradation imply the dependency of a proactive seismic rehabilitation decision-making model on outside and inside degradation. The statistical test results imply that the degradation of pipes in the water distribution network has an impact on seismic rehabilitation decision-making models of water distribution networks. Therefore, it is recommended to integrate the degradation effect with existing seismic rehabilitation decision-making models.