Seismic Reliability Assessment of Lifeline Systems

Abstract

A methodology is proposed for the seismic assessment of the reliability of urban water distribution networks (UWDN). The method is based on general seismic assessment standards, as per the American Lifelines Alliance (ALA) guidelines, and on localized historical records of critical risk-of-failure metrics. The proposed methodology is applicable to UWDN under either normal or abnormal operating conditions, and the assessment of reliability considers not only the vulnerabilities of the network components against seismic loading but also the topology of an UWDN and data of past non-seismic performance. This past performance, obtained using records of pipe burst incidents, is utilized with network-specific 'survival curves' in fine-tuning the generalized fragility curves suggested by the ALA. The resulting vulnerability analysis is used in devising 'repair-or-replace' strategies for the studied lifelines. INTRODUCTIONLifeline systems, such as water distribution networks, are of critical importance to the uninterrupted provision of services and thus to the resiliency of a city. Thus, being able to assess the reliability of the network against different hazards helps water distribution agencies prioritize their interventions and ensure a minimum reliability level of the network.A number of previous studies have assessed the vulnerability of infrastructure systems, but seldom has the non-seismic performance of such systems and the system-component interactions been considered in evaluating the seismic vulnerability of such systems. The process proposed in this paper combines data on historical non-seismic performance of urban water distribution networks (UWDN) and their components by use of survival analysis, simulation and a graph-based shortest-path algorithm. The intent is firstly to propose a methodology for assessing the vulnerability of a UWDN using available everyday measurements and secondly to extent the methodology of the American Lifelines Alliance guidelines (ALA 2001) with localized knowledge on the performance and vulnerability of such networks. The ALA guidelines present procedures and fragility relationships that can be used to evaluate the probability of earthquake damage to water transmission systems and to make informed decisions on how to mitigate risks. However, the generic form of the pipe fragility curves obtained through the ALA method does not take into consideration a network's past performance and its effects when calculating the pipe repair rates due to seismic loading. Furthermore, in examining the vulnerability of a network one cannot but consider the vulnerability of the network's components as well as the topology of the network.