Seismic Fragility Evaluation of Water Pipelines Part 2: Framework for Practical Applications

Assessment and management of seismic risk of lifeline infrastructure has been receiving increased attention in recent years. Estimation of the seismic risk is imperative to minimize damage, service interruptions and loss of lives in the event of a seismic event and to plan for emergency recovery. Seismic risk is typically expressed in the form of seismic fragility curves to quantify seismic damage estimates as a function of a select seismicity parameter representing the level of seismic intensity. For pipelines, these fragility curves would depend on the joint types and characteristics, especially the axial, translational, and rotational flexibility. Considering the types of joints, pipelines could be classified into two major groups: segmented (flexible joints); and continuous (rigid joints). Segmented pipelines would include bell and spigot, flanged and coupled joints. Continuous pipelines typically have welded or fused joints. The most commonly available fragility formulations for pipelines are based on damage and repair data collected after past earthquakes on segmented pipelines, and are primarily empirical. Since continuous pipelines typically perform better in a seismic event, direct damage data available from past earthquakes on continuous pipelines is limited. Therefore, fragility formulations for continuous pipelines are typically developed using damage data collected on segmented pipelines and modified to reflect the seismic performance of continuous pipelines in practice. This provides a reasonable approach to estimate seismic risk and has been proposed by the American Lifeline Alliance (ALA) in 2001 for water pipelines. A disadvantage of this approach is that it fails to provide a mechanism to account for variability in design codes, regulations, requirements, construction and design practices, construction quality control, and variability in material types and joints. Analytical, numerical and expert elicitation approaches are available in literature and are implemented in the 2011 risk assessment guidelines for dams and in the 1983 Nuclear Regulatory Commission guidelines for nuclear facilities. A companion paper containing brief literature review of the available approaches to develop seismic fragility formulations for water pipelines was presented in the Pipelines 2012 conference. This paper presents a simple, yet flexible, framework for seismic fragility evaluation of water pipelines applicable for both segmented and continuous pipelines.