Seismic risk assessment and mitigation of water supply systems

This paper describes a process for seismic risk assessment and identification of critical links of water supply systems subjected to earthquakes. Probabilistic performance of water supply systems is reflected by the system serviceability index (SSI), damage consequence index (DCI), and upgrade benefit index (UBI). The process is illustrated using a hypothetical water supply system subjected to a seismic damage scenario, where direct Monte Carlo simulation is used for estimating the performance indices. It is shown that probabilistic characteristics of SSI can be attributed to system characteristics (e.g., demand distribution pattern) of the water supply system. UBI is shown to be the primary index in seismic mitigation, and critical links are pipes with relatively large UBI values. It is recognized that the values of UBI corresponding to different upgrade scenarios of pipes can be estimated using conditional samples from a single run of direct Monte Carlo simulation instead of repeated runs. The concept of efficient frontier is employed to identify the system critical links. It is found that, a group of links that have the largest UBI individually do not necessarily have the largest group UBI, nor are they necessarily the group of critical links.