Abstract
This study investigates a redundancy index RE in order to discuss the reserve capacity of a complex lifeline system. This index RE is defined by an information entropy of damage modes conditioned on damage occurrence. First, mathematical relationship between RE and other index RZ proposed by Ziha is established, and it is clarified that RE is more sensitive to the probability of disconnectivity, and therefore more useful than RZ, though they are linearly related. A model for a water supply network is studied for the reserve capacity by using RE.
