Seismic risk evaluation of water elevated tanks

Maintaining the functionality of the water lifeline networks is a primary objective, not only in periods of ordinary management but also during emergencies. This paper presents the seismic risk analysis of Reinforced Concrete (RC) water elevated tanks belonging to the lifeline network managed by AcqueVenete S.p.A. In particular, the first results for five water elevated tanks located in low seismicity areas of Polesine, Italy, were presented. These structures are part of a database collecting about 100 water elevated tanks of sixteen different structural typologies, designed in the absence of specific seismic design rules. The analyses carried out made use of a probabilistic approach starting from a set of pushover analyses, from which inelastic Single Degree of Freedom (SDOF) systems, one for each structure, were defined. These SDOF systems were then subjected to nonlinear dynamic analyses for a number of scaled accelerograms, according with the Multiple Stripe Analysis technique. The fragility curves obtained, combined with the hazard curves, provided the mean annual frequency of the particular damage state considered (e.g. collapse). From here, it was possible to quantify for each structure the average annual loss index by integrating the expected annual loss curve.