Definition of seismic performances and fragility curves of unanchored cylindrical steel legged tanks used in wine making and storage

The introduction of stainless-steel legged tanks is rather recent, and their use increased in the last decades in exponential way, especially in food industry and agricultural applications since they proved to be simple to prefabricate and transport, easy to clean and chemically inert. Despite their worldwide diffusion also in high seismicity areas, most of them were not designed with earthquake-based criteria as emerged by the catastrophic consequences and heavy losses observed, even recently, after several major earthquakes. By means of incremental dynamic analyses on the finite element models of 140 winemaking and storage legged tanks, the present paper, evaluates the main features of the dynamic response and for each vessel provides the lognormal cumulative fragility functions, for three different limit states of each vessel. Then, for each limit state, by means of nonlinear regression analyses, the median and the dispersion parameters of the best fitting lognormal function of every tank were statistically elaborated in order to define the response surfaces of the parameters. The response surfaces, provided for 3-, 4- and 5-leg unanchored tanks, are defined on the basis of few geometrical tank data. The analytical expressions provided in the paper, represent a practical and useful tool to directly calculate the fragilities of legged vessel. These, obviously, will allow the fast assessment of the seismic vulnerability of the tanks in agricultural facilities located in seismic prone areas.