Seismic assessment and retrofit of two heritage-listed R/C elevated water storage tanks

A seismic assessment and advanced retrofit study on two heritage-listed reinforced concrete (R/C) elevated water storage tanks is presented in this paper. The two structures were built between the late 1920s and the early 1930s as water suppliers for a coal power plant in Santa Maria Novella Station in Florence, and are still in service. The first, taller tank has a R/C frame supporting structure and is currently used as water supplier for trains and platform services. The second, shorter tank, with a shaft-shell supporting structure, is used as water tower for the Station. The dynamic behaviour of the fluid is simulated by means of a classical convective and impulsive mass model, for which a discrete three-dimensional schematization is originally implemented in the finite element analysis. The time-history assessment enquiry highlights numerical collapse of the frame structure in the taller tank, and unsafe tensile stress states in a large portion of the shaft structure of the shorter one, under seismic action scaled at the maximum considered earthquake level. Based on these results, two retrofit hypotheses are proposed, and namely a dissipative bracing system incorporating pressurized fluid viscous spring-dampers, for the taller tank, and a base isolation system including double curved surface sliders, for the shorter one. The mechanical parameters, design criteria and technical implementation details of the two rehabilitation strategies are illustrated. The verification time-history analyses in protected conditions show that a substantial enhancement of the seismic response capacities of both structures is attained as compared to their original configurations, with little architectural intrusion, quick installation works and competitive costs.