Seismic analysis and retrofit of the oldest R/C elevated water tank in Florence

The seismic performance of an elevated water tower with reinforced concrete staging structure—the oldest one in Florence—is analyzed in this paper. The tower, erected in 1905, is a major achievement by engineer Attilio Muggia, an Italian pioneer of reinforced concrete, and is now classified as modern heritage architecture. The structure is characterized by an atypical bracing layout, with all braces rising from the bottom left corner to the upper right corner at each bay of the three upper staging levels, and no braces on the first level. The time-history assessment study, carried out by a detailed finite element simulation of the water–tank dynamic interaction, shows unsafe response conditions of the first level columns starting from seismic action scaled at the basic design earthquake level. Based on these data, two retrofit measures are proposed, consisting either in integrating the existing reinforced concrete braces of the staging skeleton with additional steel braces, or incorporating a seismic isolation system, and namely a set of double curved sliders on top of the underground columns. From an architectural viewpoint, the former strategy meets the requirement of leaving the original staging elements exposed, whereas the latter causes no intrusion in the superstructure. The design criteria and technical installation details of the two systems are illustrated, along with the results of the seismic performance assessment analyses in both rehabilitated conditions, including the cost estimation of the interventions.