A case study of modern heritage building: base isolation seismic retrofit for preservation of its architectural distinguishing features

Several Italian buildings designed by eminent architects and structural engineers in the second half of the 20th century are now included in modern heritage listings. At the same time, as they were designed before the issue of coordinate national Technical Standards, often require important structural rehabilitation interventions. One of the most representative case studies of that period in Florence, i.e. the building now housing the Automobile Club Headquarter and a B&B Hotel, is examined in this paper. A seismic assessment analysis carried out on the structure highlighted strength deficiencies in several members and potentially severe pounding conditions between the two constituting wings of the building, separated by a narrow technical gap. In order to improve the seismic performance without altering the architectural appearance of the building, characterized by large windows in the façades, free internal spaces and elegant proportions of the main structural members, a base isolation retrofit hypothesis is proposed. A substantial seismic improvement is obtained in rehabilitated conditions, as assessed by the achievement of safe stress states for all members up to the basic design normative earthquake level, as well as of maximum relative lateral displacements of the two wings constrained below the technical gap width.