Enhanced seismic retrofit of a reinforced concrete building of architectural interest

Modern heritage buildings designed in the 1950s and 1960s often feature poor seismic performance capacities and may require significant retrofit interventions. A representative case study in Florence, i.e., the edifice housing the Automobile Club Headquarters, is examined here. The building was designed in 1959 with an articulated reinforced concrete structure and presents some enterprising solutions for the time, including suspended floors accommodating large glazed curtain wall façades in the main halls. The original design documentation was collected with accurate record research and checked with detailed on-site surveys. Based on the information gained on the structural system by this preliminary investigation, a time-history assessment analysis was carried out. Remarkable strength deficiencies in most members and severe pounding conditions between the two constituting wings, which are separated by a narrow technical gap, were found. As a result, a base isolation retrofit hypothesis is proposed in order to improve the seismic response capacities of the building without altering its elegant architectural appearance, being characterized by large free internal spaces and well-balanced proportions of the main structural members. A substantial performance improvement is obtained thanks to this rehabilitation strategy, as assessed by the achievement of non-pounding response conditions and safe stress states for all members up to the maximum considered normative earthquake level. Furthermore, the very low peak inter-storey drifts evaluated in retrofitted conditions help in preventing damage to the glazed façades and the remaining drift-sensitive non-structural components.