Structural performance study and improvement of Artemio Franchi Stadium in Florence

Artemio Franchi Stadium in Florence is the first world-famous work by Pier Luigi Nervi, and is celebrated as a masterpiece of the Rationalist movement. In view of this, it has been declared a work of cultural and historical interest by the Italian Ministry for Cultural Heritage and Activities, with several specific preservation restrictions on its most distinguishing structural and architectural elements. With a view to the recently planned restyling and modernization works, a diagnostic field survey and testing campaign, and a static and seismic performance assessment study of the Stadium were commissioned by the Municipality of Florence. Furthermore, a retrofit design respectful of the architectural preservation requirements was requested for its reinforced concrete structure. The contents of the diagnostic and assessment study, as well as of the retrofit design, are presented in this paper. The results of the structural analyses, carried out by means of a detailed finite element model calibrated on the field survey and testing data, show slightly unsafe static conditions in less than 10% of the beams and columns constituting the bleacher sloped frames, and diffused unsafe conditions under seismic action scaled at the Basic Design Earthquake level. The proposed retrofit solution consists in incorporating dissipative braces equipped with fluid viscous spring-dampers in several spans oriented in orthogonal direction to the bleacher frames, and installing fluid viscous pure dampers across the majority of the technical separation gaps between adjacent bleacher blocks, so as to prevent their mutual pounding. The results of the analyses in retrofitted conditions highlight a transition to safe conditions for more than half of the unsafe members, and a remarkable reduction of the demand/capacity ratios in the remaining members. Safe stress states can be reached in the latter by means of simple additional local strengthening interventions. This substantial improvement of seismic performance is achieved with a minimal visual and functional impact on the existing structures, as prescribed by the imposed preservation restrictions.