Notes on the structural value of the Florence Stadium

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The cast-in-place reinforced concrete structural organism of the municipal stadium in Florence was conceived by Pier Luigi Nervi on the basis of his important experience in works designed and built with the same material, conducted since 1913 with the Società Anonima Costruzioni Cementizie. In the 1920s,  P.L. Nervi became the protagonist, as designer and builder with Nervi & Nebbiosi, of industrial artefacts, building complexes and infrastructures characterised by load-bearing structures in reinforced concrete (G. Guanci, Costruzioni e sperimentazione. L'attività del giovane Pier Luigi Nervi a Prato, 2008). This evolution, under Nervi's technical leadership, saw reinforced concrete take on new forms, so interesting that it was able to free itself from the wall enclosures within which it had until then been systematically relegated.

The different types of frames used to support the stadium's bleachers reveal Nervi's ability to adapt the structural scheme to planimetric requirements, resorting to innovative solutions with variable sections and curved shapes.

The famous frames of the central covered grandstand admirably fulfil the task of absorbing the stresses transmitted by the brackets supporting the 22 meters span of the canopy. A resemblance to this geometry and design can be found in Maillart’s Tavanasa Bridge of 1905. (C. Greco, Pier Luigi Nervi. Dai primi brevetti al Palazzo delle Esposizioni di Torino, 1917-1948, 2008); a comparison from which the dynamism of Nervi's solution appears even more evident due to the absence of its symmetrical counterpart. In addition to the formal success of this system, there is also the fulfilment of technical and functional requirements, such as the intradosed solution to minimise the effects induced by thermal variations and the minimum interference with the spectators' visibility (P.L. Nervi, Considerazioni tecniche e costruttive sulle gradinate e pensiline per stadiums, Casabella, vol. 12, 1933).

The spiral staircases also represent an original innovation in the use of reinforced concrete. In 1932 Nervi could not yet count on well-established calculation solutions and for the design of the helicoidal beam (whose strong reinforcement is composed of special 'X' shaped f20 brackets), from which the tapered cantilever slab departs, he relied on the mastery he had acquired through previous experience in the design of curved slanted beams. It is interesting to note that Zanaboni, in 1939, in justifying his proposal for a generally valid analytical solution for helical beams (O. Zanaboni, Travi ad elica e travi ad asse circolare orizzontale, Il cemento armato, vol. 2, 1939) refers to the instances coming from "today's architectural trends".

Finally, a mention should be made of the Marathon Tower, which synthesizes Nervi's interpretation of modernity in its 40 meters of vertical development. Within the tower, Nervi experimented with different wall thickness and forms demonstrating his great ability to work with this material: from hollow sections at the base of 45 cm thick concrete wall ornated with an elegant, cantilevered terrace to the top section of 10 cm thick concrete wall. Without any doubt, Nervi greatly contributed to the development of the modern architectural movement becoming a pioneer in the use of reinforced concrete. His legacy should be protected and celebrated for future generations to learn and be inspired by our heritage.

Prof. Francesco Romeo

Dipartimento di ingegneria strutturale e geotecnica
SAPIENZA Università di Roma