Italian Workshop on 

Shell and Spatial Structures

Turin exhibition Center 

Erica Lenticchia, Rosario Ceravolo, Amedeo Manuello (DISEG, Politecnico di Torino, Torino, Italy)

The Turin Exhibition Center was conceived in the years immediately following World War II as a public exhibition space to host primarily the annual Automobile Show. The Center houses some iconic shell and spatial structural concrete architectures by Pier Luigi Nervi and Riccardo Morandi. They consist in three grand exhibition pavilions perfectly representing the structural art of these famous protagonists of contemporary engineering and architecture.

Nervi Halls in Turin exhibition Center 

The main Hall B and the adjacent smaller Hall C of the Exhibition Center were designed and constructed by Nervi in 1947-48 and 1950, respectively. Hall B, built soon after the War, represented the first chance for Nervi to combine in a large scale project his personal technique of ferrocement with an extensive use of prefabrication. It is also the first project that Nervi undertook in the Turin context, including the important client represented by the FIAT motor company. Shaped like a cathedral, Hall B consists of a wide nave, measuring 95 m in width and 110 m in length, covered by a magnificent undulated cylindrical vault, and of an apse with a ribbed hemispherical dome. The vault, whose center line approaches the funicular of permanent loads, is formed by the union, for each arch, of 15 thin prefabricated undulated ferrocement elements of approximately 4.5 m weighing 1500 kg each. Their ends are stiffened by diaphragms leaving an empty space of 4 cm filled with cement mortar. Elegant fans connect each group of three arches of the undulated vault to the stylish inclined columns. Prefabricated ferrocement tiles, connected by reinforced concrete cast on site in the lateral ribs and on their tops, are used for the hemispherical dome of the apse. Nervi also adopted this last technique for the extremely elegant ribbed vault of Hall C. In this case, the ferrocement tiles are shaped like lozenges. The ribbed vault is supported by sculptured slanted arches.

Hall B

Hall B 

Hall C

Hall B

Hall B was inaugurated on 15 September 1948. Conceived like a cathedral, the hall consists of a nave covered by an undulated thin vault, and of an apse with a ribbed hemispherical dome. Figure 2 shows a plan of the complex, with the Hall B coloured in red (on the left), and a detail of the ribbed apse (on the right). In its first configuration, Hall B measured 96 metres in width and 110 metres in length. Between 1952-1954, Hall B was enlarged by five spans in order to move the façade on the street. Hall B reached the length of 155 metres. For the vault, the architect studied special wave-like elements in prefabricated ferrocement. The centre line of the arched vault of Hall B, approaches the funicular of permanent loads, and is formed by the union for each arch of the 13 prefabricated thin ferrocement undulated elements of approximately 4.5 m weighing 1500 kg each. Their ends are stiffened by diaphragms that leave an empty space of 4 cm to be filled with cement mortar. These waved elements were patented in August 1948 just before the inauguration of Hall B (Patent n. 445781). The idea was to shape the prefab elements using a geometry that would guarantee a high moment of inertia with a minimum amount of material. The problem of obtaining a true static collaboration of the precast elements was resolved by casting in place a concrete rib on both the top and the bottom of the undulations. These ribs were large enough to resist the principal stresses, while the sides of the precast elements assured the static tie between the ribs and re-established the monolithic nature of the whole (Nervi, 1948) (Nervi, 1965). 

As it has emerged from the preliminary knowledge phase, Hall B is a very complex building (see 3-D representation). The building is composed by a large number of elements, 390 pre-casted ferrocement pans in seven different depths, slanted pillars and innovative solutions like the fanned elements, that Nervi designed to condense loads from lightweight, folded plate roofs into the piers. 

Sections of Hall B 

Structural elements of Hall B 

Hall C

In 1949 the directors of the Turin Exhibition decided to enlarge the building by adding another hall, Salone C. They again entrusted the design to Nervi, who had to face two main problems. Firstly, the restricted time allowed to build the Hall with a size of 65x50 meters. After many trials in which Nervi also tried a cross vault, he adopted a vaulted roof completed by a perimetric slab of about 10 meters in length.  This solution permitted the use of the structural prefabrication already employed for the half dome of Hall B (Nervi, 1965); The picture below shows the Hall C during its construction in 1950, with the assembly of the diamond elements in ferrocement on the vault centring already used in the half-dome of Hall B. For the perimetral area Nervi adopted a new system of undulated ferrocement beams, which he had contemplated many times but had never actually used before. Immediately after the completion of the pavilion, Nervi registered patent no. 465636 in Rome on 19 May 1950. This patent, together with the patent no. 445781 registered on August 26th, 1948, was gradually developed until their final configuration with the construction of Turin Exhibition Centre’s Halls. These patents would be adopted by Pier Luigi Nervi in the following decades until becoming a typical feature of the globally recognized Nervi’s style. The large vault of the Hall rests on four arches with a plane inclined according to the resultant of the thrust of the vault and the weight of the perimetral roof system. The horizontal rigidity of the roof system, appropriately reinforced by two-way reinforcing in the upper slab, was conceived to redistribute and balance the thrust of the vault.  Nervi explains that the building was conceived as a static system and “the vault was calculated both as a thin membrane vault, and as a vault formed by elemental arches each resistant on their own.

Plan and section of Hall C (drawing from Rassegna tecnica della Società degli ingegneri e architetti in Torino) 

Hall C under construction in 1950 (Archivio MAXXI Roma, Fondo Nervi) 

Interior of Hall C today 

The underground Pavilion by Riccardo Morandi

The underground Pavilion (also known as Pavilion V), designed by Morandi in 1958 as an expansion of the Exhibition Center dedicated to hosting the industrial vehicle section of the Turin Automobile Show, is one of his most artistic buildings. At the same time it is one of his most complex structural artifacts. The Pavilion, largely inspired by the underground Lourdes Cathedral designed in those years by Pierre Vago and Eugène Freyssinet, consists of a single wide space, 69 m in width and 151 m in length, located 8 m below ground level. The general static scheme corresponds to the schemes frequently used by Morandi in bridges and overpasses, consisting in post‒tensioned beams on two inclined supports, with two cantilevering side spans subsequently anchored by post‒tensioned tendons at their ends, exerting a balancing effect on the bending moments in the main span. Differently from these usual schemes, in the Pavilion of the Turin Exhibition Center the main post‒tensioned ribs are not parallel beams, but are diagonally directed and reciprocally interconnected in order to obtain a spatial structure offering a high overall rigidity and lateral stability, and to contrast the instability of the very thin webs (16 cm) of the main ribs. In addition, the post‒tensioned ties at the ends of the side spans are not inclined tendons anchored on the foundations of the main inclined supports, as in the usual schemes for bridges and overpasses by Morandi, but are short ties embedded in prestressed concrete prismatic elements, whose tension forces are balanced by the lateral retaining walls and by the load of the soil acting on their foundations.

Underground Pavilion 

Underground Pavilion 

Structural scheme and cables layout of the main post-tensioned ribs 

References

Ceravolo, R.; Chiorino, C.; Chiorino, M. A.; Isola, A.; Isola, S.; Lenticchia, E.; Luciani, L.; Moneo, R. (2018) Preservation and rehabilitation strategies for the shell and spatial structures by Nervi and Morandi of Turin Exhibition Center. In: IASS Annual Symposium 2018. Creativity in Structural Design. Boston, Massachussetts (USA), 16-20 July, 2018. 

Lenticchia, E.; Ceravolo, R.; Chiorino, C. (2017). Damage scenario-driven strategies for the seismic monitoring of XX century spatial structures with application to Pier Luigi Nervi’s Turin Exhibition Centre. In: Engineering Structures, vol. 137, pp. 256-267. - ISSN 0141-0296.

Lenticchia, E.; Ceravolo, R.; Antonaci, P. (2018). Sensor Placement Strategies for the Seismic Monitoring of Complex Vaulted Structures of the Modern Architectural Heritage. In: Shock and Vibration, 2018. https://doi.org/10.1155/2018/3739690.

Nervi, P., (1950). La struttura portante del nuovo Salone del Palazzo di Torino Esposizioni. Rassegna tecnica della Società degli ingegneri e architetti in Torino, January-March. 

Nervi, P., (1965). Aesthetics and Technology in Building. The Charles Eliot Norton Lectures a cura di s.l.:Harvard University Press.

Nervi, P. L., (1948-53). Palazzo delle Esposizioni - Torino (original projects). Centro Studi e Archivio della Comunicazione (CSAC) , Parma.

Nervi, P. L., (1948). Le strutture portanti del Palazzo per le Esposizioni al Valentino. Rassegna tecnica della Società degli ingegneri e architetti in Torino, July. Issue 7.