This is my last post that reflects upon the works of Pier Luigi Nervi. This post is based on a book chapter that a senior student Mariam Wahed and I wrote . You might also be interested in my other posts written about Nervi and his works in Italy and the United States of America. I apologise for the quality of some of the images for which I could not find the original ones but I hope you will enjoy finding out more about his designs for the UK and Kuwait.
Pier Luigi Nervi’s (1891-1979) career was characterized by a search for new competitive solutions based on static and construction principles. Nervi’s technical approach to design was developed early on when he was still a student in civil engineering at the University of Bologna, which was located in a city heavily influenced by a “poly technic culture” that emphasized a combination of theory and experimentation in building  . Nervi’s structural intuition was particularly shaped by the teachings of Professor Silvio Canevazzi (1852-1918), who taught him Meccanica applica ta alle Costruzioni. Canevazzi instilled in Nervi a solid understanding of structural statics, provided a foundation for developing a critical intuition about structural behavior and taught him to be critical of established construction principles. Under Canevazzi’s tutelage, Nervi learned to appreciate the correct relationship between form and structure. Figure 1, taken from Canevazzi’s course notes, demonstrates the ideal shape for a cantilever with uniform thickness and variable height under two types of loading applications. The concept of shaping a cantilever according to static principles guided the design of Nervi’s stadium projects. Nervi’s education was further influenced by the teachings of Professor Attilio Muggia (1861-1936), who Nervi worked for at the Societa Anonima di Costruzioni Cementizie immediately after graduating in July 1913. Working with one of Italy’s finest firms in reinforced concrete design proved to be an invaluable learning experience for Nervi and laid the groundwork for his future career.
Desiring the creative freedom to pursue his own projects, a 32 year-old Nervi set out in 1923 to form his own design-and-build firm called Soc. Ing. Nervi & Nebbiosi. Nervi’s partnership with Rodolfo Nebbiosi, the team’s financier and entrepreneur, would eventually dissolve in the process of constructing the Giovanni Berta Sports Stadium in Florence (1930-1932). Nervi thereafter formed a small family-run company with his cousin Giovanni Bartoli. Nervi’s new firm Soc. Ingg. Nervi & Bartoli would soon prove itself as a strong competitor in the construction industry . The decision to form his own design-and-build firm was crucial to Nervi’s success as a master builder: an engineer who designs efficiently with a builder’s mentality. Although Nervi has been criticized for «having mixed up the role of the engineer with that of the contractor »  , many of Nervi’s profound successes could only have been realized due to his complete design and construction control over his projects. Nervi’s early experiences «had formed in [him] a habit of searching for solutions that were intrinsically and constructionally the most economic, a habit which many succeeding competitions tenders (almost the totality of [his] projects) have only succeeded in strengthening» . Construction feasibility became one of Nervi’s primary design drivers, especially when designs were developed for the purposes of a design competition. Many of the competitions that Nervi entered required competitors to submit binding cost estimates with their designs. Achieving maximum economy became an important factor in the design process to improve the chances of being selected. Nervi recognized in his writings that this design-and-build approach was not easily transferrable abroad: «Many times I have refused to accept commissions […] in countries with whose possibilities of building I was not familiar in order to avoid running the risk of de signing shapes and structures that were impossible to build » .
We investigate the role that construction, structural intuition and knowledge played in the design evolution of four sports stadium designs. The Berta Stadium and the Olympic Flaminio Stadium (1957-1959, Rome) were two projects in Italy for which Nervi was in charge of the con struction as well as the design. We also consider two later stadia – Swindon Stadium, (1963-1966, UK) and the Kuwait Sports Center (1968-1969, Kuwait) – where that was not the case to examine how Nervi’s lack of construction oversight impacted the overall quality of his projects.
The “Giovanni Berta” Stadium, now the “Artemio Franchi” Florence Municipal Stadium, was Nervi’s first sports stadium design and is shown in figure 2. The stadium commission resulted from a design competition organized by the Municipal Council of Florence in July 1930. The competition required a 35 000 seat municipal stadium with a covered grandstand in reinforced concrete. Only two other stadiums existed in Italy at the time. The lack of design precedents posed an interesting challenge and stimulated Nervi’s creativity in the search for an innovative solution.
The design requirements for the stadium included a layout spanning the length of the playing field with a covered central stand and uncovered adjacent stands. The cantilever roof design for covering the grandstand was an additional design stipulation that improved spectator visibility of the field by eliminating supports, which required the use of reinforced concrete. Nervi’s firm Soc. Ing. Nervi & Nebbiosi received the commission in September 1930. The project expanded over subsequent years to include several external helical staircases along the perimeter of the stadium to provide access to new uncovered rectilinear stands and the addition of the Marathon Tower. The stadium has a global oval shape with one asymmetric side. The asymmetry is due to a straight 200m racetrack that was required in front of the covered grand stand. The playing field contained by the stadium is 78m wide and 204.6m long.
By using reinforced concrete, Nervi was able to devise an ingenious roof shape for transferring the loads of the cantilevered roof to the frame and foundations with the cheapest resulting design. Reinforced concrete contains steel reinforcement bars encased in concrete, which is composed of cement, water, sand, and coarse aggregate. Concrete is a strong material that can resist large compressive loads. However, the self-weight of the cantilever roof in the Berta design produces tension in the concrete due to bending, particularly at the fixed end of the cantilever arm. Since concrete is a brittle material and cannot bend easily, it tends to crack under tension. The reinforcement bars in the concrete are made of steel, a more ductile material capable of resisting the tensile forces due to bending.
The forked reinforced concrete beams in the Berta Stadium, shown in figure 3, are shaped specifically to take tension in the top chord (which the steel reinforcement in the concrete is capable of resisting) and compression in the bottom chord. This forked beam shape echoes the concept of correlation be tween form and structure, first taught to Nervi by his teacher Professor Silvio Canevazzi. Nervi also increased the cross-section at the base of the cantilever arm – where the bending moment is greatest – to help resist bending by increasing the member’s moment of inertia and thereby reducing the stresses due to bending. By cleverly working out the geometry and the mass of the cantilever roof and the frame, Nervi ensured that the foundations did not experience any uplift forces and thus avoided the need for costly tensile anchorages. The entire structure was cast in place.
In addition to the design itself, Nervi’s company was required to submit a binding cost estimate along with the design. In order for the design to be competitive it also needed to be economical, and a reduction in cost was primarily achieved by reducing the amount of material needed to construct the stadium. Nervi proudly states that to achieve material economy he followed the “static guide” of the structure and that it «gave suggestions which in themselves were aesthetically expressive when translated into drawings» .
The Flaminio Stadium, shown in figure 4, represents the zenith of Nervi’s career in stadium design. Many architects and engineers have written in praise of the stadium’s sleek and minimalist form. Nervi received the commission for the Flaminio Stadium as the result of a design competition in preparation for the Olympic Games to be held in Rome in 1961. When the project started Nervi was 64 years old and presented, his son Antonio, class of 1950, as his official partner for the first time. The competition had three strict requirements for the stadium ‘s design: i) the new structure should not exceed the perim eter of the former stadium site, ii) the stadium should house a certain number of facilities, including five gymnasia and a swimming pool, and iii) the stadium should accommodate seating for 45 000 spectators 7 (with a total stadium capacity of 55 000 visitors )8. The dimensions of the stadium’s ellipsoidal plan are 85.Sm by 153.3m . The short sides of the ellipsoid were designed for standing room, and one segment of the long side as a covered grandstand with individual seating. The design and construction of this stadium clearly shows how Nervi built on his 20 years of experimentation with ferro-cement and pre-fabrication to realize an inspirational work of structural engineering.
In his 1943 patent, Nervi had described a composite material of packed steel meshes (of 1mm diameter or less) saturated with mortar. The mortar recipe contained water, cement and sand but no gravel because gravel could not be pressed into the steel mesh with a trowel. Once the mortar was applied with a trowel on one side of the mesh and pressed through to the other side, it would be smoothed out. Nervi called this invention ‘ferro- cement’. Ferro-cement elements could be very thin, strong, flexible and inexpensive. Nervi further envisaged how a structure could be broken down into light and small identical pieces. On site, these elements with protruding bars could be prepared in a series of reusable molds. Once cured, these pieces could easily be lifted and transported by light lifting equipment and assembled by low-skilled workers on scaffolding. A strong connection could then be cast between the pieces to make the system monolithic. In 1939, Nervi patented this technique and called it ‘structural prefabrication’. This artisanal construction technique is quite different from our contemporary definition of prefabrication and would prove to be perfect for a traditional building site in a post-war country that lacked skilled labor and machinery,
such as the economic context of the 1960’s Rome Olympic infrastructure of the Flaminio Stadium.
The Flaminio Stadium has three structural systems: the foundations, the ground level structure with incorporated grandstand with 45 000 seats and the corrugated cantilever roof, which arises out of the seating on only one long side of the stadium. We focus on the design and construction of the grandstand’s cantilevering roof, which consists of a series of juxtaposed V-beams connected monolithically. The roof region between the exterior and interior columns is referred to as the backspan and the overhang is referred to as the cantilever. Four V-shaped profile beams (these were Nervi’s patented “wave elements”) are monolithically joined to form a wide structural corrugated section. This section connects to the grandstand at two points. At the exterior of the stadium, the corrugated section rests on concrete supports. Halfway along the length of the corrugated section it is further supported by inclined steel tubes, filled with concrete, that arise from the seating. The interior roof support and the exterior roof support are connected with a square steel section, embedded in reinforced concrete. In order to not obscure the sightlines, Nervi positioned the interior roof support as far back as possible, thereby creating a large cantilever to cover the grandstand. To reduce the effects (high stresses in the concrete and possibly the need for tensile foundations) of an unavoidably large bending moment, Nervi took several rational measures that had visual implications. First, he introduced high-strength/low-density ferro-cement for the cantilever and normal weight/normal strength concrete for the backspan to balance he loads between those two parts. Second, he shaped the longitudinal profile of the roof section in accordance with the bending moment diagram as he had realized in the Florence Municipal design 30 years earlier. Third, he reduced the permanent loads on the cantilever even further by introducing five circular apertures in each beam web in the cantilever. And finally, as he had pioneered in the Berta Stadium, Nervi designed the cantilever roof such that the foundations only experience compressive loads.
Six factors played in favor of the economic construction of this Olympic stadium: (i) competition design, (ii) design-and-build company with a substantial track record, (iii) pre-fabrication and lightweight hoisting equipment, (iv) ferro-cement wave elements, (v) identical in-situ frames for covered and uncovered grandstands, and (vi) low cost foundations. Nervi put in a bid for the stadium for $1 280 000 or $28.44/seat. Other bids came in between $1 900 000 to over $3 000 000. The jury of the design competition evaluated the appearance of a stadium in addition to its performance, constructability, and particularly cost. In general, design competitions ensure a high level of engineering, but in this case the competition also fostered inspiration in structural design. Nervi did not devise the Flaminio Stadium solely from the laws of statics or from any belief that efficiency alone would lead to an appropriate structure. Instead, Nervi acted as an engineer and master builder. With his 13-man office, he generated this design driven by his novel ferro-cement material, and only he knew how to build it using prefabrication. With the congested urban fabric of Rome as a construction site, Nervi envisaged the decomposition of the stadium roof into separate elements. The roof beams were prepared directly on site while the identical rigid frames were cast in-situ, and therefore they had to be light and small enough to be lifted into place by lightweight hoisting cranes, which were the only widely available machinery in post-WWII Italy. The beams’ profiles also had to provide sufficient bending stiffness to bear the handling and erection stresses. Once the beams were placed on the scaffolding, ribs were cast in situ to connect the wavy elements and establish a monolithic corrugated section. For this cantilevering thin roof to be stiff enough during its erection and service life, it had to resist force by form. The “wave elements” patented in 1948 and extensively used in the roof of the Flaminio Stadium gave the roof beams a higher moment of inertia and thus increased bending stiffness and lowered bending stresses. Nervi arranged the roof topology and elements such that the cantilevering part of the cast-in-place rigid frame supports showed little stress variation between the covered and uncovered grandstands. As a result, all grandstands were designed and realized in an identical manner, which further reduced construction cost. Once the frames were cast in situ and had cured, integrated pre-cast beam/steps were placed over the supports.
The success of the Flaminio Stadium cemented Nervi’s reputation as an accomplished structural designer both domestically and internationally. Nervi’s international career subsequently grew as he received more international commissions, although many of them were not executed. One of the international commissions Nervi received four years after the completion of the Flaminio Stadium was a project for a covered sports grandstand located in Swindon, UK. The brief stated how the 104m long and 27m wide grandstand was to seat 5970 spectators, accommodate another 4000 standing spectators and hold restroom and refreshment facilities. There is little mention of the Swindon project outside of the chronological summary of Nervi’s career, which reports only that the project was not executed. The cost of the project is not documented.
The concept design of the Swindon Stadium, presented in figure 5, did not comprise a complete stadium program as the Berta and Flaminio stadiums did. The Swindon grandstand was planned as an addition to an existing stadium site that already contained two stands. Nervi designed two solutions to meet the design brief.
The solution we discuss here has three structural systems: the foundations, the grandstand and the cantilever roof, as shown in figure 6. The grandstand consists of 13 reinforced concrete frames, cast in situ and connected by a continuous 15cm reinforced concrete slab prepared in special forms to preserve the board marks on the underside of the slab. The cantilever roof arises out of the grandstand and is supported internally by steel inclined struts and rests on the edge of the top of the grandstand. These two cantilever roof supports are connected with a reinforced concrete tie. Nervi detailed the longitudinal form of the cantilevering roof such that it reflects the increasing bending action towards the internal steel strut support. This correlation of form and force in a large cantilevering roof is a recurring theme in the Berta, Flaminio and Swindon stadiums. Figure 7 shows the stocky concrete frame columns, which feature a unique form composed of intersecting planes. The inclination of the stocky columns, seen in the cross-sectional view of the grandstand, enhances the aesthetic quality of the structure but introduces a horizontal thrust at ground level. To avoid that the foundations take this thrust, Nervi placed a reinforced concrete tie between the ends of the frame columns. For this tie not to be obtrusive and not interfere with the space beneath the columns, it would have been placed beneath the finished floor of the hall located between the frame columns. As discovered in the Berta Stadium and further refined in the Flaminio Stadium, Nervi designed the topology and geometry of the Swindon Stadium so that the foundations only experienced compressive loads and again avoided the need for costly tensile anchorages. Although the Swindon Stadium was not constructed, it is nonetheless an interesting project to examine in the context of Nervi’s design evolution. The Swindon design contains significant spatial similarities to the Flaminio Stadium. Flaminio preceded the concept design of the Swindon Stadium by approximately three years. In the meantime Nervi had written a preface to the book The Works of Pier Luigi Nervi stating that he «was always anxious to arrive at independent decision free from existing aesthetic theories as well as from solutions [he] or others had already discovered». This contrast in design intent and outcome marks the Swindon Stadium as an interesting case study to understand Nervi’s design evolution.
In January 1969 the Government of Kuwait delivered an invitation to Studio Nervi, a design studio Nervi set up after 1960 with his three sons Antonio, Vittorio and Mario, to submit a proposal for a new Kuwait Sports Center. The design brief stated that the sports center must hold a multi-purpose stadium, cafeteria, training areas, parking for 10 000 cars and landscape design for the complex. The stadium had to have a main arena that could accommodate between 40 000 and 60 000 seats and a separate arena reserved for particular sports that could accommodate 7 000 to 10 000 seats. A model of Studio Nervi’s proposal is shown in figure 8. The main arena structure consists of two components that function entirely separately from one another: (i) a reinforced concrete grandstand and (ii) a 300m-diameter aluminum dome to cover the grandstand and enable year-round use. The dome is shown in figure 9.
The first component – the primary contender for the design competition – is the 30m tall and 36m wide grandstand frame. The reinforced concrete frames vary in size and are arranged and connected to create a circular external perimeter to match the dome perimeter while containing an oval playing field. This configuration provides the greatest visibility while accommodating the largest possible number of spectators. The grandstand frame features a large overhang intended to hold the upper tiers of seating. The detailing of the shape of this overhang is also found in the Flaminio and Swindon stadia designs: as the bending of this overhang increases towards the support, the depth of the overhang is increased and the forces are thereby reduced.
The second component, a separate transparent dome, connects to independent concrete buttresses at ground level. This aluminum skeletal dome, clad with a transparent material, was included in the concept design as a separate system that could be built at a later date if desired. By making the dome separate, and thus optional, Nervi’s team emphasized that they did not want he dome to detract from the primary contender, the grandstand frame itself, as the competitive element of their proposal. The primary concern that led to the inclusion of the dome was the high intensity of solar rays expected throughout the summer months. The dome could be used to provide environmental control over the stadium. Figure 10 presents a cross-section of the grandstand and dome.
At this stage Nervi had designed and constructed a number of hemispherical concrete and ferro-cement domes – the largest being the 100m diameter Large Sports Palace (1960, Rome). The Kuwait dome was not designed and developed by Studio Nervi but by a UK-based engineering design office Vickers, which consulted for Studio Nervi on the project. This aluminum triodetic dome differs from Nervi’s previous domes in (i) span (300m versus 100m) and (ii) material (aluminum versus ferro-cement and reinforced concrete). Since little literature remains about the design of the Kuwait aluminum dome, we can speculate about reasons for this departure from Nervi’s signature domes. At spans much larger than 100m, reinforced concrete and ferro-cement domes were not considered to be structurally feasible: the available cementitious materials did not have sufficient strength to allow for the construction of economical domes at much larger spans. As a reference, the largest prestressed concrete dome from that period, the Belgrade Fair Hall (1959, Serbia), had a diameter of 109m. Vickers might have preferred aluminum as their material of choice due to its superior strength-to-weight ratio, which is 41 times that of concrete (214 kNm/kg compared to 5.22 kNm/kg). The cost of the proposed stadium came down to $2 570 per seat whereas the Berta Stadium cost 99.89% less at $2.90 per seat approximately 40 years earlier in Italy. Although this comparison is not entirely justified due to differences in economic context, it does suggest the question whether Studio Nervi delivered an economic and efficient proposal.
The Kuwait Stadium is similar to the Swindon Stadium in that it was never constructed, in this case because it did not win the design competition. Three other well-established international participants were invited to submit designs: Kenzo Tange in collaboration with Frei Otto, Felix Candela, and Lloyd, Morgan and Jones. Kenzo Tange and Frei Otto submitted the winning design – a cable-net roof made of steel to link the entire complex together. The immense difference between the design of the Kuwait Stadium and its predecessors makes it an interesting case study in the evolution of Nervi’s sports stadium design. It is curious that Nervi, who maintained a high degree of control over design and construction aspects of the majority of his earlier projects, would solicit or accept such a significant design intervention as the aluminum skeletal dome proposed by Vickers. The lack of physical integration – a fundamental feature of Nervi’s most successful sports stadia – between the aluminum dome and reinforced concrete grandstand signifies a pronounced shift in his design evolution. Nervi’s relinquishment of control over the building process and the incorporation of a dome designed by external consultants are two potential explanations for Nervi’s declining success with his later international stadium designs. These elements expose how constraints, such as operating in a context outside of Italy and cooperation with external design consultants, might have impacted the quality of Nervi’s later designs.
Nervi’s career flourished during a time of great experimentation in new building materials, particularly reinforced concrete. Nervi’s ability to experiment with radically new concrete forms is evident in the design of the Berta and Flaminio stadiums. The lack of knowledge about the exact nature and behavior of reinforced concrete encouraged trial and error processes that allowed designers to attempt daring designs. At the time, all reinforced concrete design would have classified by necessity as daring because little was known about its long-term behavior. Nervi’s personal knowledge of the material behavior of reinforced concrete was gained primarily through what he witnessed over time in his own projects, and this learning process is evident in his writings.
Over the course of Nervi’s career this experimental phase slowly came to a halt as more empirical knowledge concerning the behavior of reinforced concrete became available and more restrictive building codes were developed. It is difficult to find any mention of code limits for deflections, for example, in any of Nervi’s early writings, whereas the specifications for the Kuwait dome contain numerous references to code factors and limits  Nervi required rigid control over his projects in order to accomplish his visions in addition to general flexibility within his work environment for experimentation. In Italy, socioeconomic constraints during the time of Nervi’s early career drove the need for creative and inexpensive solutions, yet the building atmosphere at the time was still experimental and flexible enough to nurture Nervi’s creative, risky, and unprecedented design process.
Later in Nervi’s career, international constraints hindered Nervi’s design process by giving flexibility where he had become accustomed to rigidity and by being inflexible in ways that were relatively free when Nervi worked in Italy. Domestic building and economic constraints, set by the social-political context of inter and post helium Italy, forced Nervi’s creativity to blossom, and these types of material and economic constraints did not seem as pressing in international design settings (notably missing in the context of the Kuwait Stadium design). A strange paradox is evident in the success Nervi experienced as a result of material and economic constraints domestically that did not exist in international contexts and these factors cannot be overlooked. The proliferation of material technologies and the increase in mathematical theories available to predict the behavior of new materials in Nervi’s late career indicated a wider process of transformation in the industry of civil engineering. The nature of the industry today has rendered the concept of a master builder infeasible. The end of Nervi’s career demonstrates the need for a new approach to contemporary engineering methods. The nature of the design industry has undergone great changes that continue to accelerate with material and technological innovations and increasingly require specialized knowledge . A better framework for collaboration is needed if the aesthetic quality and structural truth, for which Nervi is so highly praised,
is to be preserved in contemporary large-scale structures.
The original book chapter is
S. Adriaenssens and M. Wahed, ‘A critical appraisal of Nervi’s Berta, Flaminio, Swindon and Kuwait stadia’, in Gli stadi per il calico, 1st ed., M. Antonucci and A. Trentin, Ed. Bologna: Bologna University Press, 2015.
1 ANTONUCCI 2009, p. 3.
2 ADRIAENSSENS, BILLINGTON 2013, p. 170.
3 The Works of Pier Luigi Nervi 1957, p.11.
4 NERVI 1965a, p. 24.
7 NERVI 1956, p. 20.
8 NERVI 1963, p. 84.