Skill: Inflatable Concrete Domes
Frustrated by both expensive and labour-intensive methods of moulding concrete with steel or wooden formwork, Italian architect Dante Bini pioneered ‘air structures’: gigantic balloons that could be covered with a thin layer of concrete then inflated to form domes in a matter of hours
On the afternoon of 14 July 1964, a young reporter was travelling on the road that connects Bologna to a town named Crespellano. He had been assigned to write an article about a local beauty contest. Towards midnight, driving the same route on his way back, he could not help spotting a ‘sinister’ grey mass, a globular form nearly 20 feet high, illuminated by his headlights. It had certainly not been there on his trip out that afternoon.
His curiosity was such that he stopped the car and cautiously approached ‘that thing’, which in addition to a sound was also giving off a fine mist resulting from condensation. He touched the surface of the structure and realised that it was warm concrete, in the process of setting. Having first ruled out the idea that Martians had landed, he spotted the light of a nearby farmhouse window and rapped on the windowpane. When he asked the farmer what had happened, the man replied in dialect: ‘An architect from Bologna came, made this big ball, then went home!’
Dante Bini has dedicated his professional life to the development of what he calls ‘automated construction technologies’. In 1965, in Bologna, Italy he successfully constructed a 12-metre-diameter, 6-metre-high hemispherical concrete shell structure in three hours, using the unique pneumatic formwork of a giant low-pressure balloon. This first prototype did, however, have some teething problems, particularly the uneven distribution of the wet concrete caused by an unpredictable (asymmetric) inflation. Improvements were made, and in 1967 at Columbia University, New York, Bini demonstrated in a few hours the construction of another large-scale Binishell.
For this first US prototype, Bini used a complex web of helical ‘springs’ with steel reinforcement bars threaded through their middle, which allowed for a geometrically controlled inflation and thus uniform concrete distribution of the shell structure. For this demonstration and subsequent Binishell structures, an additional external membrane was also used, allowing for the vibration and compaction of the concrete, post inflation. Over 1,500 Binishells were constructed throughout the world between 1970 and 1990, with diameters between 12 and 36 metres and with a varying elliptical section.
In chapter two of Air Structures: A Survey,1 Dante Bini is credited for his work with inflated formwork. This report, co-authored by Cedric Price and Frank Newby, remains an impressively comprehensive survey on the possibilities of using air for construction. As Cedric Price said in a lecture: ‘I like air structures because the major structural element you can breathe and it smells of violets and you can’t draw it.’2
Dante Bini, while enjoying the odd ‘top drawer’ artefact of his own architecture, such as a Sardinian holiday house for film director Michelangelo Antonioni and actress Monica Vitti, was demonstrably more interested in ‘construction automation’ and inventing new lightweight processes by which space is enclosed. Less concerned with the experimental form-finding technique of engineer Heinz Isler, Bini is more interested in how to use the very same techniques as a lightweight formwork to actually build his structures.
Concrete shell structures, in particular Isler’s ‘form-found’ Swiss carapaces, are structurally efficient and elegantly enclose huge volumes with a small amount of material. However, the fabrication of the formwork required a large skilled workforce and corresponding amounts of construction materials. Bini’s inflatable formwork or ‘Pneumoform’ eradicates the need for such a large site team, reduces material use and speeds up construction.
Both Pneumoform and construction automation were developed in Bini’s university dissertation, in response to his concern that ‘the timber or steel temporary formwork used to obtain the sophisticated engineering expressions of Félix Candela and Heinz Isler cost more than the final structure’. Bini has described how a game of tennis in a snow-covered inflatable tennis court led to the realisation that the low pressure of a few hundredths of an atmosphere could literally support tons of weight.
Bini’s quest for construction automation continued outside his work with shell structures with other systems, which all shared the ‘material’ of differential air pressure. His Binix system uses a series of precast triangular frame units raised into position with a pneumatic formwork cushion. The geodetic lines are then filled with concrete and reinforcement, ‘knitting’ together the structural components. In the Binix system there are clear parallels with projects by Pier Luigi Nervi like his Palazzetto dello Sport, Rome, of 1959, where a mixture of prefabrication and in-situ concrete casting was used to create the elegant lamella dome.
In the Binistar system, a reticular spatial structure is assembled flat on the ground, and a membrane cushion is inflated which is used to raise the structure as well as providing the environmental cover. When the extensible tubular structure reaches its designed height, the specially designed node connectors lock into position, creating a rigid steel grid-shell-type structure. These structures have been used for temporary events at Expo and World Cup venues.
Bini Dome construction sequence
The sequence of Bini Dome fabrication first involves the construction of a ring beam and ground floor slab. The ring beam cleverly contains a ‘cast in’ egg-shaped void that will contain a separate inflatable tube to hold the main membrane in place during inflation, as well as air inlets and outlets. The internal pneumatic form Pneumoform of nylon-reinforced neoprene is then laid over the slab and secured at the edge on top of which a complex network of criss-crossing helical springs is stretched across the diameter. The springs have no specific structural function, but control the even distribution of steel reinforcement bars (which are threaded through the springs) and also maintain an even concrete thickness by holding the mix in place.
Once the reinforcement is in place the concrete is poured. A regular concrete mix is used with small amounts of retarders and plasticisers added to extend the workability of the mix for two to three hours. After the pour, an outer membrane of PVC is laid over the wet concrete, which will help to control evaporation during the setting process and allow for vibration of the concrete. The inflation procedure then begins using low-pressure blowers, which takes about an hour; pressure is regulated by controlling the outlet to maintain an even lift.
When the shell is fully inflated, the concrete is vibrated using rolling carts hung from cables at the top of the structure. The internal air pressure is maintained for between one and three days depending on the diameter. For a 36-metre-diameter dome the thickness of the completed shell is 125mm at the base and 75mm at the crown.
The UK’s only existing example of such a dome, is the Edinburgh Sports Dome in Malvern, 1977, by architect Michael Godwin. He used Bini’s system (licensed at the time as Parashell in the UK) to create a school sports hall. Interestingly, he raised the entire dome on a series of eight concrete pilotis to provide natural light reflected from the surrounding pool in which the dome sits. In May 2009 the scheme was Grade II listed by the Government for its rare (unique in the UK) construction method and quality of architectural execution.
I became aware of the work of Dante Bini and his remarkable Bini Dome structures through the research of restless innovator and superlative draughtsman Jonathan Adams while we both worked for Will Alsop; and whether we were just looking for ways of making blobular forms or just non-standard ones, these solidified bubbles seemed like an exotic lost art.
In his book,3 Dante Bini recounts a wonderful story about a visit from legendary engineering professor Mario Salvadori who travelled from the US to Castelfranco, near Bologna, to witness the construction of a prototype in 1965. ‘For the American professor, the local farmer set a pale blue wooden table, with a glass of water, a bottle of sparkling red wine and an old kitchen chair’, all of which sounds more like an artist studio visit rather than a visit to a construction site. Salvadori sat at the table from 9.30am until 1.30pm. At 1.30pm the 12-metre dome was complete, Salvadori stood up, took a sip of wine and prounounced:‘Look, today I saw an amazing thing! If you were an engineer you would never have conceived such nonsense!’ Following which, Bini was officially invited by Columbia University to repeat the experiment on its campus. He did so successfully in 1967.
The Binishell company is now run by Danté’s son Nicolò, and there is renewed interest in the curvilinear possibilities of the Bini Dome. In part, the interest may be inspired by a retro impulse; more significant is the environmental imperative, in Buckminster Fuller’s phrase, of ‘doing more with less’. The domes are models of structural efficiency, with corresponding minimised material use and an incredibly lightweight formwork the chief component of which is air.
1. Cedric Price & Frank Newby, Air Structures: A Survey, Department of the Environment, 1971, HMSO.
2. Cedric Price, Cause and Effect (lecture at the Architectural Association, 6 June 1984).
3. Dante Bini’s book, A cavallo di un soffio d’aria (loosely translated as ‘riding on a puff of air’) is published in Italian by Guerini e Associati, Milan. An English edition will be published by Bibliotheque McLean later this year.
Architect: Dante Bini
Photographs: Max Dupain, all except final image