Engineering the Penguin Pool at London Zoo

Designed by Berthold Lubetkin and the Tecton Group, and completed in 1934, The Penguin Pool at London Zoo is an icon of British modernist architecture. Not only was it one of the first completed buildings to propose a new direction for British architecture, it was also one of the first to demonstrate the expressive and structural potential of reinforced concrete.

The inventive design of the pool was the result of a close collaboration between Lubetkin and the structural engineer Ove Arup. Together they produced a structure that was at once a shelter for animals, an aquatic sculpture, and an impressive feat of engineering.

The Penguin Pool complex comprises a long elliptical pool with a deep glass fronted diving tank and nesting boxes around the perimeter. The design was based on 'behaviourism'; this was a popular philosophy of psychology in the 1930s that claimed that all animal behaviours were a result of external environments. The design sought to both mimic the penguin’s natural habitat and provide a stimulating environment while also creating a theatrical stage on which they would display themselves to visitors. The defining feature is a pair of impressively thin interlocking spiral ramps that extend from hidden columns and appear to hover over the pool entirely unsupported. In addition to the narrow curving ramps which tested the penguins’ balance, the enclosure included a variety of flooring materials such as exposed concrete, slate steps, and plastic rubber made of cork chippings, rubber and cement.

The Penguin Pool at London Zoo. Photograph by Frederick William Bond, 1934, UK. © ZSL

While the complex as a whole was lauded for its formal simplicity and innovation, the ramps were especially praised for their technical expertise and dynamic visual appearance. To realise the ambitious design Lubetkin turned to Ove, an emerging specialist in reinforced concrete at the time. The two met in 1933 while Ove was working for the Danish engineering firm Christiani & Nielsen. Lubetkin had been referred to their London office after seeking advice for the Gorilla House, his first commission from the London Zoo. It was also during this time that Ove joined the Architectural Association and was becoming increasingly interested in working closely with architects and other specialists on cutting-edge design projects.

In early 1934, Ove joined contractor J.L. Kier & Co., another engineering firm of Danish origin that specialised in reinforced concrete. He joined Kier with the stipulation that he could develop his professional connections with modernist architects and was made director in charge of tenders and chief designer, a position he held until he left to establish his own firm in 1938.

The Penguin Pool provided Ove the perfect opportunity to exploit the potential of reinforced concrete. He advanced the idea that the concrete slab or panel was the most effective form for reinforced concrete. This was in opposition to the traditional method of casting it as a column or beam. He also proposed that concrete structures should be cast as one unit with the joints as strong as the central elements. He argued that with this approach any shape could be achieved.

The Penguin Pool under construction, 1934. © RIBA Library Photographs Collection. Photograph by John Havinden

Aside from the decision to use cast concrete slabs, there were many important factors to consider when engineering the Penguin Pool ramps. These included the load bearing capacity, bending, and torsion of the concrete. At 14 metres long, the ramps needed to include reinforcements to support themselves and the weight of the penguins. Torsion reinforcement was placed diagonally across the ramp to help act in the direction of the principle tension stresses. These diagonal reinforcements were placed in both the horizontal and vertical axes to a sort of rectangular helix. In order to achieve the thinness desired by the architects Ove tapered the section of the ramps from 15cm to 7.6cm toward the outside of the ramps. The calculations for the ramps proved to be long and complex. Felix Samuely, a colleague of Ove’s at J.L. Kier & Co, was hired to assist with the structural analysis. He also proposed the trapezoidal section of the ramps which allowed them to decrease in thickness toward the centre of the spiral.

‘Ovafest 90’ birthday programme, 1985. © Ove Arup Family Estate

The success of the Penguin Pool effectively established Ove as the go-to expert in reinforced concrete and Lubetkin and Tecton as leading architects of their generation. The collaboration on the Penguin Pool established a professional partnership and friendship between Ove and Lubetkin. They worked together to push on the structural and formal possibilities inherent in reinforced concrete on the apartment blocks Highpoint I (1935) and Highpoint II (1938) in Highgate, and the Finsbury Health Centre (1938), among many other projects.