Eduardo Torroja

Eduardo Torroja: The Man Who Made Concrete Thin

The market hall at Algeciras, finished in 1935, is roofed by a dome of concrete nine centimetres thick spanning 47.62 metres and resting on eight slender columns. That is a ratio of thickness to span of roughly one to five hundred — proportionally far thinner than an eggshell, in a material most people associate with mass and weight. Eduardo Torroja built it before anyone could reliably calculate whether it would stand up. He tested a model instead.

A Family of Mathematicians

Torroja was born in Madrid on 27 August 1899 into a household where this sort of thing was normal. His father, Eduardo Torroja Caballé, was an architect and mathematician, professor at Valencia and Madrid and a member of the Royal Academy of Mathematics, Physics and Natural Science. All three of his brothers became distinguished: a civil engineer and astronomer, a mining engineer who became vice-chancellor of the University of Barcelona, and a doctor of physics who ran a national research institute.

He entered Madrid's Civil Engineering School — founded in 1802 on the model of the Paris École des Ponts et Chaussées — in 1917 and graduated in 1923. In 1926 he married Carmen Cavanillas Prosper and joined the construction firm Hidrocivil under the engineer José Eugenio Ribera.

Learning Concrete on Aqueducts and Bridges

His early work was infrastructure, and it was already unusual. The Tempul aqueduct near Jerez de la Frontera, of 1927, used thin reinforced concrete and pre-stressed girders. For the San Telmo bridge at Seville he founded the piers on concentric hyperboloid brick shells. Appointed in 1927 to the technical committee for the new Madrid university campus, he supplied the structures for three viaducts, a tramway station, the faculties of Science, Medicine and Pharmacy, the dormitory, the power plant and the hospital.

Then, between 1935 and 1936, came three buildings that made his international reputation.

The Shell

A concrete shell works on the principle of an eggshell. If a surface is curved in the right way, applied loads travel through the surface itself, as compression and tension running within its plane, rather than bending it. Bending is what forces a structure to be thick — a beam needs depth to resist it. Remove bending from the problem and the material can become astonishingly thin, because concrete is very good at carrying compression and needs almost no bulk to do so. The whole art lies in choosing a geometry that keeps the forces in the surface.

Torroja was among the greatest practitioners of that art. Algeciras market (1935) is a spherical shell nine centimetres thick over a 47.62-metre diameter on eight perimeter columns. The Recoletos jai-alai court in Madrid (1936) roofed a 55-metre span between its walls with two intersecting cylinders forming a shell eight centimetres thick. The grandstand at the Zarzuela racetrack (1935) is the most elegant of the three: a run of horizontal hyperboloids cantilevering 12.80 metres out over the spectators and tapering to five centimetres at the free edge, thinnest exactly where the forces are least. Nothing about these roofs is decorative. Each is the shape the forces wanted.

Later work extended the range: composite steel-and-concrete bridges around 1940; the Martín Gil viaduct of 1941, whose 209-metre central arch held the world record for years; double-curvature reinforced brick shells at the church of Pont de Suert in 1954; and the Fedala water tower in Morocco in 1956, a vertical parabolic hyperboloid whose prestressing anchorages he hid inside the structure to keep the outside smooth.

Models Instead of Mathematics

The reason Torroja could build these when others could not is methodological, and it is the most instructive thing about him. In the 1930s the mathematics of doubly-curved shells was effectively intractable by hand. So in that decade he founded a company, Investigaciones de la Construcción, to build structural models at one-tenth scale and load them until they failed.

This is experiment substituting for analysis. It let him design forms whose behaviour he understood physically but could not yet write down, and it is why the Central Laboratory for Construction Materials Testing, which he also directed, became the European benchmark for scale-model structural analysis. His book *Philosophy of Structures* (1958) is the same instinct in prose: an explanation of how structures actually behave, in terms of materials and construction methods, deliberately without recourse to mathematical calculation, and containing a chapter on structural aesthetics. It was translated into English, French, German, Italian and Japanese. His view was that every material has its own specific personality and that a structure should reflect the personality of its designer; his working values were functionality, structural veracity and formal simplicity.

The Institute

Torroja built institutions with the same energy he built roofs. In 1934 he co-founded the Instituto Técnico de la Construcción y Edificación, the first private Spanish body devoted to studying, promoting and publishing construction research; in 1935 the journal *Hormigón y Acero*; in 1948 *Informes de la Construcción*, which carried Saarinen, Nervi and Le Corbusier. From 1939 he taught structural engineering at his old school in Madrid, and after 1946 directed the institute that became the Institute for Construction and Cement Engineering.

Internationally he was everywhere: president of RILEM from 1945, successor to Eugène Freyssinet as president of the Fédération Internationale de la Précontrainte in 1958, active in the Comité Européen du Béton, and in 1959 co-founder and first president of the International Association for Shell Structures — much of it done deliberately to pull an isolated Spain back into the European technical world.

Why Eduardo Is Called a Genius

The word is used of him officially: his own institute titles its historical project *Eduardo Torroja: Vida, Obra y Legado de un genio* — the life, work and legacy of a genius. The specific quality is structural intuition, meaning the ability to see how forces will travel through a form before any calculation is made, and to choose the form accordingly. Algeciras and Zarzuela are not clever solutions to given problems; they are demonstrations that the right shape makes the problem nearly disappear. He is conventionally ranked with Robert Maillart, Eugène Freyssinet and Pier Luigi Nervi as one of the four engineers who most shaped twentieth-century concrete, and unlike most of that company he also created the research institutions, journals and international bodies through which the knowledge spread.

The counter-case is worth stating. Torroja's method was frankly empirical: he built shells he could not calculate and proved them by breaking models, which is superb engineering artistry but not, in itself, theory. The analytical foundations of shell design were substantially supplied by others, and once computers made the mathematics tractable the mystique receded. His signature form also lost its economic argument — thin shells demand elaborate timber formwork and enormous skilled labour, and as wages rose in the second half of the century they were priced out of ordinary construction, which is why his buildings look like miracles and are almost never imitated. And his most productive institutional years, from 1939 to his death, were spent inside Franco's Spain, holding state appointments and receiving state honours; his achievement in reconnecting Spanish engineering to Europe is real, but it was accomplished from within a regime, not against it.

Legacy

Torroja died on 15 June 1961, at the institute, aged sixty-one, having left his colleagues a farewell letter that suggests he knew it was coming. That year the cover of the IASS journal carried three words: Eduardo Torroja, founder. He had written more than 170 papers and monographs and held honorary doctorates from Zurich, Toulouse, Buenos Aires, Liège and the Catholic University of Chile; the title Marquis of Torroja was granted posthumously. The institute he directed is now the Eduardo Torroja Institute for Construction Science. The grandstand at Zarzuela still leans out over the racecourse on five centimetres of concrete.

Achievements

• Notable work: Zarzuela race track
• Notable work: Estadio Nacional Complutense
• Notable work: Frontón Recoletos
• Notable work: Viaduct of Martín Gil
• Educated at Technical University of Madrid and Instituto Cardenal Cisneros
• Worked as architect, civil engineer and engineer