Felix Candela

Spanish-born American structural engineer

• Born: January 27, 1910
• Birthplace: Madrid, Spain
• Died: December 7, 1997
• Place of death: Durham, North Carolina

Candela specialized in the design and engineering of thin concrete shells as an architectural form. Although not the first to use concrete shells, he was the first to carry them to new artistic heights while maintaining their practicality and economy. Candela also was a champion athlete in skiing and rugby, and he excelled at mountain climbing and track and field.

Early Life

Born in Spain and descended from Galician, Basque, and Moorish ancestors, Felix Candela (kahn-DEHL-ah) later preferred to emphasize his Moorish ancestry partly because of the Mediterranean tradition of building. Upon the death of his father in 1929, the burden of supporting the family fell upon Candela’s shoulders. Needing a vocation, and feeling no particular calling, he heeded the advice of a friend and took up architecture. He enrolled at the Escuela Técnica Superior de Arquitectura (ETSA) in Madrid, where the curriculum included highly theoretical courses such as geometry, structural theory, and the theory of elasticity. Although Candela did well in his studies, he was not particularly taken with the theory of structures, except for an intense interest in geometry. However, he impressed his instructors sufficiently that in his third year he became the assistant to materials science professor Luis Vegas.

Candela was an accomplished athlete as a youth. In 1932, he became the Spanish national champion skier, and in 1934 he led his rugby team to the Spanish national championship. He also was an excellent mountain climber and succeeded in the triple jump, the pole vault, and hurdles. His athletic experience, he once related, helped sharpen his mind and build self-confidence.

While still a student, Candela developed a strong interest in the use of thin concrete shells in building and began to compile an extensive bibliography on the subject, including articles in German, French, and English. Upon graduating from ETSA in 1935, Candela opened a small studio in Madrid with two other architects. Candela and his associates tutored students and took in drafting and calculating work from other architects. In 1936, he won a travel scholarship from the Real Academia de Bellas Artes de San Fernando to study thin concrete shells in Germany, but the outbreak of the Spanish Civil War prevented him from using the scholarship.

Candela then joined the Spanish republican army, and was promoted as captain of engineers. With the victory in the war of Spanish dictator Francisco Franco, however, Candela fled to France but was held in a concentration camp for four months. He later sailed to Mexico and arrived in Veracruz in 1939. Shortly thereafter he resumed a practice in architecture. He also married Eladia Martín, who he had met in Madrid, and the two became Mexican citizens.

Life’s Work

Candela’s first few years in Mexico were not entirely successful. First, he became the architect for a colony of Spaniards near the city of Chihuahua. After building several residences and starting a municipal building, the colony dissolved and Candela returned to Mexico City. For a short time he worked as a draftsman for a small construction firm, but in 1941 he moved to Acapulco. Entering into a partnership with a contractor, Candela built several residences, an apartment building, and a series of bungalows for a hotel.

Returning to Mexico City in 1942, Candela joined the architectural office of Jesús Marti, where he spent the next four years. By his own description, the time in Marti’s office finished what he saw as his apprenticeship. He earned enough at this time to pay for his mother, brother, and sister to join him in Mexico. He then joined forces with his brother, Antonio, also an engineer, and built more apartments and a hotel. The projects from his first decade in Mexico, however, were nondescript. Only in his last year with Martí did Candela rediscover his fascination with thin concrete shells upon reading an article about the construction of curved slabs by George Winter in the Journal of the American Concrete Institute.

Once again, Candela began compiling a reading list of works on thin shells, using foreign-language dictionaries to translate them. This renewed interest in thin concrete shells represented a renewal of his career as well. He saw, as a result of his wide reading on the subject, a new approach to building thin shells, one which relied less on scientific theory and more on aesthetic concerns and a designer’s intuition. His first building using this approach was the acclaimed Pabellón de Rayos Cósmicos (Cosmic Ray Pavilion), completed in 1951.

Candela continued to think and write about the design of thin concrete shells, and in 1953 he published in Progressive Architecture the article “Stereo-Structures” (English translation, 1954), which attacked the indiscriminate use of scientific theory by architects and engineers. He pointed out that there was nothing inherently wrong with modern structural theories, but that he did not think they applied to reinforced concrete. In 1954, at a conference at the Massachusetts Institute of Technology, he presented a paper on his method of designing thin concrete shells. When a member of the audience expressed skepticism about one of his equations, he pointed out that perhaps it was better to look at his structures, which were standing, than to rely on equations.

By the mid-1950’s, Candela had established a firm reputation for his use of shells. After some early experimentation, he settled on using the hyperbolic paraboloid shape (also known as a hypar) for virtually all of his shells. He considered the hypar the easiest and the most practical to build, an assertion supported by the economy of many of his projects. Aesthetically, a designer could accomplish much with these shells because they usually had a thickness of just one and a half inches and thus could be variously shaped. Another attractive feature of the hypar was the relative ease (compared to many other types of structures) with which the shell’s stresses could be calculated, thus giving the designer greater artistic license. In designing these shells, Candela began with an artistic shape, then determined its dimensions (based on his previous experience), estimated the stresses of the shell, and finally checked his work with mathematical analysis.

A hypar shell is a type of stereo-structure, a doubly curved shape (in conventional configurations it resembles a saddle), which can be “distorted” by lengthening one side, by squaring the edges, by leaving the edges curved, or by using many other variations of the basic form. One particularly useful form that Candela exploited is known as the umbrella. Usually rectangular in plan, it consists of four hypars and actually resembles an umbrella blown inside out. When supported on a single central column, an umbrella can function as a roof over an entrance to a building or as a shade in an outdoor work area. A series of interconnected umbrellas becomes an inexpensive means of putting a roof over a large floor area. It is not surprising, then, that Candela’s umbrellas were used in many factories and warehouses throughout Mexico.

In contrast to the flattened hypars of the umbrellas, Candela also employed more daring forms of hypars in his structures. One of his best-known churches, built in 1955, is the Iglesia de la Virgen Milagrosa (Church of the Miraculous Virgin). It has a sharply sloped roof, sixty-five feet at its highest point, and is made up of a series of hypars that extend from the peak of its roof almost to the floor. Candela actually derived the hypars in this structure by elongating and bending umbrella shapes. Although Candela is best known for his hyper shells, he also created folded plates, cylindrical vaults, and elliptical domes from concrete.

Candela departed from the angular edges of his umbrellas in designing the shells that enclose the main hall of Mexico’s stock exchange. A Mexican architectural firm, in early 1954, wanted to build a doubly curved, groined vault for the stock exchange but was unable to find an engineer who could design such vaults. The firm approached Candela for the job, and he accepted. Believing the plan was beautiful and logical, he began to study the problem. The planned vaults differed from his other shells because they had curved edges rather than the straight edges of the umbrellas a whole new structural problem. Candela found a solution, however, and successfully built the vaults.

For the El Altillo Chapel (1955), Candela created yet another form of hypar. The roof for this chapel, rhomboidal in plan, was a relatively flat hypar with a slightly tilted vertical axis, and its construction marked the first time Candela used such a hypar (it greatly complicates stress calculation). The lower two corners of the “saddle” were supported, allowing the other two corners to be cantilevered (with only minimal support, in order to check deflection caused by temperature changes). This particular hypar has been likened to a sheet of paper twisted gently in the wind.

Most of Candela’s shells were extremely thin, and he wanted to avoid the use of beams or framework, which added strength to a structure in critical areas. Candela saw these additions, as many engineers might not have, as impediments to the beauty of the shell. He viewed it as a special challenge in his work to remove the edge beams from his shells, thus expressing visually the shell’s strength and beauty. This type of shell is known as a free-edge shell, the best example of which is Los Manantiales, a restaurant in Xochimilco. This structure, built in 1958, is one of Candela’s best-known works and the one he considered his most significant. The restaurant features an octagonal groined vault made up of four hypars rotated about a common center. The structure is the shell, and its thinness is apparent even to the layperson’s eye, since there is quite literally no other supporting structure. In this way, Candela achieved the uncompromised shell its shape is its strength.

The achievement brought Candela the Gold Medal of the Structural Engineers Institution, presented in London in 1961. He later participated in the construction of the facilities for the 1968 Olympic Games in Mexico City, designing a sports palace with a 135-meter steel dome and aluminum sails. However, the majority of his approximately three hundred completed projects involved concrete, most erected in or near Mexico City. They proved to be hardy structures, holding up well during the city’s severe earthquakes of 1958 and 1985.

From 1953 until 1970, Candela was a professor at the National Autonomous University of Mexico in Mexico City, and in 1958 he built himself a house in a Mediterranean style near Tlacopac in southern Mexico. He also traveled to other countries on temporary teaching assignments. He was the Charles Eliot Norton Professor of Poetry at Harvard University in 1961-1962 and the Thomas Jefferson Foundation Visiting Professor of the University of Virginia in 1966. He moved to the United States in 1971, becoming a citizen seven years later. He was an A. D. White Professor-at-Large of Cornell University from 1969 until 1975. In 1992 he served as president of the International Academy of Architecture.

Candela died in Durham, North Carolina, on December 7, 1997. That year the Structural Association of New York, the Museum of Modern Art, and Princeton University jointly honored him by sponsoring the annual Felix Candela Lecture at the Massachusetts Institute of Technology.

Significance

Candela’s impact lies in the originality and variety he brought to thin concrete shell construction, especially in hyperbolic paraboloid shells (hypars). In fact, in Mexico, Candela’s name is synonymous with hypars, such is the extent of his work with hypars. Candela was not an architect per se; rather, he considered himself a contractor, looking after architecture, structure, and construction all at once. This combination of roles was the result of his work with hypars in the sense that the building materials and techniques create an architectural shape that provides its own structural strength. Candela placed artistic creativity before engineering as he designed his shells. He used calculations to double-check what his artistic sense and his engineer’s intuition told him was right.

Economy was also extremely important to Candela. This concern for economy followed naturally from his affinity with shells, believing shape, not mass, gives strength. A major consideration, then, is to be as economical as possible in the design of a shell, in both appearance and material. The free-edge shells, such as the restaurant in Xochimilco, carry these ideals to new limits. By finding new solutions to old architectural problems and by taking a new approach, freed from the fetters of theory, Candela made his mark on architecture and on structural engineering.

Bibliography

Billington, David P. The Tower and the Bridge: The New Art of Structural Engineering. Princeton, N.J.: Princeton University Press, 1983. A very readable and informative monograph on structural engineering from the Industrial Revolution to the 1980’s. The author clearly shows how Candela and his ideals fit into the historical context of structural engineering. Written for general readers, with sufficient illustrations.

Collins, Peter. Concrete: The Vision of a New Architecture. 2d ed. Montreal: McGill-Queen’s University Press, 2004. A comprehensive work on the historic development of the use of concrete in building and the technological evolution of reinforced concrete, or ferroconcrete. Includes black-and-white photographs.

Faber, Colin. Candela: The Shell Builder. New York: Reinhold, 1963. The most complete book on Candela and his work. Thoroughly illustrated with photographs and line drawings (many of the former by Antonio Candela and the latter by a member of Candela’s office). In addition to illustrations, the book contains a brief biographical sketch, a general discussion of his work, a discussion of hypars and their technical details, and bibliographies of works by and about Candela.

Lin, Lorraine. “Felix Candela: Creator of Poetic Structures, 1910-1997.” Structure Magazine, April, 2006. A short article that explains in clear, nontechnical language the nature of Candela’s innovations with concrete. Illustrated with photographs.

Margolis, Ivan. Architects Plus Engineers Equals Structures. Chichester, England: Wiley Academy, 2002. Examines the critical union of architecture and engineering, analyzing the work of several architect-engineers such as Candela.

Nordenson, Guy, ed. The Felix Candela Lectures. New York: Museum of Modern Art, 2006. Contains the first eight lectures of the series honoring Candela, presentations that reflect his interest in structural innovation and artistic elegance.

“Shell Concrete Today.” Architectural Forum 101 (August, 1954): 157-166. A report on a conference on thin concrete shells held at the Massachusetts Institute of Technology. Defines all types of concrete shells, from flat slabs to domes to hypars, and then discusses the major types of shells in some detail; includes illustrations. Candela’s work figures prominently in the article.

Smith, Clive Bamford. Builders in the Sun: Five Mexican Architects. New York: Architectural Book Publishing, 1967. As the title implies, this book treats five architects, one of whom is Candela. It is well illustrated, with simple explanations of Candela’s work. One particularly good feature is the use of extensive quotations from Candela.