The background behind the creation of the Candela shell

Simply put, the shape is a combination of an upward parabola and a downward parabola, and from another perspective, it is a drum- or saddle-shaped structure formed by straight lines in two directions. From a mechanical standpoint, thickness does not mean much, and construction is possible with linear formwork. Compared to domes, which are representative of large-space structures, it is characterized by a sense of tension and lightness, and Candela has created almost all forms composed of HP shells.

Last fall, I was taken by Professor Mamoru Kawaguchi (Professor Emeritus at Hosei University) to visit some of Candela's HP shells, which I had been interested in for many years. The greatest masterpiece is a restaurant located in Xochimilco, a suburb of Mexico City. This restaurant is made up of four interlocking saddle-shaped HP shells, and when viewed from above, it looks like eight open petals. It is common for HP shells to have different shapes when viewed from the outside and inside, but when viewed from the inside, this restaurant looks like a dome with an open exterior, with an internal dimension of 30m.

After seeing the splendor of Candela's HP shell, I thought about the technical background related to it. One is the structural calculation. As I wrote at the beginning, the mechanics of shells are difficult. According to Kawaguchi, Candela himself did not delve deeply into shell mechanics, especially numerical analysis. However, he was good at mathematics, and seemed to understand the essence that detailed calculations are not so meaningful. He also knew that the difficulty comes from making the shape unreasonable, especially the boundary part, and he eliminated such unsuitable shapes. And, when the actual thing speaks above all else, he moved towards a design and practical attitude rather than an analytical and research attitude. This reflected his artistic sensibility and beliefs.

The second is that Candela himself was involved in the construction. The Xochimilco restaurant was built in 1957. This may have been common in Mexico at the time, but he considered construction to be a design. In the process, he proved that it could be done cheaply and quickly. In fact, he has completed many constructions in a short period of time, from factories to churches.

The third point is the approach to durability. The shell is only 4cm thick. This is an unimaginable thinness by Japanese standards, but even now, 50 years later, it is still painted and in good condition. It is based on the original principle of reinforced concrete construction, which is to use thick concrete for proper construction and maintenance. This thinness is the key to its economy, aesthetics, and earthquake resistance.

Looking back, in today's Japan, such thinking and methods are not easily accepted under the current system. I think it is unavoidable in order to eliminate unsound construction, but at the same time, I wonder if it also makes it difficult to carry out groundbreaking construction.