39 etc... : Heinz Isler's infinite spectrum of new shapes for shells

Abstract

The first Congress of the International Association of Shell Structures (now IASS), held in Madrid in 1959, was the occasion when Heinz Isler's innovative methods for determining the shape and constructing reinforced concrete shells first became widely known. Although he had introduced his ideas at smaller conferences as early as 1955, his Madrid paper `New Shapes for Shells' (Isler [1]) was presented in front of some of the most eminent shell designers of the day. This paper included a diagram showing 39 alternative shell forms with the abbreviation "etc." at the bottom right-hand corner indicating that Isler believed there were many more possibilities yet to be revealed. Contemporary accounts of the discussion describe how his presentation completely astounded the assembled audience, which included renowned engineers such as Torroja, Esquillan and Arup. On the 50th anniversary of his presentation the content of the original paper and subsequent debate are reviewed. Isler's form-finding and analysis was unassisted by modern digital design aids yet he was able to create efficient and economical structures of great elegance. His design and construction methods will be described and some examples of his shells, both built and unbuilt will be presented. The paper concludes with a brief discussion of the influence that Isler's unconventional design philosophy, methods and extremely graceful shells have had on the development of free-forms in architecture over the last 50 years and hopefully will continue to have into the future.