Formworks in Thin Shell Construction: Past and Present

In Architectural Engineering, thin shells represent two-dimensional structures in which the third dimension, the thickness, is significantly smaller than the others, which are thus prevailing. The thin-shell construction technique has its roots in Spanish bóvedas tabicadas (dating back to at least the 12th century), the construction of which has continued to the present day. The Spanish technique, in the different countries of the Mediterranean area where it was exported (Portugal, France, Italy) has remained almost unchanged over time. However, the introduction of new building materials such as cement and steel at the end of the 19th century inevitably led to the experimentation of thin-shell structures characterised by greater slenderness and more complex shapes. Starting with Rafael Guastavino Moreno -who began to make improvements to the traditional technique-, and moving on to Eladio Dieste -who succeeded in fusing the qualities of bricks with those of reinforced concrete-, and Heinz Isler and Felix Candela -who, working in two different contexts, managed to improve the use of reinforced concrete-, we arrive to current constructions and experiments, in which the economy and ecological compatibility of the process are essential factors to be taken into account in the construction of thin shells. After a general overview on thin shells, the aim of the paper is to provide an analysis of some of the ribbing and formwork technologies used over time to build them. Similarities and differences among the various types of shells will be highlighted, having been used shape, size, and materials as variables for the analyses. A brief description of the current experiments carried out to determine alternative formwork systems to those usually used also is described at the end of the paper.