Behavior and durability of “free form” concrete shells

In the Fifties and Sixties of 20th century the research about reinforced concrete double curvature structures was a frontier in the field of architectural, spatial and technical innovation. Some engineers used mathematical formulas to describe the forms of the structures and their behavior; others reveled in physical modelling to determine the form and subsequently investigate its stability. This paper intends to investigate the case of some “free-form” shells built by Heinz Isler in Canton Ticino (Switzerland) and their behavior in time: the supermarket in Biasca (1963), another supermarket in Bellinzona built between 1964 and 1966 and the Bürgi Garden Centre at Camorino, built in 1973. The latter is particularly interesting as a testament to the transition to the most complex works, the summit of Isler’s research, the “inverted membrane” shells (for example the Motorway Service Station, Deitingen Süd, 1968 or Sicli shell in Geneva 1969). Since structural, architectural and constructional research is concentrated in a single building, the methods of repair, maintenance and reuse cannot be generalized. They have to be specific, not only with respect to the vicissitudes of each structure, but also to preserve the complex meanings these buildings embody.